文章目录[隐藏]

Xlib - C Language X Interface

Xlib - C Language X Interface

X Consortium Standard

James Gettys

Digital Equipment Corporation Cambridge Research Laboratory

Robert W. Scheifler

Massachusetts Institute of Technology Laboratory for Computer Science

Chuck Adams

Tektronix, Inc.

Vania Joloboff

Open Software Foundation

Hideki Hiura

Sun Microsystems, Inc.

Bill McMahon

Hewlett-Packard Company

Ron Newman

Massachusetts Institute of Technology

Al Tabayoyon

Tektronix, Inc.

Glenn Widener

Tektronix, Inc.

Shigeru Yamada

Fujitsu OSSI

X Version 11, Release 7.7

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files
(the “Software”), to deal in the Software without restriction,
including without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to permit
persons to whom the Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of The Open Group shall not
be used in advertising or otherwise to promote the sale, use or other dealings
in this Software without prior written authorization from The Open Group.

Permission to use, copy, modify and distribute this documentation for any
purpose and without fee is hereby granted, provided that the above copyright
notice appears in all copies and that both that copyright notice and this
permission notice appear in supporting documentation, and that the names of
Digital and Tetronix not be used in in advertising or publicity pertaining
to distribution of the software without specific, written prior permission.
Digital and Tetronix make no representations about the suitability of the
software described herein for any purpose.
It is provided “as is” without express or implied warranty.

TekHVC is a trademark of Tektronix, Inc.

Table of Contents

List of Tables

A.1. Protocol requests made by each Xlib functionA.2. Xlib functions which use each Protocol Request

Acknowledgments

The design and implementation of the first 10 versions of X
were primarily the work of three individuals: Robert Scheifler of the
MIT Laboratory for Computer Science and Jim Gettys of Digital
Equipment Corporation and Ron Newman of MIT, both at MIT
Project Athena.
X version 11, however, is the result of the efforts of
dozens of individuals at almost as many locations and organizations.
At the risk of offending some of the players by exclusion,
we would like to acknowledge some of the people who deserve special credit
and recognition for their work on Xlib.
Our apologies to anyone inadvertently overlooked.

Release 1

Our thanks does to Ron Newman (MIT Project Athena),
who contributed substantially to the
design and implementation of the Version 11 Xlib interface.

Our thanks also goes to Ralph Swick (Project Athena and Digital) who kept
it all together for us during the early releases.
He handled literally thousands of requests from people everywhere
and saved the sanity of at least one of us.
His calm good cheer was a foundation on which we could build.

Our thanks also goes to Todd Brunhoff (Tektronix) who was “loaned”
to Project Athena at exactly the right moment to provide very capable
and much-needed assistance during the alpha and beta releases.
He was responsible for the successful integration of sources
from multiple sites;
we would not have had a release without him.

Our thanks also goes to Al Mento and Al Wojtas of Digital's ULTRIX
Documentation Group.
With good humor and cheer,
they took a rough draft and made it an infinitely better and more useful
document.
The work they have done will help many everywhere.
We also would like to thank Hal Murray (Digital SRC) and
Peter George (Digital VMS) who contributed much
by proofreading the early drafts of this document.

Our thanks also goes to Jeff Dike (Digital UEG), Tom Benson,
Jackie Granfield, and Vince Orgovan (Digital VMS) who helped with the
library utilities implementation;
to Hania Gajewska (Digital UEG-WSL) who,
along with Ellis Cohen (CMU and Siemens),
was instrumental in the semantic design of the window manager properties;
and to Dave Rosenthal (Sun Microsystems) who also contributed to the protocol
and provided the sample generic color frame buffer device-dependent code.

The alpha and beta test participants deserve special recognition and thanks
as well.
It is significant
that the bug reports (and many fixes) during alpha and beta test came almost
exclusively from just a few of the alpha testers, mostly hardware vendors
working on product implementations of X.
The continued public
contribution of vendors and universities is certainly to the benefit
of the entire X community.

Our special thanks must go to Sam Fuller, Vice-President of Corporate
Research at Digital, who has remained committed to the widest public
availability of X and who made it possible to greatly supplement MIT's
resources with the Digital staff in order to make version 11 a reality.
Many of the people mentioned here are part of the Western
Software Laboratory (Digital UEG-WSL) of the ULTRIX Engineering group
and work for Smokey Wallace, who has been vital to the project's success.
Others not mentioned here worked on the toolkit and are acknowledged
in the X Toolkit documentation.

Of course,
we must particularly thank Paul Asente, formerly of Stanford University
and now of Digital UEG-WSL, who wrote W, the predecessor to X,
and Brian Reid, formerly of Stanford University and now of Digital WRL,
who had much to do with W's design.

Finally, our thanks goes to MIT, Digital Equipment Corporation,
and IBM for providing the environment where it could happen.

Release 4

Our thanks go to Jim Fulton (MIT X Consortium) for designing and
specifying the new Xlib functions for Inter-Client Communication
Conventions (ICCCM) support.

We also thank Al Mento of Digital for his continued effort in
maintaining this document and Jim Fulton and Donna Converse (MIT X Consortium)
for their much-appreciated efforts in reviewing the changes.

Release 5

The principal authors of the Input Method facilities are
Vania Joloboff (Open Software Foundation) and Bill McMahon (Hewlett-Packard).
The principal author of the rest of the internationalization facilities
is Glenn Widener (Tektronix). Our thanks to them for keeping their
sense of humor through a long and sometimes difficult design process.
Although the words and much of the design are due to them, many others
have contributed substantially to the design and implementation.
Tom McFarland (HP) and Frank Rojas (IBM) deserve particular recognition
for their contributions. Other contributors were:
Tim Anderson (Motorola), Alka Badshah (OSF), Gabe Beged-Dov (HP),
Chih-Chung Ko (III), Vera Cheng (III), Michael Collins (Digital),
Walt Daniels (IBM), Noritoshi Demizu (OMRON), Keisuke Fukui (Fujitsu),
Hitoshoi Fukumoto (Nihon Sun), Tim Greenwood (Digital), John Harvey (IBM),
Hideki Hiura (Sun), Fred Horman (AT&T), Norikazu Kaiya (Fujitsu),
Yuji Kamata (IBM),
Yutaka Kataoka (Waseda University), Ranee Khubchandani (Sun), Akira Kon (NEC),
Hiroshi Kuribayashi (OMRON), Teruhiko Kurosaka (Sun), Seiji Kuwari (OMRON),
Sandra Martin (OSF), Narita Masahiko (Fujitsu), Masato Morisaki (NTT),
Nelson Ng (Sun),
Takashi Nishimura (NTT America), Makato Nishino (IBM),
Akira Ohsone (Nihon Sun), Chris Peterson (MIT), Sam Shteingart (AT&T),
Manish Sheth (AT&T), Muneiyoshi Suzuki (NTT), Cori Mehring (Digital),
Shoji Sugiyama (IBM), and Eiji Tosa (IBM).

We are deeply indebted to Tatsuya Kato (NTT),
Hiroshi Kuribayashi (OMRON), Seiji Kuwari (OMRON), Muneiyoshi Suzuki (NTT),
and Li Yuhong (OMRON) for producing one of the first complete
sample implementation of the internationalization facilities, and
Hiromu Inukai (Nihon Sun), Takashi Fujiwara (Fujitsu), Hideki Hiura (Sun),
Yasuhiro Kawai (Oki Technosystems Laboratory), Kazunori Nishihara (Fuji Xerox),
Masaki Takeuchi (Sony), Katsuhisa Yano (Toshiba),
Makoto Wakamatsu (Sony Corporation) for producing the another complete
sample implementation of the internationalization facilities.

The principal authors (design and implementation) of the Xcms color
management facilities are Al Tabayoyon (Tektronix)
and Chuck Adams (Tektronix).
Joann Taylor (Tektronix), Bob Toole (Tektronix),
and Keith Packard (MIT X Consortium) also
contributed significantly to the design. Others who contributed are:
Harold Boll (Kodak), Ken Bronstein (HP), Nancy Cam (SGI),
Donna Converse (MIT X Consortium), Elias Israel (ISC), Deron Johnson (Sun),
Jim King (Adobe), Ricardo Motta (HP), Chuck Peek (IBM),
Wil Plouffe (IBM), Dave Sternlicht (MIT X Consortium), Kumar Talluri (AT&T),
and Richard Verberg (IBM).

We also once again thank Al Mento of Digital for his work in formatting
and reformatting text for this manual, and for producing man pages.
Thanks also to Clive Feather (IXI) for proof-reading and finding a
number of small errors.

Release 6

Stephen Gildea (X Consortium) authored the threads support.
Ovais Ashraf (Sun) and Greg Olsen (Sun) contributed substantially
by testing the facilities and reporting bugs in a timely fashion.

The principal authors of the internationalization facilities, including
Input and Output Methods, are Hideki Hiura (SunSoft) and
Shigeru Yamada (Fujitsu OSSI).
Although the words and much of the design are due to them, many others
have contributed substantially to the design and implementation.
They are: Takashi Fujiwara (Fujitsu), Yoshio Horiuchi (IBM),
Makoto Inada (Digital), Hiromu Inukai (Nihon SunSoft),
Song JaeKyung (KAIST), Franky Ling (Digital), Tom McFarland (HP),
Hiroyuki Miyamoto (Digital), Masahiko Narita (Fujitsu),
Frank Rojas (IBM), Hidetoshi Tajima (HP), Masaki Takeuchi (Sony),
Makoto Wakamatsu (Sony), Masaki Wakao (IBM), Katsuhisa Yano(Toshiba) and
Jinsoo Yoon (KAIST).

The principal producers of the sample implementation of the
internationalization facilities are:
Jeffrey Bloomfield (Fujitsu OSSI), Takashi Fujiwara (Fujitsu),
Hideki Hiura (SunSoft), Yoshio Horiuchi (IBM),
Makoto Inada (Digital), Hiromu Inukai (Nihon SunSoft),
Song JaeKyung (KAIST), Riki Kawaguchi (Fujitsu),
Franky Ling (Digital), Hiroyuki Miyamoto (Digital),
Hidetoshi Tajima (HP), Toshimitsu Terazono (Fujitsu),
Makoto Wakamatsu (Sony), Masaki Wakao (IBM),
Shigeru Yamada (Fujitsu OSSI) and Katsuhisa Yano (Toshiba).

The coordinators of the integration, testing, and release of this
implementation of the internationalization facilities are
Nobuyuki Tanaka (Sony) and Makoto Wakamatsu (Sony).

Others who have contributed to the architectural design or
testing of the sample implementation of the
internationalization facilities are:
Hector Chan (Digital), Michael Kung (IBM), Joseph Kwok (Digital),
Hiroyuki Machida (Sony), Nelson Ng (SunSoft), Frank Rojas (IBM),
Yoshiyuki Segawa (Fujitsu OSSI), Makiko Shimamura (Fujitsu),
Shoji Sugiyama (IBM), Lining Sun (SGI), Masaki Takeuchi (Sony),
Jinsoo Yoon (KAIST) and Akiyasu Zen (HP).

Jim Gettys
Cambridge Research Laboratory
Digital Equipment Corporation
Robert W. Scheifler
Laboratory for Computer Science
Massachusetts Institute of Technology

Release 7

This document is made available to you in modern formats such as HTML and PDF
thanks to the efforts of Matt Dew, who converted the original troff sources to
DocBook/XML and edited them into shape; along with Gaetan Nadon and
Alan Coopersmith, who set up the formatting machinery in the libX11 builds and
performed further editing of the DocBook markup.

Chapter 1. Introduction to Xlib

Table of Contents

Overview of the X Window SystemErrorsStandard Header FilesGeneric Values and TypesNaming and Argument Conventions within XlibProgramming ConsiderationsCharacter Sets and EncodingsFormatting Conventions

The X Window System is a network-transparent window system that was
designed at MIT. X display servers run on computers with either
monochrome or color bitmap display hardware. The server distributes
user input to and accepts output requests from various client programs
located either on the same machine or elsewhere in the network. Xlib
is a C subroutine library that application programs (clients) use to
interface with the window system by means of a stream connection.
Although a client usually runs on the same machine as the X server
it is talking to, this need not be the case.

Xlib − C Language X Interface is a reference
guide to the low-level C language interface to the X Window System
protocol. It is neither a tutorial nor a user’s guide to programming
the X Window System. Rather, it provides a detailed description of
each function in the library as well as a discussion of the related
background information. Xlib − C Language X Interface
assumes a basic understanding of a graphics window system and of the C
programming language. Other higher-level abstractions (for example,
those provided by the toolkits for X) are built on top of the Xlib
library. For further information about these higher-level libraries,
see the appropriate toolkit documentation.
The X Window System Protocol provides the
definitive word on the behavior of X.
Although additional information appears here, the protocol document is
the ruling document.

To provide an introduction to X programming, this chapter discusses:

Overview of the X Window System

Some of the terms used in this book are unique to X,
and other terms that are common to other window systems
have different meanings in X. You may find it helpful to refer to
the glossary,
which is located at the end of the book.

The X Window System supports one or more screens containing
overlapping windows or subwindows.

A screen is a physical monitor and hardware
that can be color, grayscale, or monochrome.
There can be multiple screens for each display or workstation.
A single X server can provide display services for any number of screens.
A set of screens for a single user with one keyboard and one pointer
(usually a mouse) is called a display.

All the windows in an X server are arranged in strict hierarchies.
At the top of each hierarchy is a root window,
which covers each of the display screens.
Each root window is partially or completely covered by child windows.
All windows, except for root windows, have parents.
There is usually at least one window for each application program.

Child windows may in turn have their own children.
In this way,
an application program can create an arbitrarily deep tree
on each screen.
X provides graphics, text, and raster operations for windows.

A child window can be larger than its parent.
That is, part or all of
the child window can extend beyond the boundaries of the parent,
but all output to a window is clipped by its parent.

If several children of a window have overlapping locations,
one of the children is considered to be on top of or raised over the
others, thus obscuring them.
Output to areas covered by other windows is suppressed by the window
system unless the window has backing store.
If a window is obscured by a second window,
the second window obscures only those ancestors of the second window
that are also ancestors of the first window.

A window has a border zero or more pixels in width, which can
be any pattern (pixmap) or solid color you like.
A window usually but not always has a background pattern,
which will be repainted by the window system when uncovered.
Child windows obscure their parents,
and graphic operations in the parent window usually
are clipped by the children.

Each window and pixmap has its own coordinate system.
The coordinate system has the X axis horizontal and the Y axis vertical
with the origin [0, 0] at the upper-left corner.
Coordinates are integral,
in terms of pixels,
and coincide with pixel centers.
For a window,
the origin is inside the border at the inside, upper-left corner.

X does not guarantee to preserve the contents of windows.
When part or all of a window is hidden and then brought back onto the screen,
its contents may be lost.
The server then sends the client program an
Expose
event to notify it that part or all of the window needs to be repainted.
Programs must be prepared to regenerate the contents of windows on demand.

X also provides off-screen storage of graphics objects,
called pixmaps.
Single plane (depth 1) pixmaps are sometimes referred to as
bitmaps.
Pixmaps can be used in most graphics functions interchangeably with
windows and are used in various graphics operations to define patterns or tiles.
Windows and pixmaps together are referred to as drawables.

Most of the functions in Xlib just add requests to an output buffer.
These requests later execute asynchronously on the X server.
Functions that return values of information stored in
the server do not return (that is, they block)
until an explicit reply is received or an error occurs.
You can provide an error handler,
which will be called when the error is reported.

If a client does not want a request to execute asynchronously,
it can follow the request with a call to
XSync,
which blocks until all previously buffered
asynchronous events have been sent and acted on.
As an important side effect,
the output buffer in Xlib is always flushed by a call to any function
that returns a value from the server or waits for input.

Many Xlib functions will return an integer resource ID,
which allows you to refer to objects stored on the X server.
These can be of type
Window,
Font,
Pixmap,
Colormap,
Cursor,
and
GContext,
as defined in the file
<X11/X.h>.

These resources are created by requests and are destroyed
(or freed) by requests or when connections are closed.
Most of these resources are potentially sharable between
applications, and in fact, windows are manipulated explicitly by
window manager programs.
Fonts and cursors are shared automatically across multiple screens.
Fonts are loaded and unloaded as needed and are shared by multiple clients.
Fonts are often cached in the server.
Xlib provides no support for sharing graphics contexts between applications.

Client programs are informed of events.
Events may either be side effects of a request (for example, restacking windows
generates
Expose
events) or completely asynchronous (for example, from the keyboard).
A client program asks to be informed of events.
Because other applications can send events to your application,
programs must be prepared to handle (or ignore) events of all types.

Input events (for example, a key pressed or the pointer moved)
arrive asynchronously from the server and are queued until they are
requested by an explicit call (for example,
XNextEvent
or
XWindowEvent).
In addition, some library
functions (for example,
XRaiseWindow)
generate
Expose
and
ConfigureRequest
events.
These events also arrive asynchronously, but the client may

wish to explicitly wait for them by calling
XSync
after calling a function that can cause the server to generate events.

Errors

Some functions return
Status,
an integer error indication.
If the function fails, it returns a zero.
If the function returns a status of zero,
it has not updated the return arguments.

Because C does not provide multiple return values,
many functions must return their results by writing into client-passed storage.

By default, errors are handled either by a standard library function
or by one that you provide.
Functions that return pointers to strings return NULL pointers if
the string does not exist.

The X server reports protocol errors at the time that it detects them.
If more than one error could be generated for a given request,
the server can report any of them.

Because Xlib usually does not transmit requests to the server immediately
(that is, it buffers them), errors can be reported much later than they
actually occur.
For debugging purposes, however,
Xlib provides a mechanism for forcing synchronous behavior
(see section 11.8.1).
When synchronization is enabled,
errors are reported as they are generated.

When Xlib detects an error,
it calls an error handler,
which your program can provide.
If you do not provide an error handler,
the error is printed, and your program terminates.

Standard Header Files

The following include files are part of the Xlib standard:

`<X11/Xlib.h>`	This is the main header file for Xlib. The majority of all Xlib symbols are declared by including this file. This file also contains the preprocessor symbol XlibSpecificationRelease. This symbol is defined to have the 6 in this release of the standard. (Release 5 of Xlib was the first release to have this symbol.)
`<X11/X.h>`	This file declares types and constants for the X protocol that are to be used by applications. It is included automatically from `<X11/Xlib.h>` so application code should never need to reference this file directly.
`<X11/Xcms.h>`	This file contains symbols for much of the color management facilities described in chapter 6. All functions, types, and symbols with the prefix "Xcms", plus the Color Conversion Contexts macros, are declared in this file. `<X11/Xlib.h>` must be included before including this file.
`<X11/Xutil.h>`	This file declares various functions, types, and symbols used for inter-client communication and application utility functions, which are described in chapters 14 and 16. `<X11/Xlib.h>` must be included before including this file.
`<X11/Xresource.h>`	This file declares all functions, types, and symbols for the resource manager facilities, which are described in chapter 15. `<X11/Xlib.h>` must be included before including this file.
`<X11/Xatom.h>`	This file declares all predefined atoms, which are symbols with the prefix "XA_".
`<X11/cursorfont.h>`	This file declares the cursor symbols for the standard cursor font, which are listed in Appendix B. All cursor symbols have the prefix "XC_".
`<X11/keysymdef.h>`	This file declares all standard KeySym values, which are symbols with the prefix "XK_". The KeySyms are arranged in groups, and a preprocessor symbol controls inclusion of each group. The preprocessor symbol must be defined prior to inclusion of the file to obtain the associated values. The preprocessor symbols are XK_MISCELLANY, XK_XKB_KEYS, XK_3270, XK_LATIN1, XK_LATIN2, XK_LATIN3, XK_LATIN4, XK_KATAKANA, XK_ARABIC, XK_CYRILLIC, XK_GREEK, XK_TECHNICAL, XK_SPECIAL, XK_PUBLISHING, XK_APL, XK_HEBREW, XK_THAI, and XK_KOREAN.
`<X11/keysym.h>`	This file defines the preprocessor symbols XK_MISCELLANY, XK_XKB_KEYS, XK_LATIN1, XK_LATIN2, XK_LATIN3, XK_LATIN4, and XK_GREEK and then includes `<X11/keysymdef.h>`.
`<X11/Xlibint.h>`	This file declares all the functions, types, and symbols used for extensions, which are described in Appendix C. This file automatically includes `<X11/Xlib.h>`.
`<X11/Xproto.h>`	This file declares types and symbols for the basic X protocol, for use in implementing extensions. It is included automatically from `<X11/Xlibint.h>`, so application and extension code should never need to reference this file directly.
`<X11/Xprotostr.h>`	This file declares types and symbols for the basic X protocol, for use in implementing extensions. It is included automatically from `<X11/Xproto.h>`, so application and extension code should never need to reference this file directly.
`<X11/X10.h>`	This file declares all the functions, types, and symbols used for the X10 compatibility functions, which are described in Appendix D.

Generic Values and Types

The following symbols are defined by Xlib and used throughout the manual:

Xlib defines the type
Bool
and the Boolean values
True
and
False.
None
is the universal null resource ID or atom.
The type
XID
is used for generic resource IDs.
The type XPointer is defined to be char *
and is used as a generic opaque pointer to data.

Naming and Argument Conventions within Xlib

Xlib follows a number of conventions for the naming and syntax of the functions.
Given that you remember what information the function requires,
these conventions are intended to make the syntax of the functions more
predictable.

The major naming conventions are:

To differentiate the X symbols from the other symbols,
the library uses mixed case for external symbols.
It leaves lowercase for variables and all uppercase for user macros,
as per existing convention.
All Xlib functions begin with a capital X.
The beginnings of all function names and symbols are capitalized.
All user-visible data structures begin with a capital X.
More generally,
anything that a user might dereference begins with a capital X.
Macros and other symbols do not begin with a capital X.
To distinguish them from all user symbols,
each word in the macro is capitalized.
All elements of or variables in a data structure are in lowercase.
Compound words, where needed, are constructed with underscores (_).
The display argument, where used, is always first in the argument list.
All resource objects, where used, occur at the beginning of the argument list
immediately after the display argument.
When a graphics context is present together with
another type of resource (most commonly, a drawable), the
graphics context occurs in the argument list after the other
resource.
Drawables outrank all other resources.
Source arguments always precede the destination arguments in the argument list.
The x argument always precedes the y argument in the argument list.
The width argument always precedes the height argument in the argument list.
Where the x, y, width, and height arguments are used together,
the x and y arguments always precede the width and height arguments.
Where a mask is accompanied with a structure,
the mask always precedes the pointer to the structure in the argument list.

Programming Considerations

The major programming considerations are:

Coordinates and sizes in X are actually 16-bit quantities.
This decision was made to minimize the bandwidth required for a
given level of performance.
Coordinates usually are declared as an
int
in the interface.
Values larger than 16 bits are truncated silently.
Sizes (width and height) are declared as unsigned quantities.
Keyboards are the greatest variable between different
manufacturers' workstations.
If you want your program to be portable,
you should be particularly conservative here.
Many display systems have limited amounts of off-screen memory.
If you can, you should minimize use of pixmaps and backing
store.
The user should have control of their screen real estate.
Therefore, you should write your applications to react to window management
rather than presume control of the entire screen.
What you do inside of your top-level window, however,
is up to your application.
For further information,
see chapter 14
and the Inter-Client Communication Conventions Manual.

Character Sets and Encodings

Some of the Xlib functions make reference to specific character sets
and character encodings.
The following are the most common:

X Portable Character Set	A basic set of 97 characters, which are assumed to exist in all locales supported by Xlib. This set contains the following characters: a..z A..Z 0..9 !"#$%&'()*+,-./:;<=>?@[\\]^_`{\|}~ <space>, <tab>, and <newline> This set is the left/lower half of the graphic character set of ISO8859-1 plus space, tab, and newline. It is also the set of graphic characters in 7-bit ASCII plus the same three control characters. The actual encoding of these characters on the host is system dependent.
Host Portable Character Encoding	The encoding of the X Portable Character Set on the host. The encoding itself is not defined by this standard, but the encoding must be the same in all locales supported by Xlib on the host. If a string is said to be in the Host Portable Character Encoding, then it only contains characters from the X Portable Character Set, in the host encoding.
Latin-1	The coded character set defined by the ISO8859-1 standard.
Latin Portable Character Encoding	The encoding of the X Portable Character Set using the Latin-1 codepoints plus ASCII control characters. If a string is said to be in the Latin Portable Character Encoding, then it only contains characters from the X Portable Character Set, not all of Latin-1.
STRING Encoding	Latin-1, plus tab and newline.
POSIX Portable Filename Character Set	The set of 65 characters, which can be used in naming files on a POSIX-compliant host, that are correctly processed in all locales. The set is: a..z A..Z 0..9 ._-

Formatting Conventions

Xlib − C Language X Interface uses the
following conventions:

Global symbols are printed in
thisspecialfont.
These can be either function names,
symbols defined in include files, or structure names.
When declared and defined,
function arguments are printed in italics.
In the explanatory text that follows,
they usually are printed in regular type.
Each function is introduced by a general discussion that
distinguishes it from other functions.
The function declaration itself follows,
and each argument is specifically explained.
Although ANSI C function prototype syntax is not used,
Xlib header files normally declare functions using function prototypes
in ANSI C environments.
General discussion of the function, if any is required,
follows the arguments.
Where applicable,
the last paragraph of the explanation lists the possible
Xlib error codes that the function can generate.
For a complete discussion of the Xlib error codes,
see section 11.8.2.
To eliminate any ambiguity between those arguments that you pass and those that
a function returns to you,
the explanations for all arguments that you pass start with the word
specifies or, in the case of multiple arguments, the word specify.
The explanations for all arguments that are returned to you start with the
word returns or, in the case of multiple arguments, the word return.
The explanations for all arguments that you can pass and are returned start
with the words specifies and returns.
Any pointer to a structure that is used to return a value is designated as
such by the _return suffix as part of its name.
All other pointers passed to these functions are
used for reading only.
A few arguments use pointers to structures that are used for
both input and output and are indicated by using the _in_out suffix.

Chapter 2. Display Functions

Table of Contents

Opening the DisplayObtaining Information about the Display, Image Formats, or ScreensDisplay MacrosImage Format Functions and MacrosScreen Information MacrosGenerating a NoOperation Protocol RequestFreeing Client-Created DataClosing the DisplayUsing X Server Connection Close OperationsUsing Xlib with ThreadsUsing Internal Connections

Before your program can use a display, you must establish a connection
to the X server.
Once you have established a connection,
you then can use the Xlib macros and functions discussed in this chapter
to return information about the display.
This chapter discusses how to:

Open (connect to) the display
Obtain information about the display, image formats, or screens
Generate a
NoOperation
protocol request
Free client-created data
Close (disconnect from) a display
Use X Server connection close operations
Use Xlib with threads
Use internal connections

Opening the Display

To open a connection to the X server that controls a display, use
XOpenDisplay.

Display *XOpenDisplay(char *display_name);

display_name

Specifies the hardware display name, which determines the display
and communications domain to be used.
On a POSIX-conformant system, if the display_name is NULL,
it defaults to the value of the DISPLAY environment variable.

The encoding and interpretation of the display name are
implementation-dependent.
Strings in the Host Portable Character Encoding are supported;
support for other characters is implementation-dependent.
On POSIX-conformant systems,
the display name or DISPLAY environment variable can be a string in the format:


	protocol/hostname:number.screen_number

protocol	Specifies a protocol family or an alias for a protocol family. Supported protocol families are implementation dependent. The protocol entry is optional. If protocol is not specified, the / separating protocol and hostname must also not be specified.
hostname	Specifies the name of the host machine on which the display is physically attached. You follow the hostname with either a single colon (:) or a double colon (::).
number	Specifies the number of the display server on that host machine. You may optionally follow this display number with a period (.). A single CPU can have more than one display. Multiple displays are usually numbered starting with zero.
screen_number	Specifies the screen to be used on that server. Multiple screens can be controlled by a single X server. The screen_number sets an internal variable that can be accessed by using the `DefaultScreen` macro or the `XDefaultScreen` function if you are using languages other than C (see section 2.2.1).

For example, the following would specify screen 1 of display 0 on the
machine named “dual-headed”:

dual-headed:0.1

The
XOpenDisplay
function returns a
Display
structure that serves as the
connection to the X server and that contains all the information
about that X server.
XOpenDisplay
connects your application to the X server through TCP
or DECnet communications protocols,
or through some local inter-process communication protocol.

If the protocol is specified as "tcp", "inet", or "inet6", or
if no protocol is specified and the hostname is a host machine name and a single colon (:)
separates the hostname and display number,
XOpenDisplay
connects using TCP streams. (If the protocol is specified as "inet", TCP over
IPv4 is used. If the protocol is specified as "inet6", TCP over IPv6 is used.
Otherwise, the implementation determines which IP version is used.)
If the hostname and protocol are both not specified,
Xlib uses whatever it believes is the fastest transport.
If the hostname is a host machine name and a double colon (::)
separates the hostname and display number,
XOpenDisplay
connects using DECnet.
A single X server can support any or all of these transport mechanisms
simultaneously.
A particular Xlib implementation can support many more of these transport
mechanisms.

If successful,
XOpenDisplay
returns a pointer to a
Display
structure,
which is defined in
<X11/Xlib.h>.

If
XOpenDisplay
does not succeed, it returns NULL.
After a successful call to
XOpenDisplay,
all of the screens in the display can be used by the client.
The screen number specified in the display_name argument is returned
by the
DefaultScreen
macro (or the
XDefaultScreen
function).
You can access elements of the
Display
and
Screen
structures only by using the information macros or functions.
For information about using macros and functions to obtain information from
the
Display
structure,
see section 2.2.1.

X servers may implement various types of access control mechanisms
(see section 9.8).

Obtaining Information about the Display, Image Formats, or Screens

The Xlib library provides a number of useful macros
and corresponding functions that return data from the
Display
structure.
The macros are used for C programming,
and their corresponding function equivalents are for other language bindings.
This section discusses the:

Display macros
Image format functions and macros
Screen information macros

All other members of the
Display
structure (that is, those for which no macros are defined) are private to Xlib
and must not be used.
Applications must never directly modify or inspect these private members of the
Display
structure.

The
XDisplayWidth,
XDisplayHeight,
XDisplayCells,
XDisplayPlanes,
XDisplayWidthMM,
and
XDisplayHeightMM
functions in the next sections are misnamed.
These functions really should be named Screenwhatever
and XScreenwhatever, not Displaywhatever or XDisplaywhatever.
Our apologies for the resulting confusion.

Display Macros

Applications should not directly modify any part of the
Display
and
Screen
structures.
The members should be considered read-only,
although they may change as the result of other operations on the display.

The following lists the C language macros,
their corresponding function equivalents that are for other language bindings,
and what data both can return.

AllPlanes

unsigned long XAllPlanes(void);

Both return a value with all bits set to 1 suitable for use in a plane argument to
a procedure.

Both
BlackPixel
and
WhitePixel
can be used in implementing a monochrome application.
These pixel values are for permanently allocated entries in the default
colormap.
The actual RGB (red, green, and blue) values are settable on some screens
and, in any case, may not actually be black or white.
The names are intended to convey the expected relative intensity of the colors.

BlackPixel(display, screen_number);

unsigned long XBlackPixel(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the black pixel value for the specified screen.

WhitePixel(display, screen_number);

unsigned long XWhitePixel(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the white pixel value for the specified screen.

ConnectionNumber(display);

int XConnectionNumber(Display *display);

display

Specifies the connection to the X server.

Both return a connection number for the specified display.
On a POSIX-conformant system,
this is the file descriptor of the connection.

DefaultColormap(display, screen_number);

Colormap XDefaultColormap(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the default colormap ID for allocation on the specified screen.
Most routine allocations of color should be made out of this colormap.

DefaultDepth(display, screen_number);

int XDefaultDepth(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the depth (number of planes) of the default root window for the
specified screen.
Other depths may also be supported on this screen (see
XMatchVisualInfo).

To determine the number of depths that are available on a given screen, use
XListDepths.

int *XListDepths(Display *display, int screen_number, int *count_return);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.
count_return	Returns the number of depths.

The
XListDepths
function returns the array of depths
that are available on the specified screen.
If the specified screen_number is valid and sufficient memory for the array
can be allocated,
XListDepths
sets count_return to the number of available depths.
Otherwise, it does not set count_return and returns NULL.
To release the memory allocated for the array of depths, use
XFree.

DefaultGC(display, screen_number);

GC XDefaultGC(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the default graphics context for the root window of the
specified screen.
This GC is created for the convenience of simple applications
and contains the default GC components with the foreground and
background pixel values initialized to the black and white
pixels for the screen, respectively.
You can modify its contents freely because it is not used in any Xlib
function.
This GC should never be freed.

DefaultRootWindow(display);

Window XDefaultRootWindow(Display *display);

display

Specifies the connection to the X server.

Both return the root window for the default screen.

DefaultScreenOfDisplay(display);

Screen *XDefaultScreenOfDisplay(Display *display);

display

Specifies the connection to the X server.

Both return a pointer to the default screen.

ScreenOfDisplay(display, screen_number);

Screen *XScreenOfDisplay(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return a pointer to the indicated screen.

DefaultScreen(display);

int XDefaultScreen(Display *display);

display

Specifies the connection to the X server.

Both return the default screen number referenced by the
XOpenDisplay
function.
This macro or function should be used to retrieve the screen number
in applications that will use only a single screen.

DefaultVisual(display, screen_number);

Visual *XDefaultVisual(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the default visual type for the specified screen.
For further information about visual types,
see section 3.1.

DisplayCells(display, screen_number);

int XDisplayCells(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the number of entries in the default colormap.

DisplayPlanes(display, screen_number);

int XDisplayPlanes(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the depth of the root window of the specified screen.
For an explanation of depth,
see the glossary.

DisplayString(display);

char *XDisplayString(Display *display);

display

Specifies the connection to the X server.

Both return the string that was passed to
XOpenDisplay
when the current display was opened.
On POSIX-conformant systems,
if the passed string was NULL, these return the value of
the DISPLAY environment variable when the current display was opened.

These are useful to applications that invoke the
fork
system call and want to open a new connection to the same display from the
child process as well as for printing error messages.

long XExtendedMaxRequestSize(Display *display);

display

Specifies the connection to the X server.

The
XExtendedMaxRequestSize
function returns zero if the specified display does not support an
extended-length protocol encoding; otherwise,
it returns the maximum request size (in 4-byte units) supported
by the server using the extended-length encoding.
The Xlib functions
XDrawLines,
XDrawArcs,
XFillPolygon,
XChangeProperty,
XSetClipRectangles,
and
XSetRegion
will use the extended-length encoding as necessary, if supported
by the server. Use of the extended-length encoding in other Xlib
functions (for example,
XDrawPoints,
XDrawRectangles,
XDrawSegments,
XFillArcs,
XFillRectangles,
XPutImage)
is permitted but not required; an Xlib implementation may choose to
split the data across multiple smaller requests instead.

long XMaxRequestSize(Display *display);

display

Specifies the connection to the X server.

The
XMaxRequestSize
function returns the maximum request size (in 4-byte units) supported
by the server without using an extended-length protocol encoding.
Single protocol requests to the server can be no larger than this size
unless an extended-length protocol encoding is supported by the server.
The protocol guarantees the size to be no smaller than 4096 units
(16384 bytes).
Xlib automatically breaks data up into multiple protocol requests
as necessary for the following functions:
XDrawPoints,
XDrawRectangles,
XDrawSegments,
XFillArcs,
XFillRectangles,
and
XPutImage.

LastKnownRequestProcessed(display);

unsigned long XLastKnownRequestProcessed(Display *display);

display

Specifies the connection to the X server.

Both extract the full serial number of the last request known by Xlib
to have been processed by the X server.
Xlib automatically sets this number when replies, events, and errors
are received.

NextRequest(display);

unsigned long XNextRequest(Display *display);

display

Specifies the connection to the X server.

Both extract the full serial number that is to be used for the next
request.
Serial numbers are maintained separately for each display connection.

ProtocolVersion(display);

int XProtocolVersion(Display *display);

display

Specifies the connection to the X server.

Both return the major version number (11) of the X protocol associated with
the connected display.

ProtocolRevision(display);

int XProtocolRevision(Display *display);

display

Specifies the connection to the X server.

Both return the minor protocol revision number of the X server.

QLength(display);

int XQLength(Display *display);

display

Specifies the connection to the X server.

Both return the length of the event queue for the connected display.
Note that there may be more events that have not been read into
the queue yet (see
XEventsQueued).

RootWindow(display, screen_number);

Window XRootWindow(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the root window.
These are useful with functions that need a drawable of a particular screen
and for creating top-level windows.

ScreenCount(display);

int XScreenCount(Display *display);

display

Specifies the connection to the X server.

Both return the number of available screens.

ServerVendor(display);

char *XServerVendor(Display *display);

display

Specifies the connection to the X server.

Both return a pointer to a null-terminated string that provides
some identification of the owner of the X server implementation.
If the data returned by the server is in the Latin Portable Character Encoding,
then the string is in the Host Portable Character Encoding.
Otherwise, the contents of the string are implementation-dependent.

VendorRelease(display);

int XVendorRelease(Display *display);

display

Specifies the connection to the X server.

Both return a number related to a vendor's release of the X server.

Image Format Functions and Macros

Applications are required to present data to the X server
in a format that the server demands.
To help simplify applications,
most of the work required to convert the data is provided by Xlib
(see sections
8.7 and
16.8).

The
XPixmapFormatValues
structure provides an interface to the pixmap format information
that is returned at the time of a connection setup.
It contains:

typedef struct {
	int depth;
	int bits_per_pixel;
	int scanline_pad;
} XPixmapFormatValues;

To obtain the pixmap format information for a given display, use
XListPixmapFormats.

XPixmapFormatValues *XListPixmapFormats(Display *display, int *count_return);

display	Specifies the connection to the X server.
count_return	Returns the number of pixmap formats that are supported by the display.

The
XListPixmapFormats
function returns an array of
XPixmapFormatValues
structures that describe the types of Z format images supported
by the specified display.
If insufficient memory is available,
XListPixmapFormats
returns NULL.
To free the allocated storage for the
XPixmapFormatValues
structures, use
XFree.

The following lists the C language macros,
their corresponding function equivalents that are for other language bindings,
and what data they both return for the specified server and screen.
These are often used by toolkits as well as by simple applications.

ImageByteOrder(display);

int XImageByteOrder(Display *display);

display

Specifies the connection to the X server.

Both specify the required byte order for images for each scanline unit in
XY format (bitmap) or for each pixel value in
Z format.
The macro or function can return either
LSBFirst
or
MSBFirst.

XBitmapUnit(display);

int XBitmapUnit(Display *display);

display

Specifies the connection to the X server.

Both return the size of a bitmap's scanline unit in bits.
The scanline is calculated in multiples of this value.

BitmapBitOrder(display);

int XBitmapBitOrder(Display *display);

display

Specifies the connection to the X server.

Within each bitmap unit, the left-most bit in the bitmap as displayed
on the screen is either the least significant or most significant bit in the
unit.
This macro or function can return
LSBFirst
or
MSBFirst.

BitmapPad(display);

int XBitmapPad(Display *display);

display

Specifies the connection to the X server.

Each scanline must be padded to a multiple of bits returned
by this macro or function.

DisplayHeight(display, screen_number);

int XDisplayHeight(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return an integer that describes the height of the screen
in pixels.

DisplayHeightMM(display, screen_number);

int XDisplayHeightMM(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the height of the specified screen in millimeters.

DisplayWidth(display, screen_number);

int XDisplayWidth(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the width of the screen in pixels.

DisplayWidthMM(display, screen_number);

int XDisplayWidthMM(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

Both return the width of the specified screen in millimeters.

Screen Information Macros

The following lists the C language macros,
their corresponding function equivalents that are for other language bindings,
and what data they both can return.
These macros or functions all take a pointer to the appropriate screen
structure.

BlackPixelOfScreen(screen);

unsigned long XBlackPixelOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the black pixel value of the specified screen.

XWhitePixelOfScreen(screen);

unsigned long XWhitePixelOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the white pixel value of the specified screen.

CellsOfScreen(screen);

int XCellsOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the number of colormap cells in the default colormap
of the specified screen.

DefaultColormapOfScreen(screen);

Colormap XDefaultColormapOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the default colormap of the specified screen.

DefaultDepthOfScreen(screen);

int XDefaultDepthOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the depth of the root window.

DefaultGCOfScreen(screen);

GC XDefaultGCOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return a default graphics context (GC) of the specified screen,
which has the same depth as the root window of the screen.
The GC must never be freed.

XDefaultVisualOfScreen(screen);

Visual *XDefaultVisualOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the default visual of the specified screen.
For information on visual types,
see section 3.1.

DoesBackingStore(screen);

int XDoesBackingStore(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return a value indicating whether the screen supports backing
stores.
The value returned can be one of
WhenMapped,
NotUseful,
or
Always
(see section 3.2.4).

DoesSaveUnders(screen);

Bool XDoesSaveUnders(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return a Boolean value indicating whether the
screen supports save unders.
If
True,
the screen supports save unders.
If
False,
the screen does not support save unders
(see section 3.2.5).

DisplayOfScreen(screen);

Display *XDisplayOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the display of the specified screen.

ScreenNumberOfScreen(screen);

long XScreenNumberOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

The
XScreenNumberOfScreen
function returns the screen index number of the specified screen.

EventMaskOfScreen(screen);

long XEventMaskOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the event mask of the root window for the specified screen
at connection setup time.

WidthOfScreen(screen);

int XWidthOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the width of the specified screen in pixels.

HeightOfScreen(screen);

int XHeightOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the height of the specified screen in pixels.

WidthMMOfScreen(screen);

int XWidthMMOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the width of the specified screen in millimeters.

HeightMMOfScreen(screen);

int XHeightMMOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the height of the specified screen in millimeters.

MaxCmapsOfScreen(screen);

int XMaxCmapsOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the maximum number of installed colormaps supported
by the specified screen
(see section 9.3).

MinCmapsOfScreen(screen);

int XMinCmapsOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the minimum number of installed colormaps supported
by the specified screen
(see section 9.3).

PlanesOfScreen(screen);

int XPlanesOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the depth of the root window.

RootWindowOfScreen(screen);

Window XRootWindowOfScreen(Screen *screen);

screen

Specifies the appropriate
Screen
structure.

Both return the root window of the specified screen.

Generating a NoOperation Protocol Request

To execute a
NoOperation
protocol request, use
XNoOp.

XNoOp(Display *display);

display

Specifies the connection to the X server.

The
XNoOp
function sends a
NoOperation
protocol request to the X server,
thereby exercising the connection.

Freeing Client-Created Data

To free in-memory data that was created by an Xlib function, use
XFree.

XFree(void *data);

data

Specifies the data that is to be freed.

The
XFree
function is a general-purpose Xlib routine that frees the specified data.
You must use it to free any objects that were allocated by Xlib,
unless an alternate function is explicitly specified for the object.
A NULL pointer cannot be passed to this function.

Closing the Display

To close a display or disconnect from the X server, use
XCloseDisplay.

XCloseDisplay(Display *display);

display

Specifies the connection to the X server.

The
XCloseDisplay
function closes the connection to the X server for the display specified in the
Display
structure and destroys all windows, resource IDs
(Window,
Font,
Pixmap,
Colormap,
Cursor,
and
GContext),
or other resources that the client has created
on this display, unless the close-down mode of the client has been changed
(see
XSetCloseDownMode).
Therefore, these windows, resource IDs, and other resources should never be
referenced again or an error will be generated.
Before exiting, you should call
XCloseDisplay
explicitly so that any pending errors are reported as
XCloseDisplay
performs a final
XSync
operation.

XCloseDisplay
can generate a
BadGC
error.

Xlib provides a function to permit the resources owned by a client
to survive after the client's connection is closed.
To change a client's close-down mode, use
XSetCloseDownMode.

XSetCloseDownMode(Display *display, int close_mode);

display	Specifies the connection to the X server.
close_mode	Specifies the client close-down mode. You can pass DestroyAll, RetainPermanent, or RetainTemporary.

The
XSetCloseDownMode function
defines what will happen to the client's resources at connection close.
A connection starts in
DestroyAll
mode.
For information on what happens to the client's resources when the
close_mode argument is
RetainPermanent
or
RetainTemporary,
see section 2.6.

XSetCloseDownMode
can generate a
BadValue
error.

Using X Server Connection Close Operations

When the X server's connection to a client is closed
either by an explicit call to
XCloseDisplay
or by a process that exits, the X server performs the following
automatic operations:

It disowns all selections owned by the client
(see
XSetSelectionOwner).
It performs an
XUngrabPointer
and
XUngrabKeyboard
if the client has actively grabbed the pointer
or the keyboard.
It performs an
XUngrabServer
if the client has grabbed the server.
It releases all passive grabs made by the client.
It marks all resources (including colormap entries) allocated
by the client either as permanent or temporary,
depending on whether the close-down mode is
RetainPermanent
or
RetainTemporary.
However, this does not prevent other client applications from explicitly
destroying the resources (see
XSetCloseDownMode).

When the close-down mode is
DestroyAll,
the X server destroys all of a client's resources as follows:

It examines each window in the client's save-set to determine if it is an inferior
(subwindow) of a window created by the client.
(The save-set is a list of other clients' windows
that are referred to as save-set windows.)
If so, the X server reparents the save-set window to the closest ancestor so
that the save-set window is not an inferior of a window created by the client.
The reparenting leaves unchanged the absolute coordinates (with respect to
the root window) of the upper-left outer corner of the save-set
window.
It performs a
MapWindow
request on the save-set window if the save-set window is unmapped.
The X server does this even if the save-set window was not an inferior of
a window created by the client.
It destroys all windows created by the client.
It performs the appropriate free request on each nonwindow resource created by
the client in the server (for example,
Font,
Pixmap,
Cursor,
Colormap,
and
GContext).
It frees all colors and colormap entries allocated by a client application.

Additional processing occurs when the last connection to the X server closes.
An X server goes through a cycle of having no connections and having some
connections.
When the last connection to the X server closes as a result of a connection
closing with the close_mode of
DestroyAll,
the X server does the following:

It resets its state as if it had just been
started.
The X server begins by destroying all lingering resources from
clients that have terminated in
RetainPermanent
or
RetainTemporary
mode.
It deletes all but the predefined atom identifiers.
It deletes all properties on all root windows
(see section 4.3).
It resets all device maps and attributes
(for example, key click, bell volume, and acceleration)
as well as the access control list.
It restores the standard root tiles and cursors.
It restores the default font path.
It restores the input focus to state
PointerRoot.

However, the X server does not reset if you close a connection with a close-down
mode set to
RetainPermanent
or
RetainTemporary.

Using Xlib with Threads

On systems that have threads, support may be provided to permit
multiple threads to use Xlib concurrently.

To initialize support for concurrent threads, use
XInitThreads.

Status XInitThreads(void);

The
XInitThreads
function initializes Xlib support for concurrent threads.
This function must be the first Xlib function a
multi-threaded program calls, and it must complete
before any other Xlib call is made.
This function returns a nonzero status if initialization was
successful; otherwise, it returns zero.
On systems that do not support threads, this function always returns zero.

It is only necessary to call this function if multiple threads
might use Xlib concurrently. If all calls to Xlib functions
are protected by some other access mechanism (for example,
a mutual exclusion lock in a toolkit or through explicit client
programming), Xlib thread initialization is not required.
It is recommended that single-threaded programs not call this function.

To lock a display across several Xlib calls, use
XLockDisplay.

XLockDisplay(Display *display);

display

Specifies the connection to the X server.

The
XLockDisplay
function locks out all other threads from using the specified display.
Other threads attempting to use the display will block until
the display is unlocked by this thread.
Nested calls to
XLockDisplay
work correctly; the display will not actually be unlocked until
XUnlockDisplay
has been called the same number of times as
XLockDisplay.
This function has no effect unless Xlib was successfully initialized
for threads using
XInitThreads.

To unlock a display, use
XUnlockDisplay.

XUnlockDisplay(Display *display);

display

Specifies the connection to the X server.

The
XUnlockDisplay
function allows other threads to use the specified display again.
Any threads that have blocked on the display are allowed to continue.
Nested locking works correctly; if
XLockDisplay
has been called multiple times by a thread, then
XUnlockDisplay
must be called an equal number of times before the display is
actually unlocked.
This function has no effect unless Xlib was successfully initialized
for threads using
XInitThreads.

Using Internal Connections

In addition to the connection to the X server, an Xlib implementation
may require connections to other kinds of servers (for example, to
input method servers as described in
chapter 13).
Toolkits and clients
that use multiple displays, or that use displays in combination with
other inputs, need to obtain these additional connections to correctly
block until input is available and need to process that input
when it is available. Simple clients that use a single display and
block for input in an Xlib event function do not need to use these
facilities.

To track internal connections for a display, use
XAddConnectionWatch.

typedef void (*XConnectionWatchProc)(Display *display, XPointer client_data, int fd, Bool opening, XPointer *watch_data);

Status XAddConnectionWatch(Display *display, XConnectionWatchProc procedure, XPointer client_data);

display	Specifies the connection to the X server.
procedure	Specifies the procedure to be called.
client_data	Specifies the additional client data.

The
XAddConnectionWatch
function registers a procedure to be called each time Xlib opens or closes an
internal connection for the specified display. The procedure is passed the
display, the specified client_data, the file descriptor for the connection,
a Boolean indicating whether the connection is being opened or closed, and a
pointer to a location for private watch data. If opening is
True,
the procedure can store a pointer to private data in the location pointed
to by watch_data;
when the procedure is later called for this same connection and opening is
False,
the location pointed to by watch_data will hold this same private data pointer.

This function can be called at any time after a display is opened.
If internal connections already exist, the registered procedure will
immediately be called for each of them, before
XAddConnectionWatch
returns.
XAddConnectionWatch
returns a nonzero status if the procedure is successfully registered;
otherwise, it returns zero.

The registered procedure should not call any Xlib functions.
If the procedure directly or indirectly causes the state of internal
connections or watch procedures to change, the result is not defined.
If Xlib has been initialized for threads, the procedure is called with
the display locked and the result of a call by the procedure to any
Xlib function that locks the display is not defined unless the executing
thread has externally locked the display using
XLockDisplay.

To stop tracking internal connections for a display, use
XRemoveConnectionWatch.

Status XRemoveConnectionWatch(Display *display, XConnectionWatchProc procedure, XPointer client_data);

display	Specifies the connection to the X server.
procedure	Specifies the procedure to be called.
client_data	Specifies the additional client data.

The
XRemoveConnectionWatch
function removes a previously registered connection watch procedure.
The client_data must match the client_data used when the procedure
was initially registered.

To process input on an internal connection, use
XProcessInternalConnection.

void XProcessInternalConnection(Display *display, int fd);

display	Specifies the connection to the X server.
fd	Specifies the file descriptor.

The
XProcessInternalConnection
function processes input available on an internal connection.
This function should be called for an internal connection only
after an operating system facility (for example,
select
or
poll)
has indicated that input is available; otherwise,
the effect is not defined.

To obtain all of the current internal connections for a display, use
XInternalConnectionNumbers.

Status XInternalConnectionNumbers(Display *display, int ** fd, int * count_return);

display	Specifies the connection to the X server.
fd_return	Returns the file descriptors.
count_return	Returns the number of file descriptors.

The
XInternalConnectionNumbers
function returns a list of the file descriptors for all internal
connections currently open for the specified display.
When the allocated list is no longer needed,
free it by using
XFree.
This functions returns a nonzero status if the list is successfully allocated;
otherwise, it returns zero.

Chapter 3. Window Functions

Table of Contents

Visual TypesWindow AttributesBackground AttributeBorder AttributeGravity AttributesBacking Store AttributeSave Under FlagBacking Planes and Backing Pixel AttributesEvent Mask and Do Not Propagate Mask AttributesOverride Redirect FlagColormap AttributeCursor AttributeCreating WindowsDestroying WindowsMapping WindowsUnmapping WindowsConfiguring WindowsChanging Window Stacking OrderChanging Window Attributes

Visual Types

On some display hardware,
it may be possible to deal with color resources in more than one way.
For example, you may be able to deal with a screen of either 12-bit depth
with arbitrary mapping of pixel to color (pseudo-color) or 24-bit depth
with 8 bits of the pixel dedicated to each of red, green, and blue.
These different ways of dealing with the visual aspects of the screen
are called visuals.
For each screen of the display, there may be a list of valid visual types
supported at different depths of the screen.
Because default windows and visual types are defined for each screen,
most simple applications need not deal with this complexity.
Xlib provides macros and functions that return the default root window,
the default depth of the default root window, and the default visual type
(see sections 2.2.1
and 16.7).

Xlib uses an opaque
Visual

structure that contains information about the possible color mapping.
The visual utility functions
(see section 16.7)
use an
XVisualInfo
structure to return this information to an application.
The members of this structure pertinent to this discussion are class, red_mask,
green_mask, blue_mask, bits_per_rgb, and colormap_size.
The class member specifies one of the possible visual classes of the screen
and can be

StaticGray,
StaticColor,
TrueColor,
GrayScale,
PseudoColor,
or
DirectColor.

The following concepts may serve to make the explanation of
visual types clearer.
The screen can be color or grayscale,
can have a colormap that is writable or read-only,
and can also have a colormap whose indices are decomposed into separate
RGB pieces, provided one is not on a grayscale screen.
This leads to the following diagram:

                      Color        Gray-Scale
                   R/O    R/W      R/O   R/W
----------------------------------------------
 Undecomposed    Static  Pseudo   Static  Gray
   Colormap      Color   Color    Gray    Scale

 Decomposed       True   Direct
   Colormap       Color  Color
----------------------------------------------

Conceptually,
as each pixel is read out of video memory for display on the screen,
it goes through a look-up stage by indexing into a colormap.
Colormaps can be manipulated arbitrarily on some hardware,
in limited ways on other hardware, and not at all on other hardware.
The visual types affect the colormap and
the RGB values in the following ways:

For
PseudoColor,
a pixel value indexes a colormap to produce
independent RGB values, and the RGB values can be changed dynamically.
GrayScale
is treated the same way as
PseudoColor
except that the primary that drives the screen is undefined.
Thus, the client should always store the
same value for red, green, and blue in the colormaps.
For
DirectColor,
a pixel value is decomposed into separate RGB subfields, and each
subfield separately indexes the colormap for the corresponding value.
The RGB values can be changed dynamically.
TrueColor
is treated the same way as
DirectColor
except that the colormap has predefined, read-only RGB values.
These RGB values are server dependent but provide linear or near-linear
ramps in each primary.
StaticColor
is treated the same way as
PseudoColor
except that the colormap has predefined,
read-only, server-dependent RGB values.
StaticGray
is treated the same way as
StaticColor
except that the RGB values are equal for any single pixel
value, thus resulting in shades of gray.
StaticGray
with a two-entry
colormap can be thought of as monochrome.

The red_mask, green_mask, and blue_mask members are only defined for
DirectColor
and
TrueColor.
Each has one contiguous set of bits with no
intersections.
The bits_per_rgb member specifies the log base 2 of the
number of distinct color values (individually) of red, green, and blue.
Actual RGB values are unsigned 16-bit numbers.
The colormap_size member defines the number of available colormap entries
in a newly created colormap.
For
DirectColor
and
TrueColor,
this is the size of an individual pixel subfield.

To obtain the visual ID from a
Visual,
use
XVisualIDFromVisual.

VisualID XVisualIDFromVisual(Visual *visual);

visual

Specifies the visual type.

The
XVisualIDFromVisual
function returns the visual ID for the specified visual type.

Window Attributes

All
InputOutput
windows have a border width of zero or more pixels, an optional background,
an event suppression mask (which suppresses propagation of events from
children), and a property list
(see section 4.3).
The window border and background can be a solid color or a pattern, called
a tile.
All windows except the root have a parent and are clipped by their parent.
If a window is stacked on top of another window, it obscures that other
window for the purpose of input.
If a window has a background (almost all do), it obscures the other
window for purposes of output.
Attempts to output to the obscured area do nothing,
and no input events (for example, pointer motion) are generated for the
obscured area.

Windows also have associated property lists
(see section 4.3).

Both
InputOutput
and
InputOnly
windows have the following common attributes,
which are the only attributes of an
InputOnly
window:

win-gravity
event-mask
do-not-propagate-mask
override-redirect
cursor

If you specify any other attributes for an
InputOnly
window,
a
BadMatch
error results.

InputOnly
windows are used for controlling input events in situations where
InputOutput
windows are unnecessary.
InputOnly
windows are invisible; can only be used to control such things as
cursors, input event generation, and grabbing;
and cannot be used in any graphics requests.
Note that
InputOnly
windows cannot have
InputOutput
windows as inferiors.

Windows have borders of a programmable width and pattern
as well as a background pattern or tile.

Pixel values can be used for solid colors.

The background and border pixmaps can be destroyed immediately after
creating the window if no further explicit references to them
are to be made.

The pattern can either be relative to the parent
or absolute.
If
ParentRelative,
the parent's background is used.

When windows are first created,
they are not visible (not mapped) on the screen.
Any output to a window that is not visible on the screen
and that does not have backing store will be discarded.

An application may wish to create a window long before it is
mapped to the screen.
When a window is eventually mapped to the screen
(using
XMapWindow),

the X server generates an
Expose
event for the window if backing store has not been maintained.

A window manager can override your choice of size,
border width, and position for a top-level window.
Your program must be prepared to use the actual size and position
of the top window.
It is not acceptable for a client application to resize itself
unless in direct response to a human command to do so.
Instead, either your program should use the space given to it,
or if the space is too small for any useful work, your program
might ask the user to resize the window.
The border of your top-level window is considered fair game
for window managers.

To set an attribute of a window,
set the appropriate member of the
XSetWindowAttributes
structure and OR in the corresponding value bitmask in your subsequent calls to
XCreateWindow
and
XChangeWindowAttributes,
or use one of the other convenience functions that set the appropriate
attribute.
The symbols for the value mask bits and the
XSetWindowAttributes
structure are:

/* Window attribute value mask bits */

/* Window attribute value mask bits */
#define    CWBackPixmap                    (1L<<0)
#define    CWBackPixel                     (1L<<1)
#define    CWBorderPixmap                  (1L<<2)
#define    CWBorderPixel                   (1L<<3)
#define    CWBitGravity                    (1L<<4)
#define    CWWinGravity                    (1L<<5)
#define    CWBackingStore                  (1L<<6)
#define    CWBackingPlanes                 (1L<<7)
#define    CWBackingPixel                  (1L<<8)
#define    CWOverrideRedirect              (1L<<9)
#define    CWSaveUnder                     (1L<<10)
#define    CWEventMask                     (1L<<11)
#define    CWDontPropagate                 (1L<<12)
#define    CWColormap                      (1L<<13)
#define    CWCursor                        (1L<<14)


/* Values */

typedef struct {
     Pixmap background_pixmap;     /* background, None, or ParentRelative */
     unsigned long background_pixel;     /* background pixel */
     Pixmap border_pixmap;          /* border of the window or CopyFromParent */
     unsigned long border_pixel;     /* border pixel value */
     int bit_gravity;     /* one of bit gravity values */
     int win_gravity;     /* one of the window gravity values */
     int backing_store;     /* NotUseful, WhenMapped, Always */
     unsigned long backing_planes;     /* planes to be preserved if possible */
     unsigned long backing_pixel;     /* value to use in restoring planes */
     Bool save_under;     /* should bits under be saved? (popups) */
     long event_mask;     /* set of events that should be saved */
     long do_not_propagate_mask;     /* set of events that should not propagate */
     Bool override_redirect;     /* boolean value for override_redirect */
     Colormap colormap;     /* color map to be associated with window */
     Cursor cursor;          /* cursor to be displayed (or None) */
} XSetWindowAttributes;

The following lists the defaults for each window attribute and indicates
whether the attribute is applicable to
InputOutput
and
InputOnly
windows:

Attribute	Default	InputOutput	InputOnly
background-pixmap	None	Yes	No
background-pixel	Undefined	Yes	No
border-pixmap	CopyFromParent	Yes	No
border-pixel	Undefined	Yes	No
bit-gravity	ForgetGravity	Yes	No
win-gravity	NorthWestGravity	Yes	Yes
backing-store	NotUseful	Yes	No
backing-planes	All ones	Yes	No
backing-pixel	zero	Yes	No
save-under	False	Yes	No
event-mask	empty set	Yes	Yes
do-not-propagate-mask	empty set	Yes	Yes
override-redirect	False	Yes	Yes
colormap	CopyFromParent	Yes	No
cursor	None	Yes	Yes

Background Attribute

Only
InputOutput
windows can have a background.
You can set the background of an
InputOutput
window by using a pixel or a pixmap.

The background-pixmap attribute of a window specifies the pixmap to be used for
a window's background.
This pixmap can be of any size, although some sizes may be faster than others.
The background-pixel attribute of a window specifies a pixel value used to paint
a window's background in a single color.

You can set the background-pixmap to a pixmap,
None
(default), or
ParentRelative.
You can set the background-pixel of a window to any pixel value (no default).
If you specify a background-pixel,
it overrides either the default background-pixmap
or any value you may have set in the background-pixmap.
A pixmap of an undefined size that is filled with the background-pixel is used
for the background.
Range checking is not performed on the background pixel;
it simply is truncated to the appropriate number of bits.

If you set the background-pixmap,
it overrides the default.
The background-pixmap and the window must have the same depth,
or a
BadMatch
error results.
If you set background-pixmap to
None,
the window has no defined background.
If you set the background-pixmap to
ParentRelative:

The parent window's background-pixmap is used.
The child window, however, must have the same depth as
its parent,
or a
BadMatch
error results.
If the parent window has a background-pixmap of
None,
the window also has a background-pixmap of
None.
A copy of the parent window's background-pixmap is not made.
The parent's background-pixmap is examined each time the child window's
background-pixmap is required.
The background tile origin always aligns with the parent window's
background tile origin.
If the background-pixmap is not
ParentRelative,
the background tile origin is the child window's origin.

Setting a new background, whether by setting background-pixmap or
background-pixel, overrides any previous background.
The background-pixmap can be freed immediately if no further explicit reference
is made to it (the X server will keep a copy to use when needed).
If you later draw into the pixmap used for the background,
what happens is undefined because the
X implementation is free to make a copy of the pixmap or
to use the same pixmap.

When no valid contents are available for regions of a window
and either the regions are visible or the server is maintaining backing store,
the server automatically tiles the regions with the window's background
unless the window has a background of
None.
If the background is
None,
the previous screen contents from other windows of the same depth as the window
are simply left in place as long as the contents come from the parent of the
window or an inferior of the parent.
Otherwise, the initial contents of the exposed regions are undefined.
Expose
events are then generated for the regions, even if the background-pixmap
is
None
(see section 10.9).

Border Attribute

Only
InputOutput
windows can have a border.
You can set the border of an
InputOutput
window by using a pixel or a pixmap.

The border-pixmap attribute of a window specifies the pixmap to be used
for a window's border.
The border-pixel attribute of a window specifies a pixmap of undefined size
filled with that pixel be used for a window's border.
Range checking is not performed on the background pixel;
it simply is truncated to the appropriate number of bits.
The border tile origin is always the same as the background tile origin.

You can also set the border-pixmap to a pixmap of any size (some may be faster
than others) or to
CopyFromParent
(default).
You can set the border-pixel to any pixel value (no default).

If you set a border-pixmap,
it overrides the default.
The border-pixmap and the window must have the same depth,
or a
BadMatch
error results.
If you set the border-pixmap to
CopyFromParent,
the parent window's border-pixmap is copied.
Subsequent changes to the parent window's border attribute do not affect
the child window.
However, the child window must have the same depth as the parent window,
or a
BadMatch
error results.

The border-pixmap can be freed immediately if no further explicit reference
is made to it.
If you later draw into the pixmap used for the border,
what happens is undefined because the
X implementation is free either to make a copy of the pixmap or
to use the same pixmap.
If you specify a border-pixel,
it overrides either the default border-pixmap
or any value you may have set in the border-pixmap.
All pixels in the window's border will be set to the border-pixel.
Setting a new border, whether by setting border-pixel or by setting
border-pixmap, overrides any previous border.

Output to a window is always clipped to the inside of the window.
Therefore, graphics operations never affect the window border.

Gravity Attributes

The bit gravity of a window defines which region of the window should be
retained when an
InputOutput
window is resized.
The default value for the bit-gravity attribute is
ForgetGravity.
The window gravity of a window allows you to define how the
InputOutput
or
InputOnly
window should be repositioned if its parent is resized.
The default value for the win-gravity attribute is
NorthWestGravity.

If the inside width or height of a window is not changed
and if the window is moved or its border is changed,
then the contents of the window are not lost but move with the window.
Changing the inside width or height of the window causes its contents to be
moved or lost (depending on the bit-gravity of the window) and causes
children to be reconfigured (depending on their win-gravity).
For a
change of width and height, the (x, y) pairs are defined:

Gravity Direction	Coordinates
NorthWestGravity	(0, 0)
NorthGravity	(Width/2, 0)
NorthEastGravity	(Width, 0)
WestGravity	(0, Height/2)
CenterGravity	(Width/2, Height/2)
EastGravity	(Width, Height/2)
SouthWestGravity	(0, Height)
SouthGravity	(Width/2, Height)
SouthEastGravity	(Width, Height)

When a window with one of these bit-gravity values is resized,
the corresponding pair
defines the change in position of each pixel in the window.
When a window with one of these win-gravities has its parent window resized,
the corresponding pair defines the change in position of the window
within the parent.
When a window is so repositioned, a
GravityNotify
event is generated
(see section 10.10.5).

A bit-gravity of
StaticGravity
indicates that the contents or origin should not move relative to the
origin of the root window.
If the change in size of the window is coupled with a change in position (x, y),
then for bit-gravity the change in position of each pixel is (−x, −y), and for
win-gravity the change in position of a child when its parent is so resized is
(−x, −y).
Note that
StaticGravity
still only takes effect when the width or height of the window is changed,
not when the window is moved.

A bit-gravity of
ForgetGravity
indicates that the window's contents are always discarded after a size change,
even if a backing store or save under has been requested.
The window is tiled with its background
and zero or more
Expose
events are generated.
If no background is defined, the existing screen contents are not
altered.
Some X servers may also ignore the specified bit-gravity and
always generate
Expose
events.

The contents and borders of inferiors are not affected by their parent's
bit-gravity.
A server is permitted to ignore the specified bit-gravity and use
Forget
instead.

A win-gravity of
UnmapGravity
is like
NorthWestGravity
(the window is not moved),
except the child is also
unmapped when the parent is resized,
and an
UnmapNotify
event is
generated.

Backing Store Attribute

Some implementations of the X server may choose to maintain the contents of
InputOutput
windows.
If the X server maintains the contents of a window,
the off-screen saved pixels
are known as backing store.
The backing store advises the X server on what to do
with the contents of a window.
The backing-store attribute can be set to
NotUseful
(default),
WhenMapped,
or
Always.

A backing-store attribute of
NotUseful
advises the X server that
maintaining contents is unnecessary,
although some X implementations may
still choose to maintain contents and, therefore, not generate
Expose
events.
A backing-store attribute of
WhenMapped
advises the X server that maintaining contents of
obscured regions when the window is mapped would be beneficial.
In this case,
the server may generate an
Expose
event when the window is created.
A backing-store attribute of
Always
advises the X server that maintaining contents even when
the window is unmapped would be beneficial.
Even if the window is larger than its parent,
this is a request to the X server to maintain complete contents,
not just the region within the parent window boundaries.
While the X server maintains the window's contents,
Expose
events normally are not generated,
but the X server may stop maintaining
contents at any time.

When the contents of obscured regions of a window are being maintained,
regions obscured by noninferior windows are included in the destination
of graphics requests (and source, when the window is the source).
However, regions obscured by inferior windows are not included.

Save Under Flag

Some server implementations may preserve contents of
InputOutput
windows under other
InputOutput
windows.
This is not the same as preserving the contents of a window for you.
You may get better visual
appeal if transient windows (for example, pop-up menus) request that the system
preserve the screen contents under them,
so the temporarily obscured applications do not have to repaint.

You can set the save-under flag to
True
or
False
(default).
If save-under is
True,
the X server is advised that, when this window is mapped,
saving the contents of windows it obscures would be beneficial.

Backing Planes and Backing Pixel Attributes

You can set backing planes to indicate (with bits set to 1)
which bit planes of an
InputOutput
window hold dynamic data that must be preserved in backing store
and during save unders.
The default value for the backing-planes attribute is all bits set to 1.
You can set backing pixel to specify what bits to use in planes not
covered by backing planes.
The default value for the backing-pixel attribute is all bits set to 0.
The X server is free to save only the specified bit planes in the backing store
or the save under and is free to regenerate the remaining planes with
the specified pixel value.
Any extraneous bits in these values (that is, those bits beyond
the specified depth of the window) may be simply ignored.
If you request backing store or save unders,
you should use these members to minimize the amount of off-screen memory
required to store your window.

Event Mask and Do Not Propagate Mask Attributes

The event mask defines which events the client is interested in for this
InputOutput
or
InputOnly
window (or, for some event types, inferiors of this window).
The event mask is the bitwise inclusive OR of zero or more of the
valid event mask bits.
You can specify that no maskable events are reported by setting
NoEventMask
(default).

The do-not-propagate-mask attribute
defines which events should not be propagated to
ancestor windows when no client has the event type selected in this
InputOutput
or
InputOnly
window.
The do-not-propagate-mask is the bitwise inclusive OR of zero or more
of the following masks:
KeyPress,
KeyRelease,
ButtonPress,
ButtonRelease,
PointerMotion,
Button1Motion,
Button2Motion,
Button3Motion,
Button4Motion,
Button5Motion,
and
ButtonMotion.
You can specify that all events are propagated by setting
NoEventMask
(default).

Override Redirect Flag

To control window placement or to add decoration,
a window manager often needs to intercept (redirect) any map or configure
request.
Pop-up windows, however, often need to be mapped without a window manager
getting in the way.
To control whether an
InputOutput
or
InputOnly
window is to ignore these structure control facilities,
use the override-redirect flag.

The override-redirect flag specifies whether map and configure requests
on this window should override a
SubstructureRedirectMask
on the parent.
You can set the override-redirect flag to
True
or
False
(default).
Window managers use this information to avoid tampering with pop-up windows
(see also chapter 14).

Colormap Attribute

The colormap attribute specifies which colormap best reflects the true
colors of the
InputOutput
window.
The colormap must have the same visual type as the window,
or a
BadMatch
error results.
X servers capable of supporting multiple
hardware colormaps can use this information,
and window managers can use it for calls to
XInstallColormap.
You can set the colormap attribute to a colormap or to
CopyFromParent
(default).

If you set the colormap to
CopyFromParent,
the parent window's colormap is copied and used by its child.
However, the child window must have the same visual type as the parent,
or a
BadMatch
error results.
The parent window must not have a colormap of
None,
or a
BadMatch
error results.
The colormap is copied by sharing the colormap object between the child
and parent, not by making a complete copy of the colormap contents.
Subsequent changes to the parent window's colormap attribute do
not affect the child window.

Cursor Attribute

The cursor attribute specifies which cursor is to be used when the pointer is
in the
InputOutput
or
InputOnly
window.
You can set the cursor to a cursor or
None
(default).

If you set the cursor to
None,
the parent's cursor is used when the
pointer is in the
InputOutput
or
InputOnly
window, and any change in the parent's cursor will cause an
immediate change in the displayed cursor.
By calling
XFreeCursor,
the cursor can be freed immediately as long as no further explicit reference
to it is made.

Creating Windows

Xlib provides basic ways for creating windows,
and toolkits often supply higher-level functions specifically for
creating and placing top-level windows,
which are discussed in the appropriate toolkit documentation.
If you do not use a toolkit, however,
you must provide some standard information or hints for the window
manager by using the Xlib inter-client communication functions
(see chapter 14).

If you use Xlib to create your own top-level windows
(direct children of the root window),
you must observe the following rules so that all applications interact
reasonably across the different styles of window management:

You must never fight with the window manager for the size or
placement of your top-level window.
You must be able to deal with whatever size window you get,
even if this means that your application just prints a message
like “Please make me bigger” in its window.
You should only attempt to resize or move top-level windows in
direct response to a user request.
If a request to change the size of a top-level window fails,
you must be prepared to live with what you get.
You are free to resize or move the children of top-level
windows as necessary.
(Toolkits often have facilities for automatic relayout.)
If you do not use a toolkit that automatically sets standard window properties,
you should set these properties for top-level windows before mapping them.

For further information,
see chapter 14 and
the Inter-Client Communication Conventions Manual.

XCreateWindow
is the more general function that allows you to set specific window attributes
when you create a window.
XCreateSimpleWindow
creates a window that inherits its attributes from its parent window.

The X server acts as if
InputOnly
windows do not exist for
the purposes of graphics requests, exposure processing, and
VisibilityNotify
events.
An
InputOnly
window cannot be used as a
drawable (that is, as a source or destination for graphics requests).
InputOnly
and
InputOutput
windows act identically in other respects (properties,
grabs, input control, and so on).
Extension packages can define other classes of windows.

To create an unmapped window and set its window attributes, use
XCreateWindow.

Window XCreateWindow(Display *display, Window parent, int x, int y, unsigned int width, unsigned int height, unsigned int border_width, int depth, unsigned int class, Visual *visual, unsigned long valuemask, XSetWindowAttributes *attributes);

display	Specifies the connection to the X server.
parent	Specifies the parent window.
x
y	Specify the x and y coordinates, which are the top-left outside corner of the created window's borders and are relative to the inside of the parent window's borders.
width
height	Specify the width and height, which are the created window's inside dimensions and do not include the created window's borders. The dimensions must be nonzero, or a BadValue error results.
border_width	Specifies the width of the created window's border in pixels.
depth	Specifies the window's depth. A depth of CopyFromParent means the depth is taken from the parent.
class	Specifies the created window's class. You can pass InputOutput, InputOnly, or CopyFromParent. A class of CopyFromParent means the class is taken from the parent.
visual	Specifies the visual type. A visual of CopyFromParent means the visual type is taken from the parent.
valuemask	Specifies which window attributes are defined in the attributes argument. This mask is the bitwise inclusive OR of the valid attribute mask bits. If valuemask is zero, the attributes are ignored and are not referenced.
attributes	Specifies the structure from which the values (as specified by the value mask) are to be taken. The value mask should have the appropriate bits set to indicate which attributes have been set in the structure.

The
XCreateWindow
function creates an unmapped subwindow for a specified parent window,
returns the window ID of the created window,
and causes the X server to generate a
CreateNotify
event.
The created window is placed on top in the stacking order
with respect to siblings.

The coordinate system has the X axis horizontal and the Y axis vertical
with the origin [0, 0] at the upper-left corner.
Coordinates are integral,
in terms of pixels,
and coincide with pixel centers.
Each window and pixmap has its own coordinate system.
For a window,
the origin is inside the border at the inside, upper-left corner.

The border_width for an
InputOnly
window must be zero, or a
BadMatch
error results.
For class
InputOutput,
the visual type and depth must be a combination supported for the screen,
or a
BadMatch
error results.
The depth need not be the same as the parent,
but the parent must not be a window of class
InputOnly,
or a
BadMatch
error results.
For an
InputOnly
window,
the depth must be zero, and the visual must be one supported by the screen.
If either condition is not met,
a
BadMatch
error results.
The parent window, however, may have any depth and class.
If you specify any invalid window attribute for a window, a
BadMatch
error results.

The created window is not yet displayed (mapped) on the user's display.
To display the window, call
XMapWindow.
The new window initially uses the same cursor as
its parent.
A new cursor can be defined for the new window by calling
XDefineCursor.

The window will not be visible on the screen unless it and all of its
ancestors are mapped and it is not obscured by any of its ancestors.

XCreateWindow
can generate
BadAlloc,
BadColor,
BadCursor,
BadMatch,
BadPixmap,
BadValue,
and
BadWindow
errors.

To create an unmapped
InputOutput
subwindow of a given parent window, use
XCreateSimpleWindow.

Window XCreateSimpleWindow(Display *display, Window parent, int x, int y, unsigned int width, unsigned int height, unsigned int border_width, unsigned long border, unsigned long background);

display	Specifies the connection to the X server.
parent	Specifies the parent window.
x
y	Specify the x and y coordinates, which are the top-left outside corner of the new window's borders and are relative to the inside of the parent window's borders.
width
height	Specify the width and height, which are the created window's inside dimensions and do not include the created window's borders. The dimensions must be nonzero, or a BadValue error results.
border_width	Specifies the width of the created window's border in pixels.
border	Specifies the border pixel value of the window.
background	Specifies the background pixel value of the window.

The
XCreateSimpleWindow
function creates an unmapped
InputOutput
subwindow for a specified parent window, returns the
window ID of the created window, and causes the X server to generate a
CreateNotify
event.
The created window is placed on top in the stacking order with respect to
siblings.
Any part of the window that extends outside its parent window is clipped.
The border_width for an
InputOnly
window must be zero, or a
BadMatch
error results.
XCreateSimpleWindow
inherits its depth, class, and visual from its parent.
All other window attributes, except background and border,
have their default values.

XCreateSimpleWindow
can generate
BadAlloc,
BadMatch,
BadValue,
and
BadWindow
errors.

Destroying Windows

Xlib provides functions that you can use to destroy a window or destroy all
subwindows of a window.

To destroy a window and all of its subwindows, use
XDestroyWindow.

XDestroyWindow(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XDestroyWindow
function destroys the specified window as well as all of its subwindows and causes
the X server to generate a
DestroyNotify
event for each window.
The window should never be referenced again.
If the window specified by the w argument is mapped,
it is unmapped automatically.
The ordering of the
DestroyNotify
events is such that for any given window being destroyed,
DestroyNotify
is generated on any inferiors of the window before being generated on
the window itself.
The ordering among siblings and across subhierarchies is not otherwise
constrained.
If the window you specified is a root window, no windows are destroyed.
Destroying a mapped window will generate
Expose
events on other windows that were obscured by the window being destroyed.

XDestroyWindow
can generate a
BadWindow
error.

To destroy all subwindows of a specified window, use
XDestroySubwindows.

XDestroySubwindows(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XDestroySubwindows
function destroys all inferior windows of the specified window,
in bottom-to-top stacking order.
It causes the X server to generate a
DestroyNotify
event for each window.
If any mapped
subwindows were actually destroyed,
XDestroySubwindows
causes the X server to generate
Expose
events on the specified window.
This is much more efficient than deleting many windows
one at a time because much of the work need be performed only once for all
of the windows, rather than for each window.
The subwindows should never be referenced again.

XDestroySubwindows
can generate a
BadWindow
error.

Mapping Windows

A window is considered mapped if an
XMapWindow
call has been made on it.
It may not be visible on the screen for one of the following reasons:

It is obscured by another opaque window.
One of its ancestors is not mapped.
It is entirely clipped by an ancestor.

Expose
events are generated for the window when part or all of
it becomes visible on the screen.
A client receives the
Expose
events only if it has asked for them.
Windows retain their position in the stacking order when they are unmapped.

A window manager may want to control the placement of subwindows.
If
SubstructureRedirectMask
has been selected by a window manager
on a parent window (usually a root window),
a map request initiated by other clients on a child window is not performed,
and the window manager is sent a
MapRequest
event.
However, if the override-redirect flag on the child had been set to
True
(usually only on pop-up menus),
the map request is performed.

A tiling window manager might decide to reposition and resize other clients'
windows and then decide to map the window to its final location.
A window manager that wants to provide decoration might
reparent the child into a frame first.
For further information,
see sections 3.2.8
and 10.10.
Only a single client at a time can select for
SubstructureRedirectMask.

Similarly, a single client can select for
ResizeRedirectMask
on a parent window.
Then, any attempt to resize the window by another client is suppressed, and
the client receives a
ResizeRequest
event.

To map a given window, use
XMapWindow.

XMapWindow(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XMapWindow
function
maps the window and all of its
subwindows that have had map requests.
Mapping a window that has an unmapped ancestor does not display the
window but marks it as eligible for display when the ancestor becomes
mapped.
Such a window is called unviewable.
When all its ancestors are mapped,
the window becomes viewable
and will be visible on the screen if it is not obscured by another window.
This function has no effect if the window is already mapped.

If the override-redirect of the window is
False
and if some other client has selected
SubstructureRedirectMask
on the parent window, then the X server generates a
MapRequest
event, and the
XMapWindow
function does not map the window.
Otherwise, the window is mapped, and the X server generates a
MapNotify
event.

If the window becomes viewable and no earlier contents for it are remembered,
the X server tiles the window with its background.
If the window's background is undefined,
the existing screen contents are not
altered, and the X server generates zero or more
Expose
events.
If backing-store was maintained while the window was unmapped, no
Expose
events
are generated.
If backing-store will now be maintained,
a full-window exposure is always generated.
Otherwise, only visible regions may be reported.
Similar tiling and exposure take place for any newly viewable inferiors.

If the window is an
InputOutput
window,
XMapWindow
generates
Expose
events on each
InputOutput
window that it causes to be displayed.
If the client maps and paints the window
and if the client begins processing events,
the window is painted twice.
To avoid this,
first ask for
Expose
events and then map the window,
so the client processes input events as usual.
The event list will include
Expose
for each
window that has appeared on the screen.
The client's normal response to
an
Expose
event should be to repaint the window.
This method usually leads to simpler programs and to proper interaction
with window managers.

XMapWindow
can generate a
BadWindow
error.

To map and raise a window, use
XMapRaised.

XMapRaised(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XMapRaised
function
essentially is similar to
XMapWindow
in that it maps the window and all of its
subwindows that have had map requests.
However, it also raises the specified window to the top of the stack.
For additional information,
see
XMapWindow.

XMapRaised
can generate multiple
BadWindow
errors.

To map all subwindows for a specified window, use
XMapSubwindows.

XMapSubwindows(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XMapSubwindows

function maps all subwindows for a specified window in top-to-bottom stacking
order.
The X server generates
Expose
events on each newly displayed window.
This may be much more efficient than mapping many windows
one at a time because the server needs to perform much of the work
only once, for all of the windows, rather than for each window.

XMapSubwindows
can generate a
BadWindow
error.

Unmapping Windows

Xlib provides functions that you can use to unmap a window or all subwindows.

To unmap a window, use
XUnmapWindow.

XUnmapWindow(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XUnmapWindow
function unmaps the specified window and causes the X server to generate an
UnmapNotify

event.
If the specified window is already unmapped,
XUnmapWindow
has no effect.
Normal exposure processing on formerly obscured windows is performed.
Any child window will no longer be visible until another map call is
made on the parent.
In other words, the subwindows are still mapped but are not visible
until the parent is mapped.
Unmapping a window will generate
Expose
events on windows that were formerly obscured by it.

XUnmapWindow
can generate a
BadWindow
error.

To unmap all subwindows for a specified window, use
XUnmapSubwindows.

XUnmapSubwindows(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XUnmapSubwindows
function unmaps all subwindows for the specified window in bottom-to-top
stacking order.
It causes the X server to generate an
UnmapNotify
event on each subwindow and
Expose
events on formerly obscured windows.

Using this function is much more efficient than unmapping multiple windows
one at a time because the server needs to perform much of the work
only once, for all of the windows, rather than for each window.

XUnmapSubwindows
can generate a
BadWindow
error.

Configuring Windows

Xlib provides functions that you can use to
move a window, resize a window, move and resize a window, or
change a window's border width.
To change one of these parameters,
set the appropriate member of the
XWindowChanges
structure and OR in the corresponding value mask in subsequent calls to
XConfigureWindow.
The symbols for the value mask bits and the
XWindowChanges
structure are:

/* Configure window value mask bits */
#define      CWX              (1<<0)
#define      CWY              (1<<1)
#define      CWWidth          (1<<2)
#define      CWHeight         (1<<3)
#define      CWBorderWidth    (1<<4)
#define      CWSibling        (1<<5)
#define      CWStackMode      (1<<6)

/* Values */

typedef struct {
     int x, y;
     int width, height;
     int border_width;
     Window sibling;
     int stack_mode;
} XWindowChanges;

The x and y members are used to set the window's x and y coordinates,
which are relative to the parent's origin
and indicate the position of the upper-left outer corner of the window.
The width and height members are used to set the inside size of the window,
not including the border, and must be nonzero, or a
BadValue
error results.
Attempts to configure a root window have no effect.

The border_width member is used to set the width of the border in pixels.
Note that setting just the border width leaves the outer-left corner of the window
in a fixed position but moves the absolute position of the window's origin.
If you attempt to set the border-width attribute of an
InputOnly
window nonzero, a
BadMatch
error results.

The sibling member is used to set the sibling window for stacking operations.
The stack_mode member is used to set how the window is to be restacked
and can be set to
Above,
Below,
TopIf,
BottomIf,
or
Opposite.

If the override-redirect flag of the window is
False
and if some other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no further processing is performed.
Otherwise,
if some other client has selected
ResizeRedirectMask
on the window and the inside
width or height of the window is being changed,
a
ResizeRequest
event is generated, and the current inside width and height are
used instead.
Note that the override-redirect flag of the window has no effect
on
ResizeRedirectMask
and that
SubstructureRedirectMask
on the parent has precedence over
ResizeRedirectMask
on the window.

When the geometry of the window is changed as specified,
the window is restacked among siblings, and a
ConfigureNotify
event is generated if the state of the window actually changes.
GravityNotify
events are generated after
ConfigureNotify
events.
If the inside width or height of the window has actually changed,
children of the window are affected as specified.

If a window's size actually changes,
the window's subwindows move according to their window gravity.
Depending on the window's bit gravity,
the contents of the window also may be moved
(see section 3.2.3).

If regions of the window were obscured but now are not,
exposure processing is performed on these formerly obscured windows,
including the window itself and its inferiors.
As a result of increasing the width or height,
exposure processing is also performed on any new regions of the window
and any regions where window contents are lost.

The restack check (specifically, the computation for
BottomIf,
TopIf,
and
Opposite)
is performed with respect to the window's final size and position (as
controlled by the other arguments of the request), not its initial position.
If a sibling is specified without a stack_mode,
a
BadMatch
error results.

If a sibling and a stack_mode are specified,
the window is restacked as follows:

Above	The window is placed just above the sibling.
Below	The window is placed just below the sibling.
TopIf	If the sibling occludes the window, the window is placed at the top of the stack.
BottomIf	If the window occludes the sibling, the window is placed at the bottom of the stack.
Opposite	If the sibling occludes the window, the window is placed at the top of the stack. If the window occludes the sibling, the window is placed at the bottom of the stack.

If a stack_mode is specified but no sibling is specified,
the window is restacked as follows:

Above	The window is placed at the top of the stack.
Below	The window is placed at the bottom of the stack.
TopIf	If any sibling occludes the window, the window is placed at the top of the stack.
BottomIf	If the window occludes any sibling, the window is placed at the bottom of the stack.
Opposite	If any sibling occludes the window, the window is placed at the top of the stack. If the window occludes any sibling, the window is placed at the bottom of the stack.

Attempts to configure a root window have no effect.

To configure a window's size, location, stacking, or border, use
XConfigureWindow.

XConfigureWindow(Display *display, Window w, unsigned int value_mask, XWindowChanges *values);

display	Specifies the connection to the X server.
w	Specifies the window to be reconfigured.
value_mask	Specifies which values are to be set using information in the values structure. This mask is the bitwise inclusive OR of the valid configure window values bits.
values	Specifies the XWindowChanges structure.

The
XConfigureWindow
function uses the values specified in the
XWindowChanges
structure to reconfigure a window's size, position, border, and stacking order.
Values not specified are taken from the existing geometry of the window.

If a sibling is specified without a stack_mode or if the window
is not actually a sibling,
a
BadMatch
error results.
Note that the computations for
BottomIf,
TopIf,
and
Opposite
are performed with respect to the window's final geometry (as controlled by the
other arguments passed to
XConfigureWindow),
not its initial geometry.
Any backing store contents of the window, its
inferiors, and other newly visible windows are either discarded or
changed to reflect the current screen contents
(depending on the implementation).

XConfigureWindow
can generate
BadMatch,
BadValue,
and
BadWindow
errors.

To move a window without changing its size, use
XMoveWindow.

XMoveWindow(Display *display, Window w, int x, int y);

display	Specifies the connection to the X server.
w	Specifies the window to be moved.
x
y	Specify the x and y coordinates, which define the new location of the top-left pixel of the window's border or the window itself if it has no border.

The
XMoveWindow
function moves the specified window to the specified x and y coordinates,
but it does not change the window's size, raise the window, or
change the mapping state of the window.
Moving a mapped window may or may not lose the window's contents
depending on if the window is obscured by nonchildren
and if no backing store exists.
If the contents of the window are lost,
the X server generates
Expose
events.
Moving a mapped window generates
Expose
events on any formerly obscured windows.

If the override-redirect flag of the window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no further processing is
performed.
Otherwise, the window is moved.

XMoveWindow
can generate a
BadWindow
error.

To change a window's size without changing the upper-left coordinate, use
XResizeWindow.

XResizeWindow(Display *display, Window w, unsigned int width, unsigned int height);

display	Specifies the connection to the X server.
w	Specifies the window.
width
height	Specify the width and height, which are the interior dimensions of the window after the call completes.

The
XResizeWindow
function changes the inside dimensions of the specified window, not including
its borders.
This function does not change the window's upper-left coordinate or
the origin and does not restack the window.
Changing the size of a mapped window may lose its contents and generate
Expose
events.
If a mapped window is made smaller,
changing its size generates
Expose
events on windows that the mapped window formerly obscured.

XResizeWindow
can generate
BadValue
and
BadWindow
errors.

To change the size and location of a window, use
XMoveResizeWindow.

XMoveResizeWindow(Display *display, Window w, int x, int y, unsigned int width, unsigned int height);

display	Specifies the connection to the X server.
w	Specifies the window to be reconfigured.
x
y	Specify the x and y coordinates, which define the new position of the window relative to its parent.
width
height	Specify the width and height, which define the interior size of the window.

The
XMoveResizeWindow
function changes the size and location of the specified window
without raising it.
Moving and resizing a mapped window may generate an
Expose
event on the window.
Depending on the new size and location parameters,
moving and resizing a window may generate
Expose
events on windows that the window formerly obscured.

XMoveResizeWindow
can generate
BadValue
and
BadWindow
errors.

To change the border width of a given window, use
XSetWindowBorderWidth.

XSetWindowBorderWidth(Display *display, Window w, unsigned int width);

display	Specifies the connection to the X server.
w	Specifies the window.
width	Specifies the width of the window border.

The
XSetWindowBorderWidth
function sets the specified window's border width to the specified width.

XSetWindowBorderWidth
can generate a
BadWindow
error.

Changing Window Stacking Order

Xlib provides functions that you can use to raise, lower, circulate,
or restack windows.

To raise a window so that no sibling window obscures it, use
XRaiseWindow.

XRaiseWindow(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XRaiseWindow
function
raises the specified window to the top of the stack so that no sibling window
obscures it.
If the windows are regarded as overlapping sheets of paper stacked
on a desk,
then raising a window is analogous to moving the sheet to the top of
the stack but leaving its x and y location on the desk constant.
Raising a mapped window may generate
Expose
events for the window and any mapped subwindows that were formerly obscured.

If the override-redirect attribute of the window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates a
ConfigureRequest
event, and no processing is performed.
Otherwise, the window is raised.

XRaiseWindow
can generate a
BadWindow
error.

To lower a window so that it does not obscure any sibling windows, use
XLowerWindow.

XLowerWindow(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XLowerWindow
function lowers the specified window to the bottom of the stack
so that it does not obscure any sibling
windows.
If the windows are regarded as overlapping sheets of paper
stacked on a desk, then lowering a window is analogous to moving the
sheet to the bottom of the stack but leaving its x and y location on
the desk constant.
Lowering a mapped window will generate
Expose
events on any windows it formerly obscured.

XLowerWindow
can generate a
BadWindow
error.

To circulate a subwindow up or down, use
XCirculateSubwindows.

XCirculateSubwindows(Display *display, Window w, int direction);

display	Specifies the connection to the X server.
w	Specifies the window.
direction	Specifies the direction (up or down) that you want to circulate the window. You can pass RaiseLowest or LowerHighest.

The
XCirculateSubwindows
function circulates children of the specified window in the specified
direction.
If you specify
RaiseLowest,
XCirculateSubwindows
raises the lowest mapped child (if any) that is occluded
by another child to the top of the stack.
If you specify
LowerHighest,
XCirculateSubwindows
lowers the highest mapped child (if any) that occludes another child
to the bottom of the stack.
Exposure processing is then performed on formerly obscured windows.
If some other client has selected
SubstructureRedirectMask
on the window, the X server generates a
CirculateRequest
event, and no further processing is performed.
If a child is actually restacked,
the X server generates a
CirculateNotify
event.

XCirculateSubwindows
can generate
BadValue
and
BadWindow
errors.

To raise the lowest mapped child of a window that is partially or completely
occluded by another child, use
XCirculateSubwindowsUp.

XCirculateSubwindowsUp(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XCirculateSubwindowsUp
function raises the lowest mapped child of the specified window that
is partially
or completely
occluded by another child.
Completely unobscured children are not affected.
This is a convenience function equivalent to
XCirculateSubwindows
with
RaiseLowest
specified.

XCirculateSubwindowsUp
can generate a
BadWindow
error.

To lower the highest mapped child of a window that partially or
completely occludes another child, use
XCirculateSubwindowsDown.

XCirculateSubwindowsDown(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XCirculateSubwindowsDown
function lowers the highest mapped child of the specified window that partially
or completely occludes another child.
Completely unobscured children are not affected.
This is a convenience function equivalent to
XCirculateSubwindows
with
LowerHighest
specified.

XCirculateSubwindowsDown
can generate a
BadWindow
error.

To restack a set of windows from top to bottom, use
XRestackWindows.

XRestackWindows(Display *display, Window windows[], int nwindows);

display	Specifies the connection to the X server.
windows	Specifies an array containing the windows to be restacked.
nwindows	Specifies the number of windows to be restacked.

The
XRestackWindows
function restacks the windows in the order specified,
from top to bottom.
The stacking order of the first window in the windows array is unaffected,
but the other windows in the array are stacked underneath the first window,
in the order of the array.
The stacking order of the other windows is not affected.
For each window in the window array that is not a child of the specified window,
a
BadMatch
error results.

If the override-redirect attribute of a window is
False
and some
other client has selected
SubstructureRedirectMask
on the parent, the X server generates
ConfigureRequest
events for each window whose override-redirect flag is not set,
and no further processing is performed.
Otherwise, the windows will be restacked in top-to-bottom order.

XRestackWindows
can generate a
BadWindow
error.

Changing Window Attributes

Xlib provides functions that you can use to set window attributes.
XChangeWindowAttributes
is the more general function that allows you to set one or more window
attributes provided by the
XSetWindowAttributes
structure.
The other functions described in this section allow you to set one specific
window attribute, such as a window's background.

To change one or more attributes for a given window, use
XChangeWindowAttributes.

XChangeWindowAttributes(Display *display, Window w, unsigned long valuemask, XSetWindowAttributes *attributes);

display	Specifies the connection to the X server.
w	Specifies the window.
valuemask	Specifies which window attributes are defined in the attributes argument. This mask is the bitwise inclusive OR of the valid attribute mask bits. If valuemask is zero, the attributes are ignored and are not referenced. The values and restrictions are the same as for `XCreateWindow`.

attributes	Specifies the structure from which the values (as specified by the value mask) are to be taken. The value mask should have the appropriate bits set to indicate which attributes have been set in the structure (see section 3.2).

Depending on the valuemask,
the
XChangeWindowAttributes
function uses the window attributes in the
XSetWindowAttributes
structure to change the specified window attributes.
Changing the background does not cause the window contents to be
changed.
To repaint the window and its background, use
XClearWindow.
Setting the border or changing the background such that the
border tile origin changes causes the border to be repainted.
Changing the background of a root window to
None
or
ParentRelative
restores the default background pixmap.
Changing the border of a root window to
CopyFromParent
restores the default border pixmap.
Changing the win-gravity does not affect the current position of the
window.
Changing the backing-store of an obscured window to
WhenMapped
or
Always,
or changing the backing-planes, backing-pixel, or
save-under of a mapped window may have no immediate effect.
Changing the colormap of a window (that is, defining a new map, not
changing the contents of the existing map) generates a
ColormapNotify
event.
Changing the colormap of a visible window may have no
immediate effect on the screen because the map may not be installed
(see
XInstallColormap).
Changing the cursor of a root window to
None
restores the default
cursor.
Whenever possible, you are encouraged to share colormaps.

Multiple clients can select input on the same window.
Their event masks are maintained separately.
When an event is generated,
it is reported to all interested clients.
However, only one client at a time can select for
SubstructureRedirectMask,
ResizeRedirectMask,
and
ButtonPressMask.
If a client attempts to select any of these event masks
and some other client has already selected one,
a
BadAccess
error results.
There is only one do-not-propagate-mask for a window,
not one per client.

XChangeWindowAttributes
can generate
BadAccess,
BadColor,
BadCursor,
BadMatch,
BadPixmap,
BadValue,
and
BadWindow
errors.

To set the background of a window to a given pixel, use
XSetWindowBackground.

XSetWindowBackground(Display *display, Window w, unsigned long background_pixel);

display	Specifies the connection to the X server.
w	Specifies the window.
background_pixel	Specifies the pixel that is to be used for the background.

The
XSetWindowBackground
function sets the background of the window to the specified pixel value.
Changing the background does not cause the window contents to be changed.
XSetWindowBackground
uses a pixmap of undefined size filled with the pixel value you passed.
If you try to change the background of an
InputOnly
window, a
BadMatch
error results.

XSetWindowBackground
can generate
BadMatch
and
BadWindow
errors.

To set the background of a window to a given pixmap, use
XSetWindowBackgroundPixmap.

XSetWindowBackgroundPixmap(Display *display, Window w, Pixmap background_pixmap);

display	Specifies the connection to the X server.
w	Specifies the window.
background_pixmap	Specifies the background pixmap, ParentRelative, or None.

The
XSetWindowBackgroundPixmap
function sets the background pixmap of the window to the specified pixmap.
The background pixmap can immediately be freed if no further explicit
references to it are to be made.
If
ParentRelative
is specified,
the background pixmap of the window's parent is used,
or on the root window, the default background is restored.
If you try to change the background of an
InputOnly
window, a
BadMatch
error results.
If the background is set to
None,
the window has no defined background.

XSetWindowBackgroundPixmap
can generate
BadMatch,
BadPixmap,
and
BadWindow
errors.

XSetWindowBackground
and
XSetWindowBackgroundPixmap
do not change the current contents of the window.

To change and repaint a window's border to a given pixel, use
XSetWindowBorder.

XSetWindowBorder(Display *display, Window w, unsigned long border_pixel);

display	Specifies the connection to the X server.
w	Specifies the window.
border_pixel	Specifies the entry in the colormap.

The
XSetWindowBorder
function sets the border of the window to the pixel value you specify.
If you attempt to perform this on an
InputOnly
window, a
BadMatch
error results.

XSetWindowBorder
can generate
BadMatch
and
BadWindow
errors.

To change and repaint the border tile of a given window, use
XSetWindowBorderPixmap.

XSetWindowBorderPixmap(Display *display, Window w, Pixmap border_pixmap);

display	Specifies the connection to the X server.
w	Specifies the window.
border_pixmap	Specifies the border pixmap or CopyFromParent.

The
XSetWindowBorderPixmap
function sets the border pixmap of the window to the pixmap you specify.
The border pixmap can be freed immediately if no further explicit
references to it are to be made.
If you specify
CopyFromParent,
a copy of the parent window's border pixmap is used.
If you attempt to perform this on an
InputOnly
window, a
BadMatch
error results.

XSetWindowBorderPixmap
can generate
BadMatch,
BadPixmap,
and
BadWindow
errors.

To set the colormap of a given window, use
XSetWindowColormap.

XSetWindowColormap(Display *display, Window w, Colormap colormap);

display	Specifies the connection to the X server.
w	Specifies the window.
colormap	Specifies the colormap.

The
XSetWindowColormap
function sets the specified colormap of the specified window.
The colormap must have the same visual type as the window,
or a
BadMatch
error results.

XSetWindowColormap
can generate
BadColor,
BadMatch,
and
BadWindow
errors.

To define which cursor will be used in a window, use
XDefineCursor.

XDefineCursor(Display *display, Window w, Cursor cursor);

display	Specifies the connection to the X server.
w	Specifies the window.
cursor	Specifies the cursor that is to be displayed or None.

If a cursor is set, it will be used when the pointer is in the window.
If the cursor is
None,
it is equivalent to
XUndefineCursor.

XDefineCursor
can generate
BadCursor
and
BadWindow
errors.

To undefine the cursor in a given window, use
XUndefineCursor.

XUndefineCursor(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XUndefineCursor
function undoes the effect of a previous
XDefineCursor
for this window.
When the pointer is in the window,
the parent's cursor will now be used.
On the root window,
the default cursor is restored.

XUndefineCursor
can generate a
BadWindow
error.

Chapter 4. Window Information Functions

Table of Contents

Obtaining Window InformationTranslating Screen CoordinatesProperties and AtomsObtaining and Changing Window PropertiesSelections

After you connect the display to the X server and create a window, you can use the Xlib window
information functions to:

Obtain information about a window
Translate screen coordinates
Manipulate property lists
Obtain and change window properties
Manipulate selections

Obtaining Window Information

Xlib provides functions that you can use to obtain information about
the window tree, the window's current attributes,
the window's current geometry, or the current pointer coordinates.
Because they are most frequently used by window managers,
these functions all return a status to indicate whether the window still
exists.

To obtain the parent, a list of children, and number of children for
a given window, use
XQueryTree.

Status XQueryTree(Display *display, Window w, Window *root_return, Window *parent_return, Window **children_return, unsigned int *nchildren_return);

display	Specifies the connection to the X server.
w	Specifies the window whose list of children, root, parent, and number of children you want to obtain.
root_return	Returns the root window.
parent_return	Returns the parent window.
children_return	Returns the list of children.
nchildren_return	Returns the number of children.

The
XQueryTree
function returns the root ID, the parent window ID,
a pointer to the list of children windows
(NULL when there are no children),
and the number of children in the list for the specified window.
The children are listed in current stacking order, from bottom-most
(first) to top-most (last).
XQueryTree
returns zero if it fails and nonzero if it succeeds.
To free a non-NULL children list when it is no longer needed, use
XFree.

XQueryTree
can generate a
BadWindow
error.

To obtain the current attributes of a given window, use
XGetWindowAttributes.

Status XGetWindowAttributes(Display *display, Window w, XWindowAttributes *window_attributes_return);

display	Specifies the connection to the X server.
w	Specifies the window whose current attributes you want to obtain.
window_attributes_return	Returns the specified window's attributes in the XWindowAttributes structure.

The
XGetWindowAttributes
function returns the current attributes for the specified window to an
XWindowAttributes
structure.


typedef struct {
     int x, y;                     /* location of window */
     int width, height;            /* width and height of window */
     int border_width;             /* border width of window */
     int depth;                    /* depth of window */
     Visual *visual;               /* the associated visual structure */
     Window root;                  /* root of screen containing window */
     int class;                    /* InputOutput, InputOnly*/
     int bit_gravity;              /* one of the bit gravity values */
     int win_gravity;              /* one of the window gravity values */
     int backing_store;            /* NotUseful, WhenMapped, Always */
     unsigned long backing_planes; /* planes to be preserved if possible */
     unsigned long backing_pixel;  /* value to be used when restoring planes */
     Bool save_under;              /* boolean, should bits under be saved? */
     Colormap colormap;            /* color map to be associated with window */
     Bool map_installed;           /* boolean, is color map currently installed*/
     int map_state;                /* IsUnmapped, IsUnviewable, IsViewable */
     long all_event_masks;         /* set of events all people have interest in*/
     long your_event_mask;         /* my event mask */
     long do_not_propagate_mask;   /* set of events that should not propagate */
     Bool override_redirect;       /* boolean value for override-redirect */
     Screen *screen;               /* back pointer to correct screen */
} XWindowAttributes;

The x and y members are set to the upper-left outer
corner relative to the parent window's origin.
The width and height members are set to the inside size of the window,
not including the border.
The border_width member is set to the window's border width in pixels.
The depth member is set to the depth of the window
(that is, bits per pixel for the object).
The visual member is a pointer to the screen's associated
Visual
structure.
The root member is set to the root window of the screen containing the window.
The class member is set to the window's class and can be either
InputOutput
or
InputOnly.

The bit_gravity member is set to the window's bit gravity
and can be one of the following:

ForgetGravity	EastGravity
NorthWestGravity	SouthWestGravity
NorthGravity	SouthGravity
NorthEastGravity	SouthEastGravity
WestGravity	StaticGravity

The win_gravity member is set to the window's window gravity
and can be one of the following:

UnmapGravity	SouthWestGravity
NorthWestGravity	SouthGravity
NorthGravity	SouthEastGravity
NorthEastGravity	StaticGravity
WestGravity	CenterGravity
EastGravity

For additional information on gravity,
see section 3.2.3.

The backing_store member is set to indicate how the X server should maintain
the contents of a window
and can be
WhenMapped,
Always,
or
NotUseful.
The backing_planes member is set to indicate (with bits set to 1) which bit
planes of the window hold dynamic data that must be preserved in backing_stores
and during save_unders.
The backing_pixel member is set to indicate what values to use
for planes not set in backing_planes.

The save_under member is set to
True
or
False.
The colormap member is set to the colormap for the specified window and can be
a colormap ID or
None.
The map_installed member is set to indicate whether the colormap is
currently installed and can be
True
or
False.
The map_state member is set to indicate the state of the window and can be
IsUnmapped,
IsUnviewable,
or
IsViewable.
IsUnviewable
is used if the window is mapped but some ancestor is unmapped.

The all_event_masks member is set to the bitwise inclusive OR of all event
masks selected on the window by all clients.
The your_event_mask member is set to the bitwise inclusive OR of all event
masks selected by the querying client.
The do_not_propagate_mask member is set to the bitwise inclusive OR of the
set of events that should not propagate.

The override_redirect member is set to indicate whether this window overrides
structure control facilities and can be
True
or
False.
Window manager clients should ignore the window if this member is
True.

The screen member is set to a screen pointer that gives you a back pointer
to the correct screen.
This makes it easier to obtain the screen information without
having to loop over the root window fields to see which field matches.

XGetWindowAttributes
can generate
BadDrawable
and
BadWindow
errors.

To obtain the current geometry of a given drawable, use
XGetGeometry.

Status XGetGeometry(Display *display, Drawable d, Window *root_return, int *x_return, int *y_return, unsigned int *width_return, unsigned int *height_return, unsigned int *border_width_return, unsigned int *depth_return);

display	Specifies the connection to the X server.
d	Specifies the drawable, which can be a window or a pixmap.
root_return	Returns the root window.
x_return
y_return	Return the x and y coordinates that define the location of the drawable. For a window, these coordinates specify the upper-left outer corner relative to its parent's origin. For pixmaps, these coordinates are always zero.
width_return
height_return	Return the drawable's dimensions (width and height). For a window, these dimensions specify the inside size, not including the border.
border_width_return	Returns the border width in pixels. If the drawable is a pixmap, it returns zero.
depth_return	Returns the depth of the drawable (bits per pixel for the object).

The
XGetGeometry
function returns the root window and the current geometry of the drawable.
The geometry of the drawable includes the x and y coordinates, width and height,
border width, and depth.
These are described in the argument list.
It is legal to pass to this function a window whose class is
InputOnly.

XGetGeometry
can generate a
BadDrawable
error.

Translating Screen Coordinates

Applications sometimes
need to perform a coordinate transformation from the coordinate
space of one window to another window or need to determine which
window the pointing device is in.
XTranslateCoordinates
and
XQueryPointer
fulfill these needs (and avoid any race conditions) by
asking the X server to perform these operations.

To translate a coordinate in one window to the coordinate
space of another window, use
XTranslateCoordinates.

Bool XTranslateCoordinates(Display *display, Window src_w, Window dest_w, int src_x, int src_y, int *dest_x_return, int *dest_y_return, Window *child_return);

display	Specifies the connection to the X server.
src_w	Specifies the source window.
dest_w	Specifies the destination window.
src_x
src_y	Specify the x and y coordinates within the source window.
dest_x_return
dest_y_return	Return the x and y coordinates within the destination window.
child_return	Returns the child if the coordinates are contained in a mapped child of the destination window.

If
XTranslateCoordinates
returns
True,
it takes the src_x and src_y coordinates relative
to the source window's origin and returns these coordinates to
dest_x_return and dest_y_return
relative to the destination window's origin.
If
XTranslateCoordinates
returns
False,
src_w and dest_w are on different screens,
and dest_x_return and dest_y_return are zero.
If the coordinates are contained in a mapped child of dest_w,
that child is returned to child_return.
Otherwise, child_return is set to
None.

XTranslateCoordinates
can generate a
BadWindow
error.

To obtain the screen coordinates of the pointer
or to determine the pointer coordinates relative to a specified window, use
XQueryPointer.

Bool XQueryPointer(Display *display, Window w, Window *root_return, Window *child_return, int *root_x_return, int *root_y_return, int *win_x_return, int *win_y_return, unsigned int *mask_return);

display	Specifies the connection to the X server.
w	Specifies the window.
root_return	Returns the root window that the pointer is in.
child_return	Returns the child window that the pointer is located in, if any.
root_x_return
root_y_return	Return the pointer coordinates relative to the root window's origin.
win_x_return
win_y_return	Return the pointer coordinates relative to the specified window.
mask_return	Returns the current state of the modifier keys and pointer buttons.

The
XQueryPointer
function returns the root window the pointer is logically on and the pointer
coordinates relative to the root window's origin.
If
XQueryPointer
returns
False,
the pointer is not on the same screen as the specified window, and
XQueryPointer
returns
None
to child_return and zero to win_x_return and win_y_return.
If
XQueryPointer
returns
True,
the pointer coordinates returned to win_x_return and win_y_return
are relative to the origin of the specified window.
In this case,
XQueryPointer
returns the child that contains the pointer, if any,
or else
None
to child_return.

XQueryPointer
returns the current logical state of the keyboard buttons
and the modifier keys in mask_return.
It sets mask_return to the bitwise inclusive OR of one or more
of the button or modifier key bitmasks to match
the current state of the mouse buttons and the modifier keys.

Note that the logical state of a device (as seen through Xlib)
may lag the physical state if device event processing is frozen
(see section 12.1).

XQueryPointer
can generate a
BadWindow
error.

Properties and Atoms

A property is a collection of named, typed data.
The window system has a set of predefined properties

(for example, the name of a window, size hints, and so on), and users can
define any other arbitrary information and associate it with windows.
Each property has a name,
which is an ISO Latin-1 string.
For each named property,
a unique identifier (atom) is associated with it.
A property also has a type, for example, string or integer.
These types are also indicated using atoms, so arbitrary new
types can be defined.
Data of only one type may be associated with a single
property name.
Clients can store and retrieve properties associated with windows.
For efficiency reasons,
an atom is used rather than a character string.
XInternAtom
can be used to obtain the atom for property names.

A property is also stored in one of several possible formats.
The X server can store the information as 8-bit quantities, 16-bit
quantities, or 32-bit quantities.
This permits the X server to present the data in the byte order that the
client expects.

If you define further properties of complex type,
you must encode and decode them yourself.
These functions must be carefully written if they are to be portable.
For further information about how to write a library extension,
see appendix C.

The type of a property is defined by an atom, which allows for
arbitrary extension in this type scheme.

Certain property names are
predefined in the server for commonly used functions.
The atoms for these properties are defined in
<X11/Xatom.h>.

To avoid name clashes with user symbols, the
#define
name for each atom has the XA_ prefix.
For an explanation of the functions that let you get and set
much of the information stored in these predefined properties,
see chapter 14.

The core protocol imposes no semantics on these property names,
but semantics are specified in other X Consortium standards,
such as the Inter-Client Communication Conventions Manual
and the X Logical Font Description Conventions.

You can use properties to communicate other information between
applications.
The functions described in this section let you define new properties
and get the unique atom IDs in your applications.

Although any particular atom can have some client interpretation
within each of the name spaces,
atoms occur in five distinct name spaces within the protocol:

Selections
Property names
Property types
Font properties
Type of a
ClientMessage
event (none are built into the X server)

The built-in selection property names are:

PRIMARY

SECONDARY

The built-in property names are:

CUT_BUFFER0	RESOURCE_MANAGER
CUT_BUFFER1	WM_CLASS
CUT_BUFFER2	WM_CLIENT_MACHINE
CUT_BUFFER3	WM_COLORMAP_WINDOWS
CUT_BUFFER4	WM_COMMAND
CUT_BUFFER5	WM_HINTS
CUT_BUFFER6	WM_ICON_NAME
CUT_BUFFER7	WM_ICON_SIZE
RGB_BEST_MAP	WM_NAME
RGB_BLUE_MAP	WM_NORMAL_HINTS
RGB_DEFAULT_MAP	WM_PROTOCOLS
RGB_GRAY_MAP	WM_STATE
RGB_GREEN_MAP	WM_TRANSIENT_FOR
RGB_RED_MAP	WM_ZOOM_HINTS

The built-in property types are:

ARC	PIXMAP
ATOM	POINT
BITMAP	RGB_COLOR_MAP
CARDINAL	RECTANGLE
COLORMAP	STRING
CURSOR	VISUALID
DRAWABLE	WINDOW
FONT	WM_HINTS
INTEGER	WM_SIZE_HINTS

The built-in font property names are:

MIN_SPACE	STRIKEOUT_DESCENT
NORM_SPACE	STRIKEOUT_ASCENT
MAX_SPACE	ITALIC_ANGLE
END_SPACE	X_HEIGHT
SUPERSCRIPT_X	QUAD_WIDTH
SUPERSCRIPT_Y	WEIGHT
SUBSCRIPT_X	POINT_SIZE
SUBSCRIPT_Y	RESOLUTION
UNDERLINE_POSITION	COPYRIGHT
UNDERLINE_THICKNESS	NOTICE
FONT_NAME	FAMILY_NAME
FULL_NAME	CAP_HEIGHT

For further information about font properties,
see section 8.5.

To return an atom for a given name, use
XInternAtom.

Atom XInternAtom(Display *display, char *atom_name, Bool only_if_exists);

display	Specifies the connection to the X server.
atom_name	Specifies the name associated with the atom you want returned.
only_if_exists	Specifies a Boolean value that indicates whether the atom must be created.

The
XInternAtom
function returns the atom identifier associated with the specified atom_name
string.
If only_if_exists is
False,
the atom is created if it does not exist.
Therefore,
XInternAtom
can return
None.
If the atom name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Uppercase and lowercase matter;
the strings “thing”, “Thing”, and “thinG”
all designate different atoms.
The atom will remain defined even after the client's connection closes.
It will become undefined only when the last connection to
the X server closes.

XInternAtom
can generate
BadAlloc
and
BadValue
errors.

To return atoms for an array of names, use
XInternAtoms.

Status XInternAtoms(Display *display, char **names, int count, Bool only_if_exists, Atom *atoms_return);

display	Specifies the connection to the X server.
names	Specifies the array of atom names.
count	Specifies the number of atom names in the array.
only_if_exists	Specifies a Boolean value that indicates whether the atom must be created.
atoms_return	Returns the atoms.

The
XInternAtoms
function returns the atom identifiers associated with the specified names.
The atoms are stored in the atoms_return array supplied by the caller.
Calling this function is equivalent to calling
XInternAtom
for each of the names in turn with the specified value of only_if_exists,
but this function minimizes the number of round-trip protocol exchanges
between the client and the X server.

This function returns a nonzero status if atoms are returned for
all of the names;
otherwise, it returns zero.

XInternAtoms
can generate
BadAlloc
and
BadValue
errors.

To return a name for a given atom identifier, use
XGetAtomName.

char *XGetAtomName(Display *display, Atom atom);

display	Specifies the connection to the X server.
atom	Specifies the atom for the property name you want returned.

The
XGetAtomName
function returns the name associated with the specified atom.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned string is in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
To free the resulting string,
call
XFree.

XGetAtomName
can generate a
BadAtom
error.

To return the names for an array of atom identifiers, use
XGetAtomNames.

Status XGetAtomNames(Display *display, Atom *atoms, int count, char **names_return);

display	Specifies the connection to the X server.
atoms	Specifies the array of atoms.
count	Specifies the number of atoms in the array.
names_return	Returns the atom names.

The
XGetAtomNames
function returns the names associated with the specified atoms.
The names are stored in the names_return array supplied by the caller.
Calling this function is equivalent to calling
XGetAtomName
for each of the atoms in turn,
but this function minimizes the number of round-trip protocol exchanges
between the client and the X server.

This function returns a nonzero status if names are returned for
all of the atoms;
otherwise, it returns zero.

XGetAtomNames
can generate a
BadAtom
error.

Obtaining and Changing Window Properties

You can attach a property list to every window.
Each property has a name, a type, and a value
(see section 4.3).
The value is an array of 8-bit, 16-bit, or 32-bit quantities,
whose interpretation is left to the clients. The type
char
is used to represent 8-bit quantities, the type
short
is used to represent 16-bit quantities, and the type
long
is used to represent 32-bit quantities.

Xlib provides functions that you can use to obtain,
change, update, or interchange window properties.
In addition, Xlib provides other utility functions for inter-client
communication
(see chapter 14).

To obtain the type, format, and value of a property of a given window, use
XGetWindowProperty.

int XGetWindowProperty(Display *display, Window w, Atom property, long long_offset, long long_length, Bool delete, Atom req_type, Atom *actual_type_return, int *actual_format_return, unsigned long *nitems_return, unsigned long *bytes_after_return, unsigned char **prop_return);

display	Specifies the connection to the X server.
w	Specifies the window whose property you want to obtain.
property	Specifies the property name.
long_offset	Specifies the offset in the specified property (in 32-bit quantities) where the data is to be retrieved.
long_length	Specifies the length in 32-bit multiples of the data to be retrieved.
delete	Specifies a Boolean value that determines whether the property is deleted.
req_type	Specifies the atom identifier associated with the property type or AnyPropertyType.
actual_type_return	Returns the atom identifier that defines the actual type of the property.
actual_format_return	Returns the actual format of the property.
nitems_return	Returns the actual number of 8-bit, 16-bit, or 32-bit items stored in the prop_return data.
bytes_after_return	Returns the number of bytes remaining to be read in the property if a partial read was performed.
prop_return	Returns the data in the specified format.

The
XGetWindowProperty
function returns the actual type of the property; the actual format of the property;
the number of 8-bit, 16-bit, or 32-bit items transferred; the number of bytes remaining
to be read in the property; and a pointer to the data actually returned.
XGetWindowProperty
sets the return arguments as follows:

If the specified property does not exist for the specified window,
XGetWindowProperty
returns
None
to actual_type_return and the value zero to
actual_format_return and bytes_after_return.
The nitems_return argument is empty.
In this case, the delete argument is ignored.
If the specified property exists
but its type does not match the specified type,
XGetWindowProperty
returns the actual property type to actual_type_return,
the actual property format (never zero) to actual_format_return,
and the property length in bytes
(even if the actual_format_return is 16 or 32)
to bytes_after_return.
It also ignores the delete argument.
The nitems_return argument is empty.
If the specified property exists and either you assign
AnyPropertyType
to the req_type argument or the specified type matches the actual property type,
XGetWindowProperty
returns the actual property type to actual_type_return and the actual
property format (never zero) to actual_format_return.
It also returns a value to bytes_after_return and nitems_return, by
defining the following
values:
N = actual length of the stored property in bytes
(even if the format is 16 or 32)
I = 4 * long_offset
T = N - I
L = MINIMUM(T, 4 * long_length)
A = N - (I + L)
The returned value starts at byte index I in the property (indexing
from zero), and its length in bytes is L.
If the value for long_offset causes L to be negative,
a
BadValue
error results.
The value of bytes_after_return is A,
giving the number of trailing unread bytes in the stored property.

If the returned format is 8, the returned data is represented as a
char
array.
If the returned format is 16, the returned data is represented as a
short
array and should be cast to that type to obtain the elements.
If the returned format is 32, the returned data is represented as a
long
array and should be cast to that type to obtain the elements.

XGetWindowProperty
always allocates one extra byte in prop_return
(even if the property is zero length)
and sets it to zero so that simple properties consisting of characters
do not have to be copied into yet another string before use.

If delete is
True
and bytes_after_return is zero,
XGetWindowProperty
deletes the property
from the window and generates a
PropertyNotify
event on the window.

The function returns
Success
if it executes successfully.
To free the resulting data,
use
XFree.

XGetWindowProperty
can generate
BadAtom,
BadValue,
and
BadWindow
errors.

To obtain a given window's property list, use
XListProperties.

Atom *XListProperties(Display *display, Window w, int *num_prop_return);

display	Specifies the connection to the X server.
w	Specifies the window whose property list you want to obtain.
num_prop_return	Returns the length of the properties array.

The
XListProperties
function returns a pointer to an array of atom properties that are defined for
the specified window or returns NULL if no properties were found.
To free the memory allocated by this function, use
XFree.

XListProperties
can generate a
BadWindow
error.

To change a property of a given window, use
XChangeProperty.

XChangeProperty(Display *display, Window w, Atom property, Atom type, int format, int mode, unsignedchar *data, int nelements);

display	Specifies the connection to the X server.
w	Specifies the window whose property you want to change.
property	Specifies the property name.
type	Specifies the type of the property. The X server does not interpret the type but simply passes it back to an application that later calls `XGetWindowProperty`.
format	Specifies whether the data should be viewed as a list of 8-bit, 16-bit, or 32-bit quantities. Possible values are 8, 16, and 32. This information allows the X server to correctly perform byte-swap operations as necessary. If the format is 16-bit or 32-bit, you must explicitly cast your data pointer to an (unsigned char *) in the call to `XChangeProperty`.
mode	Specifies the mode of the operation. You can pass PropModeReplace, PropModePrepend, or PropModeAppend.
data	Specifies the property data.
nelements	Specifies the number of elements of the specified data format.

The
XChangeProperty
function alters the property for the specified window and
causes the X server to generate a
PropertyNotify
event on that window.
XChangeProperty
performs the following:

If mode is
PropModeReplace,
XChangeProperty
discards the previous property value and stores the new data.
If mode is
PropModePrepend
or
PropModeAppend,
XChangeProperty
inserts the specified data before the beginning of the existing data
or onto the end of the existing data, respectively.
The type and format must match the existing property value,
or a
BadMatch
error results.
If the property is undefined,
it is treated as defined with the correct type and
format with zero-length data.

If the specified format is 8, the property data must be a
char
array.
If the specified format is 16, the property data must be a
short
array.
If the specified format is 32, the property data must be a
long
array.

The lifetime of a property is not tied to the storing client.
Properties remain until explicitly deleted, until the window is destroyed,
or until the server resets.
For a discussion of what happens when the connection to the X server is closed,
see section 2.6.
The maximum size of a property is server dependent and can vary dynamically
depending on the amount of memory the server has available.
(If there is insufficient space, a
BadAlloc
error results.)

XChangeProperty
can generate
BadAlloc,
BadAtom,
BadMatch,
BadValue,
and
BadWindow
errors.

To rotate a window's property list, use
XRotateWindowProperties.

XRotateWindowProperties(Display *display, Window w, Atom properties[], int num_prop, int npositions);

display	Specifies the connection to the X server.
w	Specifies the window.
properties	Specifies the array of properties that are to be rotated.
num_prop	Specifies the length of the properties array.
npositions	Specifies the rotation amount.

The
XRotateWindowProperties
function allows you to rotate properties on a window and causes
the X server to generate
PropertyNotify
events.
If the property names in the properties array are viewed as being numbered
starting from zero and if there are num_prop property names in the list,
then the value associated with property name I becomes the value associated
with property name (I + npositions) mod N for all I from zero to N − 1.
The effect is to rotate the states by npositions places around the virtual ring
of property names (right for positive npositions,
left for negative npositions).
If npositions mod N is nonzero,
the X server generates a
PropertyNotify
event for each property in the order that they are listed in the array.
If an atom occurs more than once in the list or no property with that
name is defined for the window,
a
BadMatch
error results.
If a
BadAtom
or
BadMatch
error results,
no properties are changed.

XRotateWindowProperties
can generate
BadAtom,
BadMatch,
and
BadWindow
errors.

To delete a property on a given window, use
XDeleteProperty.

XDeleteProperty(Display *display, Window w, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window whose property you want to delete.
property	Specifies the property name.

The
XDeleteProperty
function deletes the specified property only if the
property was defined on the specified window
and causes the X server to generate a
PropertyNotify
event on the window unless the property does not exist.

XDeleteProperty
can generate
BadAtom
and
BadWindow
errors.

Selections

Selections are one method used by applications to exchange data.
By using the property mechanism,
applications can exchange data of arbitrary types and can negotiate
the type of the data.
A selection can be thought of as an indirect property with a dynamic type.
That is, rather than having the property stored in the X server,
the property is maintained by some client (the owner).
A selection is global in nature (considered to belong to the user
but be maintained by clients) rather than being private to a particular
window subhierarchy or a particular set of clients.

Xlib provides functions that you can use to set, get, or request conversion
of selections.
This allows applications to implement the notion of current selection,
which requires that notification be sent to applications when they no
longer own the selection.
Applications that support selection often highlight the current selection
and so must be informed when another application has
acquired the selection so that they can unhighlight the selection.

When a client asks for the contents of
a selection, it specifies a selection target type.
This target type
can be used to control the transmitted representation of the contents.
For example, if the selection is “the last thing the user clicked on”
and that is currently an image, then the target type might specify
whether the contents of the image should be sent in XY format or Z format.

The target type can also be used to control the class of
contents transmitted, for example,
asking for the “looks” (fonts, line
spacing, indentation, and so forth) of a paragraph selection, not the
text of the paragraph.
The target type can also be used for other
purposes.
The protocol does not constrain the semantics.

To set the selection owner, use
XSetSelectionOwner.

XSetSelectionOwner(Display *display, Atom selection, Window owner, Time time);

display	Specifies the connection to the X server.
selection	Specifies the selection atom.
owner	Specifies the owner of the specified selection atom. You can pass a window or None.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

The
XSetSelectionOwner
function changes the owner and last-change time for the specified selection
and has no effect if the specified time is earlier than the current
last-change time of the specified selection
or is later than the current X server time.
Otherwise, the last-change time is set to the specified time,
with
CurrentTime
replaced by the current server time.
If the owner window is specified as
None,
then the owner of the selection becomes
None
(that is, no owner).
Otherwise, the owner of the selection becomes the client executing
the request.

If the new owner (whether a client or
None)
is not
the same as the current owner of the selection and the current
owner is not
None,
the current owner is sent a
SelectionClear
event.
If the client that is the owner of a selection is later
terminated (that is, its connection is closed)
or if the owner window it has specified in the request is later
destroyed,
the owner of the selection automatically
reverts to
None,
but the last-change time is not affected.
The selection atom is uninterpreted by the X server.
XGetSelectionOwner
returns the owner window, which is reported in
SelectionRequest
and
SelectionClear
events.
Selections are global to the X server.

XSetSelectionOwner
can generate
BadAtom
and
BadWindow
errors.

To return the selection owner, use
XGetSelectionOwner.

Window XGetSelectionOwner(Display *display, Atom selection);

display	Specifies the connection to the X server.
selection	Specifies the selection atom whose owner you want returned.

The
XGetSelectionOwner
function
returns the window ID associated with the window that currently owns the
specified selection.
If no selection was specified, the function returns the constant
None.
If
None
is returned,
there is no owner for the selection.

XGetSelectionOwner
can generate a
BadAtom
error.

To request conversion of a selection, use
XConvertSelection.

XConvertSelection(Display *display, Atom selection, Atom target, Atom property, Window requestor, Time time);

display	Specifies the connection to the X server.
selection	Specifies the selection atom.
target	Specifies the target atom.
property	Specifies the property name. You also can pass None.
requestor	Specifies the requestor.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

XConvertSelection
requests that the specified selection be converted to the specified target
type:

If the specified selection has an owner, the X server sends a
SelectionRequest
event to that owner.
If no owner for the specified
selection exists, the X server generates a
SelectionNotify
event to the
requestor with property
None.

The arguments are passed on unchanged in either of the events.
There are two predefined selection atoms: PRIMARY and SECONDARY.

XConvertSelection
can generate
BadAtom
and
BadWindow
errors.

Chapter 5. Pixmap and Cursor Functions

Table of Contents

Creating and Freeing PixmapsCreating, Recoloring, and Freeing Cursors

Creating and Freeing Pixmaps

Pixmaps can only be used on the screen on which they were created.
Pixmaps are off-screen resources that are used for various operations,
such as defining cursors as tiling patterns
or as the source for certain raster operations.
Most graphics requests can operate either on a window or on a pixmap.
A bitmap is a single bit-plane pixmap.

To create a pixmap of a given size, use
XCreatePixmap.

Pixmap XCreatePixmap(Display *display, Drawable d, unsigned int width, unsigned int height, unsigned int depth);

display	Specifies the connection to the X server.
d	Specifies which screen the pixmap is created on.
width
height	Specify the width and height, which define the dimensions of the pixmap.
depth	Specifies the depth of the pixmap.

The
XCreatePixmap
function creates a pixmap of the width, height, and depth you specified
and returns a pixmap ID that identifies it.
It is valid to pass an
InputOnly
window to the drawable argument.
The width and height arguments must be nonzero,
or a
BadValue
error results.
The depth argument must be one of the depths supported by the screen
of the specified drawable,
or a
BadValue
error results.

The server uses the specified drawable to determine on which screen
to create the pixmap.
The pixmap can be used only on this screen
and only with other drawables of the same depth (see
XCopyPlane
for an exception to this rule).
The initial contents of the pixmap are undefined.

XCreatePixmap
can generate
BadAlloc,
BadDrawable,
and
BadValue
errors.

To free all storage associated with a specified pixmap, use
XFreePixmap.

XFreePixmap(Display *display, Pixmap pixmap);

display	Specifies the connection to the X server.
pixmap	Specifies the pixmap.

The
XFreePixmap
function first deletes the association between the pixmap ID and the pixmap.
Then, the X server frees the pixmap storage when there are no references to it.
The pixmap should never be referenced again.

XFreePixmap
can generate a
BadPixmap
error.

Creating, Recoloring, and Freeing Cursors

Each window can have a different cursor defined for it.
Whenever the pointer is in a visible window,
it is set to the cursor defined for that window.
If no cursor was defined for that window,
the cursor is the one defined for the parent window.

From X's perspective,
a cursor consists of a cursor source, mask, colors, and a hotspot.
The mask pixmap determines the shape of the cursor and must be a depth
of one.
The source pixmap must have a depth of one,
and the colors determine the colors of the source.
The hotspot defines the point on the cursor that is reported
when a pointer event occurs.
There may be limitations imposed by the hardware on
cursors as to size and whether a mask is implemented.

XQueryBestCursor
can be used to find out what sizes are possible.
There is a standard font for creating cursors, but
Xlib provides functions that you can use to create cursors
from an arbitrary font or from bitmaps.

To create a cursor from the standard cursor font, use
XCreateFontCursor.

#include <X11/cursorfont.h>

Cursor XCreateFontCursor(Display *display, unsigned int shape);

display	Specifies the connection to the X server.
shape	Specifies the shape of the cursor.

X provides a set of standard cursor shapes in a special font named
cursor.
Applications are encouraged to use this interface for their cursors
because the font can be customized for the individual display type.
The shape argument specifies which glyph of the standard fonts
to use.

The hotspot comes from the information stored in the cursor font.
The initial colors of a cursor are a black foreground and a white
background (see
XRecolorCursor).
For further information about cursor shapes,
see appendix B.

XCreateFontCursor
can generate
BadAlloc
and
BadValue
errors.

To create a cursor from font glyphs, use
XCreateGlyphCursor.

Cursor XCreateGlyphCursor(Display *display, Font source_font, Font mask_font, unsigned int source_char, unsigned int mask_char, XColor *foreground_color, XColor *background_color);

display	Specifies the connection to the X server.
source_font	Specifies the font for the source glyph.
mask_font	Specifies the font for the mask glyph or None.
source_char	Specifies the character glyph for the source.
mask_char	Specifies the glyph character for the mask.
foreground_color	Specifies the RGB values for the foreground of the source.
background_color	Specifies the RGB values for the background of the source.

The
XCreateGlyphCursor
function is similar to
XCreatePixmapCursor
except that the source and mask bitmaps are obtained from the specified
font glyphs.
The source_char must be a defined glyph in source_font,
or a
BadValue
error results.
If mask_font is given,
mask_char must be a defined glyph in mask_font,
or a
BadValue
error results.
The mask_font and character are optional.
The origins of the source_char and mask_char (if defined) glyphs are
positioned coincidently and define the hotspot.
The source_char and mask_char need not have the same bounding box metrics,
and there is no restriction on the placement of the hotspot relative to the bounding
boxes.
If no mask_char is given, all pixels of the source are displayed.
You can free the fonts immediately by calling
XFreeFont
if no further explicit references to them are to be made.

For 2-byte matrix fonts,
the 16-bit value should be formed with the byte1
member in the most significant byte and the byte2 member in the
least significant byte.

XCreateGlyphCursor
can generate
BadAlloc,
BadFont,
and
BadValue
errors.

To create a cursor from two bitmaps,
use
XCreatePixmapCursor.

Cursor XCreatePixmapCursor(Display *display, Pixmap source, Pixmap mask, XColor *foreground_color, XColor *background_color, unsigned int x, unsigned int y);

display	Specifies the connection to the X server.
source	Specifies the shape of the source cursor.
mask	Specifies the cursor's source bits to be displayed or None.
foreground_color	Specifies the RGB values for the foreground of the source.
background_color	Specifies the RGB values for the background of the source.
x
y	Specify the x and y coordinates, which indicate the hotspot relative to the source's origin.

The
XCreatePixmapCursor
function creates a cursor and returns the cursor ID associated with it.
The foreground and background RGB values must be specified using
foreground_color and background_color,
even if the X server only has a
StaticGray
or
GrayScale
screen.
The foreground color is used for the pixels set to 1 in the
source, and the background color is used for the pixels set to 0.
Both source and mask, if specified, must have depth one (or a
BadMatch
error results) but can have any root.
The mask argument defines the shape of the cursor.
The pixels set to 1 in the mask define which source pixels are displayed,
and the pixels set to 0 define which pixels are ignored.
If no mask is given,
all pixels of the source are displayed.
The mask, if present, must be the same size as the pixmap defined by the
source argument, or a
BadMatch
error results.
The hotspot must be a point within the source,
or a
BadMatch
error results.

The components of the cursor can be transformed arbitrarily to meet
display limitations.
The pixmaps can be freed immediately if no further explicit references
to them are to be made.
Subsequent drawing in the source or mask pixmap has an undefined effect on the
cursor.
The X server might or might not make a copy of the pixmap.

XCreatePixmapCursor
can generate
BadAlloc
and
BadPixmap
errors.

To determine useful cursor sizes, use
XQueryBestCursor.

Status XQueryBestCursor(Display *display, Drawable d, unsigned int width, unsigned int height, unsigned int *width_return, unsigned int *height_return);

display	Specifies the connection to the X server.
d	Specifies the drawable, which indicates the screen.
width
height	Specify the width and height of the cursor that you want the size information for.
width_return
height_return	Return the best width and height that is closest to the specified width and height.

Some displays allow larger cursors than other displays.
The
XQueryBestCursor
function provides a way to find out what size cursors are actually
possible on the display.

It returns the largest size that can be displayed.
Applications should be prepared to use smaller cursors on displays that
cannot support large ones.

XQueryBestCursor
can generate a
BadDrawable
error.

To change the color of a given cursor, use
XRecolorCursor.

XRecolorCursor(Display *display, Cursor cursor, XColor *foreground_color, XColor *background_color);

display	Specifies the connection to the X server.
cursor	Specifies the cursor.
foreground_color	Specifies the RGB values for the foreground of the source.
background_color	Specifies the RGB values for the background of the source.

The
XRecolorCursor
function changes the color of the specified cursor, and
if the cursor is being displayed on a screen,
the change is visible immediately.
The pixel members of the
XColor
structures are ignored; only the RGB values are used.

XRecolorCursor
can generate a
BadCursor
error.

To free (destroy) a given cursor, use
XFreeCursor.

XFreeCursor(Display *display, Cursor cursor);

display	Specifies the connection to the X server.
cursor	Specifies the cursor.

The
XFreeCursor
function deletes the association between the cursor resource ID
and the specified cursor.
The cursor storage is freed when no other resource references it.
The specified cursor ID should not be referred to again.

XFreeCursor
can generate a
BadCursor
error.

Chapter 6. Color Management Functions

Table of Contents

Color StructuresColor StringsRGB Device String SpecificationRGB Intensity String SpecificationDevice-Independent String SpecificationsColor Conversion Contexts and Gamut MappingCreating, Copying, and Destroying ColormapsMapping Color Names to ValuesAllocating and Freeing Color CellsModifying and Querying Colormap CellsColor Conversion Context FunctionsGetting and Setting the Color Conversion Context of a ColormapObtaining the Default Color Conversion ContextColor Conversion Context MacrosModifying Attributes of a Color Conversion ContextCreating and Freeing a Color Conversion ContextConverting between Color SpacesCallback FunctionsPrototype Gamut Compression ProcedureSupplied Gamut Compression ProceduresPrototype White Point Adjustment ProcedureSupplied White Point Adjustment ProceduresGamut Querying FunctionsRed, Green, and Blue QueriesCIELab QueriesCIELuv QueriesTekHVC QueriesColor Management ExtensionsColor SpacesAdding Device-Independent Color SpacesQuerying Color Space Format and PrefixCreating Additional Color SpacesParse String CallbackColor Specification Conversion CallbackFunction SetsAdding Function SetsCreating Additional Function Sets

Each X window always has an associated colormap that
provides a level of indirection between pixel values and colors displayed
on the screen.
Xlib provides functions that you can use to manipulate a colormap.
The X protocol defines colors using values in the RGB color space.
The RGB color space is device dependent;
rendering an RGB value on differing output devices typically results
in different colors.
Xlib also provides a means for clients to specify color using
device-independent color spaces for consistent results across devices.
Xlib supports device-independent color spaces derivable from the CIE XYZ
color space.
This includes the CIE XYZ, xyY, L*u*v*, and L*a*b* color spaces as well as
the TekHVC color space.

This chapter discusses how to:

Create, copy, and destroy a colormap
Specify colors by name or value
Allocate, modify, and free color cells
Read entries in a colormap
Convert between color spaces
Control aspects of color conversion
Query the color gamut of a screen
Add new color spaces

All functions, types, and symbols in this chapter with the prefix “Xcms”
are defined in
<X11/Xcms.h>.

The remaining functions and types are defined in
<X11/Xlib.h>.

Functions in this chapter manipulate the representation of color on the
screen.
For each possible value that a pixel can take in a window,
there is a color cell in the colormap.
For example,
if a window is 4 bits deep, pixel values 0 through 15 are defined.
A colormap is a collection of color cells.
A color cell consists of a triple of red, green, and blue (RGB) values.
The hardware imposes limits on the number of significant
bits in these values.
As each pixel is read out of display memory, the pixel
is looked up in a colormap.
The RGB value of the cell determines what color is displayed on the screen.
On a grayscale display with a black-and-white monitor,
the values are combined to determine the brightness on the screen.

Typically, an application allocates color cells or sets of color cells
to obtain the desired colors.
The client can allocate read-only cells.
In which case,
the pixel values for these colors can be shared among multiple applications,
and the RGB value of the cell cannot be changed.
If the client allocates read/write cells,
they are exclusively owned by the client,
and the color associated with the pixel value can be changed at will.
Cells must be allocated (and, if read/write, initialized with an RGB value)
by a client to obtain desired colors.
The use of pixel value for an
unallocated cell results in an undefined color.

Because colormaps are associated with windows, X supports displays
with multiple colormaps and, indeed, different types of colormaps.
If there are insufficient colormap resources in the display,
some windows will display in their true colors, and others
will display with incorrect colors.
A window manager usually controls which windows are displayed
in their true colors if more than one colormap is required for
the color resources the applications are using.
At any time, there is a set of installed colormaps for a screen.
Windows using one of the installed colormaps display with true colors, and
windows using other colormaps generally display with incorrect colors.
You can control the set of installed colormaps by using
XInstallColormap
and
XUninstallColormap.

Colormaps are local to a particular screen.
Screens always have a default colormap,
and programs typically allocate cells out of this colormap.
Generally, you should not write applications that monopolize
color resources.
Although some hardware supports multiple colormaps installed at one time,
many of the hardware displays
built today support only a single installed colormap, so the primitives
are written to encourage sharing of colormap entries between applications.

The
DefaultColormap
macro returns the default colormap.
The
DefaultVisual
macro
returns the default visual type for the specified screen.

Possible visual types are
StaticGray,
GrayScale,
StaticColor,
PseudoColor,
TrueColor,
or
DirectColor
(see section 3.1).

Color Structures

Functions that operate only on RGB color space values use an
XColor
structure, which contains:


typedef struct {
	unsigned long pixel;	/* pixel value */
	unsigned short red, green, blue;	/* rgb values */
	char flags;	/* DoRed, DoGreen, DoBlue */	
	char pad;
} XColor;

The red, green, and blue values are always in the range 0 to 65535
inclusive, independent of the number of bits actually used in the
display hardware.
The server scales these values down to the range used by the hardware.
Black is represented by (0,0,0),
and white is represented by (65535,65535,65535).

In some functions,
the flags member controls which of the red, green, and blue members is used
and can be the inclusive OR of zero or more of
DoRed,
DoGreen,
and
DoBlue.

Functions that operate on all color space values use an
XcmsColor
structure.
This structure contains a union of substructures,
each supporting color specification encoding for a particular color space.
Like the
XColor
structure, the
XcmsColor
structure contains pixel
and color specification information (the spec member in the
XcmsColor
structure).


typedef unsigned long XcmsColorFormat;			/* Color Specification Format */

typedef struct {
	union {
		XcmsRGB RGB;
		XcmsRGBi RGBi;
		XcmsCIEXYZ CIEXYZ;
		XcmsCIEuvY CIEuvY;
		XcmsCIExyY CIExyY;
		XcmsCIELab CIELab;
		XcmsCIELuv CIELuv;
		XcmsTekHVC TekHVC;
		XcmsPad Pad;
	} spec;
	unsigned long pixel;
	XcmsColorFormat format;
} XcmsColor;			/* Xcms Color Structure */

Because the color specification can be encoded for the various color spaces,
encoding for the spec member is identified by the format member,
which is of type
XcmsColorFormat.
The following macros define standard formats.

#define          XcmsUndefinedFormat   0x00000000
#define          XcmsCIEXYZFormat      0x00000001  /* CIE XYZ */
#define          XcmsCIEuvYFormat      0x00000002  /* CIE u'v'Y */
#define          XcmsCIExyYFormat      0x00000003  /* CIE xyY */
#define          XcmsCIELabFormat      0x00000004  /* CIE L*a*b* */
#define          XcmsCIELuvFormat      0x00000005  /* CIE L*u*v* */
#define          XcmsTekHVCFormat      0x00000006  /* TekHVC */
#define          XcmsRGBFormat         0x80000000  /* RGB Device */
#define          XcmsRGBiFormat        0x80000001  /* RGB Intensity */

Formats for device-independent color spaces are
distinguishable from those for device-dependent spaces by the 32nd bit.
If this bit is set,
it indicates that the color specification is in a device-dependent form;
otherwise, it is in a device-independent form.
If the 31st bit is set,
this indicates that the color space has been added to Xlib at run time
(see section 6.12.4).
The format value for a color space added at run time may be different each
time the program is executed.
If references to such a color space must be made outside the client
(for example, storing a color specification in a file),
then reference should be made by color space string prefix
(see
XcmsFormatOfPrefix
and
XcmsPrefixOfFormat).

Data types that describe the color specification encoding for the various
color spaces are defined as follows:


typedef double XcmsFloat;

typedef struct {
	unsigned short red;	/* 0x0000 to 0xffff */
	unsigned short green;	/* 0x0000 to 0xffff */
	unsigned short blue;	/* 0x0000 to 0xffff */
} XcmsRGB;		/* RGB Device */


typedef struct {
	XcmsFloat red;	/* 0.0 to 1.0 */
	XcmsFloat green;	/* 0.0 to 1.0 */
	XcmsFloat blue;	/* 0.0 to 1.0 */
} XcmsRGBi;		/* RGB Intensity */


typedef struct {
	XcmsFloat X;
	XcmsFloat Y;	/* 0.0 to 1.0 */
	XcmsFloat Z;
} XcmsCIEXYZ;		/* CIE XYZ */


typedef struct {
	XcmsFloat u_prime;	/* 0.0 to ~0.6 */
	XcmsFloat v_prime;	/* 0.0 to ~0.6 */
	XcmsFloat Y; 	/* 0.0 to 1.0 */
} XcmsCIEuvY;		/* CIE u'v'Y */


typedef struct {
	XcmsFloat x; 	/* 0.0 to ~.75 */
	XcmsFloat y; 	/* 0.0 to ~.85 */
	XcmsFloat Y; 	/* 0.0 to 1.0 */
} XcmsCIExyY;		/* CIE xyY */


typedef struct {
	XcmsFloat L_star; 	/* 0.0 to 100.0 */
	XcmsFloat a_star;
	XcmsFloat b_star;
} XcmsCIELab;		/* CIE L*a*b* */


typedef struct {
	XcmsFloat L_star; 	/* 0.0 to 100.0 */
	XcmsFloat u_star;
	XcmsFloat v_star;
} XcmsCIELuv;		/* CIE L*u*v* */


typedef struct {
	XcmsFloat H; 	/* 0.0 to 360.0 */
	XcmsFloat V; 	/* 0.0 to 100.0 */
	XcmsFloat C; 	/* 0.0 to 100.0 */
} XcmsTekHVC;		/* TekHVC */


typedef struct {
	XcmsFloat pad0;
	XcmsFloat pad1;
	XcmsFloat pad2;
	XcmsFloat pad3;
} XcmsPad;		/* four doubles */

The device-dependent formats provided allow color specification in:

RGB Intensity
(XcmsRGBi)
Red, green, and blue linear intensity values,
floating-point values from 0.0 to 1.0,
where 1.0 indicates full intensity, 0.5 half intensity, and so on.
RGB Device
(XcmsRGB)
Red, green, and blue values appropriate for the specified output device.
XcmsRGB
values are of type unsigned short,
scaled from 0 to 65535 inclusive,
and are interchangeable with the red, green, and blue values in an
XColor
structure.

It is important to note that RGB Intensity values are not gamma corrected
values.
In contrast,
RGB Device values generated as a result of converting color specifications
are always gamma corrected, and
RGB Device values acquired as a result of querying a colormap
or passed in by the client are assumed by Xlib to be gamma corrected.
The term RGB value in this manual always refers to an RGB Device value.

Color Strings

Xlib provides a mechanism for using string names for colors.
A color string may either contain an abstract color name
or a numerical color specification.
Color strings are case-insensitive.

Color strings are used in the following functions:

Xlib supports the use of abstract color names, for example, red or blue.
A value for this abstract name is obtained by searching one or more color
name databases.
Xlib first searches zero or more client-side databases;
the number, location, and content of these databases is
implementation-dependent and might depend on the current locale.
If the name is not found, Xlib then looks for the color in the
X server's database.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.

A numerical color specification
consists of a color space name and a set of values in the following syntax:

<color_space_name>:<value>/.../<value>

The following are examples of valid color strings.

"CIEXYZ:0.3227/0.28133/0.2493"
"RGBi:1.0/0.0/0.0"
"rgb:00/ff/00"
"CIELuv:50.0/0.0/0.0"

The syntax and semantics of numerical specifications are given
for each standard color space in the following sections.

RGB Device String Specification

An RGB Device specification is identified by
the prefix “rgb:” and conforms to the following syntax:

rgb:<red>/<green>/<blue>

    <red>, <green>, <blue> := h | hh | hhh | hhhh
    h := single hexadecimal digits (case insignificant)

Note that h indicates the value scaled in 4 bits,
hh the value scaled in 8 bits,
hhh the value scaled in 12 bits,
and hhhh the value scaled in 16 bits, respectively.

Typical examples are the strings “rgb:ea/75/52” and “rgb:ccc/320/320”,
but mixed numbers of hexadecimal digit strings
(“rgb:ff/a5/0” and “rgb:ccc/32/0”)
are also allowed.

For backward compatibility, an older syntax for RGB Device is
supported, but its continued use is not encouraged.
The syntax is an initial sharp sign character followed by
a numeric specification, in one of the following formats:


#RGB	(4 bits each)
#RRGGBB	(8 bits each)
#RRRGGGBBB	(12 bits each)
#RRRRGGGGBBBB	(16 bits each)

The R, G, and B represent single hexadecimal digits.
When fewer than 16 bits each are specified,
they represent the most significant bits of the value
(unlike the “rgb:” syntax, in which values are scaled).
For example, the string “#3a7” is the same as “#3000a0007000”.

RGB Intensity String Specification

An RGB intensity specification is identified
by the prefix “rgbi:” and conforms to the following syntax:

rgbi:<red>/<green>/<blue>

Note that red, green, and blue are floating-point values
between 0.0 and 1.0, inclusive.
The input format for these values is an optional sign,
a string of numbers possibly containing a decimal point,
and an optional exponent field containing an E or e
followed by a possibly signed integer string.

Device-Independent String Specifications

The standard device-independent string specifications have
the following syntax:

CIEXYZ:<X>/<Y>/<Z>
CIEuvY:<u>/<v>/<Y>
CIExyY:<x>/<y>/<Y>
CIELab:<L>/<a>/<b>
CIELuv:<L>/<u>/<v>
TekHVC:<H>/<V>/<C>

All of the values (C, H, V, X, Y, Z, a, b, u, v, y, x) are
floating-point values.
The syntax for these values is an optional plus or minus sign,
a string of digits possibly containing a decimal point,
and an optional exponent field consisting of an “E” or “e”
followed by an optional plus or minus followed by a string of digits.

Color Conversion Contexts and Gamut Mapping

When Xlib converts device-independent color specifications
into device-dependent specifications and vice versa,
it uses knowledge about the color limitations of the screen hardware.
This information, typically called the device profile,

is available in a Color Conversion Context (CCC).

Because a specified color may be outside the color gamut of the target screen
and the white point associated with the color specification may differ
from the white point inherent to the screen,
Xlib applies gamut mapping when it encounters certain conditions:

Gamut compression occurs when conversion of device-independent
color specifications to device-dependent color specifications
results in a color out of the target screen's gamut.
White adjustment occurs when the inherent white point of the screen
differs from the white point assumed by the client.

Gamut handling methods are stored as callbacks in the CCC,
which in turn are used by the color space conversion routines.
Client data is also stored in the CCC for each callback.
The CCC also contains the white point the client assumes to be
associated with color specifications (that is, the Client White Point).

The client can specify the gamut handling callbacks and client data
as well as the Client White Point.
Xlib does not preclude the X client from performing other
forms of gamut handling (for example, gamut expansion);
however, Xlib does not provide direct support for gamut handling
other than white adjustment and gamut compression.

Associated with each colormap is an initial CCC transparently generated by
Xlib.

Therefore,
when you specify a colormap as an argument to an Xlib function,
you are indirectly specifying a CCC.

There is a default CCC associated with each screen.
Newly created CCCs inherit attributes from the default CCC,
so the default CCC attributes can be modified to affect new CCCs.

Xcms functions in which gamut mapping can occur return
Status
and have specific status values defined for them,
as follows:

XcmsFailure
indicates that the function failed.
XcmsSuccess
indicates that the function succeeded.
In addition,
if the function performed any color conversion,
the colors did not need to be compressed.
XcmsSuccessWithCompression
indicates the function performed color conversion
and at least one of the colors needed to be compressed.
The gamut compression method is determined by the gamut compression
procedure in the CCC that is specified directly as a function argument
or in the CCC indirectly specified by means of the colormap argument.

Creating, Copying, and Destroying Colormaps

To create a colormap for a screen, use
XCreateColormap.

Colormap XCreateColormap(Display *display, Window w, Visual *visual, int alloc);

display	Specifies the connection to the X server.
w	Specifies the window on whose screen you want to create a colormap.
visual	Specifies a visual type supported on the screen. If the visual type is not one supported by the screen, a BadMatch error results.
alloc	Specifies the colormap entries to be allocated. You can pass AllocNone or AllocAll.

The
XCreateColormap
function creates a colormap of the specified visual type for the screen
on which the specified window resides and returns the colormap ID
associated with it.
Note that the specified window is only used to determine the screen.

The initial values of the colormap entries are undefined for the
visual classes
GrayScale,
PseudoColor,
and
DirectColor.
For
StaticGray,
StaticColor,
and
TrueColor,
the entries have defined values,
but those values are specific to the visual and are not defined by X.
For
StaticGray,
StaticColor,
and
TrueColor,
alloc must be
AllocNone,
or a
BadMatch
error results.
For the other visual classes,
if alloc is
AllocNone,
the colormap initially has no allocated entries,
and clients can allocate them.
For information about the visual types,
see section 3.1.

If alloc is
AllocAll,
the entire colormap is allocated writable.
The initial values of all allocated entries are undefined.
For
GrayScale
and
PseudoColor,
the effect is as if an
XAllocColorCells
call returned all pixel values from zero to N - 1,
where N is the colormap entries value in the specified visual.
For
DirectColor,
the effect is as if an
XAllocColorPlanes
call returned a pixel value of zero and red_mask, green_mask,
and blue_mask values containing the same bits as the corresponding
masks in the specified visual.
However, in all cases,
none of these entries can be freed by using
XFreeColors.

XCreateColormap
can generate
BadAlloc,
BadMatch,
BadValue,
and
BadWindow
errors.

To create a new colormap when the allocation out of a previously
shared colormap has failed because of resource exhaustion, use
XCopyColormapAndFree.

Colormap XCopyColormapAndFree(Display *display, Colormap colormap);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.

The
XCopyColormapAndFree
function creates a colormap of the same visual type and for the same screen
as the specified colormap and returns the new colormap ID.
It also moves all of the client's existing allocation from the specified
colormap to the new colormap with their color values intact
and their read-only or writable characteristics intact and frees those entries
in the specified colormap.
Color values in other entries in the new colormap are undefined.
If the specified colormap was created by the client with alloc set to
AllocAll,
the new colormap is also created with
AllocAll,
all color values for all entries are copied from the specified colormap,
and then all entries in the specified colormap are freed.
If the specified colormap was not created by the client with
AllocAll,
the allocations to be moved are all those pixels and planes
that have been allocated by the client using
XAllocColor,
XAllocNamedColor,
XAllocColorCells,
or
XAllocColorPlanes
and that have not been freed since they were allocated.

XCopyColormapAndFree
can generate
BadAlloc
and
BadColor
errors.

To destroy a colormap, use
XFreeColormap.

XFreeColormap(Display *display, Colormap colormap);

display	Specifies the connection to the X server.
colormap	Specifies the colormap that you want to destroy.

The
XFreeColormap
function deletes the association between the colormap resource ID
and the colormap and frees the colormap storage.
However, this function has no effect on the default colormap for a screen.
If the specified colormap is an installed map for a screen,
it is uninstalled (see
XUninstallColormap).
If the specified colormap is defined as the colormap for a window (by
XCreateWindow,
XSetWindowColormap,
or
XChangeWindowAttributes),
XFreeColormap
changes the colormap associated with the window to
None
and generates a
ColormapNotify
event.
X does not define the colors displayed for a window with a colormap of
None.

XFreeColormap
can generate a
BadColor
error.

Mapping Color Names to Values

To map a color name to an RGB value, use
XLookupColor.

Status XLookupColor(Display *display, Colormap colormap, char *color_name, XColor *exact_def_return, XColor *screen_def_return);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color_name	Specifies the color name string (for example, red) whose color definition structure you want returned.
exact_def_return	Returns the exact RGB values.
screen_def_return	Returns the closest RGB values provided by the hardware.

The
XLookupColor
function looks up the string name of a color with respect to the screen
associated with the specified colormap.
It returns both the exact color values and
the closest values provided by the screen
with respect to the visual type of the specified colormap.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
XLookupColor
returns nonzero if the name is resolved;
otherwise, it returns zero.

XLookupColor
can generate a
BadColor
error.

To map a color name to the exact RGB value, use
XParseColor.

Status XParseColor(Display *display, Colormap colormap, char *spec, XColor *exact_def_return);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
spec	Specifies the color name string; case is ignored.
exact_def_return	Returns the exact color value for later use and sets the DoRed, DoGreen, and DoBlue flags.

The
XParseColor
function looks up the string name of a color with respect to the screen
associated with the specified colormap.
It returns the exact color value.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
XParseColor
returns nonzero if the name is resolved;
otherwise, it returns zero.

XParseColor
can generate a
BadColor
error.

To map a color name to a value in an arbitrary color space, use
XcmsLookupColor.

Status XcmsLookupColor(Display *display, Colormap colormap, char *color_string, XcmsColor *color_exact_return, XcmsColor *color_screen_return, XcmsColorFormat result_format);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color_string	Specifies the color string(St.
color_exact_return	Returns the color specification parsed from the color string or parsed from the corresponding string found in a color-name database.
color_screen_return	Returns the color that can be reproduced on the screen.
result_format	Specifies the color format for the returned color specifications (color_screen_return and color_exact_return arguments). If the format is XcmsUndefinedFormat and the color string contains a numerical color specification, the specification is returned in the format used in that numerical color specification. If the format is XcmsUndefinedFormat and the color string contains a color name, the specification is returned in the format used to store the color in the database.

The
XcmsLookupColor
function looks up the string name of a color with respect to the screen
associated with the specified colormap.
It returns both the exact color values and
the closest values provided by the screen
with respect to the visual type of the specified colormap.
The values are returned in the format specified by result_format.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
XcmsLookupColor
returns
XcmsSuccess
or
XcmsSuccessWithCompression
if the name is resolved; otherwise, it returns
XcmsFailure.
If
XcmsSuccessWithCompression
is returned, the color specification returned in
color_screen_return is the result of gamut compression.

Allocating and Freeing Color Cells

There are two ways of allocating color cells:
explicitly as read-only entries, one pixel value at a time,
or read/write,
where you can allocate a number of color cells and planes simultaneously.

A read-only cell has its RGB value set by the server.

Read/write cells do not have defined colors initially;
functions described in the next section must be used to store values into them.
Although it is possible for any client to store values into a read/write
cell allocated by another client,
read/write cells normally should be considered private to the client
that allocated them.

Read-only colormap cells are shared among clients.
The server counts each allocation and freeing of the cell by clients.
When the last client frees a shared cell, the cell is finally deallocated.
If a single client allocates the same read-only cell multiple
times, the server counts each such allocation, not just the first one.

To allocate a read-only color cell with an RGB value, use
XAllocColor.

Status XAllocColor(Display *display, Colormap colormap, XColor *screen_in_out);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
screen_in_out	Specifies and returns the values actually used in the colormap.

The
XAllocColor
function allocates a read-only colormap entry corresponding to the closest
RGB value supported by the hardware.
XAllocColor
returns the pixel value of the color closest to the specified
RGB elements supported by the hardware
and returns the RGB value actually used.
The corresponding colormap cell is read-only.
In addition,
XAllocColor
returns nonzero if it succeeded or zero if it failed.

Multiple clients that request the same effective RGB value can be assigned
the same read-only entry, thus allowing entries to be shared.
When the last client deallocates a shared cell, it is deallocated.
XAllocColor
does not use or affect the flags in the
XColor
structure.

XAllocColor
can generate a
BadColor
error.

delim %%

To allocate a read-only color cell with a color in arbitrary format, use
XcmsAllocColor.

Status XcmsAllocColor(Display *display, Colormap colormap, XcmsColor *color_in_out, XcmsColorFormat result_format);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color_in_out	Specifies the color to allocate and returns the pixel and color that is actually used in the colormap.
result_format	Specifies the color format for the returned color specification.

The
XcmsAllocColor
function is similar to
XAllocColor
except the color can be specified in any format.
The
XcmsAllocColor
function ultimately calls
XAllocColor
to allocate a read-only color cell (colormap entry) with the specified color.
XcmsAllocColor
first converts the color specified
to an RGB value and then passes this to
XAllocColor.
XcmsAllocColor
returns the pixel value of the color cell and the color specification
actually allocated.
This returned color specification is the result of converting the RGB value
returned by
XAllocColor
into the format specified with the result_format argument.
If there is no interest in a returned color specification,
unnecessary computation can be bypassed if result_format is set to
XcmsRGBFormat.
The corresponding colormap cell is read-only.
If this routine returns
XcmsFailure,
the color_in_out color specification is left unchanged.

XcmsAllocColor
can generate a
BadColor
error.

To allocate a read-only color cell using a color name and return the closest
color supported by the hardware in RGB format, use
XAllocNamedColor.

Status XAllocNamedColor(Display *display, Colormap colormap, char *color_name, XColor *screen_def_return, XColor *exact_def_return);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color_name	Specifies the color name string (for example, red) whose color definition structure you want returned.
screen_def_return	Returns the closest RGB values provided by the hardware.
exact_def_return	Returns the exact RGB values.

The
XAllocNamedColor
function looks up the named color with respect to the screen that is
associated with the specified colormap.
It returns both the exact database definition and
the closest color supported by the screen.
The allocated color cell is read-only.
The pixel value is returned in screen_def_return.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
If screen_def_return and exact_def_return
point to the same structure, the pixel field will be set correctly,
but the color values are undefined.
XAllocNamedColor
returns nonzero if a cell is allocated;
otherwise, it returns zero.

XAllocNamedColor
can generate a
BadColor
error.

To allocate a read-only color cell using a color name and return the closest
color supported by the hardware in an arbitrary format, use
XcmsAllocNamedColor.

Status XcmsAllocNamedColor(Display *display, Colormap colormap, char *color_string, XcmsColor *color_screen_return, XcmsColor *color_exact_return, XcmsColorFormat result_format);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color_string	Specifies the color string whose color definition structure is to be returned.
color_screen_return	Returns the pixel value of the color cell and color specification that actually is stored for that cell.
color_exact_return	Returns the color specification parsed from the color string or parsed from the corresponding string found in a color-name database.
result_format	Specifies the color format for the returned color specifications (color_screen_return and color_exact_return arguments). If the format is XcmsUndefinedFormat and the color string contains a numerical color specification, the specification is returned in the format used in that numerical color specification. If the format is XcmsUndefinedFormat and the color string contains a color name, the specification is returned in the format used to store the color in the database.

The
XcmsAllocNamedColor
function is similar to
XAllocNamedColor
except that the color returned can be in any format specified.
This function
ultimately calls
XAllocColor
to allocate a read-only color cell with
the color specified by a color string.
The color string is parsed into an
XcmsColor
structure (see
XcmsLookupColor),
converted
to an RGB value, and finally passed to
XAllocColor.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.

This function returns both the color specification as a result
of parsing (exact specification) and the actual color specification
stored (screen specification).
This screen specification is the result of converting the RGB value
returned by
XAllocColor
into the format specified in result_format.
If there is no interest in a returned color specification,
unnecessary computation can be bypassed if result_format is set to
XcmsRGBFormat.
If color_screen_return and color_exact_return
point to the same structure, the pixel field will be set correctly,
but the color values are undefined.

XcmsAllocNamedColor
can generate a
BadColor
error.

To allocate read/write color cell and color plane combinations for a
PseudoColor
model, use
XAllocColorCells.

Status XAllocColorCells(Display *display, Colormap colormap, Bool contig, unsigned long plane_masks_return[], unsigned int nplanes, unsigned long pixels_return[], unsigned int npixels);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
contig	Specifies a Boolean value that indicates whether the planes must be contiguous.
plane_mask_return	Returns an array of plane masks.
nplanes	Specifies the number of plane masks that are to be returned in the plane masks array.
pixels_return	Returns an array of pixel values.
npixels	Specifies the number of pixel values that are to be returned in the pixels_return array.

The
XAllocColorCells
function allocates read/write color cells.
The number of colors must be positive and the number of planes nonnegative,
or a
BadValue
error results.
If ncolors and nplanes are requested,
then ncolors pixels
and nplane plane masks are returned.
No mask will have any bits set to 1 in common with
any other mask or with any of the pixels.
By ORing together each pixel with zero or more masks,
ncolors × 2nplanes
distinct pixels can be produced.
All of these are
allocated writable by the request.
For
GrayScale
or
PseudoColor,
each mask has exactly one bit set to 1.
For
DirectColor,
each has exactly three bits set to 1.
If contig is
True
and if all masks are ORed
together, a single contiguous set of bits set to 1 will be formed for
GrayScale
or
PseudoColor
and three contiguous sets of bits set to 1 (one within each
pixel subfield) for
DirectColor.
The RGB values of the allocated
entries are undefined.
XAllocColorCells
returns nonzero if it succeeded or zero if it failed.

XAllocColorCells
can generate
BadColor
and
BadValue
errors.

To allocate read/write color resources for a
DirectColor
model, use
XAllocColorPlanes.

Status XAllocColorPlanes(Display *display, Colormap colormap, Bool contig, unsigned long pixels_return[], int ncolors, int nreds, int ngreens, int nblues, unsigned long *rmask_return, unsigned long *gmask_return, unsigned long *bmask_return);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
contig	Specifies a Boolean value that indicates whether the planes must be contiguous.
pixels_return	Returns an array of pixel values. `XAllocColorPlanes` returns the pixel values in this array.
ncolors	Specifies the number of pixel values that are to be returned in the pixels_return array.
nreds
ngreens
nblues	Specify the number of red, green, and blue planes. The value you pass must be nonnegative.
rmask_return
gmask_return
bmask_return	Return bit masks for the red, green, and blue planes.

The specified ncolors must be positive;
and nreds, ngreens, and nblues must be nonnegative,
or a
BadValue
error results.
If ncolors colors, nreds reds, ngreens greens, and nblues blues are requested,
ncolors pixels are returned; and the masks have nreds, ngreens, and
nblues bits set to 1, respectively.
If contig is
True,
each mask will have
a contiguous set of bits set to 1.
No mask will have any bits set to 1 in common with
any other mask or with any of the pixels.
For
DirectColor,
each mask
will lie within the corresponding pixel subfield.
By ORing together
subsets of masks with each pixel value,
ncolors × 2(nreds+ngreens+nblues)
distinct pixel values can be produced.
All of these are allocated by the request.
However, in the
colormap, there are only
ncolors × 2nreds
independent red entries,
ncolors × 2ngreens
independent green entries, and
ncolors × 2nblues
independent blue entries.
This is true even for
PseudoColor.
When the colormap entry of a pixel
value is changed (using
XStoreColors,
XStoreColor,
or
XStoreNamedColor),
the pixel is decomposed according to the masks,
and the corresponding independent entries are updated.
XAllocColorPlanes
returns nonzero if it succeeded or zero if it failed.

XAllocColorPlanes
can generate
BadColor
and
BadValue
errors.

To free colormap cells, use
XFreeColors.

XFreeColors(Display *display, Colormap colormap, unsigned long pixels[], int npixels, unsigned long planes);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
pixels	Specifies an array of pixel values that map to the cells in the specified colormap.
npixels	Specifies the number of pixels.
planes	Specifies the planes you want to free.

The
XFreeColors
function frees the cells represented by pixels whose values are in the
pixels array.
The planes argument should not have any bits set to 1 in common with any of the
pixels.
The set of all pixels is produced by ORing together subsets of
the planes argument with the pixels.
The request frees all of these pixels that
were allocated by the client (using

XAllocColor,
XAllocNamedColor,
XAllocColorCells,
and
XAllocColorPlanes).
Note that freeing an
individual pixel obtained from
XAllocColorPlanes
may not actually allow
it to be reused until all of its related pixels are also freed.
Similarly,
a read-only entry is not actually freed until it has been freed by all clients,
and if a client allocates the same read-only entry multiple times,
it must free the entry that many times before the entry is actually freed.

All specified pixels that are allocated by the client in the colormap are
freed, even if one or more pixels produce an error.
If a specified pixel is not a valid index into the colormap, a
BadValue
error results.
If a specified pixel is not allocated by the
client (that is, is unallocated or is only allocated by another client)
or if the colormap was created with all entries writable (by passing
AllocAll
to
XCreateColormap),
a
BadAccess
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.

XFreeColors
can generate
BadAccess,
BadColor,
and
BadValue
errors.

Modifying and Querying Colormap Cells

To store an RGB value in a single colormap cell, use
XStoreColor.

XStoreColor(Display *display, Colormap colormap, XColor *color);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color	Specifies the pixel and RGB values.

The
XStoreColor
function changes the colormap entry of the pixel value specified in the
pixel member of the
XColor
structure.
You specified this value in the
pixel member of the
XColor
structure.
This pixel value must be a read/write cell and a valid index into the colormap.
If a specified pixel is not a valid index into the colormap,
a
BadValue
error results.
XStoreColor
also changes the red, green, and/or blue color components.
You specify which color components are to be changed by setting
DoRed,
DoGreen,
and/or
DoBlue
in the flags member of the
XColor
structure.
If the colormap is an installed map for its screen,
the changes are visible immediately.

XStoreColor
can generate
BadAccess,
BadColor,
and
BadValue
errors.

To store multiple RGB values in multiple colormap cells, use
XStoreColors.

XStoreColors(Display *display, Colormap colormap, XColor color[], int ncolors);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color	Specifies an array of color definition structures to be stored.
ncolors	Specifies the number of XColor structures in the color definition array.

The
XStoreColors
function changes the colormap entries of the pixel values
specified in the pixel members of the
XColor
structures.
You specify which color components are to be changed by setting
DoRed,
DoGreen,
and/or
DoBlue
in the flags member of the
XColor
structures.
If the colormap is an installed map for its screen, the
changes are visible immediately.
XStoreColors
changes the specified pixels if they are allocated writable in the colormap
by any client, even if one or more pixels generates an error.
If a specified pixel is not a valid index into the colormap, a
BadValue
error results.
If a specified pixel either is unallocated or is allocated read-only, a
BadAccess
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.

XStoreColors
can generate
BadAccess,
BadColor,
and
BadValue
errors.

To store a color of arbitrary format in a single colormap cell, use
XcmsStoreColor.

Status XcmsStoreColor(Display *display, Colormap colormap, XcmsColor *color);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color	Specifies the color cell and the color to store. Values specified in this XcmsColor structure remain unchanged on return.

The
XcmsStoreColor
function converts the color specified in the
XcmsColor
structure into RGB values.
It then uses this RGB specification in an
XColor
structure, whose three flags
(DoRed,
DoGreen,
and
DoBlue)
are set, in a call to
XStoreColor
to change the color cell specified by the pixel member of the
XcmsColor
structure.
This pixel value must be a valid index for the specified colormap,
and the color cell specified by the pixel value must be a read/write cell.
If the pixel value is not a valid index, a
BadValue
error results.
If the color cell is unallocated or is allocated read-only, a
BadAccess
error results.
If the colormap is an installed map for its screen,
the changes are visible immediately.

Note that
XStoreColor
has no return value; therefore, an
XcmsSuccess
return value from this function indicates that the conversion
to RGB succeeded and the call to
XStoreColor
was made.
To obtain the actual color stored, use
XcmsQueryColor.
Because of the screen's hardware limitations or gamut compression,
the color stored in the colormap may not be identical
to the color specified.

XcmsStoreColor
can generate
BadAccess,
BadColor,
and
BadValue
errors.

To store multiple colors of arbitrary format in multiple colormap cells, use
XcmsStoreColors.

Status XcmsStoreColors(Display *display, Colormap colormap, XcmsColor colors[], int ncolors, Bool compression_flags_return[]);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
colors	Specifies the color specification array of XcmsColor structures, each specifying a color cell and the color to store in that cell. Values specified in the array remain unchanged upon return.
ncolors	Specifies the number of XcmsColor structures in the color-specification array.
compression_flags_return	Returns an array of Boolean values indicating compression status. If a non-NULL pointer is supplied, each element of the array is set to True if the corresponding color was compressed and False otherwise. Pass NULL if the compression status is not useful.

The
XcmsStoreColors
function converts the colors specified in the array of
XcmsColor
structures into RGB values and then uses these RGB specifications in
XColor
structures, whose three flags
(DoRed,
DoGreen,
and
DoBlue)
are set, in a call to
XStoreColors
to change the color cells specified by the pixel member of the corresponding
XcmsColor
structure.
Each pixel value must be a valid index for the specified colormap,
and the color cell specified by each pixel value must be a read/write cell.
If a pixel value is not a valid index, a
BadValue
error results.
If a color cell is unallocated or is allocated read-only, a
BadAccess
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.
If the colormap is an installed map for its screen,
the changes are visible immediately.

Note that
XStoreColors
has no return value; therefore, an
XcmsSuccess
return value from this function indicates that conversions
to RGB succeeded and the call to
XStoreColors
was made.
To obtain the actual colors stored, use
XcmsQueryColors.
Because of the screen's hardware limitations or gamut compression,
the colors stored in the colormap may not be identical
to the colors specified.

XcmsStoreColors
can generate
BadAccess,
BadColor,
and
BadValue
errors.

To store a color specified by name in a single colormap cell, use
XStoreNamedColor.

XStoreNamedColor(Display *display, Colormap colormap, char *color, unsigned long pixel, int flags);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color	Specifies the color name string (for example, red).
pixel	Specifies the entry in the colormap.
flags	Specifies which red, green, and blue components are set.

The
XStoreNamedColor
function looks up the named color with respect to the screen associated with
the colormap and stores the result in the specified colormap.
The pixel argument determines the entry in the colormap.
The flags argument determines which of the red, green, and blue components
are set.
You can set this member to the
bitwise inclusive OR of the bits
DoRed,
DoGreen,
and
DoBlue.
If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
If the specified pixel is not a valid index into the colormap, a
BadValue
error results.
If the specified pixel either is unallocated or is allocated read-only, a
BadAccess
error results.

XStoreNamedColor
can generate
BadAccess,
BadColor,
BadName,
and
BadValue
errors.

The
XQueryColor
and
XQueryColors
functions take pixel values in the pixel member of
XColor
structures and store in the structures the RGB values for those
pixels from the specified colormap.
The values returned for an unallocated entry are undefined.
These functions also set the flags member in the
XColor
structure to all three colors.
If a pixel is not a valid index into the specified colormap, a
BadValue
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.

To query the RGB value of a single colormap cell, use
XQueryColor.

XQueryColor(Display *display, Colormap colormap, XColor *def_in_out);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
def_in_out	Specifies and returns the RGB values for the pixel specified in the structure.

The
XQueryColor
function returns the current RGB value for the pixel in the
XColor
structure and sets the
DoRed,
DoGreen,
and
DoBlue
flags.

XQueryColor
can generate
BadColor
and
BadValue
errors.

To query the RGB values of multiple colormap cells, use
XQueryColors.

XQueryColors(Display *display, Colormap colormap, XColor defs_in_out[], int ncolors);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
defs_in_out	Specifies and returns an array of color definition structures for the pixel specified in the structure.
ncolors	Specifies the number of XColor structures in the color definition array.

The
XQueryColors
function returns the RGB value for each pixel in each
XColor
structure and sets the
DoRed,
DoGreen,
and
DoBlue
flags in each structure.

XQueryColors
can generate
BadColor
and
BadValue
errors.

To query the color of a single colormap cell in an arbitrary format, use
XcmsQueryColor.

Status XcmsQueryColor(Display *display, Colormap colormap, XcmsColor *color_in_out, XcmsColorFormat result_format);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
color_in_out	Specifies the pixel member that indicates the color cell to query. The color specification stored for the color cell is returned in this XcmsColor structure.
result_format	Specifies the color format for the returned color specification.

The
XcmsQueryColor
function obtains the RGB value
for the pixel value in the pixel member of the specified
XcmsColor
structure and then
converts the value to the target format as
specified by the result_format argument.
If the pixel is not a valid index in the specified colormap, a
BadValue
error results.

XcmsQueryColor
can generate
BadColor
and
BadValue
errors.

To query the color of multiple colormap cells in an arbitrary format, use
XcmsQueryColors.

Status XcmsQueryColors(Display *display, Colormap colormap, XcmsColor colors_in_out[], unsigned int ncolors, XcmsColorFormat result_format);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
colors_in_out	Specifies an array of XcmsColor structures, each pixel member indicating the color cell to query. The color specifications for the color cells are returned in these structures.
ncolors	Specifies the number of XcmsColor structures in the color-specification array.
result_format	Specifies the color format for the returned color specification.

The
XcmsQueryColors
function obtains the RGB values
for pixel values in the pixel members of
XcmsColor
structures and then
converts the values to the target format as
specified by the result_format argument.
If a pixel is not a valid index into the specified colormap, a
BadValue
error results.
If more than one pixel is in error,
the one that gets reported is arbitrary.

XcmsQueryColors
can generate
BadColor
and
BadValue
errors.

Color Conversion Context Functions

This section describes functions to create, modify,
and query Color Conversion Contexts (CCCs).

Associated with each colormap is an initial CCC transparently generated by
Xlib.

Therefore, when you specify a colormap as an argument to a function,
you are indirectly specifying a CCC.

The CCC attributes that can be modified by the X client are:

Client White Point
Gamut compression procedure and client data
White point adjustment procedure and client data

The initial values for these attributes are implementation specific.
The CCC attributes for subsequently created CCCs can be defined
by changing the CCC attributes of the default CCC.

There is a default CCC associated with each screen.

Getting and Setting the Color Conversion Context of a Colormap

To obtain the CCC associated with a colormap, use
XcmsCCCOfColormap.

XcmsCCC XcmsCCCOfColormap(Display *display, Colormap colormap);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.

The
XcmsCCCOfColormap
function returns the CCC associated with the specified colormap.
Once obtained,
the CCC attributes can be queried or modified.
Unless the CCC associated with the specified colormap is changed with
XcmsSetCCCOfColormap,
this CCC is used when the specified colormap is used as an argument
to color functions.

To change the CCC associated with a colormap, use
XcmsSetCCCOfColormap.

XcmsCCC XcmsSetCCCOfColormap(Display *display, Colormap colormap, XcmsCCC ccc);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.
ccc	Specifies the CCC.

The
XcmsSetCCCOfColormap
function changes the CCC associated with the specified colormap.
It returns the CCC previously associated with the colormap.
If they are not used again in the application,
CCCs should be freed by calling
XcmsFreeCCC.
Several colormaps may share the same CCC without restriction; this
includes the CCCs generated by Xlib with each colormap. Xlib, however,
creates a new CCC with each new colormap.

Obtaining the Default Color Conversion Context

You can change the default CCC attributes for subsequently created CCCs
by changing the CCC attributes of the default CCC.

A default CCC is associated with each screen.

To obtain the default CCC for a screen, use
XcmsDefaultCCC.

XcmsCCC XcmsDefaultCCC(Display *display, int screen_number);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.

The
XcmsDefaultCCC
function returns the default CCC for the specified screen.
Its visual is the default visual of the screen.
Its initial gamut compression and white point
adjustment procedures as well as the associated client data are implementation
specific.

Color Conversion Context Macros

Applications should not directly modify any part of the
XcmsCCC.
The following lists the C language macros, their corresponding function
equivalents for other language bindings, and what data they both
can return.

DisplayOfCCC(XcmsCCC ccc);

Display *XcmsDisplayOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the display associated with the specified CCC.

VisualOfCCC(XcmsCCC ccc);

Visual *XcmsVisualOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the visual associated with the specified CCC.

ScreenNumberOfCCC(XcmsCCC ccc);

int XcmsScreenNumberOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the number of the screen associated with the specified CCC.

ScreenWhitePointOfCCC(XcmsCCC ccc);

XcmsColor XcmsScreenWhitePointOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the white point of the screen associated with the specified CCC.

ClientWhitePointOfCCC(XcmsCCC ccc);

XcmsColor *XcmsClientWhitePointOfCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

Both return the Client White Point of the specified CCC.

Modifying Attributes of a Color Conversion Context

To set the Client White Point in the CCC, use
XcmsSetWhitePoint.

Status XcmsSetWhitePoint(XcmsCCC ccc, XcmsColor *color);

ccc	Specifies the CCC.
color	Specifies the new Client White Point.

The
XcmsSetWhitePoint
function changes the Client White Point in the specified CCC.
Note that the pixel member is ignored
and that the color specification is left unchanged upon return.
The format for the new white point must be
XcmsCIEXYZFormat,
XcmsCIEuvYFormat,
XcmsCIExyYFormat,
or
XcmsUndefinedFormat.
If the color argument is NULL, this function sets the format component of the
Client White Point specification to
XcmsUndefinedFormat,
indicating that the Client White Point is assumed to be the same as the
Screen White Point.

This function returns nonzero status
if the format for the new white point is valid;
otherwise, it returns zero.

To set the gamut compression procedure and corresponding client data
in a specified CCC, use
XcmsSetCompressionProc.

XcmsCompressionProc XcmsSetCompressionProc(XcmsCCC ccc, XcmsCompressionProc compression_proc, XPointer client_data);

ccc	Specifies the CCC.
compression_proc	Specifies the gamut compression procedure that is to be applied when a color lies outside the screen's color gamut. If NULL is specified and a function using this CCC must convert a color specification to a device-dependent format and encounters a color that lies outside the screen's color gamut, that function will return XcmsFailure.
client_data	Specifies client data for gamut compression procedure or NULL.

The
XcmsSetCompressionProc
function first sets the gamut compression procedure and client data
in the specified CCC with the newly specified procedure and client data
and then returns the old procedure.

To set the white point adjustment procedure and corresponding client data
in a specified CCC, use
XcmsSetWhiteAdjustProc.

XcmsWhiteAdjustProc XcmsSetWhiteAdjustProc(XcmsCCC ccc, XcmsWhiteAdjustProc white_adjust_proc, XPointer client_data);

ccc	Specifies the CCC.
white_adjust_proc	Specifies the white point adjustment procedure.
client_data	Specifies client data for white point adjustment procedure or NULL.

The
XcmsSetWhiteAdjustProc
function first sets the white point adjustment procedure and client data
in the specified CCC with the newly specified procedure and client data
and then returns the old procedure.

Creating and Freeing a Color Conversion Context

You can explicitly create a CCC within your application by calling
XcmsCreateCCC.
These created CCCs can then be used by those functions that explicitly
call for a CCC argument.
Old CCCs that will not be used by the application should be freed using
XcmsFreeCCC.

To create a CCC, use
XcmsCreateCCC.

XcmsCCC XcmsCreateCCC(Display *display, int screen_number, Visual *visual, XcmsColor *client_white_point, XcmsCompressionProc compression_proc, XPointer compression_client_data, XcmsWhiteAdjustProc white_adjust_proc, XPointer white_adjust_client_data);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.
visual	Specifies the visual type.
client_white_point	Specifies the Client White Point. If NULL is specified, the Client White Point is to be assumed to be the same as the Screen White Point. Note that the pixel member is ignored.
compression_proc	Specifies the gamut compression procedure that is to be applied when a color lies outside the screen's color gamut. If NULL is specified and a function using this CCC must convert a color specification to a device-dependent format and encounters a color that lies outside the screen's color gamut, that function will return XcmsFailure.
compression_client_data	Specifies client data for use by the gamut compression procedure or NULL.
white_adjust_proc	Specifies the white adjustment procedure that is to be applied when the Client White Point differs from the Screen White Point. NULL indicates that no white point adjustment is desired.
white_adjust_client_data	Specifies client data for use with the white point adjustment procedure or NULL.

The
XcmsCreateCCC
function creates a CCC for the specified display, screen, and visual.

To free a CCC, use
XcmsFreeCCC.

void XcmsFreeCCC(XcmsCCC ccc);

ccc

Specifies the CCC.

The
XcmsFreeCCC
function frees the memory used for the specified CCC.
Note that default CCCs and those currently associated with colormaps
are ignored.

Converting between Color Spaces

To convert an array of color specifications in arbitrary color formats
to a single destination format, use
XcmsConvertColors.

Status XcmsConvertColors(XcmsCCC ccc, XcmsColor colors_in_out[], unsigned int ncolors, XcmsColorFormat target_format, Bool compression_flags_return[]);

ccc	Specifies the CCC. If conversion is between device-independent color spaces only (for example, TekHVC to CIELuv), the CCC is necessary only to specify the Client White Point.
colors_in_out	Specifies an array of color specifications. Pixel members are ignored and remain unchanged upon return.
ncolors	Specifies the number of XcmsColor structures in the color-specification array.
target_format	Specifies the target color specification format.
compression_flags_return	Returns an array of Boolean values indicating compression status. If a non-NULL pointer is supplied, each element of the array is set to True if the corresponding color was compressed and False otherwise. Pass NULL if the compression status is not useful.

The
XcmsConvertColors
function converts the color specifications in the specified array of
XcmsColor
structures from their current format to a single target format,
using the specified CCC.
When the return value is
XcmsFailure,
the contents of the color specification array are left unchanged.

The array may contain a mixture of color specification formats
(for example, 3 CIE XYZ, 2 CIE Luv, and so on).
When the array contains both device-independent and
device-dependent color specifications and the target_format argument specifies
a device-dependent format (for example,
XcmsRGBiFormat,
XcmsRGBFormat),
all specifications are converted to CIE XYZ format and then to the target
device-dependent format.

Callback Functions

This section describes the gamut compression and white point
adjustment callbacks.

The gamut compression procedure specified in the CCC
is called when an attempt to convert a color specification from
XcmsCIEXYZ
to a device-dependent format (typically
XcmsRGBi)
results in a color that lies outside the screen's color gamut.
If the gamut compression procedure requires client data, this data is passed
via the gamut compression client data in the CCC.

During color specification conversion between device-independent
and device-dependent color spaces,
if a white point adjustment procedure is specified in the CCC,
it is triggered when the Client White Point and Screen White Point differ.
If required, the client data is obtained from the CCC.

Prototype Gamut Compression Procedure

The gamut compression callback interface must adhere to the
following:

typedef Status(*XcmsCompressionProc)(XcmsCCC ccc, XcmsColor colors_in_out[], unsigned int ncolors, unsigned int index, Bool compression_flags_return[]);

ccc	Specifies the CCC.
colors_in_out	Specifies an array of color specifications. Pixel members should be ignored and must remain unchanged upon return.
ncolors	Specifies the number of XcmsColor structures in the color-specification array.
index	Specifies the index into the array of XcmsColor structures for the encountered color specification that lies outside the screen's color gamut. Valid values are 0 (for the first element) to ncolors - 1.
compression_flags_return	Returns an array of Boolean values for indicating compression status. If a non-NULL pointer is supplied and a color at a given index is compressed, then True should be stored at the corresponding index in this array; otherwise, the array should not be modified.

When implementing a gamut compression procedure, consider the following
rules and assumptions:

The gamut compression procedure can attempt to compress one or multiple
specifications at a time.
When called, elements 0 to index - 1 in the color specification
array can be assumed to fall within the screen's color gamut.
In addition, these color specifications are already in some device-dependent
format (typically
XcmsRGBi).
If any modifications are made to these color specifications,
they must be in their initial device-dependent format upon return.
When called, the element in the color specification array specified
by the index argument contains the color specification outside the
screen's color gamut encountered by the calling routine.
In addition, this color specification can be assumed to be in
XcmsCIEXYZ.
Upon return, this color specification must be in
XcmsCIEXYZ.
When called, elements from index to ncolors - 1
in the color specification array may or may not fall within the
screen's color gamut.
In addition, these color specifications can be assumed to be in
XcmsCIEXYZ.
If any modifications are made to these color specifications,
they must be in
XcmsCIEXYZ
upon return.
The color specifications passed to the gamut compression procedure
have already been adjusted to the Screen White Point.
This means that at this point the color specification's white point
is the Screen White Point.
If the gamut compression procedure uses a device-independent color space not
initially accessible for use in the color management system, use
XcmsAddColorSpace
to ensure that it is added.

Supplied Gamut Compression Procedures

The following equations are useful in describing gamut compression
functions:

delim %%

%CIELab~Psychometric~Chroma ~=~ sqrt(a_star sup 2 ~+~ b_star sup 2 )%

%CIELab~Psychometric~Hue ~=~ tan sup -1 left [ b_star over a_star right ]%

%CIELuv~Psychometric~Chroma ~=~ sqrt(u_star sup 2 ~+~ v_star sup 2 )%

%CIELuv~Psychometric~Hue ~=~ tan sup -1 left [ v_star over u_star right ]%

The gamut compression callback procedures provided by Xlib are as follows:

XcmsCIELabClipL
This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing or increasing CIE metric lightness (L*)
in the CIE L*a*b* color space until the color is within the gamut.
If the Psychometric Chroma of the color specification
is beyond maximum for the Psychometric Hue Angle,
then while maintaining the same Psychometric Hue Angle,
the color will be clipped to the CIE L*a*b* coordinates of maximum
Psychometric Chroma.
See
XcmsCIELabQueryMaxC.
No client data is necessary.
XcmsCIELabClipab
This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing Psychometric Chroma,
while maintaining Psychometric Hue Angle,
until the color is within the gamut.
No client data is necessary.
XcmsCIELabClipLab
This brings the encountered out-of-gamut color specification into the
screen's color gamut by replacing it with CIE L*a*b* coordinates
that fall within the color gamut while maintaining the original
Psychometric Hue
Angle and whose vector to the original coordinates is the shortest attainable.
No client data is necessary.
XcmsCIELuvClipL
This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing or increasing CIE metric lightness (L*)
in the CIE L*u*v* color space until the color is within the gamut.
If the Psychometric Chroma of the color specification
is beyond maximum for the Psychometric Hue Angle,
then, while maintaining the same Psychometric Hue Angle,
the color will be clipped to the CIE L*u*v* coordinates of maximum
Psychometric Chroma.
See
XcmsCIELuvQueryMaxC.
No client data is necessary.
XcmsCIELuvClipuv
This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing
Psychometric Chroma, while maintaining Psychometric Hue Angle,
until the color is within the gamut.
No client data is necessary.
XcmsCIELuvClipLuv
This brings the encountered out-of-gamut color specification into the
screen's color gamut by replacing it with CIE L*u*v* coordinates
that fall within the color gamut while maintaining the original
Psychometric Hue
Angle and whose vector to the original coordinates is the shortest attainable.
No client data is necessary.
XcmsTekHVCClipV
This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing or increasing the Value dimension
in the TekHVC color space until the color is within the gamut.
If Chroma of the color specification is beyond maximum for the particular Hue,
then, while maintaining the same Hue,
the color will be clipped to the Value and Chroma coordinates
that represent maximum Chroma for that particular Hue.
No client data is necessary.
XcmsTekHVCClipC
This brings the encountered out-of-gamut color specification into the
screen's color gamut by reducing the Chroma dimension
in the TekHVC color space until the color is within the gamut.
No client data is necessary.
XcmsTekHVCClipVC
This brings the encountered out-of-gamut color specification into the
screen's color gamut by replacing it with TekHVC coordinates
that fall within the color gamut while maintaining the original Hue
and whose vector to the original coordinates is the shortest attainable.
No client data is necessary.

Prototype White Point Adjustment Procedure

The white point adjustment procedure interface must adhere to the following:

typedef Status (*XcmsWhiteAdjustProc)(XcmsCCC ccc, XcmsColor *initial_white_point, XcmsColor *target_white_point, XcmsColorFormat target_format, XcmsColor colors_in_out[], unsigned int ncolors, Bool compression_flags_return[]);

ccc	Specifies the CCC.
initial_white_point	Specifies the initial white point.
target_white_point	Specifies the target white point.
target_format	Specifies the target color specification format.
colors_in_out	Specifies an array of color specifications. Pixel members should be ignored and must remain unchanged upon return.
ncolors	Specifies the number of XcmsColor structures in the color-specification array.
compression_flags_return	Returns an array of Boolean values for indicating compression status. If a non-NULL pointer is supplied and a color at a given index is compressed, then True should be stored at the corresponding index in this array; otherwise, the array should not be modified.

Supplied White Point Adjustment Procedures

White point adjustment procedures provided by Xlib are as follows:

XcmsCIELabWhiteShiftColors
This uses the CIE L*a*b* color space for adjusting the chromatic character
of colors to compensate for the chromatic differences between the source
and destination white points.
This procedure simply converts the color specifications to
XcmsCIELab
using the source white point and then converts to the target specification
format using the destination's white point.
No client data is necessary.
XcmsCIELuvWhiteShiftColors
This uses the CIE L*u*v* color space for adjusting the chromatic character
of colors to compensate for the chromatic differences between the source
and destination white points.
This procedure simply converts the color specifications to
XcmsCIELuv
using the source white point and then converts to the target specification
format using the destination's white point.
No client data is necessary.
XcmsTekHVCWhiteShiftColors
This uses the TekHVC color space for adjusting the chromatic character
of colors to compensate for the chromatic differences between the source
and destination white points.
This procedure simply converts the color specifications to
XcmsTekHVC
using the source white point and then converts to the target specification
format using the destination's white point.
An advantage of this procedure over those previously described
is an attempt to minimize hue shift.
No client data is necessary.

From an implementation point of view,
these white point adjustment procedures convert the color specifications
to a device-independent but white-point-dependent color space
(for example, CIE L*u*v*, CIE L*a*b*, TekHVC) using one white point
and then converting those specifications to the target color space
using another white point.
In other words,
the specification goes in the color space with one white point
but comes out with another white point,
resulting in a chromatic shift based on the chromatic displacement
between the initial white point and target white point.
The CIE color spaces that are assumed to be white-point-independent
are CIE u'v'Y, CIE XYZ, and CIE xyY.
When developing a custom white point adjustment procedure that uses a
device-independent color space not initially accessible for use in the
color management system, use
XcmsAddColorSpace
to ensure that it is added.

As an example,
if the CCC specifies a white point adjustment procedure
and if the Client White Point and Screen White Point differ, the
XcmsAllocColor
function will use the white point adjustment
procedure twice:

Once to convert to
XcmsRGB
A second time to convert from
XcmsRGB

For example, assume the specification is in
XcmsCIEuvY
and the adjustment procedure is
XcmsCIELuvWhiteShiftColors.
During conversion to
XcmsRGB,
the call to
XcmsAllocColor
results in the following series of color specification conversions:

From
XcmsCIEuvY
to
XcmsCIELuv
using the Client White Point
From
XcmsCIELuv
to
XcmsCIEuvY
using the Screen White Point
From
XcmsCIEuvY
to
XcmsCIEXYZ
(CIE u'v'Y and XYZ are white-point-independent color spaces)
From
XcmsCIEXYZ
to
XcmsRGBi
From
XcmsRGBi
to
XcmsRGB

The resulting RGB specification is passed to
XAllocColor,
and the RGB
specification returned by
XAllocColor
is converted back to
XcmsCIEuvY
by reversing the color conversion sequence.

Gamut Querying Functions

This section describes the gamut querying functions that Xlib provides.
These functions allow the client to query the boundary
of the screen's color gamut in terms of the CIE L*a*b*, CIE L*u*v*,
and TekHVC color spaces.

Functions are also provided that allow you to query
the color specification of:

White (full-intensity red, green, and blue)
Red (full-intensity red while green and blue are zero)
Green (full-intensity green while red and blue are zero)
Blue (full-intensity blue while red and green are zero)
Black (zero-intensity red, green, and blue)

The white point associated with color specifications passed to
and returned from these gamut querying
functions is assumed to be the Screen White Point.

This is a reasonable assumption,
because the client is trying to query the screen's color gamut.

The following naming convention is used for the Max and Min functions:

Xcms<color_space>QueryMax<dimensions>

Xcms<color_space>QueryMin<dimensions>

The <dimensions> consists of a letter or letters
that identify the dimensions of the color space
that are not fixed.
For example,
XcmsTekHVCQueryMaxC
is given a fixed Hue and Value for which maximum Chroma is found.

Red, Green, and Blue Queries

To obtain the color specification for black
(zero-intensity red, green, and blue), use
XcmsQueryBlack.

Status XcmsQueryBlack(XcmsCCC ccc, XcmsColorFormat target_format, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
target_format	Specifies the target color specification format.
color_return	Returns the color specification in the specified target format for zero-intensity red, green, and blue. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsQueryBlack
function returns the color specification in the specified target format
for zero-intensity red, green, and blue.

To obtain the color specification for blue
(full-intensity blue while red and green are zero), use
XcmsQueryBlue.

Status XcmsQueryBlue(XcmsCCC ccc, XcmsColorFormat target_format, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
target_format	Specifies the target color specification format.
color_return	Returns the color specification in the specified target format for full-intensity blue while red and green are zero. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsQueryBlue
function returns the color specification in the specified target format
for full-intensity blue while red and green are zero.

To obtain the color specification for green
(full-intensity green while red and blue are zero), use
XcmsQueryGreen.

Status XcmsQueryGreen(XcmsCCC ccc, XcmsColorFormat target_format, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
target_format	Specifies the target color specification format.
color_return	Returns the color specification in the specified target format for full-intensity green while red and blue are zero. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsQueryGreen
function returns the color specification in the specified target format
for full-intensity green while red and blue are zero.

To obtain the color specification for red
(full-intensity red while green and blue are zero), use
XcmsQueryRed.

Status XcmsQueryRed(XcmsCCC ccc, XcmsColorFormat target_format, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
target_format	Specifies the target color specification format.
color_return	Returns the color specification in the specified target format for full-intensity red while green and blue are zero. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsQueryRed
function returns the color specification in the specified target format
for full-intensity red while green and blue are zero.

To obtain the color specification for white
(full-intensity red, green, and blue), use
XcmsQueryWhite.

Status XcmsQueryWhite(XcmsCCC ccc, XcmsColorFormat target_format, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
target_format	Specifies the target color specification format.
color_return	Returns the color specification in the specified target format for full-intensity red, green, and blue. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsQueryWhite
function returns the color specification in the specified target format
for full-intensity red, green, and blue.

CIELab Queries

The following equations are useful in describing the CIELab query functions:

delim %%

%CIELab~Psychometric~Chroma ~=~ sqrt(a_star sup 2 ~+~ b_star sup 2 )%

%CIELab~Psychometric~Hue ~=~ tan sup -1 left [ b_star over a_star right ]%

To obtain the CIE L*a*b* coordinates of maximum Psychometric Chroma
for a given Psychometric Hue Angle and CIE metric lightness (L*), use
XcmsCIELabQueryMaxC.

Status XcmsCIELabQueryMaxC(XcmsCCC ccc, XcmsFloat hue_angle, XcmsFloat L_star, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue_angle	Specifies the hue angle (in degrees) at which to find maximum chroma.
L_star	Specifies the lightness (L*) at which to find maximum chroma.
color_return	Returns the CIE Lab* coordinates of maximum chroma displayable by the screen for the given hue angle and lightness. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsCIELabQueryMaxC
function, given a hue angle and lightness,
finds the point of maximum chroma displayable by the screen.
It returns this point in CIE L*a*b* coordinates.

To obtain the CIE L*a*b* coordinates of maximum CIE metric lightness (L*)
for a given Psychometric Hue Angle and Psychometric Chroma, use
XcmsCIELabQueryMaxL.

Status XcmsCIELabQueryMaxL(XcmsCCC ccc, XcmsFloat hue_angle, XcmsFloat chroma, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue_angle	Specifies the hue angle (in degrees) at which to find maximum lightness.
chroma	Specifies the chroma at which to find maximum lightness.
color_return	Returns the CIE Lab* coordinates of maximum lightness displayable by the screen for the given hue angle and chroma. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsCIELabQueryMaxL
function, given a hue angle and chroma,
finds the point in CIE L*a*b* color space of maximum
lightness (L*) displayable by the screen.
It returns this point in CIE L*a*b* coordinates.
An
XcmsFailure
return value usually indicates that the given chroma
is beyond maximum for the given hue angle.

To obtain the CIE L*a*b* coordinates of maximum Psychometric Chroma
for a given Psychometric Hue Angle, use
XcmsCIELabQueryMaxLC.

Status XcmsCIELabQueryMaxLC(XcmsCCC ccc, XcmsFloat hue_angle, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue_angle	Specifies the hue angle (in degrees) at which to find maximum chroma.
color_return	Returns the CIE Lab* coordinates of maximum chroma displayable by the screen for the given hue angle. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsCIELabQueryMaxLC
function, given a hue angle,
finds the point of maximum chroma displayable by the screen.
It returns this point in CIE L*a*b* coordinates.

To obtain the CIE L*a*b* coordinates of minimum CIE metric lightness (L*)
for a given Psychometric Hue Angle and Psychometric Chroma, use
XcmsCIELabQueryMinL.

Status XcmsCIELabQueryMinL(XcmsCCC ccc, XcmsFloat hue_angle, XcmsFloat chroma, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue_angle	Specifies the hue angle (in degrees) at which to find minimum lightness.
chroma	Specifies the chroma at which to find minimum lightness.
color_return	Returns the CIE Lab* coordinates of minimum lightness displayable by the screen for the given hue angle and chroma. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsCIELabQueryMinL
function, given a hue angle and chroma,
finds the point of minimum lightness (L*) displayable by the screen.
It returns this point in CIE L*a*b* coordinates.
An
XcmsFailure
return value usually indicates that the given chroma
is beyond maximum for the given hue angle.

CIELuv Queries

The following equations are useful in describing the CIELuv query functions:

delim %%

%CIELuv~Psychometric~Chroma ~=~ sqrt(u_star sup 2 ~+~ v_star sup 2 )%

%CIELuv~Psychometric~Hue ~=~ tan sup -1 left [ v_star over u_star right ]%

To obtain the CIE L*u*v* coordinates of maximum Psychometric Chroma
for a given Psychometric Hue Angle and CIE metric lightness (L*), use
XcmsCIELuvQueryMaxC.

Status XcmsCIELuvQueryMaxC(XcmsCCC ccc, XcmsFloat hue_angle, XcmsFloat L_star, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue_angle	Specifies the hue angle (in degrees) at which to find maximum chroma.
L_star	Specifies the lightness (L*) at which to find maximum chroma.
color_return	Returns the CIE Luv* coordinates of maximum chroma displayable by the screen for the given hue angle and lightness. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsCIELuvQueryMaxC
function, given a hue angle and lightness,
finds the point of maximum chroma displayable by the screen.
It returns this point in CIE L*u*v* coordinates.

To obtain the CIE L*u*v* coordinates of maximum CIE metric lightness (L*)
for a given Psychometric Hue Angle and Psychometric Chroma, use
XcmsCIELuvQueryMaxL.

Status XcmsCIELuvQueryMaxL(XcmsCCC ccc, XcmsFloat hue_angle, XcmsFloat chroma, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue_angle	Specifies the hue angle (in degrees) at which to find maximum lightness.
L_star	Specifies the lightness (L*) at which to find maximum lightness.
color_return	Returns the CIE Luv* coordinates of maximum lightness displayable by the screen for the given hue angle and chroma. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsCIELuvQueryMaxL
function, given a hue angle and chroma,
finds the point in CIE L*u*v* color space of maximum
lightness (L*) displayable by the screen.
It returns this point in CIE L*u*v* coordinates.
An
XcmsFailure
return value usually indicates that the given chroma
is beyond maximum for the given hue angle.

To obtain the CIE L*u*v* coordinates of maximum Psychometric Chroma
for a given Psychometric Hue Angle, use
XcmsCIELuvQueryMaxLC.

Status XcmsCIELuvQueryMaxLC(XcmsCCC ccc, XcmsFloat hue_angle, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue_angle	Specifies the hue angle (in degrees) at which to find maximum chroma.
color_return	Returns the CIE Luv* coordinates of maximum chroma displayable by the screen for the given hue angle. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsCIELuvQueryMaxLC
function, given a hue angle,
finds the point of maximum chroma displayable by the screen.
It returns this point in CIE L*u*v* coordinates.

To obtain the CIE L*u*v* coordinates of minimum CIE metric lightness (L*)
for a given Psychometric Hue Angle and Psychometric Chroma, use
XcmsCIELuvQueryMinL.

Status XcmsCIELuvQueryMinL(XcmsCCC ccc, XcmsFloat hue_angle, XcmsFloat chroma, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue_angle	Specifies the hue angle (in degrees) at which to find minimum lightness.
chroma	Specifies the chroma at which to find minimum lightness.
color_return	Returns the CIE Luv* coordinates of minimum lightness displayable by the screen for the given hue angle and chroma. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsCIELuvQueryMinL
function, given a hue angle and chroma,
finds the point of minimum lightness (L*) displayable by the screen.
It returns this point in CIE L*u*v* coordinates.
An
XcmsFailure
return value usually indicates that the given chroma
is beyond maximum for the given hue angle.

TekHVC Queries

To obtain the maximum Chroma for a given Hue and Value, use
XcmsTekHVCQueryMaxC.

Status XcmsTekHVCQueryMaxC(XcmsCCC ccc, XcmsFloat hue, XcmsFloat value, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue	Specifies the Hue in which to find the maximum Chroma.
value	Specifies the Value in which to find the maximum Chroma.
color_return	Returns the maximum Chroma along with the actual Hue and Value at which the maximum Chroma was found. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMaxC
function, given a Hue and Value,
determines the maximum Chroma in TekHVC color space
displayable by the screen.
It returns the maximum Chroma along with the actual Hue
and Value at which the maximum Chroma was found.

To obtain the maximum Value for a given Hue and Chroma, use
XcmsTekHVCQueryMaxV.

Status XcmsTekHVCQueryMaxV(XcmsCCC ccc, XcmsFloat hue, XcmsFloat chroma, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue	Specifies the Hue in which to find the maximum Value.
chroma	Specifies the chroma at which to find maximum Value.
color_return	Returns the maximum Value along with the Hue and Chroma at which the maximum Value was found. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMaxV
function, given a Hue and Chroma,
determines the maximum Value in TekHVC color space
displayable by the screen.
It returns the maximum Value and the actual Hue and Chroma
at which the maximum Value was found.

To obtain the maximum Chroma and Value at which it is reached
for a specified Hue, use
XcmsTekHVCQueryMaxVC.

Status XcmsTekHVCQueryMaxVC(XcmsCCC ccc, XcmsFloat hue, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue	Specifies the Hue in which to find the maximum Chroma.
color_return	Returns the color specification in XcmsTekHVC for the maximum Chroma, the Value at which that maximum Chroma is reached, and the actual Hue at which the maximum Chroma was found. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMaxVC
function, given a Hue,
determines the maximum Chroma in TekHVC color space displayable by the screen
and the Value at which that maximum Chroma is reached.
It returns the maximum Chroma,
the Value at which that maximum Chroma is reached,
and the actual Hue for which the maximum Chroma was found.

To obtain a specified number of TekHVC specifications such that they
contain maximum Values for a specified Hue and the
Chroma at which the maximum Values are reached, use
XcmsTekHVCQueryMaxVSamples.

Status XcmsTekHVCQueryMaxVSamples(XcmsCCC ccc, XcmsFloat hue, XcmsColor colors_return[], unsigned int nsamples);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue	Specifies the Hue for maximum Chroma/Value samples.
nsamples	Specifies the number of samples.
colors_return	Returns nsamples of color specifications in XcmsTekHVC such that the Chroma is the maximum attainable for the Value and Hue. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMaxVSamples
returns nsamples of maximum Value, the Chroma at which that maximum Value
is reached, and the actual Hue for which the maximum Chroma was found.
These sample points may then be used to plot the maximum Value/Chroma
boundary of the screen's color gamut for the specified Hue in TekHVC color
space.

To obtain the minimum Value for a given Hue and Chroma, use
XcmsTekHVCQueryMinV.

Status XcmsTekHVCQueryMinV(XcmsCCC ccc, XcmsFloat hue, XcmsFloat chroma, XcmsColor *color_return);

ccc	Specifies the CCC. The CCC's Client White Point and white point adjustment procedures are ignored.
hue	Specifies the Hue in which to find the minimum Value.
value	Specifies the Value in which to find the minimum Value.
color_return	Returns the minimum Value and the actual Hue and Chroma at which the minimum Value was found. The white point associated with the returned color specification is the Screen White Point. The value returned in the pixel member is undefined.

The
XcmsTekHVCQueryMinV
function, given a Hue and Chroma,
determines the minimum Value in TekHVC color space displayable by the screen.
It returns the minimum Value and the actual Hue and Chroma at which
the minimum Value was found.

Color Management Extensions

The Xlib color management facilities can be extended in two ways:

Device-Independent Color Spaces
Device-independent color spaces that are derivable to CIE XYZ
space can be added using the
XcmsAddColorSpace
function.
Color Characterization Function Set
A Color Characterization Function Set consists of
device-dependent color spaces and their functions that
convert between these color spaces and the CIE XYZ
color space, bundled together for a specific class of output devices.
A function set can be added using the
XcmsAddFunctionSet
function.

Color Spaces

The CIE XYZ color space serves as the hub for all
conversions between device-independent and device-dependent color spaces.
Therefore, the knowledge to convert an
XcmsColor
structure to and from CIE XYZ format is associated with each color space.
For example, conversion from CIE L*u*v* to RGB requires the knowledge
to convert from CIE L*u*v* to CIE XYZ and from CIE XYZ to RGB.
This knowledge is stored as an array of functions that,
when applied in series, will convert the
XcmsColor
structure to or from CIE XYZ format.
This color specification conversion mechanism facilitates
the addition of color spaces.

Of course, when converting between only device-independent color spaces
or only device-dependent color spaces,
shortcuts are taken whenever possible.
For example, conversion from TekHVC to CIE L*u*v* is performed
by intermediate conversion to CIE u*v*Y and then to CIE L*u*v*,
thus bypassing conversion between CIE u*v*Y and CIE XYZ.

Adding Device-Independent Color Spaces

To add a device-independent color space, use
XcmsAddColorSpace.

Status XcmsAddColorSpace(XcmsColorSpace *color_space);

color_space

Specifies the device-independent color space to add.

The
XcmsAddColorSpace
function makes a device-independent color space (actually an
XcmsColorSpace
structure) accessible by the color management system.
Because format values for unregistered color spaces are assigned at run time,
they should be treated as private to the client.
If references to an unregistered color space must be made
outside the client (for example, storing color specifications
in a file using the unregistered color space),
then reference should be made by color space prefix
(see
XcmsFormatOfPrefix
and
XcmsPrefixOfFormat).

If the
XcmsColorSpace
structure is already accessible in the color management system,
XcmsAddColorSpace
returns
XcmsSuccess.

Note that added
XcmsColorSpaces
must be retained for reference by Xlib.

Querying Color Space Format and Prefix

To obtain the format associated with the color space
associated with a specified color string prefix, use
XcmsFormatOfPrefix.

XcmsColorFormat XcmsFormatOfPrefix(char *prefix);

prefix

Specifies the string that contains the color space prefix.

The
XcmsFormatOfPrefix
function returns the format for the specified color space prefix
(for example, the string “CIEXYZ”).
The prefix is case-insensitive.
If the color space is not accessible in the color management system,
XcmsFormatOfPrefix
returns
XcmsUndefinedFormat.

To obtain the color string prefix associated with the color space
specified by a color format, use
XcmsPrefixOfFormat.

char *XcmsPrefixOfFormat(XcmsColorFormat format);

format

Specifies the color specification format.

The
XcmsPrefixOfFormat
function returns the string prefix associated with the color specification
encoding specified by the format argument.
Otherwise, if no encoding is found, it returns NULL.
The returned string must be treated as read-only.

Creating Additional Color Spaces

Color space specific information necessary
for color space conversion and color string parsing is stored in an
XcmsColorSpace
structure.
Therefore, a new structure containing this information is required
for each additional color space.
In the case of device-independent color spaces,
a handle to this new structure (that is, by means of a global variable)
is usually made accessible to the client program for use with the
XcmsAddColorSpace
function.

If a new
XcmsColorSpace
structure specifies a color space not registered with the X Consortium,
they should be treated as private to the client
because format values for unregistered color spaces are assigned at run time.
If references to an unregistered color space must be made outside the
client (for example, storing color specifications in a file using the
unregistered color space), then reference should be made by color space prefix
(see
XcmsFormatOfPrefix
and
XcmsPrefixOfFormat).


typedef (*XcmsConversionProc)();
typedef XcmsConversionProc *XcmsFuncListPtr;
		/* A NULL terminated list of function pointers*/

typedef struct _XcmsColorSpace {
	char *prefix;
	XcmsColorFormat format;
	XcmsParseStringProc parseString;
	XcmsFuncListPtr to_CIEXYZ;
	XcmsFuncListPtr from_CIEXYZ;
	int inverse_flag;
} XcmsColorSpace;

The prefix member specifies the prefix that indicates a color string
is in this color space's string format.
For example, the strings “ciexyz” or “CIEXYZ” for CIE XYZ,
and “rgb” or “RGB” for RGB.
The prefix is case insensitive.
The format member specifies the color specification format.
Formats for unregistered color spaces are assigned at run time.
The parseString member contains a pointer to the function
that can parse a color string into an
XcmsColor
structure.
This function returns an integer (int): nonzero if it succeeded
and zero otherwise.
The to_CIEXYZ and from_CIEXYZ members contain pointers,
each to a NULL terminated list of function pointers.
When the list of functions is executed in series,
it will convert the color specified in an
XcmsColor
structure from/to the current color space format to/from the CIE XYZ format.
Each function returns an integer (int): nonzero if it succeeded
and zero otherwise.
The white point to be associated with the colors is specified
explicitly, even though white points can be found in the CCC.
The inverse_flag member, if nonzero, specifies that for each function listed
in to_CIEXYZ,
its inverse function can be found in from_CIEXYZ such that:

Given:  n = number of functions in each list

for each i, such that 0 <= i < n
    from_CIEXYZ[n - i - 1] is the inverse of to_CIEXYZ[i].

This allows Xlib to use the shortest conversion path,
thus bypassing CIE XYZ if possible (for example, TekHVC to CIE L*u*v*).

Parse String Callback

The callback in the
XcmsColorSpace
structure for parsing a color string for the particular color space must
adhere to the following software interface specification:

Status XcmsParseStringProc(char *color_string, XcmsColor *color_return);

color_string	Specifies the color string to parse.
color_return	Returns the color specification in the color space's format.

Color Specification Conversion Callback

Callback functions in the
XcmsColorSpace
structure for converting a color specification between device-independent
spaces must adhere to the
following software interface specification:

Status ConversionProc(XcmsCCC ccc, XcmsColor *white_point, XcmsColor *colors_in_out, unsigned int ncolors);

ccc	Specifies the CCC.
white_point	Specifies the white point associated with color specifications. The pixel member should be ignored, and the entire structure remain unchanged upon return.
colors_in_out	Specifies an array of color specifications. Pixel members should be ignored and must remain unchanged upon return.
ncolors	Specifies the number of XcmsColor structures in the color-specification array.

Callback functions in the
XcmsColorSpace
structure for converting a color specification to or from a device-dependent
space must adhere to the
following software interface specification:

Status ConversionProc(XcmsCCC ccc, XcmsColor *colors_in_out, unsigned int ncolors, Bool compression_flags_return[]);

ccc	Specifies the CCC.
colors_in_out	Specifies an array of color specifications. Pixel members should be ignored and must remain unchanged upon return.
ncolors	Specifies the number of XcmsColor structures in the color-specification array.
compression_flags_return	Returns an array of Boolean values for indicating compression status. If a non-NULL pointer is supplied and a color at a given index is compressed, then True should be stored at the corresponding index in this array; otherwise, the array should not be modified.

Conversion functions are available globally for use by other color
spaces.
The conversion functions provided by Xlib are:

Function	Converts from	Converts to
`XcmsCIELabToCIEXYZ`	XcmsCIELabFormat	XcmsCIEXYZFormat
`XcmsCIELuvToCIEuvY`	XcmsCIELuvFormat	XcmsCIEuvYFormat
`XcmsCIEXYZToCIELab`	XcmsCIEXYZFormat	XcmsCIELabFormat
`XcmsCIEXYZToCIEuvY`	XcmsCIEXYZFormat	XcmsCIEuvYFormat
`XcmsCIEXYZToCIExyY`	XcmsCIEXYZFormat	XcmsCIExyYFormat
`XcmsCIEXYZToRGBi`	XcmsCIEXYZFormat	XcmsRGBiFormat
`XcmsCIEuvYToCIELuv`	XcmsCIEuvYFormat	XcmsCIELabFormat
`XcmsCIEuvYToCIEXYZ`	XcmsCIEuvYFormat	XcmsCIEXYZFormat
`XcmsCIEuvYToTekHVC`	XcmsCIEuvYFormat	XcmsTekHVCFormat
`XcmsCIExyYToCIEXYZ`	XcmsCIExyYFormat	XcmsCIEXYZFormat
`XcmsRGBToRGBi`	XcmsRGBFormat	XcmsRGBiFormat
`XcmsRGBiToCIEXYZ`	XcmsRGBiFormat	XcmsCIEXYZFormat
`XcmsRGBiToRGB`	XcmsRGBiFormat	XcmsRGBFormat
`XcmsTekHVCToCIEuvY`	XcmsTekHVCFormat	XcmsCIEuvYFormat

Function Sets

Functions to convert between device-dependent color spaces
and CIE XYZ may differ for different classes of output devices
(for example, color versus gray monitors).
Therefore, the notion of a Color Characterization Function Set
has been developed.
A function set consists of device-dependent color spaces
and the functions that convert color specifications
between these device-dependent color spaces and the CIE XYZ color space
appropriate for a particular class of output devices.
The function set also contains a function that reads
color characterization data off root window properties.
It is this characterization data that will differ between devices within
a class of output devices.

For details about how color characterization data is
stored in root window properties,
see the
section on Device Color Characterization in the
Inter-Client Communication Conventions Manual.
The LINEAR_RGB function set is provided by Xlib
and will support most color monitors.
Function sets may require data that differs
from those needed for the LINEAR_RGB function set.
In that case,
its corresponding data may be stored on different root window properties.

Adding Function Sets

To add a function set, use
XcmsAddFunctionSet.

Status XcmsAddFunctionSet(XcmsFunctionSet *function_set);

function_set

Specifies the function set to add.

The
XcmsAddFunctionSet
function adds a function set to the color management system.
If the function set uses device-dependent
XcmsColorSpace
structures not accessible in the color management system,
XcmsAddFunctionSet
adds them.
If an added
XcmsColorSpace
structure is for a device-dependent color space not registered
with the X Consortium,
they should be treated as private to the client
because format values for unregistered color spaces are assigned at run time.
If references to an unregistered color space must be made outside the
client (for example, storing color specifications in a file
using the unregistered color space),
then reference should be made by color space prefix
(see
XcmsFormatOfPrefix
and
XcmsPrefixOfFormat).

Additional function sets should be added before any calls to other
Xlib routines are made.
If not, the
XcmsPerScrnInfo
member of a previously created
XcmsCCC
does not have the opportunity to initialize
with the added function set.

Creating Additional Function Sets

The creation of additional function sets should be
required only when an output device does not conform to existing
function sets or when additional device-dependent color spaces are necessary.
A function set consists primarily of a collection of device-dependent
XcmsColorSpace
structures and a means to read and store a
screen's color characterization data.
This data is stored in an
XcmsFunctionSet
structure.
A handle to this structure (that is, by means of global variable)
is usually made accessible to the client program for use with
XcmsAddFunctionSet.

If a function set uses new device-dependent
XcmsColorSpace
structures,
they will be transparently processed into the color management system.
Function sets can share an
XcmsColorSpace
structure for a device-dependent color space.
In addition, multiple
XcmsColorSpace
structures are allowed for a device-dependent color space;
however, a function set can reference only one of them.
These
XcmsColorSpace
structures will differ in the functions to convert to and from CIE XYZ,
thus tailored for the specific function set.


typedef struct _XcmsFunctionSet {
	XcmsColorSpace **DDColorSpaces;
	XcmsScreenInitProc screenInitProc;
	XcmsScreenFreeProc screenFreeProc;
} XcmsFunctionSet;

The DDColorSpaces member is a pointer to a NULL terminated list
of pointers to
XcmsColorSpace
structures for the device-dependent color spaces that are supported
by the function set.
The screenInitProc member is set to the callback procedure (see the following
interface specification) that initializes the
XcmsPerScrnInfo
structure for a particular screen.

The screen initialization callback must adhere to the following software
interface specification:

typedef Status (*XcmsScreenInitProc)(Display *display, int screen_number, ScmsPerScrnInfo *screen_info);

display	Specifies the connection to the X server.
screen_number	Specifies the appropriate screen number on the host server.
screen_info	Specifies the XcmsPerScrnInfo structure, which contains the per screen information.

The screen initialization callback in the
XcmsFunctionSet
structure fetches the color characterization data (device profile) for
the specified screen,
typically off properties on the
screen's root window.
It then initializes the specified
XcmsPerScrnInfo
structure.

If successful, the procedure fills in the
XcmsPerScrnInfo
structure as follows:

It sets the screenData member to the address
of the created device profile data structure
(contents known only by the function set).
It next sets the screenWhitePoint member.
It next sets the functionSet member to the address of the
XcmsFunctionSet
structure.
It then sets the state member to
XcmsInitSuccess
and finally returns
XcmsSuccess.

If unsuccessful, the procedure sets the state member to
XcmsInitFailure
and returns
XcmsFailure.

The
XcmsPerScrnInfo
structure contains:


typedef struct _XcmsPerScrnInfo {
	XcmsColor screenWhitePoint;
	XPointer functionSet;
	XPointer screenData;
	unsigned char state;
	char pad[3];
} XcmsPerScrnInfo;

The screenWhitePoint member specifies the white point inherent to
the screen.
The functionSet member specifies the appropriate function set.
The screenData member specifies the device profile.
The state member is set to one of the following:

XcmsInitNone
indicates initialization has not been previously attempted.
XcmsInitFailure
indicates initialization has been previously attempted but failed.
XcmsInitSuccess
indicates initialization has been previously attempted and succeeded.

The screen free callback must adhere to the following software
interface specification:

typedef void (*XcmsScreenFreeProc)(XPointer screenData);

screenData

Specifies the data to be freed.

This function is called to free the screenData stored in an
XcmsPerScrnInfo
structure.

Chapter 7. Graphics Context Functions

Table of Contents

Manipulating Graphics Context/StateUsing Graphics Context Convenience RoutinesSetting the Foreground, Background, Function, or Plane MaskSetting the Line Attributes and DashesSetting the Fill Style and Fill RuleSetting the Fill Tile and StippleSetting the Current FontSetting the Clip RegionSetting the Arc Mode, Subwindow Mode, and Graphics Exposure

A number of resources are used when performing graphics operations in X. Most information
about performing graphics (for example, foreground color, background color, line style, and so
on) is stored in resources called graphics contexts (GCs). Most graphics operations (see chapter
8) take a GC as an argument. Although in theory the X protocol permits sharing of GCs between
applications, it is expected that applications will use their own GCs when performing operations.
Sharing of GCs is highly discouraged because the library may cache GC state.

Graphics operations can be performed to either windows or pixmaps, which collectively are
called drawables. Each drawable exists on a single screen. A GC is created for a specific screen
and drawable depth and can only be used with drawables of matching screen and depth.

This chapter discusses how to:

Manipulate graphics context/state
Use graphics context convenience functions

Manipulating Graphics Context/State

Most attributes of graphics operations are stored in GCs.
These include line width, line style, plane mask, foreground, background,
tile, stipple, clipping region, end style, join style, and so on.
Graphics operations (for example, drawing lines) use these values
to determine the actual drawing operation.
Extensions to X may add additional components to GCs.
The contents of a GC are private to Xlib.

Xlib implements a write-back cache for all elements of a GC that are not
resource IDs to allow Xlib to implement the transparent coalescing of changes
to GCs.
For example,
a call to
XSetForeground
of a GC followed by a call to
XSetLineAttributes
results in only a single-change GC protocol request to the server.
GCs are neither expected nor encouraged to be shared between client
applications, so this write-back caching should present no problems.
Applications cannot share GCs without external synchronization.
Therefore,
sharing GCs between applications is highly discouraged.

To set an attribute of a GC,
set the appropriate member of the
XGCValues
structure and OR in the corresponding value bitmask in your subsequent calls to
XCreateGC.
The symbols for the value mask bits and the
XGCValues
structure are:

/* GC attribute value mask bits */

#define     GCFunction              (1L<<0)
#define     GCPlaneMask             (1L<<1)
#define     GCForeground            (1L<<2)
#define     GCBackground            (1L<<3)
#define     GCLineWidth             (1L<<4)
#define     GCLineStyle             (1L<<5)
#define     GCCapStyle              (1L<<6)
#define     GCJoinStyle             (1L<<7)
#define     GCFillStyle             (1L<<8)
#define     GCFillRule              (1L<<9)
#define     GCTile                  (1L<<10)
#define     GCStipple               (1L<<11)
#define     GCTileStipXOrigin       (1L<<12)
#define     GCTileStipYOrigin       (1L<<13)
#define     GCFont                  (1L<<14)
#define     GCSubwindowMode         (1L<<15)
#define     GCGraphicsExposures     (1L<<16)
#define     GCClipXOrigin           (1L<<17)
#define     GCClipYOrigin           (1L<<18)
#define     GCClipMask              (1L<<19)
#define     GCDashOffset            (1L<<20)
#define     GCDashList              (1L<<21)
#define     GCArcMode               (1L<<22)


/* Values */

typedef struct {
     int function;                 /* logical operation */
     unsigned long plane_mask;     /* plane mask */
     unsigned long foreground;     /* foreground pixel */
     unsigned long background;     /* background pixel */
     int line_width;               /* line width (in pixels) */
     int line_style;               /* LineSolid, LineOnOffDash, LineDoubleDash */
     int cap_style;                /* CapNotLast, CapButt, CapRound, CapProjecting */
     int join_style;               /* JoinMiter, JoinRound, JoinBevel */
     int fill_style;               /* FillSolid, FillTiled, FillStippled FillOpaqueStippled*/
     int fill_rule;                /* EvenOddRule, WindingRule */
     int arc_mode;                 /* ArcChord, ArcPieSlice */
     Pixmap tile;                  /* tile pixmap for tiling operations */
     Pixmap stipple;               /* stipple 1 plane pixmap for stippling */
     int ts_x_origin;              /* offset for tile or stipple operations */
     int ts_y_origin
     Font font;                    /* default text font for text operations */
     int subwindow_mode;           /* ClipByChildren, IncludeInferiors */
     Bool graphics_exposures;      /* boolean, should exposures be generated */
     int clip_x_origin;            /* origin for clipping */
     int clip_y_origin;
     Pixmap clip_mask;             /* bitmap clipping; other calls for rects */
     int dash_offset;              /* patterned/dashed line information */
     char dashes;
} XGCValues;

The default GC values are:

Component	Default
function	GXcopy
plane_mask	All ones
foreground	0
background	1
line_width	0
line_style	LineSolid
cap_style	CapButt
join_style	JoinMiter
fill_style	FillSolid
fill_rule	EvenOddRule
arc_mode	ArcPieSlice
tile	Pixmap of unspecified size filled with foreground pixel (that is, client specified pixel if any, else 0) (subsequent changes to foreground do not affect this pixmap)
stipple	Pixmap of unspecified size filled with ones
ts_x_origin	0
ts_y_origin	0
font	<implementation dependent>
subwindow_mode	ClipByChildren
graphics_exposures	True
clip_x_origin	0
clip_y_origin	0
clip_mask	None
dash_offset	0
dashes	4 (that is, the list [4, 4])

Note that foreground and background are not set to any values likely
to be useful in a window.

The function attributes of a GC are used when you update a section of
a drawable (the destination) with bits from somewhere else (the source).
The function in a GC defines how the new destination bits are to be
computed from the source bits and the old destination bits.
GXcopy
is typically the most useful because it will work on a color display,
but special applications may use other functions,
particularly in concert with particular planes of a color display.
The 16 GC functions, defined in
<X11/X.h>,

are:

Function Name	Value	Operation
GXclear	0x0	0
GXand	0x1	src AND dst
GXandReverse	0x2	src AND NOT dst
GXcopy	0x3	src
GXandInverted	0x4	(NOT src) AND dst
GXnoop	0x5	dst
GXxor	0x6	src XOR dst
GXor	0x7	src OR dst
GXnor	0x8	(NOT src) AND (NOT dst)
GXequiv	0x9	(NOT src) XOR dst
GXinvert	0xa	NOT dst
GXorReverse	0xb	src OR (NOT dst)
GXcopyInverted	0xc	NOT src
GXorInverted	0xd	(NOT src) OR dst
GXnand	0xe	(NOT src) OR (NOT dst)
GXset	0xf	1

Many graphics operations depend on either pixel values or planes in a GC.

The planes attribute is of type long, and it specifies which planes of the
destination are to be modified, one bit per plane.

A monochrome display has only one plane and
will be the least significant bit of the word.
As planes are added to the display hardware, they will occupy more
significant bits in the plane mask.

In graphics operations, given a source and destination pixel,
the result is computed bitwise on corresponding bits of the pixels.
That is, a Boolean operation is performed in each bit plane.
The plane_mask restricts the operation to a subset of planes.
A macro constant
AllPlanes
can be used to refer to all planes of the screen simultaneously.
The result is computed by the following:

((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))

Range checking is not performed on the values for foreground,
background, or plane_mask.
They are simply truncated to the appropriate
number of bits.
The line-width is measured in pixels and either can be greater than or equal to
one (wide line) or can be the special value zero (thin line).

Wide lines are drawn centered on the path described by the graphics request.
Unless otherwise specified by the join-style or cap-style,
the bounding box of a wide line with endpoints [x1, y1], [x2, y2] and
width w is a rectangle with vertices at the following real coordinates:


[x1-(w*sn/2), y1+(w*cs/2)], [x1+(w*sn/2), y1-(w*cs/2)],
[x2-(w*sn/2), y2+(w*cs/2)], [x2+(w*sn/2), y2-(w*cs/2)]

Here sn is the sine of the angle of the line,
and cs is the cosine of the angle of the line.
A pixel is part of the line and so is drawn
if the center of the pixel is fully inside the bounding box
(which is viewed as having infinitely thin edges).
If the center of the pixel is exactly on the bounding box,
it is part of the line if and only if the interior is immediately to its right
(x increasing direction).
Pixels with centers on a horizontal edge are a special case and are part of
the line if and only if the interior or the boundary is immediately below
(y increasing direction) and the interior or the boundary is immediately
to the right (x increasing direction).

Thin lines (zero line-width) are one-pixel-wide lines drawn using an
unspecified, device-dependent algorithm.
There are only two constraints on this algorithm.

If a line is drawn unclipped from [x1,y1] to [x2,y2] and
if another line is drawn unclipped from [x1+dx,y1+dy] to [x2+dx,y2+dy],
a point [x,y] is touched by drawing the first line
if and only if the point [x+dx,y+dy] is touched by drawing the second line.
The effective set of points comprising a line cannot be affected by clipping.
That is, a point is touched in a clipped line if and only if the point
lies inside the clipping region and the point would be touched
by the line when drawn unclipped.

A wide line drawn from [x1,y1] to [x2,y2] always draws the same pixels
as a wide line drawn from [x2,y2] to [x1,y1], not counting cap-style
and join-style.
It is recommended that this property be true for thin lines,
but this is not required.
A line-width of zero may differ from a line-width of one in which pixels are
drawn.
This permits the use of many manufacturers' line drawing hardware,
which may run many times faster than the more precisely specified
wide lines.

In general,
drawing a thin line will be faster than drawing a wide line of width one.
However, because of their different drawing algorithms,
thin lines may not mix well aesthetically with wide lines.
If it is desirable to obtain precise and uniform results across all displays,
a client should always use a line-width of one rather than a line-width of zero.

The line-style defines which sections of a line are drawn:

LineSolid	The full path of the line is drawn.
LineDoubleDash	The full path of the line is drawn, but the even dashes are filled differently from the odd dashes (see fill-style) with CapButt style used where even and odd dashes meet.
LineOnOffDash	Only the even dashes are drawn, and cap-style applies to all internal ends of the individual dashes, except CapNotLast is treated as CapButt.

The cap-style defines how the endpoints of a path are drawn:

CapNotLast	This is equivalent to CapButt except that for a line-width of zero the final endpoint is not drawn.
CapButt	The line is square at the endpoint (perpendicular to the slope of the line) with no projection beyond.
CapRound	The line has a circular arc with the diameter equal to the line-width, centered on the endpoint. (This is equivalent to CapButt for line-width of zero).
CapProjecting	The line is square at the end, but the path continues beyond the endpoint for a distance equal to half the line-width. (This is equivalent to CapButt for line-width of zero).

The join-style defines how corners are drawn for wide lines:

JoinMiter	The outer edges of two lines extend to meet at an angle. However, if the angle is less than 11 degrees, then a JoinBevel join-style is used instead.
JoinRound	The corner is a circular arc with the diameter equal to the line-width, centered on the joinpoint.
JoinBevel	The corner has CapButt endpoint styles with the triangular notch filled.

For a line with coincident endpoints (x1=x2, y1=y2),
when the cap-style is applied to both endpoints,
the semantics depends on the line-width and the cap-style:

CapNotLast	thin	The results are device dependent, but the desired effect is that nothing is drawn.
CapButt	thin	The results are device dependent, but the desired effect is that a single pixel is drawn.
CapRound	thin	The results are the same as for CapButt /thin.
CapProjecting	thin	The results are the same as for CapButt /thin.
CapButt	wide	Nothing is drawn.
CapRound	wide	The closed path is a circle, centered at the endpoint, and with the diameter equal to the line-width.
CapProjecting	wide	The closed path is a square, aligned with the coordinate axes, centered at the endpoint, and with the sides equal to the line-width.

For a line with coincident endpoints (x1=x2, y1=y2),
when the join-style is applied at one or both endpoints,
the effect is as if the line was removed from the overall path.
However, if the total path consists of or is reduced to a single point joined
with itself, the effect is the same as when the cap-style is applied at both
endpoints.

The tile/stipple represents an infinite two-dimensional plane,
with the tile/stipple replicated in all dimensions.
When that plane is superimposed on the drawable
for use in a graphics operation, the upper-left corner
of some instance of the tile/stipple is at the coordinates within
the drawable specified by the tile/stipple origin.
The tile/stipple and clip origins are interpreted relative to the
origin of whatever destination drawable is specified in a graphics
request.
The tile pixmap must have the same root and depth as the GC,
or a
BadMatch
error results.
The stipple pixmap must have depth one and must have the same root as the
GC, or a
BadMatch
error results.
For stipple operations where the fill-style is
FillStippled
but not
FillOpaqueStippled,
the stipple pattern is tiled in a
single plane and acts as an additional clip mask to be ANDed with the clip-mask.
Although some sizes may be faster to use than others,
any size pixmap can be used for tiling or stippling.

The fill-style defines the contents of the source for line, text, and
fill requests.
For all text and fill requests (for example,
XDrawText,
XDrawText16,
XFillRectangle,
XFillPolygon,
and
XFillArc);
for line requests
with line-style
LineSolid
(for example,
XDrawLine,
XDrawSegments,
XDrawRectangle,
XDrawArc);
and for the even dashes for line requests with line-style
LineOnOffDash
or
LineDoubleDash,
the following apply:

FillSolid	Foreground
FillTiled	Tile
FillOpaqueStippled	A tile with the same width and height as stipple, but with background everywhere stipple has a zero and with foreground everywhere stipple has a one
FillStippled	Foreground masked by stipple

When drawing lines with line-style
LineDoubleDash,
the odd dashes are controlled by the fill-style in the following manner:

FillSolid	Background
FillTiled	Same as for even dashes
FillOpaqueStippled	Same as for even dashes
FillStippled	Background masked by stipple

Storing a pixmap in a GC might or might not result in a copy
being made.
If the pixmap is later used as the destination for a graphics request,
the change might or might not be reflected in the GC.
If the pixmap is used simultaneously in a graphics request both as
a destination and as a tile or stipple,
the results are undefined.

For optimum performance,
you should draw as much as possible with the same GC
(without changing its components).
The costs of changing GC components relative to using different GCs
depend on the display hardware and the server implementation.
It is quite likely that some amount of GC information will be
cached in display hardware and that such hardware can only cache a small number
of GCs.

The dashes value is actually a simplified form of the
more general patterns that can be set with
XSetDashes.
Specifying a
value of N is equivalent to specifying the two-element list [N, N] in
XSetDashes.
The value must be nonzero,
or a
BadValue
error results.

The clip-mask restricts writes to the destination drawable.
If the clip-mask is set to a pixmap,
it must have depth one and have the same root as the GC,
or a
BadMatch
error results.
If clip-mask is set to
None,
the pixels are always drawn regardless of the clip origin.
The clip-mask also can be set by calling the
XSetClipRectangles
or
XSetRegion
functions.
Only pixels where the clip-mask has a bit set to 1 are drawn.
Pixels are not drawn outside the area covered by the clip-mask
or where the clip-mask has a bit set to 0.
The clip-mask affects all graphics requests.
The clip-mask does not clip sources.
The clip-mask origin is interpreted relative to the origin of whatever
destination drawable is specified in a graphics request.

You can set the subwindow-mode to
ClipByChildren
or
IncludeInferiors.
For
ClipByChildren,
both source and destination windows are
additionally clipped by all viewable
InputOutput
children.
For
IncludeInferiors,
neither source nor destination window is clipped by inferiors.
This will result in including subwindow contents in the source
and drawing through subwindow boundaries of the destination.
The use of
IncludeInferiors
on a window of one depth with mapped
inferiors of differing depth is not illegal, but the semantics are
undefined by the core protocol.

The fill-rule defines what pixels are inside (drawn) for
paths given in
XFillPolygon
requests and can be set to
EvenOddRule
or
WindingRule.
For
EvenOddRule,
a point is inside if
an infinite ray with the point as origin crosses the path an odd number
of times.
For
WindingRule,
a point is inside if an infinite ray with the
point as origin crosses an unequal number of clockwise and
counterclockwise directed path segments.
A clockwise directed path segment is one that crosses the ray from left to
right as observed from the point.
A counterclockwise segment is one that crosses the ray from right to left
as observed from the point.
The case where a directed line segment is coincident with the ray is
uninteresting because you can simply choose a different ray that is not
coincident with a segment.

For both
EvenOddRule
and
WindingRule,
a point is infinitely small,
and the path is an infinitely thin line.
A pixel is inside if the center point of the pixel is inside
and the center point is not on the boundary.
If the center point is on the boundary,
the pixel is inside if and only if the polygon interior is immediately to
its right (x increasing direction).
Pixels with centers on a horizontal edge are a special case
and are inside if and only if the polygon interior is immediately below
(y increasing direction).

The arc-mode controls filling in the
XFillArcs
function and can be set to
ArcPieSlice
or
ArcChord.
For
ArcPieSlice,
the arcs are pie-slice filled.
For
ArcChord,
the arcs are chord filled.

The graphics-exposure flag controls
GraphicsExpose
event generation
for
XCopyArea
and
XCopyPlane
requests (and any similar requests defined by extensions).

To create a new GC that is usable on a given screen with a
depth of drawable, use
XCreateGC.

GC XCreateGC(Display *display, Drawable d, unsigned long valuemask, XGCValues *values);

display	Specifies the connection to the X server.
d	Specifies the drawable.
valuemask	Specifies which components in the GC are to be set using the information in the specified values structure. This argument is the bitwise inclusive OR of zero or more of the valid GC component mask bits.
values	Specifies any values as specified by the valuemask.

The
XCreateGC
function creates a graphics context and returns a GC.
The GC can be used with any destination drawable having the same root
and depth as the specified drawable.
Use with other drawables results in a
BadMatch
error.

XCreateGC
can generate
BadAlloc,
BadDrawable,
BadFont,
BadMatch,
BadPixmap,
and
BadValue
errors.

To copy components from a source GC to a destination GC, use
XCopyGC.

XCopyGC(Display *display, GC src, GC dest, unsigned long valuemask);

display	Specifies the connection to the X server.
src	Specifies the components of the source GC.
valuemask	Specifies which components in the GC are to be copied to the destination GC. This argument is the bitwise inclusive OR of zero or more of the valid GC component mask bits.
dest	Specifies the destination GC.

The
XCopyGC
function copies the specified components from the source GC
to the destination GC.
The source and destination GCs must have the same root and depth,
or a
BadMatch
error results.
The valuemask specifies which component to copy, as for
XCreateGC.

XCopyGC
can generate
BadAlloc,
BadGC,
and
BadMatch
errors.

To change the components in a given GC, use
XChangeGC.

XChangeGC(Display *display, GC gc, unsigned long valuemask, XGCValues *values);

display	Specifies the connection to the X server.
gc	Specifies the GC.
valuemask	Specifies which components in the GC are to be changed using information in the specified values structure. This argument is the bitwise inclusive OR of zero or more of the valid GC component mask bits.
values	Specifies any values as specified by the valuemask.

The
XChangeGC
function changes the components specified by valuemask for
the specified GC.
The values argument contains the values to be set.
The values and restrictions are the same as for
XCreateGC.
Changing the clip-mask overrides any previous
XSetClipRectangles
request on the context.
Changing the dash-offset or dash-list
overrides any previous
XSetDashes
request on the context.
The order in which components are verified and altered is server dependent.
If an error is generated, a subset of the components may have been altered.

XChangeGC
can generate
BadAlloc,
BadFont,
BadGC,
BadMatch,
BadPixmap,
and
BadValue
errors.

To obtain components of a given GC, use
XGetGCValues.

Status XGetGCValues(Display *display, GC gc, unsigned long valuemask, XGCValues *values_return);

display	Specifies the connection to the X server.
gc	Specifies the GC.
valuemask	Specifies which components in the GC are to be returned in the values_return argument. This argument is the bitwise inclusive OR of zero or more of the valid GC component mask bits.
values_return	Returns the GC values in the specified XGCValues structure.

The
XGetGCValues
function returns the components specified by valuemask for the specified GC.
If the valuemask contains a valid set of GC mask bits
(GCFunction,
GCPlaneMask,
GCForeground,
GCBackground,
GCLineWidth,
GCLineStyle,
GCCapStyle,
GCJoinStyle,
GCFillStyle,
GCFillRule,
GCTile,
GCStipple,
GCTileStipXOrigin,
GCTileStipYOrigin,
GCFont,
GCSubwindowMode,
GCGraphicsExposures,
GCClipXOrigin,
GCClipYOrigin,
GCDashOffset,
or
GCArcMode)
and no error occurs,
XGetGCValues
sets the requested components in values_return and returns a nonzero status.
Otherwise, it returns a zero status.
Note that the clip-mask and dash-list (represented by the
GCClipMask
and
GCDashList
bits, respectively, in the valuemask)
cannot be requested.
Also note that an invalid resource ID (with one or more of the three
most significant bits set to 1) will be returned for
GCFont,
GCTile,
and
GCStipple
if the component has never been explicitly set by the client.

To free a given GC, use
XFreeGC.

XFreeGC(Display *display, GC gc);

display	Specifies the connection to the X server.
gc	Specifies the GC.

The
XFreeGC
function destroys the specified GC as well as all the associated storage.

XFreeGC
can generate a
BadGC
error.

To obtain the
GContext
resource ID for a given GC, use
XGContextFromGC.

GContext XGContextFromGC(GC gc);

gc	Specifies the GC for which you want the resource ID.

Xlib usually defers sending changes to the components of a GC to the server
until a graphics function is actually called with that GC.
This permits batching of component changes into a single server request.
In some circumstances, however, it may be necessary for the client
to explicitly force sending the changes to the server.
An example might be when a protocol extension uses the GC indirectly,
in such a way that the extension interface cannot know what GC will be used.
To force sending GC component changes, use
XFlushGC.

void XFlushGC(Display *display, GC gc);

display	Specifies the connection to the X server.
gc	Specifies the GC.

Using Graphics Context Convenience Routines

This section discusses how to set the:

Foreground, background, plane mask, or function components
Line attributes and dashes components
Fill style and fill rule components
Fill tile and stipple components
Font component
Clip region component
Arc mode, subwindow mode, and graphics exposure components

Setting the Foreground, Background, Function, or Plane Mask

To set the foreground, background, plane mask, and function components
for a given GC, use
XSetState.

XSetState(Display *display, GC gc, unsigned long foreground, unsigned long background, int function, unsigned long plane_mask);

display	Specifies the connection to the X server.
gc	Specifies the GC.
foreground	Specifies the foreground you want to set for the specified GC.
background	Specifies the background you want to set for the specified GC.
function	Specifies the function you want to set for the specified GC.
plane_mask	Specifies the plane mask.

XSetState
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

To set the foreground of a given GC, use
XSetForeground.

XSetForeground(Display *display, GC gc, unsigned long foreground);

display	Specifies the connection to the X server.
gc	Specifies the GC.
foreground	Specifies the foreground you want to set for the specified GC.

XSetForeground
can generate
BadAlloc
and
BadGC
errors.

To set the background of a given GC, use
XSetBackground.

XSetBackground(Display *display, GC gc, unsigned long background);

display	Specifies the connection to the X server.
gc	Specifies the GC.
background	Specifies the background you want to set for the specified GC.

XSetBackground
can generate
BadAlloc
and
BadGC
errors.

To set the display function in a given GC, use
XSetFunction.

XSetFunction(Display *display, GC gc, int function);

display	Specifies the connection to the X server.
gc	Specifies the GC.
function	Specifies the function you want to set for the specified GC.

XSetFunction
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

To set the plane mask of a given GC, use
XSetPlaneMask.

XSetPlaneMask(Display *display, GC gc, unsigned long plane_mask);

display	Specifies the connection to the X server.
gc	Specifies the GC.
plane_mask	Specifies the plane mask.

XSetPlaneMask
can generate
BadAlloc
and
BadGC
errors.

Setting the Line Attributes and Dashes

To set the line drawing components of a given GC, use
XSetLineAttributes.

XSetLineAttributes(Display *display, GC gc, unsigned int line_width, int line_style, int cap_style, int join_style);

display	Specifies the connection to the X server.
gc	Specifies the GC.
line_width	Specifies the line-width you want to set for the specified GC.
line_style	Specifies the line-style you want to set for the specified GC. You can pass LineSolid, LineOnOffDash, or LineDoubleDash.
cap_style	Specifies the line-style and cap-style you want to set for the specified GC. You can pass CapNotLast, CapButt, CapRound, or CapProjecting.
join_style	Specifies the line join-style you want to set for the specified GC. You can pass JoinMiter, JoinRound, or JoinBevel.

XSetLineAttributes
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

To set the dash-offset and dash-list for dashed line styles of a given GC, use
XSetDashes.

XSetDashes(Display *display, GC gc, int dash_offset, char dash_list[], int n);

display	Specifies the connection to the X server.
gc	Specifies the GC.
dash_offset	Specifies the phase of the pattern for the dashed line-style you want to set for the specified GC.
dash_list	Specifies the dash-list for the dashed line-style you want to set for the specified GC.
n	Specifies the number of elements in dash_list.

The
XSetDashes
function sets the dash-offset and dash-list attributes for dashed line styles
in the specified GC.
There must be at least one element in the specified dash_list,
or a
BadValue
error results.
The initial and alternating elements (second, fourth, and so on)
of the dash_list are the even dashes, and
the others are the odd dashes.
Each element specifies a dash length in pixels.
All of the elements must be nonzero,
or a
BadValue
error results.
Specifying an odd-length list is equivalent to specifying the same list
concatenated with itself to produce an even-length list.

The dash-offset defines the phase of the pattern,
specifying how many pixels into the dash-list the pattern
should actually begin in any single graphics request.
Dashing is continuous through path elements combined with a join-style
but is reset to the dash-offset between each sequence of joined lines.

The unit of measure for dashes is the same for the ordinary coordinate system.
Ideally, a dash length is measured along the slope of the line, but implementations
are only required to match this ideal for horizontal and vertical lines.
Failing the ideal semantics, it is suggested that the length be measured along the
major axis of the line.
The major axis is defined as the x axis for lines drawn at an angle of between
−45 and +45 degrees or between 135 and 225 degrees from the x axis.
For all other lines, the major axis is the y axis.

XSetDashes
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

Setting the Fill Style and Fill Rule

To set the fill-style of a given GC, use
XSetFillStyle.

XSetFillStyle(Display *display, GC gc, int fill_style);

display	Specifies the connection to the X server.
gc	Specifies the GC.
fill_style	Specifies the fill-style you want to set for the specified GC. You can pass FillSolid, FillTiled, FillStippled, or FillOpaqueStippled.

XSetFillStyle
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

To set the fill-rule of a given GC, use
XSetFillRule.

XSetFillRule(Display *display, GC gc, int fill_rule);

display	Specifies the connection to the X server.
gc	Specifies the GC.
fill_rule	Specifies the fill-rule you want to set for the specified GC. You can pass EvenOddRule or WindingRule.

XSetFillRule
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

Setting the Fill Tile and Stipple

Some displays have hardware support for tiling or
stippling with patterns of specific sizes.
Tiling and stippling operations that restrict themselves to those specific
sizes run much faster than such operations with arbitrary size patterns.
Xlib provides functions that you can use to determine the best size,
tile, or stipple for the display
as well as to set the tile or stipple shape and the tile or stipple origin.

To obtain the best size of a tile, stipple, or cursor, use
XQueryBestSize.

Status XQueryBestSize(Display *display, int class, Drawable which_screen, unsigned int width, unsigned int height, unsigned int *width_return, unsigned int *height_return);

display	Specifies the connection to the X server.
class	Specifies the class that you are interested in. You can pass TileShape, CursorShape, or StippleShape.
which_screen	Specifies any drawable on the screen.
width
height	Specify the width and height.
width_return
height_return	Return the width and height of the object best supported by the display hardware.

The
XQueryBestSize
function returns the best or closest size to the specified size.
For
CursorShape,
this is the largest size that can be fully displayed on the screen specified by
which_screen.
For
TileShape,
this is the size that can be tiled fastest.
For
StippleShape,
this is the size that can be stippled fastest.
For
CursorShape,
the drawable indicates the desired screen.
For
TileShape
and
StippleShape,
the drawable indicates the screen and possibly the window class and depth.
An
InputOnly
window cannot be used as the drawable for
TileShape
or
StippleShape,
or a
BadMatch
error results.

XQueryBestSize
can generate
BadDrawable,
BadMatch,
and
BadValue
errors.

To obtain the best fill tile shape, use
XQueryBestTile.

Status XQueryBestTile(Display *display, Drawable which_screen, unsigned int width, unsigned int height, unsigned int *width_return, unsigned int *height_return);

display	Specifies the connection to the X server.
which_screen	Specifies any drawable on the screen.
width
height	Specify the width and height.
width_return
height_return	Return the width and height of the object best supported by the display hardware.

The
XQueryBestTile
function returns the best or closest size, that is, the size that can be
tiled fastest on the screen specified by which_screen.
The drawable indicates the screen and possibly the window class and depth.
If an
InputOnly
window is used as the drawable, a
BadMatch
error results.

XQueryBestTile
can generate
BadDrawable
and
BadMatch
errors.

To obtain the best stipple shape, use
XQueryBestStipple.

Status XQueryBestStipple(Display *display, Drawable which_screen, unsigned int width, unsigned int height, unsigned int *width_return, unsigned int *height_return);

display	Specifies the connection to the X server.
which_screen	Specifies any drawable on the screen.
width
height	Specify the width and height.
width_return
height_return	Return the width and height of the object best supported by the display hardware.

The
XQueryBestStipple
function returns the best or closest size, that is, the size that can be
stippled fastest on the screen specified by which_screen.
The drawable indicates the screen and possibly the window class and depth.
If an
InputOnly
window is used as the drawable, a
BadMatch
error results.

XQueryBestStipple
can generate
BadDrawable
and
BadMatch
errors.

To set the fill tile of a given GC, use
XSetTile.

XSetTile(Display *display, GC gc, Pixmap tile);

display	Specifies the connection to the X server.
gc	Specifies the GC.
tile	Specifies the fill tile you want to set for the specified GC.

The tile and GC must have the same depth,
or a
BadMatch
error results.

XSetTile
can generate
BadAlloc,
BadGC,
BadMatch,
and
BadPixmap
errors.

To set the stipple of a given GC, use
XSetStipple.

XSetStipple(Display *display, GC gc, Pixmap stipple);

display	Specifies the connection to the X server.
gc	Specifies the GC.
stipple	Specifies the stipple you want to set for the specified GC.

The stipple must have a depth of one,
or a
BadMatch
error results.

XSetStipple
can generate
BadAlloc,
BadGC,
BadMatch,
and
BadPixmap
errors.

To set the tile or stipple origin of a given GC, use
XSetTSOrigin.

XSetTSOrigin(Display *display, GC gc, int ts_x_origin, int ts_y_origin);

display	Specifies the connection to the X server.
gc	Specifies the GC.
ts_x_origin
ts_y_origin	Specify the x and y coordinates of the tile and stipple origin.

When graphics requests call for tiling or stippling,
the parent's origin will be interpreted relative to whatever destination
drawable is specified in the graphics request.

XSetTSOrigin
can generate
BadAlloc
and
BadGC
errors.

Setting the Current Font

To set the current font of a given GC, use
XSetFont.

XSetFont(Display *display, GC gc, Font font);

display	Specifies the connection to the X server.
gc	Specifies the GC.
font	Specifies the font.

XSetFont
can generate
BadAlloc,
BadFont,
and
BadGC
errors.

Setting the Clip Region

Xlib provides functions that you can use to set the clip-origin
and the clip-mask or set the clip-mask to a list of rectangles.

To set the clip-origin of a given GC, use
XSetClipOrigin.

XSetClipOrigin(Display *display, GC gc, int clip_x_origin, int clip_y_origin);

display	Specifies the connection to the X server.
gc	Specifies the GC.
clip_x_origin
clip_y_origin	Specify the x and y coordinates of the clip-mask origin.

The clip-mask origin is interpreted relative to the origin of whatever
destination drawable is specified in the graphics request.

XSetClipOrigin
can generate
BadAlloc
and
BadGC
errors.

To set the clip-mask of a given GC to the specified pixmap, use
XSetClipMask.

XSetClipMask(Display *display, GC gc, Pixmap pixmap);

display	Specifies the connection to the X server.
gc	Specifies the GC.
pixmap	Specifies the pixmap or None.

If the clip-mask is set to
None,
the pixels are always drawn (regardless of the clip-origin).

XSetClipMask
can generate
BadAlloc,
BadGC,
BadMatch,
and
BadPixmap
errors.

To set the clip-mask of a given GC to the specified list of rectangles, use
XSetClipRectangles.

XSetClipRectangles(Display *display, GC gc, int clip_x_origin, int clip_y_origin, XRectangle rectangles[], int n, int ordering);

display	Specifies the connection to the X server.
gc	Specifies the GC.
clip_x_origin
clip_y_origin	Specify the x and y coordinates of the clip-mask origin.
rectangles	Specifies an array of rectangles that define the clip-mask.
n	Specifies the number of rectangles.
ordering	Specifies the ordering relations on the rectangles. You can pass Unsorted, YSorted, YXSorted, or YXBanded.

The
XSetClipRectangles
function changes the clip-mask in the specified GC
to the specified list of rectangles and sets the clip origin.
The output is clipped to remain contained within the
rectangles.
The clip-origin is interpreted relative to the origin of
whatever destination drawable is specified in a graphics request.
The rectangle coordinates are interpreted relative to the clip-origin.
The rectangles should be nonintersecting, or the graphics results will be
undefined.
Note that the list of rectangles can be empty,
which effectively disables output.
This is the opposite of passing
None
as the clip-mask in
XCreateGC,
XChangeGC,
and
XSetClipMask.

If known by the client, ordering relations on the rectangles can be
specified with the ordering argument.
This may provide faster operation
by the server.
If an incorrect ordering is specified, the X server may generate a
BadMatch
error, but it is not required to do so.
If no error is generated, the graphics
results are undefined.
Unsorted
means the rectangles are in arbitrary order.
YSorted
means that the rectangles are nondecreasing in their Y origin.
YXSorted
additionally constrains
YSorted
order in that all
rectangles with an equal Y origin are nondecreasing in their X
origin.
YXBanded
additionally constrains
YXSorted
by requiring that,
for every possible Y scanline, all rectangles that include that
scanline have an identical Y origins and Y extents.

XSetClipRectangles
can generate
BadAlloc,
BadGC,
BadMatch,
and
BadValue
errors.

Xlib provides a set of basic functions for performing
region arithmetic.
For information about these functions,
see section 16.5.

Setting the Arc Mode, Subwindow Mode, and Graphics Exposure

To set the arc mode of a given GC, use
XSetArcMode.

XSetArcMode(Display *display, GC gc, int arc_mode);

display	Specifies the connection to the X server.
gc	Specifies the GC.
arc_mode	Specifies the arc mode. You can pass ArcChord or ArcPieSlice.

XSetArcMode
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

To set the subwindow mode of a given GC, use
XSetSubwindowMode.

XSetSubwindowMode(Display *display, GC gc, int subwindow_mode);

display	Specifies the connection to the X server.
gc	Specifies the GC.
subwindow_mode	Specifies the subwindow mode. You can pass ClipByChildren or IncludeInferiors.

XSetSubwindowMode
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

To set the graphics-exposures flag of a given GC, use
XSetGraphicsExposures.

XSetGraphicsExposures(Display *display, GC gc, Bool graphics_exposures);

display	Specifies the connection to the X server.
gc	Specifies the GC.
graphics_exposures	Specifies a Boolean value that indicates whether you want GraphicsExpose and NoExpose events to be reported when calling `XCopyArea` and `XCopyPlane` with this GC.

XSetGraphicsExposures
can generate
BadAlloc,
BadGC,
and
BadValue
errors.

Chapter 8. Graphics Functions

Table of Contents

Clearing AreasCopying AreasDrawing Points, Lines, Rectangles, and ArcsDrawing Single and Multiple PointsDrawing Single and Multiple LinesDrawing Single and Multiple RectanglesDrawing Single and Multiple ArcsFilling AreasFilling Single and Multiple RectanglesFilling a Single PolygonFilling Single and Multiple ArcsFont MetricsLoading and Freeing FontsObtaining and Freeing Font Names and InformationComputing Character String SizesComputing Logical ExtentsQuerying Character String SizesDrawing TextDrawing Complex TextDrawing Text CharactersDrawing Image Text CharactersTransferring Images between Client and Server

Once you have established a connection to a display, you can use the Xlib graphics functions to:

Clear and copy areas
Draw points, lines, rectangles, and arcs
Fill areas
Manipulate fonts
Draw text
Transfer images between clients and the server

If the same drawable and GC is used for each call, Xlib batches back-to-back
calls to XDrawPoint, XDrawLine, XDrawRectangle, XFillArc, and XFillRectangle.
Note that this reduces the total number of requests sent to the server.

Clearing Areas

Xlib provides functions that you can use to clear an area or the entire window.
Because pixmaps do not have defined backgrounds,
they cannot be filled by using the functions described in this section.
Instead, to accomplish an analogous operation on a pixmap,
you should use
XFillRectangle,
which sets the pixmap to a known value.

To clear a rectangular area of a given window, use
XClearArea.

XClearArea(Display *display, Window w, int x, int y, unsigned int width, unsigned int height, Bool exposures);

display	Specifies the connection to the X server.
w	Specifies the window.
x
y	Specify the x and y coordinates, which are relative to the origin of the window and specify the upper-left corner of the rectangle.
width
height	Specify the width and height, which are the dimensions of the rectangle.
exposures	Specifies a Boolean value that indicates if Expose events are to be generated.

The
XClearArea
function paints a rectangular area in the specified window according to the
specified dimensions with the window's background pixel or pixmap.
The subwindow-mode effectively is
ClipByChildren.
If width is zero, it
is replaced with the current width of the window minus x.
If height is
zero, it is replaced with the current height of the window minus y.
If the window has a defined background tile,
the rectangle clipped by any children is filled with this tile.
If the window has
background
None,
the contents of the window are not changed.
In either
case, if exposures is
True,
one or more
Expose
events are generated for regions of the rectangle that are either visible or are
being retained in a backing store.
If you specify a window whose class is
InputOnly,
a
BadMatch
error results.

XClearArea
can generate
BadMatch,
BadValue,
and
BadWindow
errors.

To clear the entire area in a given window, use
XClearWindow.

XClearWindow(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XClearWindow
function clears the entire area in the specified window and is
equivalent to
XClearArea
(display, w, 0, 0, 0, 0,
False).
If the window has a defined background tile, the rectangle is tiled with a
plane-mask of all ones and
GXcopy
function.
If the window has
background
None,
the contents of the window are not changed.
If you specify a window whose class is
InputOnly,
a
BadMatch
error results.

XClearWindow
can generate
BadMatch
and
BadWindow
errors.

Copying Areas

Xlib provides functions that you can use to copy an area or a bit plane.

To copy an area between drawables of the same
root and depth, use
XCopyArea.

XCopyArea(Display *display, Drawable src, Drawable dest, GC gc, int src_x, int src_y, unsigned int width, unsigned int height, int dest_x, int dest_y);

display	Specifies the connection to the X server.
src
dest	Specify the source and destination rectangles to be combined.
gc	Specifies the GC.
src_x
src_y	Specify the x and y coordinates, which are relative to the origin of the source rectangle and specify its upper-left corner.
width
height	Specify the width and height, which are the dimensions of both the source and destination rectangles.
dest_x
dest_y	Specify the x and y coordinates, which are relative to the origin of the destination rectangle and specify its upper-left corner.

The
XCopyArea
function combines the specified rectangle of src with the specified rectangle
of dest.
The drawables must have the same root and depth,
or a
BadMatch
error results.

If regions of the source rectangle are obscured and have not been
retained in backing store
or if regions outside the boundaries of the source drawable are specified,
those regions are not copied.
Instead, the
following occurs on all corresponding destination regions that are either
visible or are retained in backing store.
If the destination is a window with a background other than
None,
corresponding regions
of the destination are tiled with that background
(with plane-mask of all ones and
GXcopy
function).
Regardless of tiling or whether the destination is a window or a pixmap,
if graphics-exposures is
True,
then
GraphicsExpose
events for all corresponding destination regions are generated.
If graphics-exposures is
True
but no
GraphicsExpose
events are generated, a
NoExpose
event is generated.
Note that by default graphics-exposures is
True
in new GCs.

This function uses these GC components: function, plane-mask,
subwindow-mode, graphics-exposures, clip-x-origin,
clip-y-origin, and clip-mask.

XCopyArea
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.

To copy a single bit plane of a given drawable, use
XCopyPlane.

XCopyPlane(Display *display, Drawable src, Drawable dest, GC gc, int src_x, int src_y, unsigned int width, unsigned int height, int dest_x, int dest_y, unsigned long plane);

display	Specifies the connection to the X server.
src
dest	Specify the source and destination rectangles to be combined.
gc	Specifies the GC.
src_x
src_y	Specify the x and y coordinates, which are relative to the origin of the source rectangle and specify its upper-left corner.
width
height	Specify the width and height, which are the dimensions of both the source and destination rectangles.
dest_x
dest_y	Specify the x and y coordinates, which are relative to the origin of the destination rectangle and specify its upper-left corner.
plane	Specifies the bit plane. You must set exactly one bit to 1.

The
XCopyPlane
function uses a single bit plane of the specified source rectangle
combined with the specified GC to modify the specified rectangle of dest.
The drawables must have the same root but need not have the same depth.
If the drawables do not have the same root, a
BadMatch
error results.
If plane does not have exactly one bit set to 1 and the value of plane
is not less than %2 sup n%, where n is the depth of src, a
BadValue
error results.

Effectively,
XCopyPlane
forms a pixmap of the same depth as the rectangle of dest and with a
size specified by the source region.
It uses the foreground/background pixels in the GC (foreground
everywhere the bit plane in src contains a bit set to 1,
background everywhere the bit plane in src contains a bit set to 0)
and the equivalent of a
CopyArea
protocol request is performed with all the same exposure semantics.
This can also be thought of as using the specified region of the source
bit plane as a stipple with a fill-style of
FillOpaqueStippled
for filling a rectangular area of the destination.

This function uses these GC components: function, plane-mask, foreground,
background, subwindow-mode, graphics-exposures, clip-x-origin, clip-y-origin,
and clip-mask.

XCopyPlane
can generate
BadDrawable,
BadGC,
BadMatch,
and
BadValue
errors.

Drawing Points, Lines, Rectangles, and Arcs

Xlib provides functions that you can use to draw:

A single point or multiple points
A single line or multiple lines
A single rectangle or multiple rectangles
A single arc or multiple arcs

Some of the functions described in the following sections
use these structures:


typedef struct {
     short x1, y1, x2, y2;
} XSegment;


typedef struct {
     short x, y;
} XPoint;


typedef struct {
     short x, y;
     unsigned short width, height;
} XRectangle;


typedef struct {
     short x, y;
     unsigned short width, height;
     short angle1, angle2;             /* Degrees * 64 */
} XArc;

All x and y members are signed integers.
The width and height members are 16-bit unsigned integers.
You should be careful not to generate coordinates and sizes
out of the 16-bit ranges, because the protocol only has 16-bit fields
for these values.

Drawing Single and Multiple Points

To draw a single point in a given drawable, use
XDrawPoint.

XDrawPoint(Display *display, Drawable d, GC gc, int x, int y);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates where you want the point drawn.

To draw multiple points in a given drawable, use
XDrawPoints.

XDrawPoints(Display *display, Drawable d, GC gc, XPoint *points, int npoints, int mode);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
points	Specifies an array of points.
npoints	Specifies the number of points in the array.
mode	Specifies the coordinate mode. You can pass CoordModeOrigin or CoordModePrevious.

The
XDrawPoint
function uses the foreground pixel and function components of the
GC to draw a single point into the specified drawable;
XDrawPoints
draws multiple points this way.
CoordModeOrigin
treats all coordinates as relative to the origin,
and
CoordModePrevious
treats all coordinates after the first as relative to the previous point.
XDrawPoints
draws the points in the order listed in the array.

Both functions use these GC components: function, plane-mask,
foreground, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask.

XDrawPoint
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.
XDrawPoints
can generate
BadDrawable,
BadGC,
BadMatch,
and
BadValue
errors.

Drawing Single and Multiple Lines

To draw a single line between two points in a given drawable, use
XDrawLine.

XDrawLine(Display *display, Drawable d, GC gc, int x1, int y1, int x2, int y2);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x1
y1
x2
y2	Specify the points (x1, y1) and (x2, y2) to be connected.

To draw multiple lines in a given drawable, use
XDrawLines.

XDrawLines(Display *display, Drawable d, GC gc, XPoint *points, int npoints, int mode);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
points	Specifies an array of points.
npoints	Specifies the number of points in the array.
mode	Specifies the coordinate mode. You can pass CoordModeOrigin or CoordModePrevious.

To draw multiple, unconnected lines in a given drawable,
use
XDrawSegments.

XDrawSegments(Display *display, Drawable d, GC gc, XSegment *segments, int nsegments);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
segments	Specifies an array of segments.
nsegments	Specifies the number of segments in the array.

The
XDrawLine
function uses the components of the specified GC to
draw a line between the specified set of points (x1, y1) and (x2, y2).
It does not perform joining at coincident endpoints.
For any given line,
XDrawLine
does not draw a pixel more than once.
If lines intersect, the intersecting pixels are drawn multiple times.

The
XDrawLines
function uses the components of the specified GC to draw
npoints-1 lines between each pair of points (point[i], point[i+1])
in the array of
XPoint
structures.
It draws the lines in the order listed in the array.
The lines join correctly at all intermediate points, and if the first and last
points coincide, the first and last lines also join correctly.
For any given line,
XDrawLines
does not draw a pixel more than once.
If thin (zero line-width) lines intersect,
the intersecting pixels are drawn multiple times.
If wide lines intersect, the intersecting pixels are drawn only once, as though
the entire
PolyLine
protocol request were a single, filled shape.
CoordModeOrigin
treats all coordinates as relative to the origin,
and
CoordModePrevious
treats all coordinates after the first as relative to the previous point.

The
XDrawSegments
function draws multiple, unconnected lines.
For each segment,
XDrawSegments
draws a
line between (x1, y1) and (x2, y2).
It draws the lines in the order listed in the array of
XSegment
structures and does not perform joining at coincident endpoints.
For any given line,
XDrawSegments
does not draw a pixel more than once.
If lines intersect, the intersecting pixels are drawn multiple times.

All three functions use these GC components:
function, plane-mask, line-width,
line-style, cap-style, fill-style, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask.
The
XDrawLines
function also uses the join-style GC component.
All three functions also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
tile-stipple-y-origin, dash-offset, and dash-list.

XDrawLine,
XDrawLines,
and
XDrawSegments
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.
XDrawLines
also can generate
BadValue
errors.

Drawing Single and Multiple Rectangles

To draw the outline of a single rectangle in a given drawable, use
XDrawRectangle.

XDrawRectangle(Display *display, Drawable d, GC gc, int x, int y, unsigned int width, unsigned int height);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which specify the upper-left corner of the rectangle.
width
height	Specify the width and height, which specify the dimensions of the rectangle.

To draw the outline of multiple rectangles
in a given drawable, use
XDrawRectangles.

XDrawRectangles(Display *display, Drawable d, GC gc, XRectangle rectangles[], int nrectangles);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
rectangles	Specifies an array of rectangles.
nrectangles	Specifies the number of rectangles in the array.

The
XDrawRectangle
and
XDrawRectangles
functions draw the outlines of the specified rectangle or rectangles as
if a five-point
PolyLine
protocol request were specified for each rectangle:

[x,y] [x+width,y] [x+width,y+height] [x,y+height] [x,y]

For the specified rectangle or rectangles,
these functions do not draw a pixel more than once.
XDrawRectangles
draws the rectangles in the order listed in the array.
If rectangles intersect,
the intersecting pixels are drawn multiple times.

Both functions use these GC components:
function, plane-mask, line-width,
line-style, cap-style, join-style, fill-style,
subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
tile-stipple-y-origin, dash-offset, and dash-list.

XDrawRectangle
and
XDrawRectangles
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.

Drawing Single and Multiple Arcs

To draw a single arc in a given drawable, use
XDrawArc.

XDrawArc(Display *display, Drawable d, GC gc, int x, int y, unsigned int width, unsigned int height, int angle1, int angle2);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the drawable and specify the upper-left corner of the bounding rectangle.
width
height	Specify the width and height, which are the major and minor axes of the arc.
angle1	Specifies the start of the arc relative to the three-o'clock position from the center, in units of degrees * 64.
angle2	Specifies the path and extent of the arc relative to the start of the arc, in units of degrees * 64.

To draw multiple arcs in a given drawable, use
XDrawArcs.

XDrawArcs(Display *display, Drawable d, GC gc, XArc *arcs, int narcs);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
arcs	Specifies an array of arcs.
narcs	Specifies the number of arcs in the array.

delim %%

XDrawArc
draws a single circular or elliptical arc, and
XDrawArcs
draws multiple circular or elliptical arcs.
Each arc is specified by a rectangle and two angles.
The center of the circle or ellipse is the center of the
rectangle, and the major and minor axes are specified by the width and height.
Positive angles indicate counterclockwise motion,
and negative angles indicate clockwise motion.
If the magnitude of angle2 is greater than 360 degrees,
XDrawArc
or
XDrawArcs
truncates it to 360 degrees.

For an arc specified as %[ ~x, ~y, ~width , ~height, ~angle1, ~angle2 ]%,
the origin of the major and minor axes is at
% [ x +^ {width over 2} , ~y +^ {height over 2} ]%,
and the infinitely thin path describing the entire circle or ellipse
intersects the horizontal axis at % [ x, ~y +^ {height over 2} ]% and
% [ x +^ width , ~y +^ { height over 2 }] %
and intersects the vertical axis at % [ x +^ { width over 2 } , ~y ]% and
% [ x +^ { width over 2 }, ~y +^ height ]%.
These coordinates can be fractional
and so are not truncated to discrete coordinates.
The path should be defined by the ideal mathematical path.
For a wide line with line-width lw,
the bounding outlines for filling are given
by the two infinitely thin paths consisting of all points whose perpendicular
distance from the path of the circle/ellipse is equal to lw/2
(which may be a fractional value).
The cap-style and join-style are applied the same as for a line
corresponding to the tangent of the circle/ellipse at the endpoint.

For an arc specified as % [ ~x, ~y, ~width, ~height, ~angle1, ~angle2 ]%,
the angles must be specified
in the effectively skewed coordinate system of the ellipse (for a
circle, the angles and coordinate systems are identical). The
relationship between these angles and angles expressed in the normal
coordinate system of the screen (as measured with a protractor) is as
follows:

% roman "skewed-angle" ~ = ~ atan left ( tan ( roman "normal-angle" )
 * width over height right ) +^ adjust%

The skewed-angle and normal-angle are expressed in radians (rather
than in degrees scaled by 64) in the range % [ 0 , ~2 pi ]% and where atan
returns a value in the range % [ - pi over 2 , ~pi over 2 ] %
and adjust is:


%0%     for normal-angle in the range % [ 0 , ~pi over 2  ]%
%pi%     for normal-angle in the range % [ pi over 2 , ~{3 pi} over 2  ]%
%2 pi%     for normal-angle in the range % [ {3 pi} over 2 , ~2 pi  ]%

For any given arc,
XDrawArc
and
XDrawArcs
do not draw a pixel more than once.
If two arcs join correctly and if the line-width is greater than zero
and the arcs intersect,
XDrawArc
and
XDrawArcs
do not draw a pixel more than once.
Otherwise,
the intersecting pixels of intersecting arcs are drawn multiple times.
Specifying an arc with one endpoint and a clockwise extent draws the same pixels
as specifying the other endpoint and an equivalent counterclockwise extent,
except as it affects joins.

If the last point in one arc coincides with the first point in the following
arc, the two arcs will join correctly.
If the first point in the first arc coincides with the last point in the last
arc, the two arcs will join correctly.
By specifying one axis to be zero, a horizontal or vertical line can be
drawn.
Angles are computed based solely on the coordinate system and ignore the
aspect ratio.

Both functions use these GC components:
function, plane-mask, line-width, line-style, cap-style, join-style,
fill-style, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
tile-stipple-y-origin, dash-offset, and dash-list.

XDrawArc
and
XDrawArcs
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.

Filling Areas

Xlib provides functions that you can use to fill:

A single rectangle or multiple rectangles
A single polygon
A single arc or multiple arcs

Filling Single and Multiple Rectangles

To fill a single rectangular area in a given drawable, use
XFillRectangle.

XFillRectangle(Display *display, Drawable d, GC gc, int x, int y, unsigned int width, unsigned int height);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the drawable and specify the upper-left corner of the rectangle.
width
height	Specify the width and height, which are the dimensions of the rectangle to be filled.

To fill multiple rectangular areas in a given drawable, use
XFillRectangles.

XFillRectangles(Display *display, Drawable d, GC gc, XRectangle *rectangles, int nrectangles);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
rectangles	Specifies an array of rectangles.
nrectangles	Specifies the number of rectangles in the array.

The
XFillRectangle
and
XFillRectangles
functions fill the specified rectangle or rectangles
as if a four-point
FillPolygon
protocol request were specified for each rectangle:

[x,y] [x+width,y] [x+width,y+height] [x,y+height]

Each function uses the x and y coordinates,
width and height dimensions, and GC you specify.

XFillRectangles
fills the rectangles in the order listed in the array.
For any given rectangle,
XFillRectangle
and
XFillRectangles
do not draw a pixel more than once.
If rectangles intersect, the intersecting pixels are
drawn multiple times.

Both functions use these GC components:
function, plane-mask, fill-style, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

XFillRectangle
and
XFillRectangles
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.

Filling a Single Polygon

To fill a polygon area in a given drawable, use
XFillPolygon.

XFillPolygon(Display *display, Drawable d, GC gc, XPoint *points, int npoints, int shape, int mode);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
points	Specifies an array of points.
npoints	Specifies the number of points in the array.
shape	Specifies a shape that helps the server to improve performance. You can pass Complex, Convex, or Nonconvex.
mode	Specifies the coordinate mode. You can pass CoordModeOrigin or CoordModePrevious.

XFillPolygon
fills the region closed by the specified path.
The path is closed
automatically if the last point in the list does not coincide with the
first point.
XFillPolygon
does not draw a pixel of the region more than once.
CoordModeOrigin
treats all coordinates as relative to the origin,
and
CoordModePrevious
treats all coordinates after the first as relative to the previous point.

Depending on the specified shape, the following occurs:

If shape is
Complex,
the path may self-intersect.
Note that contiguous coincident points in the path are not treated
as self-intersection.
If shape is
Convex,
for every pair of points inside the polygon,
the line segment connecting them does not intersect the path.
If known by the client,
specifying
Convex
can improve performance.
If you specify
Convex
for a path that is not convex,
the graphics results are undefined.
If shape is
Nonconvex,
the path does not self-intersect, but the shape is not
wholly convex.
If known by the client,
specifying
Nonconvex
instead of
Complex
may improve performance.
If you specify
Nonconvex
for a self-intersecting path, the graphics results are undefined.

The fill-rule of the GC controls the filling behavior of
self-intersecting polygons.

This function uses these GC components:
function, plane-mask, fill-style, fill-rule, subwindow-mode, clip-x-origin,
clip-y-origin, and clip-mask.
It also uses these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

XFillPolygon
can generate
BadDrawable,
BadGC,
BadMatch,
and
BadValue
errors.

Filling Single and Multiple Arcs

To fill a single arc in a given drawable, use
XFillArc.

XFillArc(Display *display, Drawable d, GC gc, int x, int y, unsigned int width, unsigned int height, int angle1, int angle2);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the drawable and specify the upper-left corner of the bounding rectangle.
width
height	Specify the width and height, which are the major and minor axes of the arc.
angle1	Specifies the start of the arc relative to the three-o'clock position from the center, in units of degrees * 64.
angle2	Specifies the path and extent of the arc relative to the start of the arc, in units of degrees * 64.

To fill multiple arcs in a given drawable, use
XFillArcs.

XFillArcs(Display *display, Drawable d, GC gc, XArc *arcs, int narcs);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
arcs	Specifies an array of arcs.
narcs	Specifies the number of arcs in the array.

For each arc,
XFillArc
or
XFillArcs
fills the region closed by the infinitely thin path
described by the specified arc and, depending on the
arc-mode specified in the GC, one or two line segments.
For
ArcChord,
the single line segment joining the endpoints of the arc is used.
For
ArcPieSlice,
the two line segments joining the endpoints of the arc with the center
point are used.
XFillArcs
fills the arcs in the order listed in the array.
For any given arc,
XFillArc
and
XFillArcs
do not draw a pixel more than once.
If regions intersect,
the intersecting pixels are drawn multiple times.

Both functions use these GC components:
function, plane-mask, fill-style, arc-mode, subwindow-mode, clip-x-origin,
clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

XFillArc
and
XFillArcs
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.

Font Metrics

A font is a graphical description of a set of characters that are used to
increase efficiency whenever a set of small, similar sized patterns are
repeatedly used.

This section discusses how to:

Load and free fonts
Obtain and free font names
Compute character string sizes
Compute logical extents
Query character string sizes

The X server loads fonts whenever a program requests a new font.
The server can cache fonts for quick lookup.
Fonts are global across all screens in a server.
Several levels are possible when dealing with fonts.
Most applications simply use
XLoadQueryFont
to load a font and query the font metrics.

Characters in fonts are regarded as masks.
Except for image text requests,
the only pixels modified are those in which bits are set to 1 in the character.
This means that it makes sense to draw text using stipples or tiles
(for example, many menus gray-out unusable entries).

The
XFontStruct
structure contains all of the information for the font
and consists of the font-specific information as well as
a pointer to an array of
XCharStruct
structures for the
characters contained in the font.
The
XFontStruct,
XFontProp,
and
XCharStruct
structures contain:


typedef struct {
     short lbearing;               /* origin to left edge of raster */
     short rbearing;               /* origin to right edge of raster */
     short width;                  /* advance to next char's origin */
     short ascent;                 /* baseline to top edge of raster */
     short descent;                /* baseline to bottom edge of raster */
     unsigned short attributes;    /* per char flags (not predefined) */
} XCharStruct;


typedef struct {
     Atom     name;
     unsigned long card32;
} XFontProp;


typedef struct {     /* normal 16 bit characters are two bytes */
    unsigned char byte1;
    unsigned char byte2;
} XChar2b;


typedef struct {
     XExtData *ext_data;               /* hook for extension to hang data */
     Font fid;                         /* Font id for this font */
     unsigned direction;               /* hint about the direction font is painted */
     unsigned min_char_or_byte2;       /* first character */
     unsigned max_char_or_byte2;       /* last character */
     unsigned min_byte1;               /* first row that exists */
     unsigned max_byte1;               /* last row that exists */
     Bool all_chars_exist;             /* flag if all characters have nonzero size */
     unsigned default_char;            /* char to print for undefined character */
     int n_properties;                 /* how many properties there are */
     XFontProp *properties;            /* pointer to array of additional properties */
     XCharStruct min_bounds;           /* minimum bounds over all existing char */
     XCharStruct max_bounds;           /* maximum bounds over all existing char */
     XCharStruct *per_char;            /* first_char to last_char information */
     int ascent;                       /* logical extent above baseline for spacing */
     int descent;                      /* logical descent below baseline for spacing */
} XFontStruct;

X supports single byte/character, two bytes/character matrix,
and 16-bit character text operations.
Note that any of these forms can be used with a font, but a
single byte/character text request can only specify a single byte
(that is, the first row of a 2-byte font).
You should view 2-byte fonts as a two-dimensional matrix of defined
characters: byte1 specifies the range of defined rows and
byte2 defines the range of defined columns of the font.
Single byte/character fonts have one row defined, and the byte2 range
specified in the structure defines a range of characters.

The bounding box of a character is defined by the
XCharStruct
of that character.
When characters are absent from a font,
the default_char is used.
When fonts have all characters of the same size,
only the information in the
XFontStruct
min and max bounds are used.

The members of the
XFontStruct
have the following semantics:

The direction member can be either
FontLeftToRight
or
FontRightToLeft.
It is just a hint as to whether most
XCharStruct
elements
have a positive
(FontLeftToRight)
or a negative
(FontRightToLeft)
character width
metric.
The core protocol defines no support for vertical text.
If the min_byte1 and max_byte1 members are both zero, min_char_or_byte2
specifies the linear character index corresponding to the first element
of the per_char array, and max_char_or_byte2 specifies the linear character
index of the last element.
If either min_byte1 or max_byte1 are nonzero, both
min_char_or_byte2 and max_char_or_byte2 are less than 256,
and the 2-byte character index values corresponding to the
per_char array element N (counting from 0) are:
byte1 = N/D + min_byte1

byte2 = N\\D + min_char_or_byte2
where:
D = max_char_or_byte2 - min_char_or_byte2 + 1
/ = integer division
\\ = integer modulus
If the per_char pointer is NULL,
all glyphs between the first and last character indexes
inclusive have the same information,
as given by both min_bounds and max_bounds.
If all_chars_exist is
True,
all characters in the per_char array have nonzero bounding boxes.
The default_char member specifies the character that will be used when an
undefined or nonexistent character is printed.
The default_char is a 16-bit character (not a 2-byte character).
For a font using 2-byte matrix format,
the default_char has byte1 in the most-significant byte
and byte2 in the least significant byte.
If the default_char itself specifies an undefined or nonexistent character,
no printing is performed for an undefined or nonexistent character.
The min_bounds and max_bounds members contain the most extreme values of
each individual
XCharStruct
component over all elements of this array
(and ignore nonexistent characters).
The bounding box of the font (the smallest
rectangle enclosing the shape obtained by superimposing all of the
characters at the same origin [x,y]) has its upper-left coordinate at:
```
     [x + min_bounds.lbearing, y - max_bounds.ascent]
```

Its width is:

     max_bounds.rbearing - min_bounds.lbearing

Its height is:

     max_bounds.ascent + max_bounds.descent

The ascent member is the logical extent of the font above the baseline that is
used for determining line spacing.
Specific characters may extend beyond
this.
The descent member is the logical extent of the font at or below the
baseline that is used for determining line spacing.
Specific characters may extend beyond this.
If the baseline is at Y-coordinate y,
the logical extent of the font is inclusive between the Y-coordinate
values (y - font.ascent) and (y + font.descent - 1).
Typically,
the minimum interline spacing between rows of text is given
by ascent + descent.

For a character origin at [x,y],
the bounding box of a character (that is,
the smallest rectangle that encloses the character's shape)
described in terms of
XCharStruct
components is a rectangle with its upper-left corner at:

[x + lbearing, y - ascent]

Its width is:

rbearing - lbearing

Its height is:

ascent + descent

The origin for the next character is defined to be:

[x + width, y]

The lbearing member defines the extent of the left edge of the character ink
from the origin.
The rbearing member defines the extent of the right edge of the character ink
from the origin.
The ascent member defines the extent of the top edge of the character ink
from the origin.
The descent member defines the extent of the bottom edge of the character ink
from the origin.
The width member defines the logical width of the character.

Note that the baseline (the y position of the character origin)
is logically viewed as being the scanline just below nondescending characters.
When descent is zero,
only pixels with Y-coordinates less than y are drawn,
and the origin is logically viewed as being coincident with the left edge of
a nonkerned character.
When lbearing is zero,
no pixels with X-coordinate less than x are drawn.
Any of the
XCharStruct
metric members could be negative.
If the width is negative,
the next character will be placed to the left of the current origin.

The X protocol does not define the interpretation of the attributes member
in the
XCharStruct
structure.
A nonexistent character is represented with all members of its
XCharStruct
set to zero.

A font is not guaranteed to have any properties.
The interpretation of the property value (for example, long or unsigned long)
must be derived from a priori knowledge of the property.
A basic set of font properties is specified in the X Consortium standard
X Logical Font Description Conventions.

Loading and Freeing Fonts

Xlib provides functions that you can use to load fonts, get font information,
unload fonts, and free font information.

A few font functions use a
GContext
resource ID or a font ID interchangeably.

To load a given font, use
XLoadFont.

Font XLoadFont(Display *display, char *name);

display	Specifies the connection to the X server.
name	Specifies the name of the font, which is a null-terminated string.

The
XLoadFont
function loads the specified font and returns its associated font ID.
If the font name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
When the characters “?” and “*” are used in a font name, a
pattern match is performed and any matching font is used.
In the pattern,
the “?” character will match any single character,
and the “*” character will match any number of characters.
A structured format for font names is specified in the X Consortium standard
X Logical Font Description Conventions.
If
XLoadFont
was unsuccessful at loading the specified font,
a
BadName
error results.
Fonts are not associated with a particular screen
and can be stored as a component
of any GC.
When the font is no longer needed, call
XUnloadFont.

XLoadFont
can generate
BadAlloc
and
BadName
errors.

To return information about an available font, use
XQueryFont.

XFontStruct *XQueryFont(Display *display, XID font_ID);

display	Specifies the connection to the X server.
font_ID	Specifies the font ID or the GContext ID.

The
XQueryFont
function returns a pointer to the
XFontStruct
structure, which contains information associated with the font.
You can query a font or the font stored in a GC.
The font ID stored in the
XFontStruct
structure will be the
GContext
ID, and you need to be careful when using this ID in other functions
(see
XGContextFromGC).
If the font does not exist,
XQueryFont
returns NULL.
To free this data, use
XFreeFontInfo.

To perform a
XLoadFont
and
XQueryFont
in a single operation, use
XLoadQueryFont.

XFontStruct *XLoadQueryFont(Display *display, char *name);

display	Specifies the connection to the X server.
name	Specifies the name of the font, which is a null-terminated string.

The
XLoadQueryFont
function provides the most common way for accessing a font.
XLoadQueryFont
both opens (loads) the specified font and returns a pointer to the
appropriate
XFontStruct
structure.
If the font name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
If the font does not exist,
XLoadQueryFont
returns NULL.

XLoadQueryFont
can generate a
BadAlloc
error.

To unload the font and free the storage used by the font structure
that was allocated by
XQueryFont
or
XLoadQueryFont,
use
XFreeFont.

XFreeFont(Display *display, XFontStruct *font_struct);

display	Specifies the connection to the X server.
font_struct	Specifies the storage associated with the font.

The
XFreeFont
function deletes the association between the font resource ID and the specified
font and frees the
XFontStruct
structure.
The font itself will be freed when no other resource references it.
The data and the font should not be referenced again.

XFreeFont
can generate a
BadFont
error.

To return a given font property, use
XGetFontProperty.

Bool XGetFontProperty(XFontStruct *font_struct, Atom atom, unsigned long *value_return);

font_struct	Specifies the storage associated with the font.
atom	Specifies the atom for the property name you want returned.
value_return	Returns the value of the font property.

Given the atom for that property,
the
XGetFontProperty
function returns the value of the specified font property.
XGetFontProperty
also returns
False
if the property was not defined or
True
if it was defined.
A set of predefined atoms exists for font properties,
which can be found in
<X11/Xatom.h>.

This set contains the standard properties associated with
a font.
Although it is not guaranteed,
it is likely that the predefined font properties will be present.

To unload a font that was loaded by
XLoadFont,
use
XUnloadFont.

XUnloadFont(Display *display, Font font);

display	Specifies the connection to the X server.
font	Specifies the font.

The
XUnloadFont
function deletes the association between the font resource ID and the specified font.
The font itself will be freed when no other resource references it.
The font should not be referenced again.

XUnloadFont
can generate a
BadFont
error.

Obtaining and Freeing Font Names and Information

You obtain font names and information by matching a wildcard specification
when querying a font type for a list of available sizes and so on.

To return a list of the available font names, use
XListFonts.

char **XListFonts(Display *display, char *pattern, int maxnames, int *actual_count_return);

display	Specifies the connection to the X server.
pattern	Specifies the null-terminated pattern string that can contain wildcard characters.
maxnames	Specifies the maximum number of names to be returned.
actual_count_return	Returns the actual number of font names.

The
XListFonts
function returns an array of available font names
(as controlled by the font search path; see
XSetFontPath)
that match the string you passed to the pattern argument.
The pattern string can contain any characters,
but each asterisk (*) is a wildcard for any number of characters,
and each question mark (?) is a wildcard for a single character.
If the pattern string is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
Each returned string is null-terminated.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
If there are no matching font names,
XListFonts
returns NULL.
The client should call
XFreeFontNames
when finished with the result to free the memory.

To free a font name array, use
XFreeFontNames.

XFreeFontNames(char *list[]);

list

Specifies the array of strings you want to free.

The
XFreeFontNames
function frees the array and strings returned by
XListFonts
or
XListFontsWithInfo.

To obtain the names and information about available fonts, use
XListFontsWithInfo.

char **XListFontsWithInfo(Display *display, char *pattern, int maxnames, int *count_return, XFontStruct **info_return);

display	Specifies the connection to the X server.
pattern	Specifies the null-terminated pattern string that can contain wildcard characters.
maxnames	Specifies the maximum number of names to be returned.
count_return	Returns the actual number of matched font names.
info_return	Returns the font information.

The
XListFontsWithInfo
function returns a list of font names that match the specified pattern and their
associated font information.
The list of names is limited to size specified by maxnames.
The information returned for each font is identical to what
XLoadQueryFont
would return except that the per-character metrics are not returned.
The pattern string can contain any characters,
but each asterisk (*) is a wildcard for any number of characters,
and each question mark (?) is a wildcard for a single character.
If the pattern string is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
Each returned string is null-terminated.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
If there are no matching font names,
XListFontsWithInfo
returns NULL.

To free only the allocated name array,
the client should call
XFreeFontNames.
To free both the name array and the font information array
or to free just the font information array,
the client should call
XFreeFontInfo.

To free font structures and font names, use
XFreeFontInfo.

XFreeFontInfo(char **names, XFontStruct *free_info, int actual_count);

names	Specifies the list of font names.
free_info	Specifies the font information.
actual_count	Specifies the actual number of font names.

The
XFreeFontInfo
function frees a font structure or an array of font structures
and optionally an array of font names.
If NULL is passed for names, no font names are freed.
If a font structure for an open font (returned by
XLoadQueryFont)
is passed, the structure is freed,
but the font is not closed; use
XUnloadFont
to close the font.

Computing Character String Sizes

Xlib provides functions that you can use to compute the width,
the logical extents,
and the server information about 8-bit and 2-byte text strings.

The width is computed by adding the character widths of all the characters.
It does not matter if the font is an 8-bit or 2-byte font.
These functions return the sum of the character metrics in pixels.

To determine the width of an 8-bit character string, use
XTextWidth.

int XTextWidth(XFontStruct *font_struct, char *string, int count);

font_struct	Specifies the font used for the width computation.
string	Specifies the character string.
count	Specifies the character count in the specified string.

To determine the width of a 2-byte character string, use
XTextWidth16.

int XTextWidth16(XFontStruct *font_struct, XChar2b *string, int count);

font_struct	Specifies the font used for the width computation.
string	Specifies the character string.
count	Specifies the character count in the specified string.

Computing Logical Extents

To compute the bounding box of an 8-bit character string in a given font, use
XTextExtents.

XTextExtents(XFontStruct *font_struct, char *string, int nchars, int *direction_return, int *font_ascent_return, int *font_descent_return, XCharStruct *overall_return);

font_struct	Specifies the XFontStruct structure.
string	Specifies the character string.
nchars	Specifies the number of characters in the character string.
direction_return	Returns the value of the direction hint (FontLeftToRight or FontRightToLeft).
font_ascent_return	Returns the font ascent.
font_descent_return	Returns the font descent.
overall_return	Returns the overall size in the specified XCharStruct structure.

To compute the bounding box of a 2-byte character string in a given font, use
XTextExtents16.

XTextExtents16(XFontStruct *font_struct, XChar2b *string, int nchars, int *direction_return, int *font_ascent_return, int *font_descent_return, XCharStruct *overall_return);

font_struct	Specifies the XFontStruct structure.
string	Specifies the character string.
nchars	Specifies the number of characters in the character string.
direction_return	Returns the value of the direction hint (FontLeftToRight or FontRightToLeft).
font_ascent_return	Returns the font ascent.
font_descent_return	Returns the font descent.
overall_return	Returns the overall size in the specified XCharStruct structure.

The
XTextExtents
and
XTextExtents16
functions
perform the size computation locally and, thereby,
avoid the round-trip overhead of
XQueryTextExtents
and
XQueryTextExtents16.
Both functions return an
XCharStruct
structure, whose members are set to the values as follows.

The ascent member is set to the maximum of the ascent metrics of all
characters in the string.
The descent member is set to the maximum of the descent metrics.
The width member is set to the sum of the character-width metrics of all
characters in the string.
For each character in the string,
let W be the sum of the character-width metrics of all characters preceding
it in the string.
Let L be the left-side-bearing metric of the character plus W.
Let R be the right-side-bearing metric of the character plus W.
The lbearing member is set to the minimum L of all characters in the string.
The rbearing member is set to the maximum R.

For fonts defined with linear indexing rather than 2-byte matrix indexing,
each
XChar2b
structure is interpreted as a 16-bit number with byte1 as the
most significant byte.
If the font has no defined default character,
undefined characters in the string are taken to have all zero metrics.

Querying Character String Sizes

To query the server for the bounding box of an 8-bit character string in a
given font, use
XQueryTextExtents.

XQueryTextExtents(Display *display, XID font_ID, char *string, int nchars, int *direction_return, int *font_ascent_return, int *font_descent_return, XCharStruct *overall_return);

display	Specifies the connection to the X server.
font_ID	Specifies either the font ID or the GContext ID that contains the font.
string	Specifies the character string.
nchars	Specifies the number of characters in the character string.
direction_return	Returns the value of the direction hint (FontLeftToRight or FontRightToLeft).
font_ascent_return	Returns the font ascent.
font_descent_return	Returns the font descent.
overall_return	Returns the overall size in the specified XCharStruct structure.

To query the server for the bounding box of a 2-byte character string
in a given font, use
XQueryTextExtents16.

XQueryTextExtents16(Display *display, XID font_ID, XChar2b *string, int nchars, int *direction_return, int *font_ascent_return, int *font_descent_return, XCharStruct *overall_return);

display	Specifies the connection to the X server.
font_ID	Specifies either the font ID or the GContext ID that contains the font.
string	Specifies the character string.
nchars	Specifies the number of characters in the character string.
direction_return	Returns the value of the direction hint (FontLeftToRight or FontRightToLeft).
font_ascent_return	Returns the font ascent.
font_descent_return	Returns the font descent.
overall_return	Returns the overall size in the specified XCharStruct structure.

The
XQueryTextExtents
and
XQueryTextExtents16
functions return the bounding box of the specified 8-bit and 16-bit
character string in the specified font or the font contained in the
specified GC.
These functions query the X server and, therefore, suffer the round-trip
overhead that is avoided by
XTextExtents
and
XTextExtents16.
Both functions return a
XCharStruct
structure, whose members are set to the values as follows.

The ascent member is set to the maximum of the ascent metrics
of all characters in the string.
The descent member is set to the maximum of the descent metrics.
The width member is set to the sum of the character-width metrics
of all characters in the string.
For each character in the string,
let W be the sum of the character-width metrics of all characters preceding
it in the string.
Let L be the left-side-bearing metric of the character plus W.
Let R be the right-side-bearing metric of the character plus W.
The lbearing member is set to the minimum L of all characters in the string.
The rbearing member is set to the maximum R.

Characters with all zero metrics are ignored.
If the font has no defined default_char,
the undefined characters in the string are also ignored.

XQueryTextExtents
and
XQueryTextExtents16
can generate
BadFont
and
BadGC
errors.

Drawing Text

This section discusses how to draw:

Complex text
Text characters
Image text characters

The fundamental text functions
XDrawText
and
XDrawText16
use the following structures:


typedef struct {
     char *chars;     /* pointer to string */
     int nchars;      /* number of characters */
     int delta;       /* delta between strings */
     Font font;       /* Font to print it in, None don't change */
} XTextItem;


typedef struct {
     XChar2b *chars;     /* pointer to two-byte characters */
     int nchars;         /* number of characters */
     int delta;         /* delta between strings */
     Font font;         /* font to print it in, None don't change */
} XTextItem16;

If the font member is not
None,
the font is changed before printing and also is stored in the GC.
If an error was generated during text drawing,
the previous items may have been drawn.
The baseline of the characters are drawn starting at the x and y
coordinates that you pass in the text drawing functions.

For example, consider the background rectangle drawn by
XDrawImageString.
If you want the upper-left corner of the background rectangle
to be at pixel coordinate (x,y), pass the (x,y + ascent)
as the baseline origin coordinates to the text functions.
The ascent is the font ascent, as given in the
XFontStruct
structure.
If you want the lower-left corner of the background rectangle
to be at pixel coordinate (x,y), pass the (x,y - descent + 1)
as the baseline origin coordinates to the text functions.
The descent is the font descent, as given in the
XFontStruct
structure.

Drawing Complex Text

To draw 8-bit characters in a given drawable, use
XDrawText.

XDrawText(Display *display, Drawable d, GC gc, int x, int y, XTextItem *items, int nitems);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the specified drawable and define the origin of the first character.
items	Specifies an array of text items.
nitems	Specifies the number of text items in the array.

To draw 2-byte characters in a given drawable, use
XDrawText16.

XDrawText16(Display *display, Drawable d, GC gc, int x, int y, XTextItem16 *items, int nitems);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the specified drawable and define the origin of the first character.
items	Specifies an array of text items.
nitems	Specifies the number of text items in the array.

The
XDrawText16
function is similar to
XDrawText
except that it uses 2-byte or 16-bit characters.
Both functions allow complex spacing and font shifts between counted strings.

Each text item is processed in turn.
A font member other than
None
in an item causes the font to be stored in the GC
and used for subsequent text.
A text element delta specifies an additional change
in the position along the x axis before the string is drawn.
The delta is always added to the character origin
and is not dependent on any characteristics of the font.
Each character image, as defined by the font in the GC, is treated as an
additional mask for a fill operation on the drawable.
The drawable is modified only where the font character has a bit set to 1.
If a text item generates a
BadFont
error, the previous text items may have been drawn.

For fonts defined with linear indexing rather than 2-byte matrix indexing,
each
XChar2b
structure is interpreted as a 16-bit number with byte1 as the
most significant byte.

Both functions use these GC components:
function, plane-mask, fill-style, font, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

XDrawText
and
XDrawText16
can generate
BadDrawable,
BadFont,
BadGC,
and
BadMatch
errors.

Drawing Text Characters

To draw 8-bit characters in a given drawable, use
XDrawString.

XDrawString(Display *display, Drawable d, GC gc, int x, int y, char *string, int length);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the specified drawable and define the origin of the first character.
string	Specifies the character string.
length	Specifies the number of characters in the string argument.

To draw 2-byte characters in a given drawable, use
XDrawString16.

XDrawString16(Display *display, Drawable d, GC gc, int x, int y, XChar2b *string, int length);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the specified drawable and define the origin of the first character.
string	Specifies the character string.
length	Specifies the number of characters in the string argument.

Each character image, as defined by the font in the GC, is treated as an
additional mask for a fill operation on the drawable.
The drawable is modified only where the font character has a bit set to 1.
For fonts defined with 2-byte matrix indexing
and used with
XDrawString16,
each byte is used as a byte2 with a byte1 of zero.

Both functions use these GC components:
function, plane-mask, fill-style, font, subwindow-mode, clip-x-origin,
clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
and tile-stipple-y-origin.

XDrawString
and
XDrawString16
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.

Drawing Image Text Characters

Some applications, in particular terminal emulators, need to
print image text in which both the foreground and background bits of
each character are painted.
This prevents annoying flicker on many displays.

To draw 8-bit image text characters in a given drawable, use
XDrawImageString.

XDrawImageString(Display *display, Drawable d, GC gc, int x, int y, char *string, int length);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the specified drawable and define the origin of the first character.
string	Specifies the character string.
length	Specifies the number of characters in the string argument.

To draw 2-byte image text characters in a given drawable, use
XDrawImageString16.

XDrawImageString16(Display *display, Drawable d, GC gc, int x, int y, XChar2b *string, int length);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates, which are relative to the origin of the specified drawable and define the origin of the first character.
string	Specifies the character string.
length	Specifies the number of characters in the string argument.

The
XDrawImageString16
function is similar to
XDrawImageString
except that it uses 2-byte or 16-bit characters.
Both functions also use both the foreground and background pixels
of the GC in the destination.

The effect is first to fill a
destination rectangle with the background pixel defined in the GC and then
to paint the text with the foreground pixel.
The upper-left corner of the filled rectangle is at:

[x, y - font-ascent]

The width is:

overall-width

The height is:

font-ascent + font-descent

The overall-width, font-ascent, and font-descent
are as would be returned by
XQueryTextExtents
using gc and string.
The function and fill-style defined in the GC are ignored for these functions.
The effective function is
GXcopy,
and the effective fill-style is
FillSolid.

For fonts defined with 2-byte matrix indexing
and used with
XDrawImageString,
each byte is used as a byte2 with a byte1 of zero.

Both functions use these GC components:
plane-mask, foreground, background, font, subwindow-mode, clip-x-origin,
clip-y-origin, and clip-mask.

XDrawImageString
and
XDrawImageString16
can generate
BadDrawable,
BadGC,
and
BadMatch
errors.

Transferring Images between Client and Server

Xlib provides functions that you can use to transfer images between a client
and the server.
Because the server may require diverse data formats,
Xlib provides an image object that fully describes the data in memory
and that provides for basic operations on that data.
You should reference the data
through the image object rather than referencing the data directly.
However, some implementations of the Xlib library may efficiently deal with
frequently used data formats by replacing
functions in the procedure vector with special case functions.
Supported operations include destroying the image, getting a pixel,
storing a pixel, extracting a subimage of an image, and adding a constant
to an image (see section 16.8).

All the image manipulation functions discussed in this section make use of
the
XImage
structure,
which describes an image as it exists in the client's memory.


typedef struct _XImage {
     int width, height;         /* size of image */
     int xoffset;               /* number of pixels offset in X direction */
     int format;                /* XYBitmap, XYPixmap, ZPixmap */
     char *data;                /* pointer to image data */
     int byte_order;            /* data byte order, LSBFirst, MSBFirst */
     int bitmap_unit;           /* quant. of scanline 8, 16, 32 */
     int bitmap_bit_order;      /* LSBFirst, MSBFirst */
     int bitmap_pad;            /* 8, 16, 32 either XY or ZPixmap */
     int depth;                 /* depth of image */
     int bytes_per_line;        /* accelerator to next scanline */
     int bits_per_pixel;        /* bits per pixel (ZPixmap) */
     unsigned long red_mask;    /* bits in z arrangement */
     unsigned long green_mask;
     unsigned long blue_mask;
     XPointer obdata;           /* hook for the object routines to hang on */
     struct funcs {             /* image manipulation routines */
          struct _XImage *(*create_image)();
          int             (*destroy_image)();
          unsigned long   (*get_pixel)();
          int             (*put_pixel)();
          struct _XImage  *(*sub_image)();
          int            (*add_pixel)();
     } f;
} XImage;

To initialize the image manipulation routines of an image structure, use
XInitImage.

Status XInitImage(XImage *image);

ximage

Specifies the image.

The
XInitImage
function initializes the internal image manipulation routines of an
image structure, based on the values of the various structure members.
All fields other than the manipulation routines must already be initialized.
If the bytes_per_line member is zero,
XInitImage
will assume the image data is contiguous in memory and set the
bytes_per_line member to an appropriate value based on the other
members; otherwise, the value of bytes_per_line is not changed.
All of the manipulation routines are initialized to functions
that other Xlib image manipulation functions need to operate on the
type of image specified by the rest of the structure.

This function must be called for any image constructed by the client
before passing it to any other Xlib function.
Image structures created or returned by Xlib do not need to be
initialized in this fashion.

This function returns a nonzero status if initialization of the
structure is successful. It returns zero if it detected some error
or inconsistency in the structure, in which case the image is not changed.

To combine an image with a rectangle of a drawable on the display,
use
XPutImage.

XPutImage(Display *display, Drawable d, GC gc, XImage *image, int src_x, int src_y, int dest_x, int dest_y, unsigned int width, unsigned int height);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
image	Specifies the image you want combined with the rectangle.
src_x	Specifies the offset in X from the left edge of the image defined by the XImage structure.
src_y	Specifies the offset in Y from the top edge of the image defined by the XImage structure.
dest_x
dest_y	Specify the x and y coordinates, which are relative to the origin of the drawable and are the coordinates of the subimage.
width
height	Specify the width and height of the subimage, which define the dimensions of the rectangle.

The
XPutImage
function
combines an image with a rectangle of the specified drawable.
The section of the image defined by the src_x, src_y, width, and height
arguments is drawn on the specified part of the drawable.
If
XYBitmap
format is used, the depth of the image must be one,
or a
BadMatch
error results.
The foreground pixel in the GC defines the source for the one bits in the image,
and the background pixel defines the source for the zero bits.
For
XYPixmap
and
ZPixmap,
the depth of the image must match the depth of the drawable,
or a
BadMatch
error results.

If the characteristics of the image (for example, byte_order and bitmap_unit)
differ from what the server requires,
XPutImage
automatically makes the appropriate
conversions.

This function uses these GC components:
function, plane-mask, subwindow-mode, clip-x-origin, clip-y-origin,
and clip-mask.
It also uses these GC mode-dependent components:
foreground and background.

XPutImage
can generate
BadDrawable,
BadGC,
BadMatch,
and
BadValue
errors.

To return the contents of a rectangle in a given drawable on the display,
use
XGetImage.
This function specifically supports rudimentary screen dumps.

XImage *XGetImage(Display *display, Drawable d, int x, int y, unsigned int width, unsigned int height, unsigned long plane_mask, int format);

display	Specifies the connection to the X server.
d	Specifies the drawable.
x
y	Specify the x and y coordinates, which are relative to the origin of the drawable and define the upper-left corner of the rectangle.
width
height	Specify the width and height of the subimage, which define the dimensions of the rectangle.
plane_mask	Specifies the plane mask.
format	Specifies the format for the image. You can pass XYPixmap or ZPixmap.

The
XGetImage
function returns a pointer to an
XImage
structure.
This structure provides you with the contents of the specified rectangle of
the drawable in the format you specify.
If the format argument is
XYPixmap,
the image contains only the bit planes you passed to the plane_mask argument.
If the plane_mask argument only requests a subset of the planes of the
display, the depth of the returned image will be the number of planes
requested.
If the format argument is
ZPixmap,
XGetImage
returns as zero the bits in all planes not
specified in the plane_mask argument.
The function performs no range checking on the values in plane_mask and ignores
extraneous bits.

XGetImage
returns the depth of the image to the depth member of the
XImage
structure.
The depth of the image is as specified when the drawable was created,
except when getting a subset of the planes in
XYPixmap
format, when the depth is given by the number of bits set to 1 in plane_mask.

If the drawable is a pixmap,
the given rectangle must be wholly contained within the pixmap,
or a
BadMatch
error results.
If the drawable is a window,
the window must be viewable,
and it must be the case that if there were no inferiors or overlapping windows,
the specified rectangle of the window would be fully visible on the screen
and wholly contained within the outside edges of the window,
or a
BadMatch
error results.
Note that the borders of the window can be included and read with
this request.
If the window has backing-store, the backing-store contents are
returned for regions of the window that are obscured by noninferior
windows.
If the window does not have backing-store,
the returned contents of such obscured regions are undefined.
The returned contents of visible regions of inferiors
of a different depth than the specified window's depth are also undefined.
The pointer cursor image is not included in the returned contents.
If a problem occurs,
XGetImage
returns NULL.

XGetImage
can generate
BadDrawable,
BadMatch,
and
BadValue
errors.

To copy the contents of a rectangle on the display
to a location within a preexisting image structure, use
XGetSubImage.

XImage *XGetSubImage(Display *display, Drawable d, int x, int y, unsigned int width, unsigned int height, unsigned long plane_mask, int format, XImage *dest_image, int dest_x, int dest_y);

display	Specifies the connection to the X server.
d	Specifies the drawable.
x
y	Specify the x and y coordinates, which are relative to the origin of the drawable and define the upper-left corner of the rectangle.
width
height	Specify the width and height of the subimage, which define the dimensions of the rectangle.
plane_mask	Specifies the plane mask.
format	Specifies the format for the image. You can pass XYPixmap or ZPixmap.
dest_image	Specifies the destination image.
dest_x
dest_y	Specify the x and y coordinates, which are relative to the origin of the destination rectangle, specify its upper-left corner, and determine where the subimage is placed in the destination image.

The
XGetSubImage
function updates dest_image with the specified subimage in the same manner as
XGetImage.
If the format argument is
XYPixmap,
the image contains only the bit planes you passed to the plane_mask argument.
If the format argument is
ZPixmap,
XGetSubImage
returns as zero the bits in all planes not
specified in the plane_mask argument.
The function performs no range checking on the values in plane_mask and ignores
extraneous bits.
As a convenience,
XGetSubImage
returns a pointer to the same
XImage
structure specified by dest_image.

The depth of the destination
XImage
structure must be the same as that of the drawable.
If the specified subimage does not fit at the specified location
on the destination image, the right and bottom edges are clipped.
If the drawable is a pixmap,
the given rectangle must be wholly contained within the pixmap,
or a
BadMatch
error results.
If the drawable is a window,
the window must be viewable,
and it must be the case that if there were no inferiors or overlapping windows,
the specified rectangle of the window would be fully visible on the screen
and wholly contained within the outside edges of the window,
or a
BadMatch
error results.
If the window has backing-store,
then the backing-store contents are returned for regions of the window
that are obscured by noninferior windows.
If the window does not have backing-store,
the returned contents of such obscured regions are undefined.
The returned contents of visible regions of inferiors
of a different depth than the specified window's depth are also undefined.
If a problem occurs,
XGetSubImage
returns NULL.

XGetSubImage
can generate
BadDrawable,
BadGC,
BadMatch,
and
BadValue
errors.

Chapter 9. Window and Session Manager Functions

Table of Contents

Changing the Parent of a WindowControlling the Lifetime of a WindowManaging Installed ColormapsSetting and Retrieving the Font Search PathGrabbing the ServerKilling ClientsControlling the Screen SaverControlling Host AccessAdding, Getting, or Removing HostsChanging, Enabling, or Disabling Access Control

Although it is difficult to categorize functions as exclusively for an application,
a window manager, or a session manager, the functions in this chapter are most
often used by window managers and session managers. It is not expected that
these functions will be used by most application programs. Xlib provides
management functions to:

Change the parent of a window
Control the lifetime of a window
Manage installed colormaps
Set and retrieve the font search path
Grab the server
Kill a client
Control the screen saver
Control host access

Changing the Parent of a Window

To change a window's parent to another window on the same screen, use
XReparentWindow.
There is no way to move a window between screens.

XReparentWindow(Display *display, Window w, Window parent, int x, int y);

display	Specifies the connection to the X server.
w	Specifies the window.
parent	Specifies the parent window.
x
y	Specify the x and y coordinates of the position in the new parent window.

If the specified window is mapped,
XReparentWindow
automatically performs an
UnmapWindow
request on it, removes it from its current position in the hierarchy,
and inserts it as the child of the specified parent.
The window is placed in the stacking order on top with respect to
sibling windows.

After reparenting the specified window,
XReparentWindow
causes the X server to generate a
ReparentNotify
event.
The override_redirect member returned in this event is
set to the window's corresponding attribute.
Window manager clients usually should ignore this window if this member
is set to
True.
Finally, if the specified window was originally mapped,
the X server automatically performs a
MapWindow
request on it.

The X server performs normal exposure processing on formerly obscured
windows.
The X server might not generate
Expose
events for regions from the initial
UnmapWindow
request that are immediately obscured by the final
MapWindow
request.
A
BadMatch
error results if:

The new parent window is not on the same screen as
the old parent window.
The new parent window is the specified window or an inferior of the
specified window.
The new parent is
InputOnly,
and the window is not.
The specified window has a
ParentRelative
background, and the new parent window is not the same depth as the
specified window.

XReparentWindow
can generate
BadMatch
and
BadWindow
errors.

Controlling the Lifetime of a Window

The save-set of a client is a list of other clients' windows that,
if they are inferiors of one of the client's windows at connection close,
should not be destroyed and should be remapped if they are unmapped.
For further information about close-connection processing,
see section 2.6.
To allow an application's window to survive when a window manager that
has reparented a window fails,
Xlib provides the save-set functions that you can
use to control the longevity of subwindows
that are normally destroyed when the parent is destroyed.
For example, a window manager that wants to add decoration
to a window by adding a frame might reparent an application's
window.
When the frame is destroyed,
the application's window should not be destroyed
but be returned to its previous place in the window hierarchy.

The X server automatically removes windows from the save-set
when they are destroyed.

To add or remove a window from the client's save-set, use
XChangeSaveSet.

XChangeSaveSet(Display *display, Window w, int change_mode);

display	Specifies the connection to the X server.
w	Specifies the window that you want to add to or delete from the client's save-set.
change_mode	Specifies the mode. You can pass SetModeInsert or SetModeDelete.

Depending on the specified mode,
XChangeSaveSet
either inserts or deletes the specified window from the client's save-set.
The specified window must have been created by some other client,
or a
BadMatch
error results.

XChangeSaveSet
can generate
BadMatch,
BadValue,
and
BadWindow
errors.

To add a window to the client's save-set, use
XAddToSaveSet.

XAddToSaveSet(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window that you want to add to the client's save-set.

The
XAddToSaveSet
function adds the specified window to the client's save-set.
The specified window must have been created by some other client,
or a
BadMatch
error results.

XAddToSaveSet
can generate
BadMatch
and
BadWindow
errors.

To remove a window from the client's save-set, use
XRemoveFromSaveSet.

XRemoveFromSaveSet(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window that you want to delete from the client's save-set.

The
XRemoveFromSaveSet
function removes the specified window from the client's save-set.
The specified window must have been created by some other client,
or a
BadMatch
error results.

XRemoveFromSaveSet
can generate
BadMatch
and
BadWindow
errors.

Managing Installed Colormaps

The X server maintains a list of installed colormaps.
Windows using these colormaps are guaranteed to display with
correct colors; windows using other colormaps may or may not display
with correct colors.
Xlib provides functions that you can use to install a colormap,
uninstall a colormap, and obtain a list of installed colormaps.

At any time,
there is a subset of the installed maps that is viewed as an ordered list
and is called the required list.
The length of the required list is at most M,
where M is the minimum number of installed colormaps specified for the screen
in the connection setup.
The required list is maintained as follows.
When a colormap is specified to
XInstallColormap,
it is added to the head of the list;
the list is truncated at the tail, if necessary, to keep its length to
at most M.
When a colormap is specified to
XUninstallColormap
and it is in the required list,
it is removed from the list.
A colormap is not added to the required list when it is implicitly installed
by the X server,
and the X server cannot implicitly uninstall a colormap that is in the
required list.

To install a colormap, use
XInstallColormap.

XInstallColormap(Display *display, Colormap colormap);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.

The
XInstallColormap
function installs the specified colormap for its associated screen.
All windows associated with this colormap immediately display with
true colors.
You associated the windows with this colormap when you created them by calling
XCreateWindow,
XCreateSimpleWindow,
XChangeWindowAttributes,
or
XSetWindowColormap.

If the specified colormap is not already an installed colormap,
the X server generates a
ColormapNotify
event on each window that has that colormap.
In addition, for every other colormap that is installed as
a result of a call to
XInstallColormap,
the X server generates a
ColormapNotify
event on each window that has that colormap.

XInstallColormap
can generate a
BadColor
error.

To uninstall a colormap, use
XUninstallColormap.

XUninstallColormap(Display *display, Colormap colormap);

display	Specifies the connection to the X server.
colormap	Specifies the colormap.

The
XUninstallColormap
function removes the specified colormap from the required
list for its screen.
As a result,
the specified colormap might be uninstalled,
and the X server might implicitly install or uninstall additional colormaps.
Which colormaps get installed or uninstalled is server dependent
except that the required list must remain installed.

If the specified colormap becomes uninstalled,
the X server generates a
ColormapNotify
event on each window that has that colormap.
In addition, for every other colormap that is installed or uninstalled as a
result of a call to
XUninstallColormap,
the X server generates a
ColormapNotify
event on each window that has that colormap.

XUninstallColormap
can generate a
BadColor
error.

To obtain a list of the currently installed colormaps for a given screen, use
XListInstalledColormaps.

Colormap *XListInstalledColormaps(Display *display, Window w, int *num_return);

display	Specifies the connection to the X server.
w	Specifies the window that determines the screen.
num_return	Returns the number of currently installed colormaps.

The
XListInstalledColormaps
function returns a list of the currently installed colormaps for the screen
of the specified window.
The order of the colormaps in the list is not significant
and is no explicit indication of the required list.
When the allocated list is no longer needed,
free it by using
XFree.

XListInstalledColormaps
can generate a
BadWindow
error.

Setting and Retrieving the Font Search Path

The set of fonts available from a server depends on a font
search path. Xlib provides functions to set and retrieve the
search path for a server.

To set the font search path, use
XSetFontPath.

XSetFontPath(Display *display, char **directories, int ndirs);

display	Specifies the connection to the X server.
directories	Specifies the directory path used to look for a font. Setting the path to the empty list restores the default path defined for the X server.
ndirs	Specifies the number of directories in the path.

The
XSetFontPath
function defines the directory search path for font lookup.
There is only one search path per X server, not one per client.
The encoding and interpretation of the strings are implementation-dependent,
but typically they specify directories or font servers to be searched
in the order listed.
An X server is permitted to cache font information internally;
for example, it might cache an entire font from a file and not
check on subsequent opens of that font to see if the underlying
font file has changed.
However,
when the font path is changed,
the X server is guaranteed to flush all cached information about fonts
for which there currently are no explicit resource IDs allocated.
The meaning of an error from this request is implementation-dependent.

XSetFontPath
can generate a
BadValue
error.

To get the current font search path, use
XGetFontPath.

char **XGetFontPath(Display *display, int *npaths_return);

display	Specifies the connection to the X server.
npaths_return	Returns the number of strings in the font path array.

The
XGetFontPath
function allocates and returns an array of strings containing the search path.
The contents of these strings are implementation-dependent
and are not intended to be interpreted by client applications.
When it is no longer needed,
the data in the font path should be freed by using
XFreeFontPath.

To free data returned by
XGetFontPath,
use
XFreeFontPath.

XFreeFontPath(char **list);

list

Specifies the array of strings you want to free.

The
XFreeFontPath
function
frees the data allocated by
XGetFontPath.

Grabbing the Server

Xlib provides functions that you can use to grab and ungrab the server.
These functions can be used to control processing of output on other
connections by the window system server.
While the server is grabbed,
no processing of requests or close downs on any other connection will occur.
A client closing its connection automatically ungrabs the server.

Although grabbing the server is highly discouraged, it is sometimes necessary.

To grab the server, use
XGrabServer.

XGrabServer(Display *display);

display

Specifies the connection to the X server.

The
XGrabServer
function disables processing of requests and close downs on all other
connections than the one this request arrived on.
You should not grab the X server any more than is absolutely necessary.

To ungrab the server, use
XUngrabServer.

XUngrabServer(Display *display);

display

Specifies the connection to the X server.

The
XUngrabServer
function restarts processing of requests and close downs on other connections.
You should avoid grabbing the X server as much as possible.

Killing Clients

Xlib provides a function to cause the connection to
a client to be closed and its resources to be destroyed.
To destroy a client, use
XKillClient.

XKillClient(Display *display, XID resource);

display	Specifies the connection to the X server.
resource	Specifies any resource associated with the client that you want to destroy or AllTemporary.

The
XKillClient
function
forces a close down of the client
that created the resource
if a valid resource is specified.
If the client has already terminated in
either
RetainPermanent
or
RetainTemporary
mode, all of the client's
resources are destroyed.
If
AllTemporary
is specified, the resources of all clients that have terminated in
RetainTemporary
are destroyed (see section 2.5).
This permits implementation of window manager facilities that aid debugging.
A client can set its close-down mode to
RetainTemporary.
If the client then crashes,
its windows would not be destroyed.
The programmer can then inspect the application's window tree
and use the window manager to destroy the zombie windows.

XKillClient
can generate a
BadValue
error.

Controlling the Screen Saver

Xlib provides functions that you can use to set or reset the mode
of the screen saver, to force or activate the screen saver,
or to obtain the current screen saver values.

To set the screen saver mode, use
XSetScreenSaver.

XSetScreenSaver(Display *display, int timeout, int interval, int prefer_blanking, int allow_exposures);

display	Specifies the connection to the X server.
timeout	Specifies the timeout, in seconds, until the screen saver turns on.
interval	Specifies the interval, in seconds, between screen saver alterations.
prefer_blanking	Specifies how to enable screen blanking. You can pass DontPreferBlanking, PreferBlanking, or DefaultBlanking.
allow_exposures	Specifies the screen save control values. You can pass DontAllowExposures, AllowExposures, or DefaultExposures.

Timeout and interval are specified in seconds.
A timeout of 0 disables the screen saver
(but an activated screen saver is not deactivated),
and a timeout of −1 restores the default.
Other negative values generate a
BadValue
error.
If the timeout value is nonzero,
XSetScreenSaver
enables the screen saver.
An interval of 0 disables the random-pattern motion.
If no input from devices (keyboard, mouse, and so on) is generated
for the specified number of timeout seconds once the screen saver is enabled,
the screen saver is activated.

For each screen,
if blanking is preferred and the hardware supports video blanking,
the screen simply goes blank.
Otherwise, if either exposures are allowed or the screen can be regenerated
without sending
Expose
events to clients,
the screen is tiled with the root window background tile randomly
re-origined each interval seconds.
Otherwise, the screens' state do not change,
and the screen saver is not activated.
The screen saver is deactivated,
and all screen states are restored at the next
keyboard or pointer input or at the next call to
XForceScreenSaver
with mode
ScreenSaverReset.

If the server-dependent screen saver method supports periodic change,
the interval argument serves as a hint about how long the change period
should be, and zero hints that no periodic change should be made.
Examples of ways to change the screen include scrambling the colormap
periodically, moving an icon image around the screen periodically, or tiling
the screen with the root window background tile, randomly re-origined
periodically.

XSetScreenSaver
can generate a
BadValue
error.

To force the screen saver on or off, use
XForceScreenSaver.

XForceScreenSaver(Display *display, int mode);

display	Specifies the connection to the X server.
mode	Specifies the mode that is to be applied. You can pass ScreenSaverActive or ScreenSaverReset.

If the specified mode is
ScreenSaverActive
and the screen saver currently is deactivated,
XForceScreenSaver
activates the screen saver even if the screen saver had been disabled
with a timeout of zero.
If the specified mode is
ScreenSaverReset
and the screen saver currently is enabled,
XForceScreenSaver
deactivates the screen saver if it was activated,
and the activation timer is reset to its initial state
(as if device input had been received).

XForceScreenSaver
can generate a
BadValue
error.

To activate the screen saver, use
XActivateScreenSaver.

XActivateScreenSaver(Display *display);

display

Specifies the connection to the X server.

To reset the screen saver, use
XResetScreenSaver.

XResetScreenSaver(Display *display);

display

Specifies the connection to the X server.

To get the current screen saver values, use
XGetScreenSaver.

XGetScreenSaver(Display *display, int *timeout_return, int *interval_return, int *prefer_blanking_return, int *allow_exposures_return);

display	Specifies the connection to the X server.
timeout_return	Returns the timeout, in seconds, until the screen saver turns on.
interval_return	Returns the interval between screen saver invocations.
prefer_blanking_return	Returns the current screen blanking preference (DontPreferBlanking, PreferBlanking, or DefaultBlanking).
allow_exposures_return	Returns the current screen save control value (DontAllowExposures, AllowExposures, or DefaultExposures).

Controlling Host Access

This section discusses how to:

Add, get, or remove hosts from the access control list
Change, enable, or disable access

X does not provide any protection on a per-window basis.
If you find out the resource ID of a resource, you can manipulate it.
To provide some minimal level of protection, however,
connections are permitted only from machines you trust.
This is adequate on single-user workstations but obviously
breaks down on timesharing machines.
Although provisions exist in the X protocol for proper connection
authentication, the lack of a standard authentication server
leaves host-level access control as the only common mechanism.

The initial set of hosts allowed to open connections typically consists of:

The host the window system is running on.
On POSIX-conformant systems, each host listed in the
/etc/X?.hosts
file.
The ? indicates the number of the
display.

This file should consist of host names separated by newlines.
DECnet nodes must terminate in :: to distinguish them from Internet hosts.

If a host is not in the access control list when the access control
mechanism is enabled and if the host attempts to establish a connection,
the server refuses the connection.
To change the access list,
the client must reside on the same host as the server and/or must
have been granted permission in the initial authorization at connection
setup.

Servers also can implement other access control policies in addition to
or in place of this host access facility.
For further information about other access control implementations,
see X Window System Protocol.

Adding, Getting, or Removing Hosts

Xlib provides functions that you can use to add, get, or remove hosts
from the access control list.
All the host access control functions use the
XHostAddress
structure, which contains:


typedef struct {
     int family;        /* for example FamilyInternet */
     int length;        /* length of address, in bytes */
     char *address;     /* pointer to where to find the address */
} XHostAddress;

The family member specifies which protocol address family to use
(for example, TCP/IP or DECnet) and can be
FamilyInternet,
FamilyInternet6,
FamilyServerInterpreted,
FamilyDECnet,
or
FamilyChaos.
The length member specifies the length of the address in bytes.
The address member specifies a pointer to the address.

For TCP/IP, the address should be in network byte order.
For IP version 4 addresses, the family should be FamilyInternet
and the length should be 4 bytes. For IP version 6 addresses, the
family should be FamilyInternet6 and the length should be 16 bytes.

For the DECnet family,
the server performs no automatic swapping on the address bytes.
A Phase IV address is 2 bytes long.
The first byte contains the least significant 8 bits of the node number.
The second byte contains the most significant 2 bits of the
node number in the least significant 2 bits of the byte
and the area in the most significant 6 bits of the byte.

For the ServerInterpreted family, the length is ignored and the address
member is a pointer to a
XServerInterpretedAddress
structure, which contains:


typedef struct {
     int typelength;     /* length of type string, in bytes */
     int valuelength;    /* length of value string, in bytes */
     char *type;         /* pointer to where to find the type string */
     char *value;        /* pointer to where to find the address */
} XServerInterpretedAddress;

The type and value members point to strings representing the type and value of
the server interpreted entry. These strings may not be NULL-terminated so care
should be used when accessing them. The typelength and valuelength members
specify the length in byte of the type and value strings.

To add a single host, use
XAddHost.

XAddHost(Display *display, XHostAddress *host);

display	Specifies the connection to the X server.
host	Specifies the host that is to be added.

The
XAddHost
function adds the specified host to the access control list for that display.
The server must be on the same host as the client issuing the command, or a
BadAccess
error results.

XAddHost
can generate
BadAccess
and
BadValue
errors.

To add multiple hosts at one time, use
XAddHosts.

XAddHosts(Display *display, XHostAddress *hosts, int num_hosts);

display	Specifies the connection to the X server.
hosts	Specifies each host that is to be added.
num_hosts	Specifies the number of hosts.

The
XAddHosts
function adds each specified host to the access control list for that display.
The server must be on the same host as the client issuing the command, or a
BadAccess
error results.

XAddHosts
can generate
BadAccess
and
BadValue
errors.

To obtain a host list, use
XListHosts.

XHostAddress *XListHosts(Display *display, int *nhosts_return, Bool *state_return);

display	Specifies the connection to the X server.
nhosts_return	Returns the number of hosts currently in the access control list.
state_return	Returns the state of the access control.

The
XListHosts
function returns the current access control list as well as whether the use
of the list at connection setup was enabled or disabled.
XListHosts
allows a program to find out what machines can make connections.
It also returns a pointer to a list of host structures that
were allocated by the function.
When no longer needed,
this memory should be freed by calling
XFree.

To remove a single host, use
XRemoveHost.

XRemoveHost(Display *display, XHostAddress *host);

display	Specifies the connection to the X server.
host	Specifies the host that is to be removed.

The
XRemoveHost
function removes the specified host from the access control list
for that display.
The server must be on the same host as the client process, or a
BadAccess
error results.
If you remove your machine from the access list,
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.

XRemoveHost
can generate
BadAccess
and
BadValue
errors.

To remove multiple hosts at one time, use
XRemoveHosts.

XRemoveHosts(Display *display, XHostAddress *hosts, int num_hosts);

display	Specifies the connection to the X server.
hosts	Specifies each host that is to be removed.
num_hosts	Specifies the number of hosts.

The
XRemoveHosts
function removes each specified host from the access control list for that
display.
The X server must be on the same host as the client process, or a
BadAccess
error results.
If you remove your machine from the access list,
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.

XRemoveHosts
can generate
BadAccess
and
BadValue
errors.

Changing, Enabling, or Disabling Access Control

Xlib provides functions that you can use to enable, disable,
or change access control.

For these functions to execute successfully,
the client application must reside on the same host as the X server
and/or have been given permission in the initial authorization
at connection setup.

To change access control, use
XSetAccessControl.

XSetAccessControl(Display *display, int mode);

display	Specifies the connection to the X server.
mode	Specifies the mode. You can pass EnableAccess or DisableAccess.

The
XSetAccessControl
function either enables or disables the use of the access control list
at each connection setup.

XSetAccessControl
can generate
BadAccess
and
BadValue
errors.

To enable access control, use
XEnableAccessControl.

XEnableAccessControl(Display *display);

display

Specifies the connection to the X server.

The
XEnableAccessControl
function enables the use of the access control list at each connection setup.

XEnableAccessControl
can generate a
BadAccess
error.

To disable access control, use
XDisableAccessControl.

XDisableAccessControl(Display *display);

display

Specifies the connection to the X server.

The
XDisableAccessControl
function disables the use of the access control list at each connection setup.

XDisableAccessControl
can generate a
BadAccess
error.

Chapter 10. Events

Table of Contents

Event TypesEvent StructuresEvent MasksEvent Processing OverviewKeyboard and Pointer EventsPointer Button EventsKeyboard and Pointer EventsWindow Entry/Exit EventsNormal Entry/Exit EventsGrab and Ungrab Entry/Exit EventsInput Focus EventsNormal Focus Events and Focus Events While GrabbedFocus Events Generated by GrabsKey Map State Notification EventsExposure EventsExpose EventsGraphicsExpose and NoExpose EventsWindow State Change EventsCirculateNotify EventsConfigureNotify EventsCreateNotify EventsDestroyNotify EventsGravityNotify EventsMapNotify EventsMappingNotify EventsReparentNotify EventsUnmapNotify EventsVisibilityNotify EventsStructure Control EventsCirculateRequest EventsConfigureRequest EventsMapRequest EventsResizeRequest EventsColormap State Change EventsClient Communication EventsClientMessage EventsPropertyNotify EventsSelectionClear EventsSelectionRequest EventsSelectionNotify Events

A client application communicates with the X server through the connection you establish with
the XOpenDisplay function. A client application sends requests to the X server over this
connection. These requests are made by the Xlib functions that are called in the client application.
Many Xlib functions cause the X server to generate events, and the user’s typing or moving the
pointer can generate events asynchronously. The X server returns events to the client on the same
connection.

This chapter discusses the following topics associated with events:

Event types
Event structures
Event masks
Event processing

Functions for handling events are dealt with in
the next chapter.

Event Types

An event is data generated asynchronously by the X server as a result of some
device activity or as side effects of a request sent by an Xlib function.

Device-related events propagate from the source window to ancestor windows
until some client application has selected that event type
or until the event is explicitly discarded.
The X server generally sends an event to a client application
only if the client has specifically asked to be informed of that event type,
typically by setting the event-mask attribute of the window.
The mask can also be set when you create a window
or by changing the window's
event-mask.
You can also mask out events that would propagate to ancestor windows
by manipulating the
do-not-propagate mask of the window's attributes.
However,
MappingNotify
events are always sent to all clients.

An event type describes a specific event generated by the X server.
For each event type,
a corresponding constant name is defined in
<X11/X.h>,

which is used when referring to an event type.

The following table lists the event category
and its associated event type or types.
The processing associated with these events is discussed in section 10.5.

Event Category	Event Type
Keyboard events	KeyPress, KeyRelease
Pointer events	ButtonPress, ButtonRelease, MotionNotify
Window crossing events	EnterNotify, LeaveNotify
Input focus events	FocusIn, FocusOut
Keymap state notification event	KeymapNotify
Exposure events	Expose, GraphicsExpose, NoExpose
Structure control events	CirculateRequest, ConfigureRequest, MapRequest, ResizeRequest
Window state notification events	CirculateNotify, ConfigureNotify, CreateNotify, DestroyNotify, GravityNotify, MapNotify, MappingNotify, ReparentNotify, UnmapNotify, VisibilityNotify
Colormap state notification event	ColormapNotify
Client communication events	ClientMessage, PropertyNotify, SelectionClear, SelectionNotify, SelectionRequest

Event Structures

For each event type,
a corresponding structure is declared in
<X11/Xlib.h>.

All the event structures have the following common members:


typedef struct {
     int           type;
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        window;
} XAnyEvent;

The type member is set to the event type constant name that uniquely identifies
it.
For example, when the X server reports a
GraphicsExpose
event to a client application, it sends an
XGraphicsExposeEvent
structure with the type member set to
GraphicsExpose.
The display member is set to a pointer to the display the event was read on.
The send_event member is set to
True
if the event came from a
SendEvent
protocol request.
The serial member is set from the serial number reported in the protocol
but expanded from the 16-bit least-significant bits to a full 32-bit value.
The window member is set to the window that is most useful to toolkit
dispatchers.

The X server can send events at any time in the input stream.
Xlib stores any events received while waiting for a reply in an event queue
for later use.
Xlib also provides functions that allow you to check events in the event queue
(see section 11.3).

In addition to the individual structures declared for each event type, the
XEvent
structure is a union of the individual structures declared for each event type.
Depending on the type,
you should access members of each event by using the
XEvent
union.


typedef union _XEvent {
     int                            type;          /* must not be changed */
     XAnyEvent                      xany;
     XKeyEvent                      xkey;
     XButtonEvent                   xbutton;
     XMotionEvent                   xmotion;
     XCrossingEvent                 xcrossing;
     XFocusChangeEvent              xfocus;
     XExposeEvent                   xexpose;
     XGraphicsExposeEvent           xgraphicsexpose;
     XNoExposeEvent                 xnoexpose;
     XVisibilityEvent               xvisibility;
     XCreateWindowEvent             xcreatewindow;
     XDestroyWindowEvent            xdestroywindow;
     XUnmapEvent                    xunmap;
     XMapEvent                      xmap;
     XMapRequestEvent               xmaprequest;
     XReparentEvent                 xreparent;
     XConfigureEvent                xconfigure;
     XGravityEvent                  xgravity;
     XResizeRequestEvent            xresizerequest;
     XConfigureRequestEvent         xconfigurerequest;
     XCirculateEvent                xcirculate;
     XCirculateRequestEvent         xcirculaterequest;
     XPropertyEvent                 xproperty;
     XSelectionClearEvent           xselectionclear;
     XSelectionRequestEvent         xselectionrequest;
     XSelectionEvent                xselection;
     XColormapEvent                 xcolormap;
     XClientMessageEvent            xclient;
     XMappingEvent                  xmapping;
     XErrorEvent                    xerror;
     XKeymapEvent                   xkeymap;
     long                           pad[24];
} XEvent;

An
XEvent
structure's first entry always is the type member,
which is set to the event type.
The second member always is the serial number of the protocol request
that generated the event.
The third member always is send_event,
which is a
Bool
that indicates if the event was sent by a different client.
The fourth member always is a display,
which is the display that the event was read from.
Except for keymap events,
the fifth member always is a window,
which has been carefully selected to be useful to toolkit dispatchers.
To avoid breaking toolkits,
the order of these first five entries is not to change.
Most events also contain a time member,
which is the time at which an event occurred.
In addition, a pointer to the generic event must be cast before it
is used to access any other information in the structure.

Event Masks

Clients select event reporting of most events relative to a window.
To do this, pass an event mask to an Xlib event-handling
function that takes an event_mask argument.
The bits of the event mask are defined in
<X11/X.h>.

Each bit in the event mask maps to an event mask name,
which describes the event or events you want the X server to
return to a client application.

Unless the client has specifically asked for them,
most events are not reported to clients when they are generated.
Unless the client suppresses them by setting graphics-exposures in the GC to
False,
GraphicsExpose
and
NoExpose
are reported by default as a result of
XCopyPlane
and
XCopyArea.
SelectionClear,
SelectionRequest,
SelectionNotify,
or
ClientMessage
cannot be masked.
Selection-related events are only sent to clients cooperating
with selections
(see section 4.5).
When the keyboard or pointer mapping is changed,
MappingNotify
is always sent to clients.

The following table
lists the event mask constants you can pass to
the event_mask argument and
the circumstances in which you would want to specify the
event mask:

Event Mask	Circumstances
NoEventMask	No events wanted
KeyPressMask	Keyboard down events wanted
KeyReleaseMask	Keyboard up events wanted
ButtonPressMask	Pointer button down events wanted
ButtonReleaseMask	Pointer button up events wanted
EnterWindowMask	Pointer window entry events wanted
LeaveWindowMask	Pointer window leave events wanted
PointerMotionMask	Pointer motion events wanted
PointerMotionHintMask	Pointer motion hints wanted
Button1MotionMask	Pointer motion while button 1 down
Button2MotionMask	Pointer motion while button 2 down
Button3MotionMask	Pointer motion while button 3 down
Button4MotionMask	Pointer motion while button 4 down
Button5MotionMask	Pointer motion while button 5 down
ButtonMotionMask	Pointer motion while any button down
KeymapStateMask	Keyboard state wanted at window entry and focus in
ExposureMask	Any exposure wanted
VisibilityChangeMask	Any change in visibility wanted
StructureNotifyMask	Any change in window structure wanted
ResizeRedirectMask	Redirect resize of this window
SubstructureNotifyMask	Substructure notification wanted
SubstructureRedirectMask	Redirect structure requests on children
FocusChangeMask	Any change in input focus wanted
PropertyChangeMask	Any change in property wanted
ColormapChangeMask	Any change in colormap wanted
OwnerGrabButtonMask	Automatic grabs should activate with owner_events set to True

Event Processing Overview

The event reported to a client application during event processing
depends on which event masks you provide as the event-mask attribute
for a window.
For some event masks, there is a one-to-one correspondence between
the event mask constant and the event type constant.
For example, if you pass the event mask
ButtonPressMask,
the X server sends back only
ButtonPress
events.

Most events contain a time member,
which is the time at which an event occurred.

In other cases, one event mask constant can map to several event type constants.
For example, if you pass the event mask
SubstructureNotifyMask,
the X server can send back
CirculateNotify,
ConfigureNotify,
CreateNotify,
DestroyNotify,
GravityNotify,
MapNotify,
ReparentNotify,
or
UnmapNotify
events.

In another case,
two event masks can map to one event type.
For example,
if you pass either
PointerMotionMask
or
ButtonMotionMask,
the X server sends back
a
MotionNotify
event.

The following table
lists the event mask,
its associated event type or types,
and the structure name associated with the event type.
Some of these structures actually are typedefs to a generic structure
that is shared between two event types.
Note that N.A. appears in columns for which the information is not applicable.

Event Mask	Event Type	Structure	Generic Structure
ButtonMotionMask Button1MotionMask Button2MotionMask Button3MotionMask Button4MotionMask Button5MotionMask	MotionNotify	XPointerMovedEvent	XMotionEvent
ButtonPressMask	ButtonPress	XButtonPressedEvent	XButtonEvent
ButtonReleaseMask	ButtonRelease	XButtonReleasedEvent	XButtonEvent
ColormapChangeMask	ColormapNotify	XColormapEvent
EnterWindowMask	EnterNotify	XEnterWindowEvent	XCrossingEvent
LeaveWindowMask	LeaveNotify	XLeaveWindowEvent	XCrossingEvent
ExposureMask	Expose	XExposeEvent
GCGraphicsExposures in GC	GraphicsExpose	XGraphicsExposeEvent
GCGraphicsExposures in GC	NoExpose	XNoExposeEvent
FocusChangeMask	FocusIn	XFocusInEvent	XFocusChangeEvent
FocusChangeMask	FocusOut	XFocusOutEvent	XFocusChangeEvent
KeymapStateMask	KeymapNotify	XKeymapEvent
KeyPressMask	KeyPress	XKeyPressedEvent	XKeyEvent
KeyReleaseMask	KeyRelease	XKeyReleasedEvent	XKeyEvent
OwnerGrabButtonMask	N.A.	N.A.
PointerMotionMask	MotionNotify	XPointerMovedEvent	XMotionEvent
PointerMotionHintMask	N.A.	N.A.
PropertyChangeMask	PropertyNotify	XPropertyEvent
ResizeRedirectMask	ResizeRequest	XResizeRequestEvent
StructureNotifyMask	CirculateNotify	XCirculateEvent
	ConfigureNotify	XConfigureEvent
	DestroyNotify	XDestroyWindowEvent
	GravityNotify	XGravityEvent
	MapNotify	XMapEvent
	ReparentNotify	XReparentEvent
	UnmapNotify	XUnmapEvent
SubstructureNotifyMask	CirculateNotify	XCirculateEvent
	ConfigureNotify	XConfigureEvent
	CreateNotify	XCreateWindowEvent
	DestroyNotify	XDestroyWindowEvent
	GravityNotify	XGravityEvent
	MapNotify	XMapEvent
	ReparentNotify	XReparentEvent
	UnmapNotify	XUnmapEvent
SubstructureRedirectMask	CirculateRequest	XCirculateRequestEvent
	ConfigureRequest	XConfigureRequestEvent
	MapRequest	XMapRequestEvent
N.A.	ClientMessage	XClientMessageEvent
N.A.	MappingNotify	XMappingEvent
N.A.	SelectionClear	XSelectionClearEvent
N.A.	SelectionNotify	XSelectionEvent
N.A.	SelectionRequest	XSelectionRequestEvent
VisibilityChangeMask	VisibilityNotify	XVisibilityEvent

The sections that follow describe the processing that occurs
when you select the different event masks.
The sections are organized according to these processing categories:

Keyboard and pointer events
Window crossing events
Input focus events
Keymap state notification events
Exposure events
Window state notification events
Structure control events
Colormap state notification events
Client communication events

Keyboard and Pointer Events

This section discusses:

Pointer button events
Keyboard and pointer events

Pointer Button Events

The following describes the event processing that occurs when a pointer button
press is processed with the pointer in some window w and
when no active pointer grab is in progress.

The X server searches the ancestors of w from the root down,
looking for a passive grab to activate.
If no matching passive grab on the button exists,
the X server automatically starts an active grab for the client receiving
the event and sets the last-pointer-grab time to the current server time.
The effect is essentially equivalent to an
XGrabButton
with these client passed arguments:

Argument	Value
w	The event window
event_mask	The client's selected pointer events on the event window
pointer_mode	GrabModeAsync
keyboard_mode	GrabModeAsync
owner_events	True, if the client has selected OwnerGrabButtonMask on the event window, otherwise False
confine_to	None
cursor	None

The active grab is automatically terminated when
the logical state of the pointer has all buttons released.
Clients can modify the active grab by calling
XUngrabPointer
and
XChangeActivePointerGrab.

Keyboard and Pointer Events

This section discusses the processing that occurs for the
keyboard events
KeyPress
and
KeyRelease
and the pointer events
ButtonPress,
ButtonRelease,
and
MotionNotify.
For information about the keyboard event-handling utilities,
see chapter 11.

The X server reports
KeyPress
or
KeyRelease
events to clients wanting information about keys that logically change state.
Note that these events are generated for all keys,
even those mapped to modifier bits.

The X server reports
ButtonPress
or
ButtonRelease
events to clients wanting information about buttons that logically change state.

The X server reports
MotionNotify
events to clients wanting information about when the pointer logically moves.
The X server generates this event whenever the pointer is moved
and the pointer motion begins and ends in the window.
The granularity of
MotionNotify
events is not guaranteed,
but a client that selects this event type is guaranteed
to receive at least one event when the pointer moves and then rests.

The generation of the logical changes lags the physical changes
if device event processing is frozen.

To receive
KeyPress,
KeyRelease,
ButtonPress,
and
ButtonRelease
events, set
KeyPressMask,
KeyReleaseMask,
ButtonPressMask,
and
ButtonReleaseMask
bits in the event-mask attribute of the window.

To receive
MotionNotify
events, set one or more of the following event
masks bits in the event-mask attribute of the window.

Button1MotionMask - Button5MotionMask
The client application receives
MotionNotify
events only when one or more of the specified buttons is pressed.
ButtonMotionMask
The client application receives
MotionNotify
events only when at least one button is pressed.
PointerMotionMask
The client application receives
MotionNotify
events independent of the state of
the pointer buttons.
PointerMotionHintMask
If
PointerMotionHintMask
is selected in combination with one or more of the above masks,
the X server is free to send only one
MotionNotify
event (with the is_hint member of the
XPointerMovedEvent
structure set to
NotifyHint)
to the client for the event window,
until either the key or button state changes,
the pointer leaves the event window, or the client calls
XQueryPointer
or
.
The server still may send
MotionNotify
events without is_hint set to
NotifyHint.

The source of the event is the viewable window that the pointer is in.
The window used by the X server to report these events depends on
the window's position in the window hierarchy
and whether any intervening window prohibits the generation of these events.
Starting with the source window,
the X server searches up the window hierarchy until it locates the first
window specified by a client as having an interest in these events.
If one of the intervening windows has its do-not-propagate-mask
set to prohibit generation of the event type,
the events of those types will be suppressed.
Clients can modify the actual window used for reporting by performing
active grabs and, in the case of keyboard events, by using the focus window.

The structures for these event types contain:

typedef struct {
     int            type;            /* ButtonPress or ButtonRelease */
     unsigned long  serial;          /* # of last request processed by server */
     Bool           send_event;      /* true if this came from a SendEvent request */
     Display        *display;        /* Display the event was read from */
     Window         window;          /* “event” window it is reported relative to */
     Window         root;            /* root window that the event occurred on */
     Window         subwindow;       /* child window */
     Time           time;            /* milliseconds */
     int            x, y;            /* pointer x, y coordinates in event window */
     int            x_root, y_root;  /* coordinates relative to root */
     unsigned int   state;           /* key or button mask */
     unsigned int   button;          /* detail */
     Bool           same_screen;     /* same screen flag */
} XButtonEvent;
typedef XButtonEvent XButtonPressedEvent;
typedef XButtonEvent XButtonReleasedEvent;

typedef struct {
     int            type;            /* KeyPress or KeyRelease */
     unsigned long  serial;          /* # of last request processed by server */
     Bool           send_event;      /* true if this came from a SendEvent request */
     Display        *display;        /* Display the event was read from */
     Window         window;          /* “event” window it is reported relative to */
     Window         root;            /* root window that the event occurred on */
     Window         subwindow;       /* child window */
     Time           time;            /* milliseconds */
     int            x, y;            /* pointer x, y coordinates in event window */
     int            x_root, y_root;  /* coordinates relative to root */
     unsigned int   state;           /* key or button mask */
     unsigned int   keycode;         /* detail */
     Bool           same_screen;     /* same screen flag */
} XKeyEvent;
typedef XKeyEvent XKeyPressedEvent;
typedef XKeyEvent XKeyReleasedEvent;

typedef struct {
     int            type;              /* MotionNotify */
     unsigned long  serial;            /* # of last request processed by server */
     Bool           send_event;        /* true if this came from a SendEvent request */
     Display        *display;          /* Display the event was read from */
     Window         window;            /* “event” window reported relative to */
     Window         root;              /* root window that the event occurred on */
     Window         subwindow;         /* child window */
     Time           time;              /* milliseconds */
     int            x, y;              /* pointer x, y coordinates in event window */
     int            x_root, y_root;    /* coordinates relative to root */
     unsigned int   state;             /* key or button mask */
     char           is_hint;           /* detail */
     Bool           same_screen;       /* same screen flag */
} XMotionEvent;
typedef XMotionEvent XPointerMovedEvent;

These structures have the following common members:
window, root, subwindow, time, x, y, x_root, y_root, state, and same_screen.
The window member is set to the window on which the
event was generated and is referred to as the event window.
As long as the conditions previously discussed are met,
this is the window used by the X server to report the event.
The root member is set to the source window's root window.
The x_root and y_root members are set to the pointer's coordinates
relative to the root window's origin at the time of the event.

The same_screen member is set to indicate whether the event
window is on the same screen
as the root window and can be either
True
or
False.
If
True,
the event and root windows are on the same screen.
If
False,
the event and root windows are not on the same screen.

If the source window is an inferior of the event window,
the subwindow member of the structure is set to the child of the event window
that is the source window or the child of the event window that is
an ancestor of the source window.
Otherwise, the X server sets the subwindow member to
None.
The time member is set to the time when the event was generated
and is expressed in milliseconds.

If the event window is on the same screen as the root window,
the x and y members
are set to the coordinates relative to the event window's origin.
Otherwise, these members are set to zero.

The state member is set to indicate the logical state of the pointer buttons
and modifier keys just prior to the event,
which is the bitwise inclusive OR of one or more of the
button or modifier key masks:
Button1Mask,
Button2Mask,
Button3Mask,
Button4Mask,
Button5Mask,
ShiftMask,
LockMask,
ControlMask,
Mod1Mask,
Mod2Mask,
Mod3Mask,
Mod4Mask,
and
Mod5Mask.

Each of these structures also has a member that indicates the detail.
For the
XKeyPressedEvent
and
XKeyReleasedEvent
structures, this member is called a keycode.
It is set to a number that represents a physical key on the keyboard.
The keycode is an arbitrary representation for any key on the keyboard
(see sections 12.7
and 16.1).

For the
XButtonPressedEvent
and
XButtonReleasedEvent
structures, this member is called button.
It represents the pointer button that changed state and can be the
Button1,
Button2,
Button3,
Button4,
or
Button5
value.
For the
XPointerMovedEvent
structure, this member is called is_hint.
It can be set to
NotifyNormal
or
NotifyHint.

Some of the symbols mentioned in this section have fixed values, as
follows:

Symbol	Value
Button1MotionMask	(1L<<8)
Button2MotionMask	(1L<<9)
Button3MotionMask	(1L<<10)
Button4MotionMask	(1L<<11)
Button5MotionMask	(1L<<12)
Button1Mask	(1<<8)
Button2Mask	(1<<9)
Button3Mask	(1<<10)
Button4Mask	(1<<11)
Button5Mask	(1<<12)
ShiftMask	(1<<0)
LockMask	(1<<1)
ControlMask	(1<<2)
Mod1Mask	(1<<3)
Mod2Mask	(1<<4)
Mod3Mask	(1<<5)
Mod4Mask	(1<<6)
Mod5Mask	(1<<7)
Button1	1
Button2	2
Button3	3
Button4	4
Button5	5

Window Entry/Exit Events

This section describes the processing that
occurs for the window crossing events
EnterNotify
and
LeaveNotify.

If a pointer motion or a window hierarchy change causes the
pointer to be in a different window than before, the X server reports
EnterNotify
or
LeaveNotify
events to clients who have selected for these events.
All
EnterNotify
and
LeaveNotify
events caused by a hierarchy change are
generated after any hierarchy event
(UnmapNotify,
MapNotify,
ConfigureNotify,
GravityNotify,
CirculateNotify)
caused by that change;
however, the X protocol does not constrain the ordering of
EnterNotify
and
LeaveNotify
events with respect to
FocusOut,
VisibilityNotify,
and
Expose
events.

This contrasts with
MotionNotify
events, which are also generated when the pointer moves
but only when the pointer motion begins and ends in a single window.
An
EnterNotify
or
LeaveNotify
event also can be generated when some client application calls
XGrabPointer
and
XUngrabPointer.

To receive
EnterNotify
or
LeaveNotify
events, set the
EnterWindowMask
or
LeaveWindowMask
bits of the event-mask attribute of the window.

The structure for these event types contains:


typedef struct {
     int           type;           /* EnterNotify or LeaveNotify */
     unsigned long serial;         /* # of last request processed by server */
     Bool          send_event;     /* true if this came from a SendEvent request */
     Display       *display;       /* Display the event was read from */
     Window        window;         /* “event” window reported relative to */
     Window        root;           /* root window that the event occurred on */
     Window        subwindow;      /* child window */
     Time          time;           /* milliseconds */
     int           x, y;           /* pointer x, y coordinates in event window */
     int           x_root, y_root; /* coordinates relative to root */
     int           mode;           /* NotifyNormal, NotifyGrab, NotifyUngrab */
     int           detail;
                   /*
                    * NotifyAncestor, NotifyVirtual, NotifyInferior, 
                    * NotifyNonlinear,NotifyNonlinearVirtual
                    */
     Bool          same_screen;    /* same screen flag */
     Bool          focus;          /* boolean focus */
     unsigned int  state;          /* key or button mask */
} XCrossingEvent;
typedef XCrossingEvent XEnterWindowEvent;
typedef XCrossingEvent XLeaveWindowEvent;

The window member is set to the window on which the
EnterNotify
or
LeaveNotify
event was generated and is referred to as the event window.
This is the window used by the X server to report the event,
and is relative to the root
window on which the event occurred.
The root member is set to the root window of the screen
on which the event occurred.

For a
LeaveNotify
event,
if a child of the event window contains the initial position of the pointer,
the subwindow component is set to that child.
Otherwise, the X server sets the subwindow member to
None.
For an
EnterNotify
event, if a child of the event window contains the final pointer position,
the subwindow component is set to that child or
None.

The time member is set to the time when the event was generated
and is expressed in milliseconds.
The x and y members are set to the coordinates of the pointer position in
the event window.
This position is always the pointer's final position,
not its initial position.
If the event window is on the same
screen as the root window, x and y are the pointer coordinates
relative to the event window's origin.
Otherwise, x and y are set to zero.
The x_root and y_root members are set to the pointer's coordinates relative to the
root window's origin at the time of the event.

The same_screen member is set to indicate whether the event window is on the same screen
as the root window and can be either
True
or
False.
If
True,
the event and root windows are on the same screen.
If
False,
the event and root windows are not on the same screen.

The focus member is set to indicate whether the event window is the focus window or an
inferior of the focus window.
The X server can set this member to either
True
or
False.
If
True,
the event window is the focus window or an inferior of the focus window.
If
False,
the event window is not the focus window or an inferior of the focus window.

The state member is set to indicate the state of the pointer buttons and
modifier keys just prior to the
event.
The X server can set this member to the bitwise inclusive OR of one
or more of the button or modifier key masks:
Button1Mask,
Button2Mask,
Button3Mask,
Button4Mask,
Button5Mask,
ShiftMask,
LockMask,
ControlMask,
Mod1Mask,
Mod2Mask,
Mod3Mask,
Mod4Mask,
Mod5Mask.

The mode member is set to indicate whether the events are normal events,
pseudo-motion events
when a grab activates, or pseudo-motion events when a grab deactivates.
The X server can set this member to
NotifyNormal,
NotifyGrab,
or
NotifyUngrab.

The detail member is set to indicate the notify detail and can be
NotifyAncestor,
NotifyVirtual,
NotifyInferior,
NotifyNonlinear,
or
NotifyNonlinearVirtual.

Normal Entry/Exit Events

EnterNotify
and
LeaveNotify
events are generated when the pointer moves from
one window to another window.
Normal events are identified by
XEnterWindowEvent
or
XLeaveWindowEvent
structures whose mode member is set to
NotifyNormal.

When the pointer moves from window A to window B and A is an inferior of B,
the X server does the following:
It generates a
LeaveNotify
event on window A, with the detail member of the
XLeaveWindowEvent
structure set to
NotifyAncestor.
It generates a
LeaveNotify
event on each window between window A and window B, exclusive,
with the detail member of each
XLeaveWindowEvent
structure set to
NotifyVirtual.
It generates an
EnterNotify
event on window B, with the detail member of the
XEnterWindowEvent
structure set to
NotifyInferior.
When the pointer moves from window A to window B and B is an inferior of A,
the X server does the following:
It generates a
LeaveNotify
event on window A,
with the detail member of the
XLeaveWindowEvent
structure set to
NotifyInferior.
It generates an
EnterNotify
event on each window between window A and window B, exclusive, with the
detail member of each
XEnterWindowEvent
structure set to
NotifyVirtual.
It generates an
EnterNotify
event on window B, with the detail member of the
XEnterWindowEvent
structure set to
NotifyAncestor.
When the pointer moves from window A to window B
and window C is their least common ancestor,
the X server does the following:
It generates a
LeaveNotify
event on window A,
with the detail member of the
XLeaveWindowEvent
structure set to
NotifyNonlinear.
It generates a
LeaveNotify
event on each window between window A and window C, exclusive,
with the detail member of each
XLeaveWindowEvent
structure set to
NotifyNonlinearVirtual.
It generates an
EnterNotify
event on each window between window C and window B, exclusive,
with the detail member of each
XEnterWindowEvent
structure set to
NotifyNonlinearVirtual.
It generates an
EnterNotify
event on window B, with the detail member of the
XEnterWindowEvent
structure set to
NotifyNonlinear.
When the pointer moves from window A to window B on different screens,
the X server does the following:
It generates a
LeaveNotify
event on window A,
with the detail member of the
XLeaveWindowEvent
structure set to
NotifyNonlinear.
If window A is not a root window,
it generates a
LeaveNotify
event on each window above window A up to and including its root,
with the detail member of each
XLeaveWindowEvent
structure set to
NotifyNonlinearVirtual.
If window B is not a root window,
it generates an
EnterNotify
event on each window from window B's root down to but not including
window B, with the detail member of each
XEnterWindowEvent
structure set to
NotifyNonlinearVirtual.
It generates an
EnterNotify
event on window B, with the detail member of the
XEnterWindowEvent
structure set to
NotifyNonlinear.

Grab and Ungrab Entry/Exit Events

Pseudo-motion mode
EnterNotify
and
LeaveNotify
events are generated when a pointer grab activates or deactivates.
Events in which the pointer grab activates
are identified by
XEnterWindowEvent
or
XLeaveWindowEvent
structures whose mode member is set to
NotifyGrab.
Events in which the pointer grab deactivates
are identified by
XEnterWindowEvent
or
XLeaveWindowEvent
structures whose mode member is set to
NotifyUngrab
(see
XGrabPointer).

When a pointer grab activates after any initial warp into a confine_to
window and before generating any actual
ButtonPress
event that activates the grab,
G is the grab_window for the grab,
and P is the window the pointer is in,
the X server does the following:
It generates
EnterNotify
and
LeaveNotify
events (see section 10.6.1)
with the mode members of the
XEnterWindowEvent
and
XLeaveWindowEvent
structures set to
NotifyGrab.
These events are generated
as if the pointer were to suddenly warp from
its current position in P to some position in G.
However, the pointer does not warp, and the X server uses the pointer position
as both the initial and final positions for the events.
When a pointer grab deactivates after generating any actual
ButtonRelease
event that deactivates the grab,
G is the grab_window for the grab,
and P is the window the pointer is in,
the X server does the following:
It generates
EnterNotify
and
LeaveNotify
events (see section 10.6.1)
with the mode members of the
XEnterWindowEvent
and
XLeaveWindowEvent
structures set to
NotifyUngrab.
These events are generated as if the pointer were to suddenly warp from
some position in G to its current position in P.
However, the pointer does not warp, and the X server uses the
current pointer position as both the
initial and final positions for the events.

Input Focus Events

This section describes the processing that occurs for the input focus events
FocusIn
and
FocusOut.

The X server can report
FocusIn
or
FocusOut
events to clients wanting information about when the input focus changes.
The keyboard is always attached to some window
(typically, the root window or a top-level window),
which is called the focus window.
The focus window and the position of the pointer determine the window that
receives keyboard input.
Clients may need to know when the input focus changes
to control highlighting of areas on the screen.

To receive
FocusIn
or
FocusOut
events, set the
FocusChangeMask
bit in the event-mask attribute of the window.

The structure for these event types contains:


typedef struct {
     int           type;       /* FocusIn or FocusOut */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        window;     /* window of event */
     int           mode;       /* NotifyNormal, NotifyGrab, NotifyUngrab */
     int           detail;
                   /*
                    * NotifyAncestor, NotifyVirtual, NotifyInferior, 
                    * NotifyNonlinear,NotifyNonlinearVirtual, NotifyPointer,
                    * NotifyPointerRoot, NotifyDetailNone 
                    */
} XFocusChangeEvent;
typedef XFocusChangeEvent XFocusInEvent;
typedef XFocusChangeEvent XFocusOutEvent;

The window member is set to the window on which the
FocusIn
or
FocusOut
event was generated.
This is the window used by the X server to report the event.
The mode member is set to indicate whether the focus events
are normal focus events,
focus events while grabbed,
focus events
when a grab activates, or focus events when a grab deactivates.
The X server can set the mode member to
NotifyNormal,
NotifyWhileGrabbed,
NotifyGrab,
or
NotifyUngrab.

All
FocusOut
events caused by a window unmap are generated after any
UnmapNotify
event; however, the X protocol does not constrain the ordering of
FocusOut
events with respect to
generated
EnterNotify,
LeaveNotify,
VisibilityNotify,
and
Expose
events.

Depending on the event mode,
the detail member is set to indicate the notify detail and can be
NotifyAncestor,
NotifyVirtual,
NotifyInferior,
NotifyNonlinear,
NotifyNonlinearVirtual,
NotifyPointer,
NotifyPointerRoot,
or
NotifyDetailNone.

Normal Focus Events and Focus Events While Grabbed

Normal focus events are identified by
XFocusInEvent
or
XFocusOutEvent
structures whose mode member is set to
NotifyNormal.
Focus events while grabbed are identified by
XFocusInEvent
or
XFocusOutEvent
structures whose mode member is set to
NotifyWhileGrabbed.
The X server processes normal focus and focus events while grabbed according to
the following:

When the focus moves from window A to window B, A is an inferior of B,
and the pointer is in window P,
the X server does the following:
It generates a
FocusOut
event on window A, with the detail member of the
XFocusOutEvent
structure set to
NotifyAncestor.
It generates a
FocusOut
event on each window between window A and window B, exclusive,
with the detail member of each
XFocusOutEvent
structure set to
NotifyVirtual.
It generates a
FocusIn
event on window B, with the detail member of the
XFocusOutEvent
structure set to
NotifyInferior.
If window P is an inferior of window B
but window P is not window A or an inferior or ancestor of window A,
it generates a
FocusIn
event on each window below window B, down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.
When the focus moves from window A to window B, B is an inferior of A,
and the pointer is in window P,
the X server does the following:
If window P is an inferior of window A
but P is not an inferior of window B or an ancestor of B,
it generates a
FocusOut
event on each window from window P up to but not including window A,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.
It generates a
FocusOut
event on window A,
with the detail member of the
XFocusOutEvent
structure set to
NotifyInferior.
It generates a
FocusIn
event on each window between window A and window B, exclusive, with the
detail member of each
XFocusInEvent
structure set to
NotifyVirtual.
It generates a
FocusIn
event on window B, with the detail member of the
XFocusInEvent
structure set to
NotifyAncestor.
When the focus moves from window A to window B,
window C is their least common ancestor,
and the pointer is in window P,
the X server does the following:
If window P is an inferior of window A,
it generates a
FocusOut
event on each window from window P up to but not including window A,
with the detail member of the
XFocusOutEvent
structure set to
NotifyPointer.
It generates a
FocusOut
event on window A,
with the detail member of the
XFocusOutEvent
structure set to
NotifyNonlinear.
It generates a
FocusOut
event on each window between window A and window C, exclusive,
with the detail member of each
XFocusOutEvent
structure set to
NotifyNonlinearVirtual.
It generates a
FocusIn
event on each window between C and B, exclusive,
with the detail member of each
XFocusInEvent
structure set to
NotifyNonlinearVirtual.
It generates a
FocusIn
event on window B, with the detail member of the
XFocusInEvent
structure set to
NotifyNonlinear.
If window P is an inferior of window B, it generates a
FocusIn
event on each window below window B down to and including window P,
with the detail member of the
XFocusInEvent
structure set to
NotifyPointer.
When the focus moves from window A to window B on different screens
and the pointer is in window P,
the X server does the following:
If window P is an inferior of window A, it generates a
FocusOut
event on each window from window P up to but not including window A,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.
It generates a
FocusOut
event on window A,
with the detail member of the
XFocusOutEvent
structure set to
NotifyNonlinear.
If window A is not a root window,
it generates a
FocusOut
event on each window above window A up to and including its root,
with the detail member of each
XFocusOutEvent
structure set to
NotifyNonlinearVirtual.
If window B is not a root window,
it generates a
FocusIn
event on each window from window B's root down to but not including
window B, with the detail member of each
XFocusInEvent
structure set to
NotifyNonlinearVirtual.
It generates a
FocusIn
event on window B, with the detail member of each
XFocusInEvent
structure set to
NotifyNonlinear.
If window P is an inferior of window B, it generates a
FocusIn
event on each window below window B down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.
When the focus moves from window A to
PointerRoot
(events sent to the window under the pointer)
or
None
(discard), and the pointer is in window P,
the X server does the following:
If window P is an inferior of window A, it generates a
FocusOut
event on each window from window P up to but not including window A,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.
It generates a
FocusOut
event on window A, with the detail member of the
XFocusOutEvent
structure set to
NotifyNonlinear.
If window A is not a root window,
it generates a
FocusOut
event on each window above window A up to and including its root,
with the detail member of each
XFocusOutEvent
structure set to
NotifyNonlinearVirtual.
It generates a
FocusIn
event on the root window of all screens, with the detail member of each
XFocusInEvent
structure set to
NotifyPointerRoot
(or
NotifyDetailNone).
If the new focus is
PointerRoot,
it generates a
FocusIn
event on each window from window P's root down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.
When the focus moves from
PointerRoot
(events sent to the window under the pointer)
or
None
to window A, and the pointer is in window P,
the X server does the following:
If the old focus is
PointerRoot,
it generates a
FocusOut
event on each window from window P up to and including window P's root,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.
It generates a
FocusOut
event on all root windows,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointerRoot
(or
NotifyDetailNone).
If window A is not a root window,
it generates a
FocusIn
event on each window from window A's root down to but not including window A,
with the detail member of each
XFocusInEvent
structure set to
NotifyNonlinearVirtual.
It generates a
FocusIn
event on window A,
with the detail member of the
XFocusInEvent
structure set to
NotifyNonlinear.
If window P is an inferior of window A, it generates a
FocusIn
event on each window below window A down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.
When the focus moves from
PointerRoot
(events sent to the window under the pointer)
to
None
(or vice versa), and the pointer is in window P,
the X server does the following:
If the old focus is
PointerRoot,
it generates a
FocusOut
event on each window from window P up to and including window P's root,
with the detail member of each
XFocusOutEvent
structure set to
NotifyPointer.
It generates a
FocusOut
event on all root windows,
with the detail member of each
XFocusOutEvent
structure set to either
NotifyPointerRoot
or
NotifyDetailNone.
It generates a
FocusIn
event on all root windows,
with the detail member of each
XFocusInEvent
structure set to
NotifyDetailNone
or
NotifyPointerRoot.
If the new focus is
PointerRoot,
it generates a
FocusIn
event on each window from window P's root down to and including window P,
with the detail member of each
XFocusInEvent
structure set to
NotifyPointer.

Focus Events Generated by Grabs

Focus events in which the keyboard grab activates
are identified by
XFocusInEvent
or
XFocusOutEvent
structures whose mode member is set to
NotifyGrab.
Focus events in which the keyboard grab deactivates
are identified by
XFocusInEvent
or
XFocusOutEvent
structures whose mode member is set to
NotifyUngrab
(see
XGrabKeyboard).

When a keyboard grab activates before generating any actual
KeyPress
event that activates the grab,
G is the grab_window, and F is the current focus,
the X server does the following:
It generates
FocusIn
and
FocusOut
events, with the mode members of the
XFocusInEvent
and
XFocusOutEvent
structures set to
NotifyGrab.
These events are generated
as if the focus were to change from
F to G.
When a keyboard grab deactivates after generating any actual
KeyRelease
event that deactivates the grab,
G is the grab_window, and F is the current focus,
the X server does the following:
It generates
FocusIn
and
FocusOut
events, with the mode members of the
XFocusInEvent
and
XFocusOutEvent
structures set to
NotifyUngrab.
These events are generated
as if the focus were to change from
G to F.

Key Map State Notification Events

The X server can report
KeymapNotify
events to clients that want information about changes in their keyboard state.

To receive
KeymapNotify
events, set the
KeymapStateMask
bit in the event-mask attribute of the window.
The X server generates this event immediately after every
EnterNotify
and
FocusIn
event.

The structure for this event type contains:


/* generated on EnterWindow and FocusIn when KeymapState selected */
typedef struct {
     int            type;           /* KeymapNotify */
     unsigned long  serial;         /* # of last request processed by server */
     Bool           send_event;     /* true if this came from a SendEvent request */
     Display        *display;       /* Display the event was read from */
     Window         window;
     char           key_vector[32];
} XKeymapEvent;

The window member is not used but is present to aid some toolkits.
The key_vector member is set to the bit vector of the keyboard.
Each bit set to 1 indicates that the corresponding key
is currently pressed.
The vector is represented as 32 bytes.
Byte N (from 0) contains the bits for keys 8N to 8N + 7
with the least significant bit in the byte representing key 8N.

Exposure Events

The X protocol does not guarantee to preserve the contents of window
regions when
the windows are obscured or reconfigured.
Some implementations may preserve the contents of windows.
Other implementations are free to destroy the contents of windows
when exposed.
X expects client applications to assume the responsibility for
restoring the contents of an exposed window region.
(An exposed window region describes a formerly obscured window whose
region becomes visible.)
Therefore, the X server sends
Expose
events describing the window and the region of the window that has been exposed.
A naive client application usually redraws the entire window.
A more sophisticated client application redraws only the exposed region.

Expose Events

The X server can report
Expose
events to clients wanting information about when the contents of window regions
have been lost.
The circumstances in which the X server generates
Expose
events are not as definite as those for other events.
However, the X server never generates
Expose
events on windows whose class you specified as
InputOnly.
The X server can generate
Expose
events when no valid contents are available for regions of a window
and either the regions are visible,
the regions are viewable and the server is (perhaps newly) maintaining
backing store on the window,
or the window is not viewable but the server is (perhaps newly) honoring the
window's backing-store attribute of
Always
or
WhenMapped.
The regions decompose into an (arbitrary) set of rectangles,
and an
Expose
event is generated for each rectangle.
For any given window,
the X server guarantees to report contiguously
all of the regions exposed by some action that causes
Expose
events, such as raising a window.

To receive
Expose
events, set the
ExposureMask
bit in the event-mask attribute of the window.

The structure for this event type contains:


typedef struct {
     int           type;           /* Expose */
     unsigned long serial;         /* # of last request processed by server */
     Bool          send_event;     /* true if this came from a SendEvent request */
     Display       *display;       /* Display the event was read from */
     Window        window;
     int           x, y;
     int           width, height;
     int           count;          /* if nonzero, at least this many more */
} XExposeEvent;

The window member is set to the exposed (damaged) window.
The x and y members are set to the coordinates relative to the window's origin
and indicate the upper-left corner of the rectangle.
The width and height members are set to the size (extent) of the rectangle.
The count member is set to the number of
Expose
events that are to follow.
If count is zero, no more
Expose
events follow for this window.
However, if count is nonzero, at least that number of
Expose
events (and possibly more) follow for this window.
Simple applications that do not want to optimize redisplay by distinguishing
between subareas of its window can just ignore all
Expose
events with nonzero counts and perform full redisplays
on events with zero counts.

GraphicsExpose and NoExpose Events

The X server can report
GraphicsExpose
events to clients wanting information about when a destination region could not
be computed during certain graphics requests:
XCopyArea
or
XCopyPlane.
The X server generates this event whenever a destination region could not be
computed because of an obscured or out-of-bounds source region.
In addition, the X server guarantees to report contiguously all of the regions exposed by
some graphics request
(for example, copying an area of a drawable to a destination
drawable).

The X server generates a
NoExpose
event whenever a graphics request that might
produce a
GraphicsExpose
event does not produce any.
In other words, the client is really asking for a
GraphicsExpose
event but instead receives a
NoExpose
event.

To receive
GraphicsExpose
or
NoExpose
events, you must first set the graphics-exposure
attribute of the graphics context to
True.
You also can set the graphics-expose attribute when creating a graphics
context using
XCreateGC
or by calling
XSetGraphicsExposures.

The structures for these event types contain:


typedef struct {
     int            type;           /* GraphicsExpose */
     unsigned long  serial;         /* # of last request processed by server */
     Bool           send_event;     /* true if this came from a SendEvent request */
     Display        *display;       /* Display the event was read from */
     Drawable       drawable;
     int            x, y;
     int            width, height;
     int            count;          /* if nonzero, at least this many more */
     int            major_code;     /* core is CopyArea or CopyPlane */
     int            minor_code;     /* not defined in the core */
} XGraphicsExposeEvent;


typedef struct {
     int           type;         /* NoExpose */
     unsigned long serial;       /* # of last request processed by server */
     Bool          send_event;   /* true if this came from a SendEvent request */
     Display       *display;     /* Display the event was read from */
     Drawable      drawable;
     int           major_code;   /* core is CopyArea or CopyPlane */
     int           minor_code;   /* not defined in the core */
} XNoExposeEvent;

Both structures have these common members: drawable, major_code, and minor_code.
The drawable member is set to the drawable of the destination region on
which the graphics request was to be performed.
The major_code member is set to the graphics request initiated by the client
and can be either
X_CopyArea
or
X_CopyPlane.
If it is
X_CopyArea,
a call to
XCopyArea
initiated the request.
If it is
X_CopyPlane,
a call to
XCopyPlane
initiated the request.
These constants are defined in
<X11/Xproto.h>.

The minor_code member,
like the major_code member,
indicates which graphics request was initiated by
the client.
However, the minor_code member is not defined by the core
X protocol and will be zero in these cases,
although it may be used by an extension.

The
XGraphicsExposeEvent
structure has these additional members: x, y, width, height, and count.
The x and y members are set to the coordinates relative to the drawable's origin
and indicate the upper-left corner of the rectangle.
The width and height members are set to the size (extent) of the rectangle.
The count member is set to the number of
GraphicsExpose
events to follow.
If count is zero, no more
GraphicsExpose
events follow for this window.
However, if count is nonzero, at least that number of
GraphicsExpose
events (and possibly more) are to follow for this window.

Window State Change Events

The following sections discuss:

CirculateNotify
events
ConfigureNotify
events
CreateNotify
events
DestroyNotify
events
GravityNotify
events
MapNotify
events
MappingNotify
events
ReparentNotify
events
UnmapNotify
events
VisibilityNotify
events

CirculateNotify Events

The X server can report
CirculateNotify
events to clients wanting information about when a window changes
its position in the stack.
The X server generates this event type whenever a window is actually restacked
as a result of a client application calling
XCirculateSubwindows,
XCirculateSubwindowsUp,
or
XCirculateSubwindowsDown.

To receive
CirculateNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window
or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, circulating any child generates an event).

The structure for this event type contains:


typedef struct {
     int type;     /* CirculateNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool send_event;     /* true if this came from a SendEvent request */
     Display *display;     /* Display the event was read from */
     Window event;
     Window window;
     int place;     /* PlaceOnTop, PlaceOnBottom */
} XCirculateEvent;

The event member is set either to the restacked window or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window that was restacked.
The place member is set to the window's position after the restack occurs and
is either
PlaceOnTop
or
PlaceOnBottom.
If it is
PlaceOnTop,
the window is now on top of all siblings.
If it is
PlaceOnBottom,
the window is now below all siblings.

ConfigureNotify Events

The X server can report
ConfigureNotify
events to clients wanting information about actual changes to a window's
state, such as size, position, border, and stacking order.
The X server generates this event type whenever one of the following configure
window requests made by a client application actually completes:

A window's size, position, border, and/or stacking order is reconfigured
by calling
XConfigureWindow.
The window's position in the stacking order is changed by calling
XLowerWindow,
XRaiseWindow,
or
XRestackWindows.
A window is moved by calling
XMoveWindow.
A window's size is changed by calling
XResizeWindow.
A window's size and location is changed by calling
XMoveResizeWindow.
A window is mapped and its position in the stacking order is changed
by calling
XMapRaised.
A window's border width is changed by calling
XSetWindowBorderWidth.

To receive
ConfigureNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, configuring any child generates an event).

The structure for this event type contains:


typedef struct {
     int           type;       /* ConfigureNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        event;
     Window        window;
     int           x, y;
     int           width, height;
     int           border_width;
     Window        above;
     Bool          override_redirect;
} XConfigureEvent;

The event member is set either to the reconfigured window or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window whose size, position,
border, and/or stacking
order was changed.

The x and y members are set to the coordinates relative to the parent window's
origin and indicate the position of the upper-left outside corner of the window.
The width and height members are set to the inside size of the window,
not including
the border.
The border_width member is set to the width of the window's border, in pixels.

The above member is set to the sibling window and is used
for stacking operations.
If the X server sets this member to
None,
the window whose state was changed is on the bottom of the stack
with respect to sibling windows.
However, if this member is set to a sibling window,
the window whose state was changed is placed on top of this sibling window.

The override_redirect member is set to the override-redirect attribute of the
window.
Window manager clients normally should ignore this window if the
override_redirect member
is
True.

CreateNotify Events

The X server can report
CreateNotify
events to clients wanting information about creation of windows.
The X server generates this event whenever a client
application creates a window by calling
XCreateWindow
or
XCreateSimpleWindow.

To receive
CreateNotify
events, set the
SubstructureNotifyMask
bit in the event-mask attribute of the window.
Creating any children then generates an event.

The structure for the event type contains:


typedef struct {
     int           type;               /* CreateNotify */
     unsigned long serial;             /* # of last request processed by server */
     Bool          send_event;         /* true if this came from a SendEvent request */
     Display       *display;           /* Display the event was read from */
     Window        parent;             /* parent of the window */
     Window        window;             /* window id of window created */
     int           x, y;               /* window location */
     int           width, height;      /* size of window */
     int           border_width;       /* border width */
     Bool          override_redirect;  /* creation should be overridden */
} XCreateWindowEvent;

The parent member is set to the created window's parent.
The window member specifies the created window.
The x and y members are set to the created window's coordinates relative
to the parent window's origin and indicate the position of the upper-left
outside corner of the created window.
The width and height members are set to the inside size of the created window
(not including the border) and are always nonzero.
The border_width member is set to the width of the created window's border, in pixels.
The override_redirect member is set to the override-redirect attribute of the
window.
Window manager clients normally should ignore this window
if the override_redirect member is
True.

DestroyNotify Events

The X server can report
DestroyNotify
events to clients wanting information about which windows are destroyed.
The X server generates this event whenever a client application destroys a
window by calling
XDestroyWindow
or
XDestroySubwindows.

The ordering of the
DestroyNotify
events is such that for any given window,
DestroyNotify
is generated on all inferiors of the window
before being generated on the window itself.
The X protocol does not constrain the ordering among
siblings and across subhierarchies.

To receive
DestroyNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, destroying any child generates an event).

The structure for this event type contains:


typedef struct {
     int           type;       /* DestroyNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        event;
     Window        window;
} XDestroyWindowEvent;

The event member is set either to the destroyed window or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window that is destroyed.

GravityNotify Events

The X server can report
GravityNotify
events to clients wanting information about when a window is moved because of a
change in the size of its parent.
The X server generates this event whenever a client
application actually moves a child window as a result of resizing its parent by calling
XConfigureWindow,
XMoveResizeWindow,
or
XResizeWindow.

To receive
GravityNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, any child that is moved because its parent has been resized
generates an event).

The structure for this event type contains:


typedef struct {
     int           type;       /* GravityNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        event;
     Window        window;
     int           x, y;
} XGravityEvent;

The event member is set either to the window that was moved or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the child window that was moved.
The x and y members are set to the coordinates relative to the
new parent window's origin
and indicate the position of the upper-left outside corner of the
window.

MapNotify Events

The X server can report
MapNotify
events to clients wanting information about which windows are mapped.
The X server generates this event type whenever a client application changes the
window's state from unmapped to mapped by calling
XMapWindow,
XMapRaised,
XMapSubwindows,
XReparentWindow,
or as a result of save-set processing.

To receive
MapNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, mapping any child generates an event).

The structure for this event type contains:


typedef struct {
     int           type;                  /* MapNotify */
     unsigned long serial;                /* # of last request processed by server */
     Bool          send_event;            /* true if this came from a SendEvent request */
     Display       *display;              /* Display the event was read from */
     Window        event;
     Window        window;
     Bool          override_redirect;     /* boolean, is override set... */
} XMapEvent;

The event member is set either to the window that was mapped or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window that was mapped.
The override_redirect member is set to the override-redirect attribute
of the window.
Window manager clients normally should ignore this window
if the override-redirect attribute is
True,
because these events usually are generated from pop-ups,
which override structure control.

MappingNotify Events

The X server reports
MappingNotify
events to all clients.
There is no mechanism to express disinterest in this event.
The X server generates this event type whenever a client application
successfully calls:

XSetModifierMapping
to indicate which KeyCodes are to be used as modifiers
XChangeKeyboardMapping
to change the keyboard mapping
XSetPointerMapping
to set the pointer mapping

The structure for this event type contains:


typedef struct {
     int           type;           /* MappingNotify */
     unsigned long serial;         /* # of last request processed by server */
     Bool          send_event;     /* true if this came from a SendEvent request */
     Display       *display;       /* Display the event was read from */
     Window        window;         /* unused */
     int           request;        /* one of MappingModifier, MappingKeyboard,
                   MappingPointer  */
     int           first_keycode;  /* first keycode */
     int           count;          /* defines range of change w. first_keycode*/
} XMappingEvent;

The request member is set to indicate the kind of mapping change that occurred
and can be
MappingModifier,
MappingKeyboard,
or
MappingPointer.
If it is
MappingModifier,
the modifier mapping was changed.
If it is
MappingKeyboard,
the keyboard mapping was changed.
If it is
MappingPointer,
the pointer button mapping was changed.
The first_keycode and count members are set only
if the request member was set to
MappingKeyboard.
The number in first_keycode represents the first number in the range
of the altered mapping,
and count represents the number of keycodes altered.

To update the client application's knowledge of the keyboard,
you should call
XRefreshKeyboardMapping.

ReparentNotify Events

The X server can report
ReparentNotify
events to clients wanting information about changing a window's parent.
The X server generates this event whenever a client
application calls
XReparentWindow
and the window is actually reparented.

To receive
ReparentNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of either the old or the new parent window
(in which case, reparenting any child generates an event).

The structure for this event type contains:


typedef struct {
     int           type;       /* ReparentNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        event;
     Window        window;
     Window        parent;
     int           x, y;
     Bool          override_redirect;
} XReparentEvent;

The event member is set either to the reparented window
or to the old or the new parent, depending on whether
StructureNotify
or
SubstructureNotify
was selected.
The window member is set to the window that was reparented.
The parent member is set to the new parent window.
The x and y members are set to the reparented window's coordinates relative
to the new parent window's
origin and define the upper-left outer corner of the reparented window.
The override_redirect member is set to the override-redirect attribute of the
window specified by the window member.
Window manager clients normally should ignore this window
if the override_redirect member is
True.

UnmapNotify Events

The X server can report
UnmapNotify
events to clients wanting information about which windows are unmapped.
The X server generates this event type whenever a client application changes the
window's state from mapped to unmapped.

To receive
UnmapNotify
events, set the
StructureNotifyMask
bit in the event-mask attribute of the window or the
SubstructureNotifyMask
bit in the event-mask attribute of the parent window
(in which case, unmapping any child window generates an event).

The structure for this event type contains:


typedef struct {
     int           type;       /* UnmapNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        event;
     Window        window;
     Bool          from_configure;
} XUnmapEvent;

The event member is set either to the unmapped window or to its parent,
depending on whether
StructureNotify
or
SubstructureNotify
was selected.
This is the window used by the X server to report the event.
The window member is set to the window that was unmapped.
The from_configure member is set to
True
if the event was generated as a result of a resizing of the window's parent when
the window itself had a win_gravity of
UnmapGravity.

VisibilityNotify Events

The X server can report
VisibilityNotify
events to clients wanting any change in the visibility of the specified window.
A region of a window is visible if someone looking at the screen can
actually see it.
The X server generates this event whenever the visibility changes state.
However, this event is never generated for windows whose class is
InputOnly.

All
VisibilityNotify
events caused by a hierarchy change are generated
after any hierarchy event
(UnmapNotify,
MapNotify,
ConfigureNotify,
GravityNotify,
CirculateNotify)
caused by that change. Any
VisibilityNotify
event on a given window is generated before any
Expose
events on that window, but it is not required that all
VisibilityNotify
events on all windows be generated before all
Expose
events on all windows.
The X protocol does not constrain the ordering of
VisibilityNotify
events with
respect to
FocusOut,
EnterNotify,
and
LeaveNotify
events.

To receive
VisibilityNotify
events, set the
VisibilityChangeMask
bit in the event-mask attribute of the window.

The structure for this event type contains:


typedef struct {
     int           type;       /* VisibilityNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        window;
     int           state;
} XVisibilityEvent;

The window member is set to the window whose visibility state changes.
The state member is set to the state of the window's visibility and can be
VisibilityUnobscured,
VisibilityPartiallyObscured,
or
VisibilityFullyObscured.
The X server ignores all of a window's subwindows
when determining the visibility state of the window and processes
VisibilityNotify
events according to the following:

When the window changes state from partially obscured, fully obscured,
or not viewable to viewable and completely unobscured,
the X server generates the event with the state member of the
XVisibilityEvent
structure set to
VisibilityUnobscured.
When the window changes state from viewable and completely unobscured or
not viewable to viewable and partially obscured,
the X server generates the event with the state member of the
XVisibilityEvent
structure set to
VisibilityPartiallyObscured.
When the window changes state from viewable and completely unobscured,
viewable and partially obscured, or not viewable to viewable and
fully obscured,
the X server generates the event with the state member of the
XVisibilityEvent
structure set to
VisibilityFullyObscured.

Structure Control Events

This section discusses:

CirculateRequest
events
ConfigureRequest
events
MapRequest
events
ResizeRequest
events

CirculateRequest Events

The X server can report
CirculateRequest
events to clients wanting information about
when another client initiates a circulate window request
on a specified window.
The X server generates this event type whenever a client initiates a circulate
window request on a window and a subwindow actually needs to be restacked.
The client initiates a circulate window request on the window by calling
XCirculateSubwindows,
XCirculateSubwindowsUp,
or
XCirculateSubwindowsDown.

To receive
CirculateRequest
events, set the
SubstructureRedirectMask
in the event-mask attribute of the window.
Then, in the future,
the circulate window request for the specified window is not executed,
and thus, any subwindow's position in the stack is not changed.
For example, suppose a client application calls
XCirculateSubwindowsUp
to raise a subwindow to the top of the stack.
If you had selected
SubstructureRedirectMask
on the window, the X server reports to you a
CirculateRequest
event and does not raise the subwindow to the top of the stack.

The structure for this event type contains:


typedef struct {
     int           type;       /* CirculateRequest */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        parent;
     Window        window;
     int place;                /* PlaceOnTop, PlaceOnBottom */
} XCirculateRequestEvent;

The parent member is set to the parent window.
The window member is set to the subwindow to be restacked.
The place member is set to what the new position in the stacking order should be
and is either
PlaceOnTop
or
PlaceOnBottom.
If it is
PlaceOnTop,
the subwindow should be on top of all siblings.
If it is
PlaceOnBottom,
the subwindow should be below all siblings.

ConfigureRequest Events

The X server can report
ConfigureRequest
events to clients wanting information about when a different client initiates
a configure window request on any child of a specified window.
The configure window request attempts to
reconfigure a window's size, position, border, and stacking order.
The X server generates this event whenever a different client initiates
a configure window request on a window by calling
XConfigureWindow,
XLowerWindow,
XRaiseWindow,
XMapRaised,
XMoveResizeWindow,
XMoveWindow,
XResizeWindow,
XRestackWindows,
or
XSetWindowBorderWidth.

To receive
ConfigureRequest
events, set the
SubstructureRedirectMask
bit in the event-mask attribute of the window.
ConfigureRequest
events are generated when a
ConfigureWindow
protocol request is issued on a child window by another client.
For example, suppose a client application calls
XLowerWindow
to lower a window.
If you had selected
SubstructureRedirectMask
on the parent window and if the override-redirect attribute
of the window is set to
False,
the X server reports a
ConfigureRequest
event to you and does not lower the specified window.

The structure for this event type contains:


typedef struct {
     int           type;         /* ConfigureRequest */
     unsigned long serial;       /* # of last request processed by server */
     Bool          send_event;   /* true if this came from a SendEvent request */
     Display       *display;     /* Display the event was read from */
     Window        parent;
     Window        window;
     int           x, y;
     int           width, height;
     int           border_width;
     Window        above;
     int           detail;       /* Above, Below, TopIf, BottomIf, Opposite */
     unsigned long value_mask;
} XConfigureRequestEvent;

The parent member is set to the parent window.
The window member is set to the window whose size, position, border width,
and/or stacking order is to be reconfigured.
The value_mask member indicates which components were specified in the
ConfigureWindow
protocol request.
The corresponding values are reported as given in the request.
The remaining values are filled in from the current geometry of the window,
except in the case of above (sibling) and detail (stack-mode),
which are reported as
None
and
Above,
respectively, if they are not given in the request.

MapRequest Events

The X server can report
MapRequest
events to clients wanting information about a different client's desire
to map windows.
A window is considered mapped when a map window request completes.
The X server generates this event whenever a different client initiates
a map window request on an unmapped window whose override_redirect member
is set to
False.
Clients initiate map window requests by calling
XMapWindow,
XMapRaised,
or
XMapSubwindows.

To receive
MapRequest
events, set the
SubstructureRedirectMask
bit in the event-mask attribute of the window.
This means another client's attempts to map a child window by calling one of
the map window request functions is intercepted, and you are sent a
MapRequest
instead.
For example, suppose a client application calls
XMapWindow
to map a window.
If you (usually a window manager) had selected
SubstructureRedirectMask
on the parent window and if the override-redirect attribute
of the window is set to
False,
the X server reports a
MapRequest
event to you
and does not map the specified window.
Thus, this event gives your window manager client the ability
to control the placement of subwindows.

The structure for this event type contains:


typedef struct {
     int           type;       /* MapRequest */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        parent;
     Window        window;
} XMapRequestEvent;

The parent member is set to the parent window.
The window member is set to the window to be mapped.

ResizeRequest Events

The X server can report
ResizeRequest
events to clients wanting information about another client's attempts to change the
size of a window.
The X server generates this event whenever some other client attempts to change
the size of the specified window by calling
XConfigureWindow,
XResizeWindow,
or
XMoveResizeWindow.

To receive
ResizeRequest
events, set the
ResizeRedirect
bit in the event-mask attribute of the window.
Any attempts to change the size by other clients are then redirected.

The structure for this event type contains:


typedef struct {
     int           type;        /* ResizeRequest */
     unsigned long serial;      /* # of last request processed by server */
     Bool          send_event;  /* true if this came from a SendEvent request */
     Display       *display;    /* Display the event was read from */
     Window        window;
     int           width, height;
} XResizeRequestEvent;

The window member is set to the window whose size another
client attempted to change.
The width and height members are set to the inside size of the window,
excluding the border.

Colormap State Change Events

The X server can report
ColormapNotify
events to clients wanting information about when the colormap changes
and when a colormap is installed or uninstalled.
The X server generates this event type whenever a client application:

Changes the colormap member of the
XSetWindowAttributes
structure by
calling
XChangeWindowAttributes,
XFreeColormap,
or
XSetWindowColormap
Installs or uninstalls the colormap by calling
XInstallColormap
or
XUninstallColormap

To receive
ColormapNotify
events, set the
ColormapChangeMask
bit in the event-mask attribute of the window.

The structure for this event type contains:


typedef struct {
     int           type;       /* ColormapNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        window;
     Colormap      colormap;   /* colormap or None */
     Bool          new;
     int           state;      /* ColormapInstalled, ColormapUninstalled */
} XColormapEvent;

The window member is set to the window whose associated
colormap is changed, installed, or uninstalled.
For a colormap that is changed, installed, or uninstalled,
the colormap member is set to the colormap associated with the window.
For a colormap that is changed by a call to
XFreeColormap,
the colormap member is set to
None.
The new member is set to indicate whether the colormap
for the specified window was changed or installed or uninstalled
and can be
True
or
False.
If it is
True,
the colormap was changed.
If it is
False,
the colormap was installed or uninstalled.
The state member is always set to indicate whether the colormap is installed or
uninstalled and can be
ColormapInstalled
or
ColormapUninstalled.

Client Communication Events

This section discusses:

ClientMessage
events
PropertyNotify
events
SelectionClear
events
SelectionNotify
events
SelectionRequest
events

ClientMessage Events

The X server generates
ClientMessage
events only when a client calls the function
XSendEvent.

The structure for this event type contains:


typedef struct {
     int           type;           /* ClientMessage */
     unsigned long serial;         /* # of last request processed by server */
     Bool          send_event;     /* true if this came from a SendEvent request */
     Display       *display;       /* Display the event was read from */
     Window        window;
     Atom          message_type;
     int           format;
     union         {
                     char  b[20];
                     short s[10];
                     long  l[5];
                   } data;
} XClientMessageEvent;

The message_type member is set to an atom that indicates how the data
should be interpreted by the receiving client.
The format member is set to 8, 16, or 32 and specifies whether the data
should be viewed as a list of bytes, shorts, or longs.
The data member is a union that contains the members b, s, and l.
The b, s, and l members represent data of twenty 8-bit values,
ten 16-bit values, and five 32-bit values.
Particular message types might not make use of all these values.
The X server places no interpretation on the values in the window,
message_type, or data members.

PropertyNotify Events

The X server can report
PropertyNotify
events to clients wanting information about property changes
for a specified window.

To receive
PropertyNotify
events, set the
PropertyChangeMask
bit in the event-mask attribute of the window.

The structure for this event type contains:


typedef struct {
     int           type;       /* PropertyNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        window;
     Atom atom;
     Time time;
     int state;                /* PropertyNewValue or PropertyDelete */
} XPropertyEvent;

The window member is set to the window whose associated
property was changed.
The atom member is set to the property's atom and indicates which
property was changed or desired.
The time member is set to the server time when the property was changed.
The state member is set to indicate whether the property was changed
to a new value or deleted and can be
PropertyNewValue
or
PropertyDelete.
The state member is set to
PropertyNewValue
when a property of the window is changed using
XChangeProperty
or
XRotateWindowProperties
(even when adding zero-length data using
XChangeProperty)
and when replacing all or part of a property with identical data using
XChangeProperty
or
XRotateWindowProperties.
The state member is set to
PropertyDelete
when a property of the window is deleted using
XDeleteProperty
or, if the delete argument is
True,
XGetWindowProperty.

SelectionClear Events

The X server reports
SelectionClear
events to the client losing ownership of a selection.
The X server generates this event type when another client
asserts ownership of the selection by calling
XSetSelectionOwner.

The structure for this event type contains:


typedef struct {
     int           type;       /* SelectionClear */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        window;
     Atom          selection;
     Time          time;
} XSelectionClearEvent;

The selection member is set to the selection atom.
The time member is set to the last change time recorded for the
selection.
The window member is the window that was specified by the current owner
(the owner losing the selection) in its
XSetSelectionOwner
call.

SelectionRequest Events

The X server reports
SelectionRequest
events to the owner of a selection.
The X server generates this event whenever a client
requests a selection conversion by calling
XConvertSelection
for the owned selection.

The structure for this event type contains:


typedef struct {
     int           type;       /* SelectionRequest */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        owner;
     Window        requestor;
     Atom          selection;
     Atom          target;
     Atom          property;
     Time          time;
} XSelectionRequestEvent;

The owner member is set to the window
that was specified by the current owner in its
XSetSelectionOwner
call.
The requestor member is set to the window requesting the selection.
The selection member is set to the atom that names the selection.
For example, PRIMARY is used to indicate the primary selection.
The target member is set to the atom that indicates the type
the selection is desired in.
The property member can be a property name or
None.
The time member is set to the timestamp or
CurrentTime
value from the
ConvertSelection
request.

The owner should convert the selection based on the specified target type
and send a
SelectionNotify
event back to the requestor.
A complete
specification for using selections is given in the X Consortium
standard Inter-Client Communication Conventions Manual.

SelectionNotify Events

This event is generated by the X server in response to a
ConvertSelection
protocol request when there is no owner for the selection.
When there is an owner, it should be generated by the owner
of the selection by using
XSendEvent.
The owner of a selection should send this event to a requestor when a selection
has been converted and stored as a property
or when a selection conversion could
not be performed (which is indicated by setting the property member to
None).

If
None
is specified as the property in the
ConvertSelection
protocol request, the owner should choose a property name,
store the result as that property on the requestor window,
and then send a
SelectionNotify
giving that actual property name.

The structure for this event type contains:


typedef struct {
     int           type;       /* SelectionNotify */
     unsigned long serial;     /* # of last request processed by server */
     Bool          send_event; /* true if this came from a SendEvent request */
     Display       *display;   /* Display the event was read from */
     Window        requestor;
     Atom          selection;
     Atom          target;
     Atom          property;   /* atom or None */
     Time          time;
} XSelectionEvent;

The requestor member is set to the window associated with
the requestor of the selection.
The selection member is set to the atom that indicates the selection.
For example, PRIMARY is used for the primary selection.
The target member is set to the atom that indicates the converted type.
For example, PIXMAP is used for a pixmap.
The property member is set to the atom that indicates which
property the result was stored on.
If the conversion failed,
the property member is set to
None.
The time member is set to the time the conversion took place and
can be a timestamp or
CurrentTime.

Chapter 11. Event Handling Functions

Table of Contents

Selecting EventsHandling the Output BufferEvent Queue ManagementManipulating the Event QueueReturning the Next EventSelecting Events Using a Predicate ProcedureSelecting Events Using a Window or Event MaskPutting an Event Back into the QueueSending Events to Other ApplicationsGetting Pointer Motion HistoryHandling Protocol ErrorsEnabling or Disabling SynchronizationUsing the Default Error Handlers

This chapter discusses the Xlib functions you can use to:

Select events
Handle the output buffer and the event queue
Select events from the event queue
Send and get events
Handle protocol errors

Note

Some toolkits use their own event-handling functions and do not allow you to
interchange these event-handling functions with those in Xlib. For further
information, see the documentation supplied with the toolkit.

Most applications simply are event loops: they wait for an event, decide what to do with it,
execute some amount of code that results in changes to the display, and then wait for the next
event.

Selecting Events

There are two ways to select the events you want reported to your client
application.
One way is to set the event_mask member of the
XSetWindowAttributes
structure when you call
XCreateWindow
and
XChangeWindowAttributes.
Another way is to use
XSelectInput.

XSelectInput(Display *display, Window w, long event_mask);

display	Specifies the connection to the X server.
w	Specifies the window whose events you are interested in.
event_mask	Specifies the event mask.

The
XSelectInput
function requests that the X server report the events associated with the
specified event mask.
Initially, X will not report any of these events.
Events are reported relative to a window.
If a window is not interested in a device event, it usually propagates to
the closest ancestor that is interested,
unless the do_not_propagate mask prohibits it.

Setting the event-mask attribute of a window overrides any previous call
for the same window but not for other clients.
Multiple clients can select for the same events on the same window
with the following restrictions:

Multiple clients can select events on the same window because their event masks
are disjoint.
When the X server generates an event, it reports it
to all interested clients.
Only one client at a time can select
CirculateRequest,
ConfigureRequest,
or
MapRequest
events, which are associated with
the event mask
SubstructureRedirectMask.
Only one client at a time can select
a
ResizeRequest
event, which is associated with
the event mask
ResizeRedirectMask.
Only one client at a time can select a
ButtonPress
event, which is associated with
the event mask
ButtonPressMask.

The server reports the event to all interested clients.

XSelectInput
can generate a
BadWindow
error.

Handling the Output Buffer

The output buffer is an area used by Xlib to store requests.
The functions described in this section flush the output buffer
if the function would block or not return an event.
That is, all requests residing in the output buffer that
have not yet been sent are transmitted to the X server.
These functions differ in the additional tasks they might perform.

To flush the output buffer, use
XFlush.

XFlush(Display *display);

display

Specifies the connection to the X server.

The
XFlush
function
flushes the output buffer.
Most client applications need not use this function because the output
buffer is automatically flushed as needed by calls to
XPending,
XNextEvent,
and
XWindowEvent.

Events generated by the server may be enqueued into the library's event queue.

To flush the output buffer and then wait until all requests have been processed,
use
XSync.

XSync(Display *display, Bool discard);

display	Specifies the connection to the X server.
discard	Specifies a Boolean value that indicates whether `XSync` discards all events on the event queue.

The
XSync
function
flushes the output buffer and then waits until all requests have been received
and processed by the X server.
Any errors generated must be handled by the error handler.
For each protocol error received by Xlib,
XSync
calls the client application's error handling routine
(see section 11.8.2).
Any events generated by the server are enqueued into the library's
event queue.

Finally, if you passed
False,
XSync
does not discard the events in the queue.
If you passed
True,
XSync
discards all events in the queue,
including those events that were on the queue before
XSync
was called.
Client applications seldom need to call
XSync.

Event Queue Management

Xlib maintains an event queue.
However, the operating system also may be buffering data
in its network connection that is not yet read into the event queue.

To check the number of events in the event queue, use
XEventsQueued.

int XEventsQueued(Display *display, int mode);

display	Specifies the connection to the X server.
mode	Specifies the mode. You can pass QueuedAlready, QueuedAfterFlush, or QueuedAfterReading.

If mode is
QueuedAlready,
XEventsQueued
returns the number of events
already in the event queue (and never performs a system call).
If mode is
QueuedAfterFlush,
XEventsQueued
returns the number of events already in the queue if the number is nonzero.
If there are no events in the queue,
XEventsQueued
flushes the output buffer,
attempts to read more events out of the application's connection,
and returns the number read.
If mode is
QueuedAfterReading,
XEventsQueued
returns the number of events already in the queue if the number is nonzero.
If there are no events in the queue,
XEventsQueued
attempts to read more events out of the application's connection
without flushing the output buffer and returns the number read.

XEventsQueued
always returns immediately without I/O if there are events already in the
queue.
XEventsQueued
with mode
QueuedAfterFlush
is identical in behavior to
XPending.
XEventsQueued
with mode
QueuedAlready
is identical to the
XQLength
function.

To return the number of events that are pending, use
XPending.

int XPending(Display *display);

display

Specifies the connection to the X server.

The
XPending
function returns the number of events that have been received from the
X server but have not been removed from the event queue.
XPending
is identical to
XEventsQueued
with the mode
QueuedAfterFlush
specified.

Manipulating the Event Queue

Xlib provides functions that let you manipulate the event queue.
This section discusses how to:

Obtain events, in order, and remove them from the queue
Peek at events in the queue without removing them
Obtain events that match the event mask or the arbitrary
predicate procedures that you provide

Returning the Next Event

To get the next event and remove it from the queue, use
XNextEvent.

XNextEvent(Display *display, XEvent *event_return);

display	Specifies the connection to the X server.
event_return	Returns the next event in the queue.

The
XNextEvent
function copies the first event from the event queue into the specified
XEvent
structure and then removes it from the queue.
If the event queue is empty,
XNextEvent
flushes the output buffer and blocks until an event is received.

To peek at the event queue, use
XPeekEvent.

XPeekEvent(Display *display, XEvent *event_return);

display	Specifies the connection to the X server.
event_return	Returns a copy of the matched event's associated structure.

The
XPeekEvent
function returns the first event from the event queue,
but it does not remove the event from the queue.
If the queue is empty,
XPeekEvent
flushes the output buffer and blocks until an event is received.
It then copies the event into the client-supplied
XEvent
structure without removing it from the event queue.

Selecting Events Using a Predicate Procedure

Each of the functions discussed in this section requires you to
pass a predicate procedure that determines if an event matches
what you want.
Your predicate procedure must decide if the event is useful
without calling any Xlib functions.
If the predicate directly or indirectly causes the state of the event queue
to change, the result is not defined.
If Xlib has been initialized for threads, the predicate is called with
the display locked and the result of a call by the predicate to any
Xlib function that locks the display is not defined unless the caller
has first called
XLockDisplay.

The predicate procedure and its associated arguments are:

Bool(Display *display, XEvent *event, XPointer arg);

display	Specifies the connection to the X server.
event	Specifies the XEvent structure.
arg	Specifies the argument passed in from the `XIfEvent`, `XCheckIfEvent`, or `XPeekIfEvent` function.

The predicate procedure is called once for each
event in the queue until it finds a match.
After finding a match, the predicate procedure must return
True.
If it did not find a match, it must return
False.

To check the event queue for a matching event
and, if found, remove the event from the queue, use
XIfEvent.

XIfEvent(Display *display, XEvent *event_return, Bool (*predicate)(), XPointer arg);

display	Specifies the connection to the X server.
event_return	Returns the matched event's associated structure.
predicate	Specifies the procedure that is to be called to determine if the next event in the queue matches what you want.
arg	Specifies the user-supplied argument that will be passed to the predicate procedure.

The
XIfEvent
function completes only when the specified predicate
procedure returns
True
for an event,
which indicates an event in the queue matches.
XIfEvent
flushes the output buffer if it blocks waiting for additional events.
XIfEvent
removes the matching event from the queue
and copies the structure into the client-supplied
XEvent
structure.

To check the event queue for a matching event without blocking, use
XCheckIfEvent.

Bool XCheckIfEvent(Display *display, XEvent *event_return, Bool (*predicate)(), XPointer arg);

display	Specifies the connection to the X server.
event_return	Returns a copy of the matched event's associated structure.
predicate	Specifies the procedure that is to be called to determine if the next event in the queue matches what you want.
arg	Specifies the user-supplied argument that will be passed to the predicate procedure.

When the predicate procedure finds a match,
XCheckIfEvent
copies the matched event into the client-supplied
XEvent
structure and returns
True.
(This event is removed from the queue.)
If the predicate procedure finds no match,
XCheckIfEvent
returns
False,
and the output buffer will have been flushed.
All earlier events stored in the queue are not discarded.

To check the event queue for a matching event
without removing the event from the queue, use
XPeekIfEvent.

XPeekIfEvent(Display *display, XEvent *event_return, Bool (*predicate)(), XPointer arg);

display	Specifies the connection to the X server.
event_return	Returns a copy of the matched event's associated structure.
predicate	Specifies the procedure that is to be called to determine if the next event in the queue matches what you want.
arg	Specifies the user-supplied argument that will be passed to the predicate procedure.

The
XPeekIfEvent
function returns only when the specified predicate
procedure returns
True
for an event.
After the predicate procedure finds a match,
XPeekIfEvent
copies the matched event into the client-supplied
XEvent
structure without removing the event from the queue.
XPeekIfEvent
flushes the output buffer if it blocks waiting for additional events.

Selecting Events Using a Window or Event Mask

The functions discussed in this section let you select events by window
or event types, allowing you to process events out of order.

To remove the next event that matches both a window and an event mask, use
XWindowEvent.

XWindowEvent(Display *display, Window w, long event_mask, XEvent *event_return);

display	Specifies the connection to the X server.
w	Specifies the window whose events you are interested in.
event_mask	Specifies the event mask.
event_return	Returns the matched event's associated structure.

The
XWindowEvent
function searches the event queue for an event that matches both the specified
window and event mask.
When it finds a match,
XWindowEvent
removes that event from the queue and copies it into the specified
XEvent
structure.
The other events stored in the queue are not discarded.
If a matching event is not in the queue,
XWindowEvent
flushes the output buffer and blocks until one is received.

To remove the next event that matches both a window and an event mask (if any),
use
XCheckWindowEvent.

This function is similar to
XWindowEvent
except that it never blocks and it returns a
Bool
indicating if the event was returned.

Bool XCheckWindowEvent(Display *display, Window w, long event_mask, XEvent *event_return);

display	Specifies the connection to the X server.
w	Specifies the window whose events you are interested in.
event_mask	Specifies the event mask.
event_return	Returns the matched event's associated structure.

The
XCheckWindowEvent
function searches the event queue and then the events available
on the server connection for the first event that matches the specified window
and event mask.
If it finds a match,
XCheckWindowEvent
removes that event, copies it into the specified
XEvent
structure, and returns
True.
The other events stored in the queue are not discarded.
If the event you requested is not available,
XCheckWindowEvent
returns
False,
and the output buffer will have been flushed.

To remove the next event that matches an event mask, use
XMaskEvent.

XMaskEvent(Display *display, long event_mask, XEvent *event_return);

display	Specifies the connection to the X server.
event_mask	Specifies the event mask.
event_return	Returns the matched event's associated structure.

The
XMaskEvent
function searches the event queue for the events associated with the
specified mask.
When it finds a match,
XMaskEvent
removes that event and copies it into the specified
XEvent
structure.
The other events stored in the queue are not discarded.
If the event you requested is not in the queue,
XMaskEvent
flushes the output buffer and blocks until one is received.

To return and remove the next event that matches an event mask (if any), use
XCheckMaskEvent.
This function is similar to
XMaskEvent
except that it never blocks and it returns a
Bool
indicating if the event was returned.

Bool XCheckMaskEvent(Display *display, long event_mask, XEvent *event_return);

display	Specifies the connection to the X server.
event_mask	Specifies the event mask.
event_return	Returns the matched event's associated structure.

The
XCheckMaskEvent
function searches the event queue and then any events available on the
server connection for the first event that matches the specified mask.
If it finds a match,
XCheckMaskEvent
removes that event, copies it into the specified
XEvent
structure, and returns
True.
The other events stored in the queue are not discarded.
If the event you requested is not available,
XCheckMaskEvent
returns
False,
and the output buffer will have been flushed.

To return and remove the next event in the queue that matches an event type, use
XCheckTypedEvent.

Bool XCheckTypedEvent(Display *display, int event_type, XEvent *event_return);

display	Specifies the connection to the X server.
event_type	Specifies the event type to be compared.
event_return	Returns the matched event's associated structure.

The
XCheckTypedEvent
function searches the event queue and then any events available
on the server connection for the first event that matches the specified type.
If it finds a match,
XCheckTypedEvent
removes that event, copies it into the specified
XEvent
structure, and returns
True.
The other events in the queue are not discarded.
If the event is not available,
XCheckTypedEvent
returns
False,
and the output buffer will have been flushed.

To return and remove the next event in the queue that matches an event type
and a window, use
XCheckTypedWindowEvent.

Bool XCheckTypedWindowEvent(Display *display, Window w, int event_type, XEvent *event_return);

display	Specifies the connection to the X server.
w	Specifies the window.
event_type	Specifies the event type to be compared.
event_return	Returns the matched event's associated structure.

The
XCheckTypedWindowEvent
function searches the event queue and then any events available
on the server connection for the first event that matches the specified
type and window.
If it finds a match,
XCheckTypedWindowEvent
removes the event from the queue, copies it into the specified
XEvent
structure, and returns
True.
The other events in the queue are not discarded.
If the event is not available,
XCheckTypedWindowEvent
returns
False,
and the output buffer will have been flushed.

Putting an Event Back into the Queue

To push an event back into the event queue, use
XPutBackEvent.

XPutBackEvent(Display *display, XEvent *event);

display	Specifies the connection to the X server.
event	Specifies the event.

The
XPutBackEvent
function pushes an event back onto the head of the display's event queue
by copying the event into the queue.
This can be useful if you read an event and then decide that you
would rather deal with it later.
There is no limit to the number of times in succession that you can call
XPutBackEvent.

Sending Events to Other Applications

To send an event to a specified window, use
XSendEvent.

This function is often used in selection processing.
For example, the owner of a selection should use
XSendEvent
to send a
SelectionNotify
event to a requestor when a selection has been converted
and stored as a property.

Status XSendEvent(Display *display, Window w, Bool propagate, long event_mask, XEvent *event_send);

display	Specifies the connection to the X server.
w	Specifies the window the event is to be sent to, or PointerWindow, or InputFocus.
propagate	Specifies a Boolean value.
event_mask	Specifies the event mask.
event_send	Specifies the event that is to be sent.

The
XSendEvent
function identifies the destination window,
determines which clients should receive the specified events,
and ignores any active grabs.
This function requires you to pass an event mask.
For a discussion of the valid event mask names,
see section 10.3.
This function uses the w argument to identify the destination window as follows:

If w is
PointerWindow,
the destination window is the window that contains the pointer.
If w is
InputFocus
and if the focus window contains the pointer,
the destination window is the window that contains the pointer;
otherwise, the destination window is the focus window.

To determine which clients should receive the specified events,
XSendEvent
uses the propagate argument as follows:

If event_mask is the empty set,
the event is sent to the client that created the destination window.
If that client no longer exists,
no event is sent.
If propagate is
False,
the event is sent to every client selecting on destination any of the event
types in the event_mask argument.
If propagate is
True
and no clients have selected on destination any of
the event types in event-mask, the destination is replaced with the
closest ancestor of destination for which some client has selected a
type in event-mask and for which no intervening window has that type in its
do-not-propagate-mask.
If no such window exists or if the window is
an ancestor of the focus window and
InputFocus
was originally specified
as the destination, the event is not sent to any clients.
Otherwise, the event is reported to every client selecting on the final
destination any of the types specified in event_mask.

The event in the
XEvent
structure must be one of the core events or one of the events
defined by an extension (or a
BadValue
error results) so that the X server can correctly byte-swap
the contents as necessary.
The contents of the event are
otherwise unaltered and unchecked by the X server except to force send_event to
True
in the forwarded event and to set the serial number in the event correctly;
therefore these fields
and the display field are ignored by
XSendEvent.

XSendEvent
returns zero if the conversion to wire protocol format failed
and returns nonzero otherwise.

XSendEvent
can generate
BadValue
and
BadWindow
errors.

Getting Pointer Motion History

Some X server implementations will maintain a more complete
history of pointer motion than is reported by event notification.
The pointer position at each pointer hardware interrupt may be
stored in a buffer for later retrieval.
This buffer is called the motion history buffer.
For example, a few applications, such as paint programs,
want to have a precise history of where the pointer
traveled.
However, this historical information is highly excessive for most applications.

To determine the approximate maximum number of elements in the motion buffer,
use
XDisplayMotionBufferSize.

unsigned long(Display *display);

display

Specifies the connection to the X server.

The server may retain the recent history of the pointer motion
and do so to a finer granularity than is reported by
MotionNotify
events.
The

function makes this history available.

To get the motion history for a specified window and time, use
.

XTimeCoord *XGetMotionEvents(Display *display, Window w, Time start, Time stop, int *nevents_return);

display	Specifies the connection to the X server.
w	Specifies the window.
start
stop	Specify the time interval in which the events are returned from the motion history buffer. You can pass a timestamp or CurrentTime.
nevents_return	Returns the number of events from the motion history buffer.

The

function returns all events in the motion history buffer that fall between the
specified start and stop times, inclusive, and that have coordinates
that lie within the specified window (including its borders) at its present
placement.
If the server does not support motion history,
if the start time is later than the stop time,
or if the start time is in the future,
no events are returned;

returns NULL.
If the stop time is in the future, it is equivalent to specifying
CurrentTime.
The return type for this function is a structure defined as follows:


typedef struct {
	Time time;
	short x, y;
} XTimeCoord;

The time member is set to the time, in milliseconds.
The x and y members are set to the coordinates of the pointer and
are reported relative to the origin
of the specified window.
To free the data returned from this call, use
XFree.

can generate a
BadWindow
error.

Handling Protocol Errors

Xlib provides functions that you can use to enable or disable synchronization
and to use the default error handlers.

Enabling or Disabling Synchronization

When debugging X applications,
it often is very convenient to require Xlib to behave synchronously
so that errors are reported as they occur.
The following function lets you disable or enable synchronous behavior.
Note that graphics may occur 30 or more times more slowly when
synchronization is enabled.

On POSIX-conformant systems,
there is also a global variable
_Xdebug
that, if set to nonzero before starting a program under a debugger, will force
synchronous library behavior.

After completing their work,
all Xlib functions that generate protocol requests call what is known as
an after function.

sets which function is to be called.

int(Display *display, int (*procedure)());

display	Specifies the connection to the X server.
procedure	Specifies the procedure to be called.

The specified procedure is called with only a display pointer.

returns the previous after function.

To enable or disable synchronization, use
XSynchronize.

int(Display *display, Bool onoff);

display	Specifies the connection to the X server.
onoff	Specifies a Boolean value that indicates whether to enable or disable synchronization.

The
XSynchronize
function returns
the previous after function.
If onoff is
True,
XSynchronize
turns on synchronous behavior.
If onoff is
False,
XSynchronize
turns off synchronous behavior.

Using the Default Error Handlers

There are two default error handlers in Xlib:
one to handle typically fatal conditions (for example,
the connection to a display server dying because a machine crashed)
and one to handle protocol errors from the X server.
These error handlers can be changed to user-supplied routines if you
prefer your own error handling and can be changed as often as you like.
If either function is passed a NULL pointer, it will
reinvoke the default handler.
The action of the default handlers is to print an explanatory
message and exit.

To set the error handler, use
XSetErrorHandler.

int *XSetErrorHandler(int *handler);

handler

Specifies the program's supplied error handler.

Xlib generally calls the program's
supplied error handler whenever an error is received.
It is not called on
BadName
errors from
OpenFont,
LookupColor,
or
AllocNamedColor
protocol requests or on
BadFont
errors from a
QueryFont
protocol request.
These errors generally are reflected back to the program through the
procedural interface.
Because this condition is not assumed to be fatal,
it is acceptable for your error handler to return;
the returned value is ignored.
However, the error handler should not
call any functions (directly or indirectly) on the display
that will generate protocol requests or that will look for input events.
The previous error handler is returned.

The
XErrorEvent
structure contains:


typedef struct {
	int type;
	Display *display;	/* Display the event was read from */
	unsigned long serial;		/* serial number of failed request */
	unsigned char error_code;	/* error code of failed request */
	unsigned char request_code;	/* Major op-code of failed request */
	unsigned char minor_code;	/* Minor op-code of failed request */
	XID resourceid;		/* resource id */
} XErrorEvent;

The serial member is the number of requests, starting from one,
sent over the network connection since it was opened.
It is the number that was the value of
NextRequest
immediately before the failing call was made.
The request_code member is a protocol request
of the procedure that failed, as defined in
<X11/Xproto.h>.
The following error codes can be returned by the functions described in this
chapter:

Error Code	Description
BadAccess	A client attempts to grab a key/button combination already grabbed by another client. A client attempts to free a colormap entry that it had not already allocated or to free an entry in a colormap that was created with all entries writable. A client attempts to store into a read-only or unallocated colormap entry. A client attempts to modify the access control list from other than the local (or otherwise authorized) host. A client attempts to select an event type that another client has already selected.
BadAlloc	The server fails to allocate the requested resource. Note that the explicit listing of BadAlloc errors in requests only covers allocation errors at a very coarse level and is not intended to (nor can it in practice hope to) cover all cases of a server running out of allocation space in the middle of service. The semantics when a server runs out of allocation space are left unspecified, but a server may generate a BadAlloc error on any request for this reason, and clients should be prepared to receive such errors and handle or discard them.
BadAtom	A value for an atom argument does not name a defined atom.
BadColor	A value for a colormap argument does not name a defined colormap.
BadCursor	A value for a cursor argument does not name a defined cursor.
BadDrawable	A value for a drawable argument does not name a defined window or pixmap.
BadFont	A value for a font argument does not name a defined font (or, in some cases, GContext).
BadGC	A value for a GContext argument does not name a defined GContext.
BadIDChoice	The value chosen for a resource identifier either is not included in the range assigned to the client or is already in use. Under normal circumstances, this cannot occur and should be considered a server or Xlib error.
BadImplementation	The server does not implement some aspect of the request. A server that generates this error for a core request is deficient. As such, this error is not listed for any of the requests, but clients should be prepared to receive such errors and handle or discard them.
BadLength	The length of a request is shorter or longer than that required to contain the arguments. This is an internal Xlib or server error. The length of a request exceeds the maximum length accepted by the server.
BadMatch	In a graphics request, the root and depth of the graphics context do not match those of the drawable. An InputOnly window is used as a drawable. Some argument or pair of arguments has the correct type and range, but it fails to match in some other way required by the request. An InputOnly window lacks this attribute.
BadName	A font or color of the specified name does not exist.
BadPixmap	A value for a pixmap argument does not name a defined pixmap.
BadRequest	The major or minor opcode does not specify a valid request. This usually is an Xlib or server error.
BadValue	Some numeric value falls outside of the range of values accepted by the request. Unless a specific range is specified for an argument, the full range defined by the argument's type is accepted. Any argument defined as a set of alternatives typically can generate this error (due to the encoding).
BadWindow	A value for a window argument does not name a defined window.

Note

The
BadAtom,
BadColor,
BadCursor,
BadDrawable,
BadFont,
BadGC,
BadPixmap,
and
BadWindow
errors are also used when the argument type is extended by a set of
fixed alternatives.

To obtain textual descriptions of the specified error code, use
XGetErrorText.

XGetErrorText(Display *display, int code, char *buffer_return, int length);

display	Specifies the connection to the X server.
code	Specifies the error code for which you want to obtain a description.
buffer_return	Returns the error description.
length	Specifies the size of the buffer.

The
XGetErrorText
function copies a null-terminated string describing the specified error code
into the specified buffer.
The returned text is in the encoding of the current locale.
It is recommended that you use this function to obtain an error description
because extensions to Xlib may define their own error codes
and error strings.

To obtain error messages from the error database, use
XGetErrorDatabaseText.

XGetErrorDatabaseText(Display *display, char *name, char *message, char *default_string, char *buffer_return, int length);

display	Specifies the connection to the X server.
name	Specifies the name of the application.
message	Specifies the type of the error message.
default_string	Specifies the default error message if none is found in the database.
buffer_return	Returns the error description.
length	Specifies the size of the buffer.

The
XGetErrorDatabaseText
function returns a null-terminated message
(or the default message) from the error message
database.
Xlib uses this function internally to look up its error messages.
The text in the default_string argument is assumed
to be in the encoding of the current locale,
and the text stored in the buffer_return argument
is in the encoding of the current locale.

The name argument should generally be the name of your application.
The message argument should indicate which type of error message you want.
If the name and message are not in the Host Portable Character Encoding,
the result is implementation-dependent.
Xlib uses three predefined “application names” to report errors.
In these names,
uppercase and lowercase matter.

XProtoError	The protocol error number is used as a string for the message argument.
XlibMessage	These are the message strings that are used internally by the library.
XRequest	For a core protocol request, the major request protocol number is used for the message argument. For an extension request, the extension name (as given by `InitExtension`) followed by a period (.) and the minor request protocol number is used for the message argument. If no string is found in the error database, the default_string is returned to the buffer argument.

To report an error to the user when the requested display does not exist, use
XDisplayName.

char *XDisplayName(char *string);

string

Specifies the character string.

The
XDisplayName
function returns the name of the display that
XOpenDisplay
would attempt to use.
If a NULL string is specified,
XDisplayName
looks in the environment for the display and returns the display name that
XOpenDisplay
would attempt to use.
This makes it easier to report to the user precisely which display the
program attempted to open when the initial connection attempt failed.

To handle fatal I/O errors, use
XSetIOErrorHandler.

int(int(*handler)(Display *));

handler

Specifies the program's supplied error handler.

The
XSetIOErrorHandler
sets the fatal I/O error handler.
Xlib calls the program's supplied error handler if any sort of system call
error occurs (for example, the connection to the server was lost).
This is assumed to be a fatal condition,
and the called routine should not return.
If the I/O error handler does return,
the client process exits.

Note that the previous error handler is returned.

Chapter 12. Input Device Functions

Table of Contents

Pointer GrabbingKeyboard GrabbingResuming Event ProcessingMoving the PointerControlling Input FocusManipulating the Keyboard and Pointer SettingsManipulating the Keyboard Encoding

You can use the Xlib input device functions to:

Grab the pointer and individual buttons on the pointer
Grab the keyboard and individual keys on the keyboard
Resume event processing
Move the pointer
Set the input focus
Manipulate the keyboard and pointer settings
Manipulate the keyboard encoding

Pointer Grabbing

Xlib provides functions that you can use to control input from the pointer,
which usually is a mouse.
Usually, as soon as keyboard and mouse events occur,
the X server delivers them to the appropriate client,
which is determined by the window and input focus.
The X server provides sufficient control over event delivery to
allow window managers to support mouse ahead and various other
styles of user interface.
Many of these user interfaces depend on synchronous delivery of events.
The delivery of pointer and keyboard events can be controlled
independently.

When mouse buttons or keyboard keys are grabbed, events
will be sent to the grabbing client rather than the normal
client who would have received the event.
If the keyboard or pointer is in asynchronous mode,
further mouse and keyboard events will continue to be processed.
If the keyboard or pointer is in synchronous mode, no
further events are processed until the grabbing client
allows them (see
XAllowEvents).
The keyboard or pointer is considered frozen during this
interval.
The event that triggered the grab can also be replayed.

Note that the logical state of a device (as seen by client applications)
may lag the physical state if device event processing is frozen.

There are two kinds of grabs:
active and passive.
An active grab occurs when a single client grabs the keyboard and/or pointer
explicitly (see
XGrabPointer
and
XGrabKeyboard).

A passive grab occurs when clients grab a particular keyboard key
or pointer button in a window,
and the grab will activate when the key or button is actually pressed.
Passive grabs are convenient for implementing reliable pop-up menus.
For example, you can guarantee that the pop-up is mapped
before the up pointer button event occurs by
grabbing a button requesting synchronous behavior.
The down event will trigger the grab and freeze further
processing of pointer events until you have the chance to
map the pop-up window.
You can then allow further event processing.
The up event will then be correctly processed relative to the
pop-up window.

For many operations,
there are functions that take a time argument.
The X server includes a timestamp in various events.
One special time, called

CurrentTime,
represents the current server time.
The X server maintains the time when the input focus was last changed,
when the keyboard was last grabbed,
when the pointer was last grabbed,
or when a selection was last changed.
Your
application may be slow reacting to an event.
You often need some way to specify that your
request should not occur if another application has in the meanwhile
taken control of the keyboard, pointer, or selection.
By providing the timestamp from the event in the request,
you can arrange that the operation not take effect
if someone else has performed an operation in the meanwhile.

A timestamp is a time value, expressed in milliseconds.
It typically is the time since the last server reset.
Timestamp values wrap around (after about 49.7 days).
The server, given its current time is represented by timestamp T,
always interprets timestamps from clients by treating half of the timestamp
space as being later in time than T.
One timestamp value, named
CurrentTime,
is never generated by the server.
This value is reserved for use in requests to represent the current server time.

For many functions in this section,
you pass pointer event mask bits.
The valid pointer event mask bits are:
ButtonPressMask,
ButtonReleaseMask,
EnterWindowMask,
LeaveWindowMask,
PointerMotionMask,
PointerMotionHintMask,
Button1MotionMask,
Button2MotionMask,
Button3MotionMask,
Button4MotionMask,
Button5MotionMask,
ButtonMotionMask,
and
KeymapStateMask.
For other functions in this section,
you pass keymask bits.
The valid keymask bits are:
ShiftMask,
LockMask,
ControlMask,
Mod1Mask,
Mod2Mask,
Mod3Mask,
Mod4Mask,
and
Mod5Mask.

To grab the pointer, use
XGrabPointer.

int XGrabPointer(Display *display, Window grab_window, Bool owner_events, unsigned int event_mask, int pointer_mode, int keyboard_mode, Window confine_to, Cursor cursor, Time time);

display	Specifies the connection to the X server.
grab_window	Specifies the grab window.
owner_events	Specifies a Boolean value that indicates whether the pointer events are to be reported as usual or reported with respect to the grab window if selected by the event mask.
event_mask	Specifies which pointer events are reported to the client. The mask is the bitwise inclusive OR of the valid pointer event mask bits.
pointer_mode	Specifies further processing of pointer events. You can pass GrabModeSync or GrabModeAsync.
keyboard_mode	Specifies further processing of keyboard events. You can pass GrabModeSync or GrabModeAsync.
confine_to	Specifies the window to confine the pointer in or None.
cursor	Specifies the cursor that is to be displayed during the grab or None.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

The
XGrabPointer
function actively grabs control of the pointer and returns
GrabSuccess
if the grab was successful.
Further pointer events are reported only to the grabbing client.
XGrabPointer
overrides any active pointer grab by this client.
If owner_events is
False,
all generated pointer events
are reported with respect to grab_window and are reported only if
selected by event_mask.
If owner_events is
True
and if a generated
pointer event would normally be reported to this client,
it is reported as usual.
Otherwise, the event is reported with respect to the
grab_window and is reported only if selected by event_mask.
For either value of owner_events, unreported events are discarded.

If the pointer_mode is
GrabModeAsync,
pointer event processing continues as usual.
If the pointer is currently frozen by this client,
the processing of events for the pointer is resumed.
If the pointer_mode is
GrabModeSync,
the state of the pointer, as seen by
client applications,
appears to freeze, and the X server generates no further pointer events
until the grabbing client calls
XAllowEvents
or until the pointer grab is released.
Actual pointer changes are not lost while the pointer is frozen;
they are simply queued in the server for later processing.

If the keyboard_mode is
GrabModeAsync,
keyboard event processing is unaffected by activation of the grab.
If the keyboard_mode is
GrabModeSync,
the state of the keyboard, as seen by
client applications,
appears to freeze, and the X server generates no further keyboard events
until the grabbing client calls
XAllowEvents
or until the pointer grab is released.
Actual keyboard changes are not lost while the pointer is frozen;
they are simply queued in the server for later processing.

If a cursor is specified, it is displayed regardless of what
window the pointer is in.
If
None
is specified,
the normal cursor for that window is displayed
when the pointer is in grab_window or one of its subwindows;
otherwise, the cursor for grab_window is displayed.

If a confine_to window is specified,
the pointer is restricted to stay contained in that window.
The confine_to window need have no relationship to the grab_window.
If the pointer is not initially in the confine_to window,
it is warped automatically to the closest edge
just before the grab activates and enter/leave events are generated as usual.
If the confine_to window is subsequently reconfigured,
the pointer is warped automatically, as necessary,
to keep it contained in the window.

The time argument allows you to avoid certain circumstances that come up
if applications take a long time to respond or if there are long network
delays.
Consider a situation where you have two applications, both
of which normally grab the pointer when clicked on.
If both applications specify the timestamp from the event,
the second application may wake up faster and successfully grab the pointer
before the first application.
The first application then will get an indication that the other application
grabbed the pointer before its request was processed.

XGrabPointer
generates
EnterNotify
and
LeaveNotify
events.

Either if grab_window or confine_to window is not viewable
or if the confine_to window lies completely outside the boundaries of the root
window,
XGrabPointer
fails and returns
GrabNotViewable.
If the pointer is actively grabbed by some other client,
it fails and returns
AlreadyGrabbed.
If the pointer is frozen by an active grab of another client,
it fails and returns
GrabFrozen.
If the specified time is earlier than the last-pointer-grab time or later
than the current X server time, it fails and returns
GrabInvalidTime.
Otherwise, the last-pointer-grab time is set to the specified time
(CurrentTime
is replaced by the current X server time).

XGrabPointer
can generate
BadCursor,
BadValue,
and
BadWindow
errors.

To ungrab the pointer, use
XUngrabPointer.

XUngrabPointer(Display *display, Time time);

display	Specifies the connection to the X server.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

The
XUngrabPointer
function releases the pointer and any queued events
if this client has actively grabbed the pointer from
XGrabPointer,
XGrabButton,
or from a normal button press.
XUngrabPointer
does not release the pointer if the specified
time is earlier than the last-pointer-grab time or is later than the
current X server time.
It also generates
EnterNotify
and
LeaveNotify
events.
The X server performs an
UngrabPointer
request automatically if the event window or confine_to window
for an active pointer grab becomes not viewable
or if window reconfiguration causes the confine_to window to lie completely
outside the boundaries of the root window.

To change an active pointer grab, use
XChangeActivePointerGrab.

XChangeActivePointerGrab(Display *display, unsigned int event_mask, Cursor cursor, Time time);

display	Specifies the connection to the X server.
event_mask	Specifies which pointer events are reported to the client. The mask is the bitwise inclusive OR of the valid pointer event mask bits.
cursor	Specifies the cursor that is to be displayed or None.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

The
XChangeActivePointerGrab
function changes the specified dynamic parameters if the pointer is actively
grabbed by the client and if the specified time is no earlier than the
last-pointer-grab time and no later than the current X server time.
This function has no effect on the passive parameters of an
XGrabButton.
The interpretation of event_mask and cursor is the same as described in
XGrabPointer.

XChangeActivePointerGrab
can generate
BadCursor
and
BadValue
errors.

To grab a pointer button, use
XGrabButton.

XGrabButton(Display *display, unsigned int button, unsigned int modifiers, Window grab_window, Bool owner_events, unsigned int event_mask, int pointer_mode, int keyboard_mode, Window confine_to, Cursor cursor);

display	Specifies the connection to the X server.
button	Specifies the pointer button that is to be grabbed or AnyButton.
modifiers	Specifies the set of keymasks or AnyModifier. The mask is the bitwise inclusive OR of the valid keymask bits.
grab_window	Specifies the grab window.
owner_events	Specifies a Boolean value that indicates whether the pointer events are to be reported as usual or reported with respect to the grab window if selected by the event mask.
event_mask	Specifies which pointer events are reported to the client. The mask is the bitwise inclusive OR of the valid pointer event mask bits.
pointer_mode	Specifies further processing of pointer events. You can pass GrabModeSync or GrabModeAsync.
keyboard_mode	Specifies further processing of keyboard events. You can pass GrabModeSync or GrabModeAsync.
confine_to	Specifies the window to confine the pointer in or None.
cursor	Specifies the cursor that is to be displayed or None.

The
XGrabButton
function establishes a passive grab.
In the future,
the pointer is actively grabbed (as for
XGrabPointer),
the last-pointer-grab time is set to the time at which the button was pressed
(as transmitted in the
ButtonPress
event), and the
ButtonPress
event is reported if all of the following conditions are true:

The pointer is not grabbed, and the specified button is logically pressed
when the specified modifier keys are logically down,
and no other buttons or modifier keys are logically down.
The grab_window contains the pointer.
The confine_to window (if any) is viewable.
A passive grab on the same button/key combination does not exist
on any ancestor of grab_window.

The interpretation of the remaining arguments is as for
XGrabPointer.
The active grab is terminated automatically when the logical state of the
pointer has all buttons released
(independent of the state of the logical modifier keys).

Note that the logical state of a device (as seen by client applications)
may lag the physical state if device event processing is frozen.

This request overrides all previous grabs by the same client on the same
button/key combinations on the same window.
A modifiers of
AnyModifier
is equivalent to issuing the grab request for all
possible modifier combinations (including the combination of no modifiers).
It is not required that all modifiers specified have currently assigned
KeyCodes.
A button of
AnyButton
is equivalent to
issuing the request for all possible buttons.
Otherwise, it is not required that the specified button currently be assigned
to a physical button.

If some other client has already issued an
XGrabButton
with the same button/key combination on the same window, a
BadAccess
error results.
When using
AnyModifier
or
AnyButton,
the request fails completely,
and a
BadAccess
error results (no grabs are
established) if there is a conflicting grab for any combination.
XGrabButton
has no effect on an active grab.

XGrabButton
can generate
BadCursor,
BadValue,
and
BadWindow
errors.

To ungrab a pointer button, use
XUngrabButton.

XUngrabButton(Display *display, unsigned int button, unsigned int modifiers, Window grab_window);

display	Specifies the connection to the X server.
button	Specifies the pointer button that is to be released or AnyButton.
modifiers	Specifies the set of keymasks or AnyModifier. The mask is the bitwise inclusive OR of the valid keymask bits.
grab_window	Specifies the grab window.

The
XUngrabButton
function releases the passive button/key combination on the specified window if
it was grabbed by this client.
A modifiers of
AnyModifier
is
equivalent to issuing
the ungrab request for all possible modifier combinations, including
the combination of no modifiers.
A button of
AnyButton
is equivalent to issuing the
request for all possible buttons.
XUngrabButton
has no effect on an active grab.

XUngrabButton
can generate
BadValue
and
BadWindow
errors.

Keyboard Grabbing

Xlib provides functions that you can use to grab or ungrab the keyboard
as well as allow events.

For many functions in this section,
you pass keymask bits.
The valid keymask bits are:
ShiftMask,
LockMask,
ControlMask,
Mod1Mask,
Mod2Mask,
Mod3Mask,
Mod4Mask,
and
Mod5Mask.

To grab the keyboard, use
XGrabKeyboard.

int XGrabKeyboard(Display *display, Window grab_window, Bool owner_events, int pointer_mode, int keyboard_mode, Time time);

display	Specifies the connection to the X server.
grab_window	Specifies the grab window.
owner_events	Specifies a Boolean value that indicates whether the keyboard events are to be reported as usual.
pointer_mode	Specifies further processing of pointer events. You can pass GrabModeSync or GrabModeAsync.
keyboard_mode	Specifies further processing of keyboard events. You can pass GrabModeSync or GrabModeAsync.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

The
XGrabKeyboard
function actively grabs control of the keyboard and generates
FocusIn
and
FocusOut
events.
Further key events are reported only to the
grabbing client.
XGrabKeyboard
overrides any active keyboard grab by this client.
If owner_events is
False,
all generated key events are reported with
respect to grab_window.
If owner_events is
True
and if a generated
key event would normally be reported to this client, it is reported
normally; otherwise, the event is reported with respect to the
grab_window.
Both
KeyPress
and
KeyRelease
events are always reported,
independent of any event selection made by the client.

If the keyboard_mode argument is
GrabModeAsync,
keyboard event processing continues
as usual.
If the keyboard is currently frozen by this client,
then processing of keyboard events is resumed.
If the keyboard_mode argument is
GrabModeSync,
the state of the keyboard (as seen by client applications) appears to freeze,
and the X server generates no further keyboard events until the
grabbing client issues a releasing
XAllowEvents
call or until the keyboard grab is released.
Actual keyboard changes are not lost while the keyboard is frozen;
they are simply queued in the server for later processing.

If pointer_mode is
GrabModeAsync,
pointer event processing is unaffected
by activation of the grab.
If pointer_mode is
GrabModeSync,
the state of the pointer (as seen by client applications) appears to freeze,
and the X server generates no further pointer events
until the grabbing client issues a releasing
XAllowEvents
call or until the keyboard grab is released.
Actual pointer changes are not lost while the pointer is frozen;
they are simply queued in the server for later processing.

If the keyboard is actively grabbed by some other client,
XGrabKeyboard
fails and returns
AlreadyGrabbed.
If grab_window is not viewable,
it fails and returns
GrabNotViewable.
If the keyboard is frozen by an active grab of another client,
it fails and returns
GrabFrozen.
If the specified time is earlier than the last-keyboard-grab time
or later than the current X server time,
it fails and returns
GrabInvalidTime.
Otherwise, the last-keyboard-grab time is set to the specified time
(CurrentTime
is replaced by the current X server time).

XGrabKeyboard
can generate
BadValue
and
BadWindow
errors.

To ungrab the keyboard, use
XUngrabKeyboard.

XUngrabKeyboard(Display *display, Time time);

display	Specifies the connection to the X server.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

The
XUngrabKeyboard
function
releases the keyboard and any queued events if this client has it actively grabbed from
either
XGrabKeyboard
or
XGrabKey.
XUngrabKeyboard
does not release the keyboard and any queued events
if the specified time is earlier than
the last-keyboard-grab time or is later than the current X server time.
It also generates
FocusIn
and
FocusOut
events.
The X server automatically performs an
UngrabKeyboard
request if the event window for an
active keyboard grab becomes not viewable.

To passively grab a single key of the keyboard, use
XGrabKey.

XGrabKey(Display *display, int keycode, unsigned int modifiers, Window grab_window, Bool owner_events, int pointer_mode, int keyboard_mode);

display	Specifies the connection to the X server.
keycode	Specifies the KeyCode or AnyKey.
modifiers	Specifies the set of keymasks or AnyModifier. The mask is the bitwise inclusive OR of the valid keymask bits.
grab_window	Specifies the grab window.
owner_events	Specifies a Boolean value that indicates whether the keyboard events are to be reported as usual.
pointer_mode	Specifies further processing of pointer events. You can pass GrabModeSync or GrabModeAsync.
keyboard_mode	Specifies further processing of keyboard events. You can pass GrabModeSync or GrabModeAsync.

The
XGrabKey
function establishes a passive grab on the keyboard.
In the future,
the keyboard is actively grabbed (as for
XGrabKeyboard),
the last-keyboard-grab time is set to the time at which the key was pressed
(as transmitted in the
KeyPress
event), and the
KeyPress
event is reported if all of the following conditions are true:

The keyboard is not grabbed and the specified key
(which can itself be a modifier key) is logically pressed
when the specified modifier keys are logically down,
and no other modifier keys are logically down.
Either the grab_window is an ancestor of (or is) the focus window,
or the grab_window is a descendant of the focus window and contains the pointer.
A passive grab on the same key combination does not exist
on any ancestor of grab_window.

The interpretation of the remaining arguments is as for
XGrabKeyboard.
The active grab is terminated automatically when the logical state of the
keyboard has the specified key released
(independent of the logical state of the modifier keys).

Note that the logical state of a device (as seen by client applications)
may lag the physical state if device event processing is frozen.

A modifiers argument of
AnyModifier
is equivalent to issuing the request for all
possible modifier combinations (including the combination of no
modifiers).
It is not required that all modifiers specified have
currently assigned KeyCodes.
A keycode argument of
AnyKey
is equivalent to issuing
the request for all possible KeyCodes.
Otherwise, the specified keycode must be in
the range specified by min_keycode and max_keycode in the connection
setup,
or a
BadValue
error results.

If some other client has issued a
XGrabKey
with the same key combination on the same window, a
BadAccess
error results.
When using
AnyModifier
or
AnyKey,
the request fails completely,
and a
BadAccess
error results (no grabs are established)
if there is a conflicting grab for any combination.

XGrabKey
can generate
BadAccess,
BadValue,
and
BadWindow
errors.

To ungrab a key, use
XUngrabKey.

XUngrabKey(Display *display, int keycode, unsigned int modifiers, Window grab_window);

display	Specifies the connection to the X server.
keycode	Specifies the KeyCode or AnyKey.
modifiers	Specifies the set of keymasks or AnyModifier. The mask is the bitwise inclusive OR of the valid keymask bits.
grab_window	Specifies the grab window.

The
XUngrabKey
function releases the key combination on the specified window if it was grabbed
by this client.
It has no effect on an active grab.
A modifiers of
AnyModifier
is equivalent to issuing
the request for all possible modifier combinations
(including the combination of no modifiers).
A keycode argument of
AnyKey
is equivalent to issuing the request for all possible key codes.

XUngrabKey
can generate
BadValue
and
BadWindow
errors.

Resuming Event Processing

The previous sections discussed grab mechanisms with which processing
of events by the server can be temporarily suspended. This section
describes the mechanism for resuming event processing.

To allow further events to be processed when the device has been frozen, use
XAllowEvents.

XAllowEvents(Display *display, int event_mode, Time time);

display	Specifies the connection to the X server.
event_mode	Specifies the event mode. You can pass AsyncPointer, SyncPointer, AsyncKeyboard, SyncKeyboard, ReplayPointer, ReplayKeyboard, AsyncBoth, or SyncBoth.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

The
XAllowEvents
function releases some queued events if the client has caused a device
to freeze.
It has no effect if the specified time is earlier than the last-grab
time of the most recent active grab for the client or if the specified time
is later than the current X server time.
Depending on the event_mode argument, the following occurs:

AsyncPointer	If the pointer is frozen by the client, pointer event processing continues as usual. If the pointer is frozen twice by the client on behalf of two separate grabs, AsyncPointer thaws for both. AsyncPointer has no effect if the pointer is not frozen by the client, but the pointer need not be grabbed by the client.
SyncPointer	If the pointer is frozen and actively grabbed by the client, pointer event processing continues as usual until the next ButtonPress or ButtonRelease event is reported to the client. At this time, the pointer again appears to freeze. However, if the reported event causes the pointer grab to be released, the pointer does not freeze. SyncPointer has no effect if the pointer is not frozen by the client or if the pointer is not grabbed by the client.
ReplayPointer	If the pointer is actively grabbed by the client and is frozen as the result of an event having been sent to the client (either from the activation of an `XGrabButton` or from a previous `XAllowEvents` with mode SyncPointer but not from an `XGrabPointer`), the pointer grab is released and that event is completely reprocessed. This time, however, the function ignores any passive grabs at or above (toward the root of) the grab_window of the grab just released. The request has no effect if the pointer is not grabbed by the client or if the pointer is not frozen as the result of an event.
AsyncKeyboard	If the keyboard is frozen by the client, keyboard event processing continues as usual. If the keyboard is frozen twice by the client on behalf of two separate grabs, AsyncKeyboard thaws for both. AsyncKeyboard has no effect if the keyboard is not frozen by the client, but the keyboard need not be grabbed by the client.
SyncKeyboard	If the keyboard is frozen and actively grabbed by the client, keyboard event processing continues as usual until the next KeyPress or KeyRelease event is reported to the client. At this time, the keyboard again appears to freeze. However, if the reported event causes the keyboard grab to be released, the keyboard does not freeze. SyncKeyboard has no effect if the keyboard is not frozen by the client or if the keyboard is not grabbed by the client.
ReplayKeyboard	If the keyboard is actively grabbed by the client and is frozen as the result of an event having been sent to the client (either from the activation of an `XGrabKey` or from a previous `XAllowEvents` with mode SyncKeyboard but not from an `XGrabKeyboard`), the keyboard grab is released and that event is completely reprocessed. This time, however, the function ignores any passive grabs at or above (toward the root of) the grab_window of the grab just released. The request has no effect if the keyboard is not grabbed by the client or if the keyboard is not frozen as the result of an event.
SyncBoth	If both pointer and keyboard are frozen by the client, event processing for both devices continues as usual until the next ButtonPress, ButtonRelease, KeyPress, or KeyRelease event is reported to the client for a grabbed device (button event for the pointer, key event for the keyboard), at which time the devices again appear to freeze. However, if the reported event causes the grab to be released, then the devices do not freeze (but if the other device is still grabbed, then a subsequent event for it will still cause both devices to freeze). SyncBoth has no effect unless both pointer and keyboard are frozen by the client. If the pointer or keyboard is frozen twice by the client on behalf of two separate grabs, SyncBoth thaws for both (but a subsequent freeze for SyncBoth will only freeze each device once).
AsyncBoth	If the pointer and the keyboard are frozen by the client, event processing for both devices continues as usual. If a device is frozen twice by the client on behalf of two separate grabs, AsyncBoth thaws for both. AsyncBoth has no effect unless both pointer and keyboard are frozen by the client.

AsyncPointer,
SyncPointer,
and
ReplayPointer
have no effect on the
processing of keyboard events.
AsyncKeyboard,
SyncKeyboard,
and
ReplayKeyboard
have no effect on the
processing of pointer events.
It is possible for both a pointer grab and a keyboard grab (by the same
or different clients) to be active simultaneously.
If a device is frozen on behalf of either grab,
no event processing is performed for the device.
It is possible for a single device to be frozen because of both grabs.
In this case,
the freeze must be released on behalf of both grabs before events can
again be processed.
If a device is frozen twice by a single client,
then a single
XAllowEvents
releases both.

XAllowEvents
can generate a
BadValue
error.

Moving the Pointer

Although movement of the pointer normally should be left to the
control of the end user, sometimes it is necessary to move the
pointer to a new position under program control.

To move the pointer to an arbitrary point in a window, use
XWarpPointer.

XWarpPointer(Display *display, Window src_w, Window dest_w, int src_x, int src_y, unsigned int src_width, unsigned int src_height, int dest_x, int dest_y);

display	Specifies the connection to the X server.
src_w	Specifies the source window or None.
dest_w	Specifies the destination window or None.
src_x
src_y
src_width
src_height	Specify a rectangle in the source window.
dest_x
dest_y	Specify the x and y coordinates within the destination window.

If dest_w is
None,
XWarpPointer
moves the pointer by the offsets (dest_x, dest_y) relative to the current
position of the pointer.
If dest_w is a window,
XWarpPointer
moves the pointer to the offsets (dest_x, dest_y) relative to the origin of
dest_w.
However, if src_w is a window,
the move only takes place if the window src_w contains the pointer
and if the specified rectangle of src_w contains the pointer.

The src_x and src_y coordinates are relative to the origin of src_w.
If src_height is zero,
it is replaced with the current height of src_w minus src_y.
If src_width is zero,
it is replaced with the current width of src_w minus src_x.

There is seldom any reason for calling this function.
The pointer should normally be left to the user.
If you do use this function, however, it generates events just as if the user
had instantaneously moved the pointer from one position to another.
Note that you cannot use
XWarpPointer
to move the pointer outside the confine_to window of an active pointer grab.
An attempt to do so will only move the pointer as far as the closest edge of the
confine_to window.

XWarpPointer
can generate a
BadWindow
error.

Controlling Input Focus

Xlib provides functions that you can use to set and get the input focus.
The input focus is a shared resource, and cooperation among clients is
required for correct interaction. See the
Inter-Client Communication Conventions Manual
for input focus policy.

To set the input focus, use
XSetInputFocus.

XSetInputFocus(Display *display, Window focus, int revert_to, Time time);

display	Specifies the connection to the X server.
focus	Specifies the window, PointerRoot, or None.
revert_to	Specifies where the input focus reverts to if the window becomes not viewable. You can pass RevertToParent, RevertToPointerRoot, or RevertToNone.
time	Specifies the time. You can pass either a timestamp or CurrentTime.

The
XSetInputFocus
function changes the input focus and the last-focus-change time.
It has no effect if the specified time is earlier than the current
last-focus-change time or is later than the current X server time.
Otherwise, the last-focus-change time is set to the specified time
(CurrentTime
is replaced by the current X server time).
XSetInputFocus
causes the X server to generate
FocusIn
and
FocusOut
events.

Depending on the focus argument,
the following occurs:

If focus is
None,
all keyboard events are discarded until a new focus window is set,
and the revert_to argument is ignored.
If focus is a window,
it becomes the keyboard's focus window.
If a generated keyboard event would normally be reported to this window
or one of its inferiors, the event is reported as usual.
Otherwise, the event is reported relative to the focus window.
If focus is
PointerRoot,
the focus window is dynamically taken to be the root window of whatever screen
the pointer is on at each keyboard event.
In this case, the revert_to argument is ignored.

The specified focus window must be viewable at the time
XSetInputFocus
is called,
or a
BadMatch
error results.
If the focus window later becomes not viewable,
the X server
evaluates the revert_to argument to determine the new focus window as follows:

If revert_to is
RevertToParent,
the focus reverts to the parent (or the closest viewable ancestor),
and the new revert_to value is taken to be
RevertToNone.
If revert_to is
RevertToPointerRoot
or
RevertToNone,
the focus reverts to
PointerRoot
or
None,
respectively.
When the focus reverts,
the X server generates
FocusIn
and
FocusOut
events, but the last-focus-change time is not affected.

XSetInputFocus
can generate
BadMatch,
BadValue,
and
BadWindow
errors.

To obtain the current input focus, use
XGetInputFocus.

XGetInputFocus(Display *display, Window *focus_return, int *revert_to_return);

display	Specifies the connection to the X server.
focus_return	Returns the focus window, PointerRoot, or None.
revert_to_return	Returns the current focus state (RevertToParent, RevertToPointerRoot, or RevertToNone).

The
XGetInputFocus
function returns the focus window and the current focus state.

Manipulating the Keyboard and Pointer Settings

Xlib provides functions that you can use to
change the keyboard control, obtain a list of the auto-repeat keys,
turn keyboard auto-repeat on or off, ring the bell,
set or obtain the pointer button or keyboard mapping,
and obtain a bit vector for the keyboard.

This section discusses
the user-preference options of bell, key click,
pointer behavior, and so on.
The default values for many of these options are server dependent.
Not all implementations will actually be able to control all of these
parameters.

The
XChangeKeyboardControl
function changes control of a keyboard and operates on a
XKeyboardControl
structure:

/* Mask bits for ChangeKeyboardControl */


#define     KBBellPercent           (1L<<0)
#define     KBBellPitch             (1L<<1)
#define     KBBellDuration          (1L<<2)
#define     KBLed                   (1L<<3)
#define     KBLedMode               (1L<<4)
#define     KBKey                   (1L<<5)
#define     KBAutoRepeatMode        (1L<<6)


/* Values */

typedef struct {
int key_click_percent;
int bell_percent;
int bell_pitch;
int bell_duration;
int led;
int led_mode;                /* LedModeOn, LedModeOff */
int key;
int auto_repeat_mode;        /* AutoRepeatModeOff, AutoRepeatModeOn,
                                AutoRepeatModeDefault */
} XKeyboardControl;

The key_click_percent member sets the volume for key clicks between 0 (off)
and 100 (loud) inclusive, if possible.
A setting of -1 restores the default.
Other negative values generate a
BadValue
error.

The bell_percent sets the base volume for the bell between 0 (off) and 100
(loud) inclusive, if possible.
A setting of -1 restores the default.
Other negative values generate a
BadValue
error.
The bell_pitch member sets the pitch (specified in Hz) of the bell, if possible.
A setting of -1 restores the default.
Other negative values generate a
BadValue
error.
The bell_duration member sets the duration of the
bell specified in milliseconds, if possible.
A setting of -1 restores the default.
Other negative values generate a
BadValue
error.

If both the led_mode and led members are specified,
the state of that LED is changed, if possible.
The led_mode member can be set to
LedModeOn
or
LedModeOff.
If only led_mode is specified, the state of
all LEDs are changed, if possible.
At most 32 LEDs numbered from one are supported.
No standard interpretation of LEDs is defined.
If led is specified without led_mode, a
BadMatch
error results.

If both the auto_repeat_mode and key members are specified,
the auto_repeat_mode of that key is changed (according to
AutoRepeatModeOn,
AutoRepeatModeOff,
or
AutoRepeatModeDefault),
if possible.
If only auto_repeat_mode is
specified, the global auto_repeat_mode for the entire keyboard is
changed, if possible, and does not affect the per-key settings.
If a key is specified without an auto_repeat_mode, a
BadMatch
error results.
Each key has an individual mode of whether or not it should auto-repeat
and a default setting for the mode.
In addition,
there is a global mode of whether auto-repeat should be enabled or not
and a default setting for that mode.
When global mode is
AutoRepeatModeOn,
keys should obey their individual auto-repeat modes.
When global mode is
AutoRepeatModeOff,
no keys should auto-repeat.
An auto-repeating key generates alternating
KeyPress
and
KeyRelease
events.
When a key is used as a modifier,
it is desirable for the key not to auto-repeat,
regardless of its auto-repeat setting.

A bell generator connected with the console but not directly on a
keyboard is treated as if it were part of the keyboard.
The order in which controls are verified and altered is server-dependent.
If an error is generated, a subset of the controls may have been altered.

XChangeKeyboardControl(Display *display, unsigned long value_mask, XKeyboardControl *values);

display	Specifies the connection to the X server.
value_mask	Specifies which controls to change. This mask is the bitwise inclusive OR of the valid control mask bits.
values	Specifies one value for each bit set to 1 in the mask.

The
XChangeKeyboardControl
function controls the keyboard characteristics defined by the
XKeyboardControl
structure.
The value_mask argument specifies which values are to be changed.

XChangeKeyboardControl
can generate
BadMatch
and
BadValue
errors.

To obtain the current control values for the keyboard, use
XGetKeyboardControl.

XGetKeyboardControl(Display *display, XKeyboardState *values_return);

display	Specifies the connection to the X server.
values_return	Returns the current keyboard controls in the specified XKeyboardState structure.

The
XGetKeyboardControl
function returns the current control values for the keyboard to the
XKeyboardState
structure.


typedef struct {
	int key_click_percent;
	int bell_percent;
	unsigned int bell_pitch, bell_duration;
	unsigned long led_mask;
	int global_auto_repeat;
	char auto_repeats[32];
} XKeyboardState;

For the LEDs,
the least significant bit of led_mask corresponds to LED one,
and each bit set to 1 in led_mask indicates an LED that is lit.
The global_auto_repeat member can be set to
AutoRepeatModeOn
or
AutoRepeatModeOff.
The auto_repeats member is a bit vector.
Each bit set to 1 indicates that auto-repeat is enabled
for the corresponding key.
The vector is represented as 32 bytes.
Byte N (from 0) contains the bits for keys 8N to 8N + 7
with the least significant bit in the byte representing key 8N.

To turn on keyboard auto-repeat, use
XAutoRepeatOn.

XAutoRepeatOn(Display *display);

display

Specifies the connection to the X server.

The
XAutoRepeatOn
function turns on auto-repeat for the keyboard on the specified display.

To turn off keyboard auto-repeat, use
XAutoRepeatOff.

XAutoRepeatOff(Display *display);

display

Specifies the connection to the X server.

The
XAutoRepeatOff
function turns off auto-repeat for the keyboard on the specified display.

To ring the bell, use
XBell.

XBell(Display *display, int percent);

display	Specifies the connection to the X server.
percent	Specifies the volume for the bell, which can range from -100 to 100 inclusive.

The
XBell
function rings the bell on the keyboard on the specified display, if possible.
The specified volume is relative to the base volume for the keyboard.
If the value for the percent argument is not in the range -100 to 100
inclusive, a
BadValue
error results.
The volume at which the bell rings
when the percent argument is nonnegative is:

base - [(base * percent) / 100] + percent

The volume at which the bell rings
when the percent argument is negative is:

base + [(base * percent) / 100]

To change the base volume of the bell, use
XChangeKeyboardControl.

XBell
can generate a
BadValue
error.

To obtain a bit vector that describes the state of the keyboard, use
XQueryKeymap.

XQueryKeymap(Display *display, char keys_return[32]);

display	Specifies the connection to the X server.
keys_return	Returns an array of bytes that identifies which keys are pressed down. Each bit represents one key of the keyboard.

The
XQueryKeymap
function returns a bit vector for the logical state of the keyboard,
where each bit set to 1 indicates that the corresponding key is currently
pressed down.
The vector is represented as 32 bytes.
Byte N (from 0) contains the bits for keys 8N to 8N + 7
with the least significant bit in the byte representing key 8N.

Note that the logical state of a device (as seen by client applications)
may lag the physical state if device event processing is frozen.

To set the mapping of the pointer buttons, use
XSetPointerMapping.

int XSetPointerMapping(Display *display, unsignedchar map[], int nmap);

display	Specifies the connection to the X server.
map	Specifies the mapping list.
nmap	Specifies the number of items in the mapping list.

The
XSetPointerMapping
function sets the mapping of the pointer.
If it succeeds, the X server generates a
MappingNotify
event, and
XSetPointerMapping
returns
MappingSuccess.
Element map[i] defines the logical button number for the physical button
i+1.
The length of the list must be the same as
XGetPointerMapping
would return,
or a
BadValue
error results.
A zero element disables a button, and elements are not restricted in
value by the number of physical buttons.
However, no two elements can have the same nonzero value,
or a
BadValue
error results.
If any of the buttons to be altered are logically in the down state,
XSetPointerMapping
returns
MappingBusy,
and the mapping is not changed.

XSetPointerMapping
can generate a
BadValue
error.

To get the pointer mapping, use
XGetPointerMapping.

int XGetPointerMapping(Display *display, unsignedchar map_return[], int nmap);

display	Specifies the connection to the X server.
map_return	Returns the mapping list.
nmap	Specifies the number of items in the mapping list.

The
XGetPointerMapping
function returns the current mapping of the pointer.
Pointer buttons are numbered starting from one.
XGetPointerMapping
returns the number of physical buttons actually on the pointer.
The nominal mapping for a pointer is map[i]=i+1.
The nmap argument specifies the length of the array where the pointer
mapping is returned, and only the first nmap elements are returned
in map_return.

To control the pointer's interactive feel, use
XChangePointerControl.

XChangePointerControl(Display *display, Bool do_accel, Bool do_threshold, int accel_numerator, int accel_denominator, int threshold);

display	Specifies the connection to the X server.
do_accel	Specifies a Boolean value that controls whether the values for the accel_numerator or accel_denominator are used.
do_threshold	Specifies a Boolean value that controls whether the value for the threshold is used.
accel_numerator	Specifies the numerator for the acceleration multiplier.
accel_denominator	Specifies the denominator for the acceleration multiplier.
threshold	Specifies the acceleration threshold.

The
XChangePointerControl
function defines how the pointing device moves.
The acceleration, expressed as a fraction, is a
multiplier for movement.
For example,
specifying 3/1 means the pointer moves three times as fast as normal.
The fraction may be rounded arbitrarily by the X server.
Acceleration
only takes effect if the pointer moves more than threshold pixels at
once and only applies to the amount beyond the value in the threshold argument.
Setting a value to -1 restores the default.
The values of the do_accel and do_threshold arguments must be
True
for the pointer values to be set,
or the parameters are unchanged.
Negative values (other than -1) generate a
BadValue
error, as does a zero value
for the accel_denominator argument.

XChangePointerControl
can generate a
BadValue
error.

To get the current pointer parameters, use
XGetPointerControl.

XGetPointerControl(Display *display, int *accel_numerator_return, int *accel_denominator_return, int *threshold_return);

display	Specifies the connection to the X server.
accel_numerator_return	Returns the numerator for the acceleration multiplier.
accel_denominator_return	Returns the denominator for the acceleration multiplier.
threshold_return	Returns the acceleration threshold.

The
XGetPointerControl
function returns the pointer's current acceleration multiplier
and acceleration threshold.

Manipulating the Keyboard Encoding

A KeyCode represents a physical (or logical) key.
KeyCodes lie in the inclusive range [8,255].
A KeyCode value carries no intrinsic information,
although server implementors may attempt to encode geometry
(for example, matrix) information in some fashion so that it can
be interpreted in a server-dependent fashion.
The mapping between keys and KeyCodes cannot be changed.

A KeySym is an encoding of a symbol on the cap of a key.
The set of defined KeySyms includes the ISO Latin character sets (1-4),
Katakana, Arabic, Cyrillic, Greek, Technical,
Special, Publishing, APL, Hebrew, Thai, Korean
and a miscellany of keys found
on keyboards (Return, Help, Tab, and so on).
To the extent possible, these sets are derived from international
standards.
In areas where no standards exist,
some of these sets are derived from Digital Equipment Corporation standards.
The list of defined symbols can be found in
<X11/keysymdef.h>.

Unfortunately, some C preprocessors have
limits on the number of defined symbols.
If you must use KeySyms not
in the Latin 1-4, Greek, and miscellaneous classes,
you may have to define a symbol for those sets.
Most applications usually only include
<X11/keysym.h>,

which defines symbols for ISO Latin 1-4, Greek, and miscellaneous.

A list of KeySyms is associated with each KeyCode.
The list is intended to convey the set of symbols on the corresponding key.
If the list (ignoring trailing
NoSymbol
entries) is
a single KeySym “K”,
then the list is treated as if it were the list
“K NoSymbol K NoSymbol”.
If the list (ignoring trailing
NoSymbol
entries) is a pair of KeySyms “K1 K2”,
then the list is treated as if it were the list “K1 K2 K1 K2”.
If the list (ignoring trailing
NoSymbol
entries) is a triple of KeySyms “K1 K2 K3”,
then the list is treated as if it were the list “K1 K2 K3 NoSymbol”.
When an explicit “void” element is desired in the list,
the value
VoidSymbol
can be used.

The first four elements of the list are split into two groups of KeySyms.
Group 1 contains the first and second KeySyms;
Group 2 contains the third and fourth KeySyms.
Within each group,
if the second element of the group is
NoSymbol,
then the group should be treated as if the second element were
the same as the first element,
except when the first element is an alphabetic KeySym “K”
for which both lowercase and uppercase forms are defined.
In that case,
the group should be treated as if the first element were
the lowercase form of “K” and the second element were
the uppercase form of “K”.

The standard rules for obtaining a KeySym from a
KeyPress
event make use of only the Group 1 and Group 2 KeySyms;
no interpretation of other KeySyms in the list is given.
Which group to use is determined by the modifier state.
Switching between groups is controlled by the KeySym named MODE SWITCH,
by attaching that KeySym to some KeyCode and attaching
that KeyCode to any one of the modifiers
Mod1
through
Mod5.
This modifier is called the group modifier.
For any KeyCode,
Group 1 is used when the group modifier is off,
and Group 2 is used when the group modifier is on.

The
Lock
modifier is interpreted as CapsLock when the KeySym named XK_Caps_Lock
is attached to some KeyCode and that KeyCode is attached to the
Lock
modifier. The
Lock
modifier is interpreted as ShiftLock when the KeySym named XK_Shift_Lock
is attached to some KeyCode and that KeyCode is attached to the
Lock
modifier. If the
Lock
modifier could be interpreted as both
CapsLock and ShiftLock, the CapsLock interpretation is used.

The operation of keypad keys is controlled by the KeySym named XK_Num_Lock,
by attaching that KeySym to some KeyCode and attaching that KeyCode to any
one of the modifiers
Mod1
through
Mod5.
This modifier is called the
numlock modifier. The standard KeySyms with the prefix “XK_KP_”
in their
name are called keypad KeySyms; these are KeySyms with numeric value in
the hexadecimal range 0xFF80 to 0xFFBD inclusive. In addition,
vendor-specific KeySyms in the hexadecimal range 0x11000000 to 0x1100FFFF
are also keypad KeySyms.

Within a group, the choice of KeySym is determined by applying the first
rule that is satisfied from the following list:

The numlock modifier is on and the second KeySym is a keypad KeySym. In
this case, if the
Shift
modifier is on, or if the
Lock
modifier is on and
is interpreted as ShiftLock, then the first KeySym is used, otherwise the
second KeySym is used.
The
Shift
and
Lock
modifiers are both off. In this case, the first
KeySym is used.
The
Shift
modifier is off, and the
Lock
modifier is on and is
interpreted as CapsLock. In this case, the first KeySym is used, but if
that KeySym is lowercase alphabetic, then the corresponding uppercase
KeySym is used instead.
The
Shift
modifier is on, and the
Lock
modifier is on and is interpreted
as CapsLock. In this case, the second KeySym is used, but if that KeySym
is lowercase alphabetic, then the corresponding uppercase KeySym is used
instead.
The
Shift
modifier is on, or the
Lock
modifier is on and is interpreted
as ShiftLock, or both. In this case, the second KeySym is used.

No spatial geometry of the symbols on the key is defined by
their order in the KeySym list,
although a geometry might be defined on a
server-specific basis.
The X server does not use the mapping between KeyCodes and KeySyms.
Rather, it merely stores it for reading and writing by clients.

To obtain the legal KeyCodes for a display, use
XDisplayKeycodes.

XDisplayKeycodes(Display *display, int *min_keycodes_return, int *max_keycodes_return);

display	Specifies the connection to the X server.
min_keycodes_return	Returns the minimum number of KeyCodes.
max_keycodes_return	Returns the maximum number of KeyCodes.

The
XDisplayKeycodes
function returns the min-keycodes and max-keycodes supported by the
specified display.
The minimum number of KeyCodes returned is never less than 8,
and the maximum number of KeyCodes returned is never greater than 255.
Not all KeyCodes in this range are required to have corresponding keys.

To obtain the symbols for the specified KeyCodes, use
XGetKeyboardMapping.

KeySym *XGetKeyboardMapping(Display *display, KeyCode first_keycode, int keycode_count, int *keysyms_per_keycode_return);

display	Specifies the connection to the X server.
first_keycode	Specifies the first KeyCode that is to be returned.
keycode_count	Specifies the number of KeyCodes that are to be returned.
keysyms_per_keycode_return	Returns the number of KeySyms per KeyCode.

The
XGetKeyboardMapping
function returns the symbols for the specified number of KeyCodes
starting with first_keycode.
The value specified in first_keycode must be greater than
or equal to min_keycode as returned by
XDisplayKeycodes,
or a
BadValue
error results.
In addition, the following expression must be less than or equal
to max_keycode as returned by
XDisplayKeycodes:

first_keycode + keycode_count - 1

If this is not the case, a
BadValue
error results.
The number of elements in the KeySyms list is:

keycode_count * keysyms_per_keycode_return

KeySym number N, counting from zero, for KeyCode K has the following index
in the list, counting from zero:

(K - first_code) * keysyms_per_code_return + N

The X server arbitrarily chooses the keysyms_per_keycode_return value
to be large enough to report all requested symbols.
A special KeySym value of
NoSymbol
is used to fill in unused elements for
individual KeyCodes.
To free the storage returned by
XGetKeyboardMapping,
use
XFree.

XGetKeyboardMapping
can generate a
BadValue
error.

To change the keyboard mapping, use
XChangeKeyboardMapping.

XChangeKeyboardMapping(Display *display, int first_keycode, int keysyms_per_keycode, KeySym *keysyms, int num_codes);

display	Specifies the connection to the X server.
first_keycode	Specifies the first KeyCode that is to be changed.
keysyms_per_keycode	Specifies the number of KeySyms per KeyCode.
keysyms	Specifies an array of KeySyms.
num_codes	Specifies the number of KeyCodes that are to be changed.

The
XChangeKeyboardMapping
function defines the symbols for the specified number of KeyCodes
starting with first_keycode.
The symbols for KeyCodes outside this range remain unchanged.
The number of elements in keysyms must be:

num_codes * keysyms_per_keycode

The specified first_keycode must be greater than or equal to min_keycode
returned by
XDisplayKeycodes,
or a
BadValue
error results.
In addition, the following expression must be less than or equal to
max_keycode as returned by
XDisplayKeycodes,
or a
BadValue
error results:

first_keycode + num_codes - 1

KeySym number N, counting from zero, for KeyCode K has the following index
in keysyms, counting from zero:

(K - first_keycode) * keysyms_per_keycode + N

The specified keysyms_per_keycode can be chosen arbitrarily by the client
to be large enough to hold all desired symbols.
A special KeySym value of
NoSymbol
should be used to fill in unused elements
for individual KeyCodes.
It is legal for
NoSymbol
to appear in nontrailing positions
of the effective list for a KeyCode.
XChangeKeyboardMapping
generates a
MappingNotify
event.

There is no requirement that the X server interpret this mapping.
It is merely stored for reading and writing by clients.

XChangeKeyboardMapping
can generate
BadAlloc
and
BadValue
errors.

The next six functions make use of the
XModifierKeymap
data structure, which contains:


typedef struct {
	int max_keypermod;	/* This server's max number of keys per modifier */
	KeyCode *modifiermap;	/* An 8 by max_keypermod array of the modifiers */
} XModifierKeymap;

To create an
XModifierKeymap
structure, use
XNewModifiermap.

XModifierKeymap *XNewModifiermap(int max_keys_per_mod);

max_keys_per_mod

Specifies the number of KeyCode entries preallocated to the modifiers
in the map.

The
XNewModifiermap
function returns a pointer to
XModifierKeymap
structure for later use.

To add a new entry to an
XModifierKeymap
structure, use
XInsertModifiermapEntry.

XModifierKeymap *XInsertModifiermapEntry(XModifierKeymap *modmap, KeyCode keycode_entry, int modifier);

modmap	Specifies the XModifierKeymap structure.
keycode_entry	Specifies the KeyCode.
modifier	Specifies the modifier.

The
XInsertModifiermapEntry
function adds the specified KeyCode to the set that controls the specified
modifier and returns the resulting
XModifierKeymap
structure (expanded as needed).

To delete an entry from an
XModifierKeymap
structure, use
XDeleteModifiermapEntry.

XModifierKeymap *XDeleteModifiermapEntry(XModifierKeymap *modmap, KeyCode keycode_entry, int modifier);

modmap	Specifies the XModifierKeymap structure.
keycode_entry	Specifies the KeyCode.
modifier	Specifies the modifier.

The
XDeleteModifiermapEntry
function deletes the specified KeyCode from the set that controls the
specified modifier and returns a pointer to the resulting
XModifierKeymap
structure.

To destroy an
XModifierKeymap
structure, use
XFreeModifiermap.

XFreeModifiermap(XModifierKeymap *modmap);

modmap

Specifies the
XModifierKeymap
structure.

The
XFreeModifiermap
function frees the specified
XModifierKeymap
structure.

To set the KeyCodes to be used as modifiers, use
XSetModifierMapping.

int XSetModifierMapping(Display *display, XModifierKeymap *modmap);

display	Specifies the connection to the X server.
modmap	Specifies the XModifierKeymap structure.

The
XSetModifierMapping
function specifies the KeyCodes of the keys (if any) that are to be used
as modifiers.
If it succeeds,
the X server generates a
MappingNotify
event, and
XSetModifierMapping
returns
MappingSuccess.
X permits at most 8 modifier keys.
If more than 8 are specified in the
XModifierKeymap
structure, a
BadLength
error results.

The modifiermap member of the
XModifierKeymap
structure contains 8 sets of max_keypermod KeyCodes,
one for each modifier in the order
Shift,
Lock,
Control,
Mod1,
Mod2,
Mod3,
Mod4,
and
Mod5.
Only nonzero KeyCodes have meaning in each set,
and zero KeyCodes are ignored.
In addition, all of the nonzero KeyCodes must be in the range specified by
min_keycode and max_keycode in the
Display
structure,
or a
BadValue
error results.

An X server can impose restrictions on how modifiers can be changed,
for example,
if certain keys do not generate up transitions in hardware,
if auto-repeat cannot be disabled on certain keys,
or if multiple modifier keys are not supported.
If some such restriction is violated,
the status reply is
MappingFailed,
and none of the modifiers are changed.
If the new KeyCodes specified for a modifier differ from those
currently defined and any (current or new) keys for that modifier are
in the logically down state,
XSetModifierMapping
returns
MappingBusy,
and none of the modifiers is changed.

XSetModifierMapping
can generate
BadAlloc
and
BadValue
errors.

To obtain the KeyCodes used as modifiers, use
XGetModifierMapping.

XModifierKeymap *XGetModifierMapping(Display *display);

display

Specifies the connection to the X server.

The
XGetModifierMapping
function returns a pointer to a newly created
XModifierKeymap
structure that contains the keys being used as modifiers.
The structure should be freed after use by calling
XFreeModifiermap.
If only zero values appear in the set for any modifier,
that modifier is disabled.

Chapter 13. Locales and Internationalized Text Functions

Table of Contents

X Locale ManagementLocale and Modifier DependenciesVariable Argument ListsOutput MethodsOutput Method OverviewOutput Method FunctionsX Output Method ValuesOutput Context FunctionsOutput Context ValuesCreating and Freeing a Font SetObtaining Font Set MetricsDrawing Text Using Font SetsInput MethodsInput Method OverviewInput Method ManagementInput Method FunctionsInput Method ValuesInput Context FunctionsInput Context ValuesInput Method Callback SemanticsEvent FilteringGetting Keyboard InputInput Method ConventionsString Constants

An internationalized application is one that is adaptable to the requirements of different native
languages, local customs, and character string encodings. The process of adapting the operation
to a particular native language, local custom, or string encoding is called localization. A goal of
internationalization is to permit localization without program source modifications or recompilation.

As one of the localization mechanisms, Xlib provides an X Input Method (XIM)
functional interface for internationalized text input and an X Output Method
(XOM) functional interface for internationalized text output.

Internationalization in X is based on the concept of a locale. A locale defines the localized
behavior of a program at run time. Locales affect Xlib in its:

Encoding and processing of input method text
Encoding of resource files and values
Encoding and imaging of text strings
Encoding and decoding for inter-client text communication

•
Encoding and decoding for inter-client text communication
Characters from various languages are represented in a computer using an encoding.
Different languages have different encodings, and there are even different
encodings for the same characters in the same language.

This chapter defines support for localized text imaging and text input and describes the locale
mechanism that controls all locale-dependent Xlib functions. Sets of functions are provided for
multibyte (char *) text as well as wide character (wchar_t) text in the form supported by the host
C language environment. The multibyte and wide character functions are equivalent except for
the form of the text argument.

The Xlib internationalization functions are not meant to provide support for
multilingual applications (mixing multiple languages within a single piece of text),
but they make it possible to implement applications that work in limited
fashion with more than one language in independent contexts.

The remainder of this chapter discusses:

X locale management
Locale and modifier dependencies
Variable argument lists
Output methods
Input methods
String constants

X Locale Management

X supports one or more of the locales defined by the host environment.
On implementations that conform to the ANSI C library,
the locale announcement method is
setlocale.
This function configures the locale operation of both
the host C library and Xlib.
The operation of Xlib is governed by the LC_CTYPE category;
this is called the current locale.
An implementation is permitted to provide implementation-dependent
mechanisms for announcing the locale in addition to
setlocale.

On implementations that do not conform to the ANSI C library,
the locale announcement method is Xlib implementation-dependent.

The mechanism by which the semantic operation of Xlib is defined
for a specific locale is implementation-dependent.

X is not required to support all the locales supported by the host.
To determine if the current locale is supported by X, use
XSupportsLocale.

Bool XSupportsLocale(void);

The
XSupportsLocale
function returns
True
if Xlib functions are capable of operating under the current locale.
If it returns
False,
Xlib locale-dependent functions for which the
XLocaleNotSupported
return status is defined will return
XLocaleNotSupported.
Other Xlib locale-dependent routines will operate in the “C” locale.

The client is responsible for selecting its locale and X modifiers.
Clients should provide a means for the user to override the clients'
locale selection at client invocation.
Most single-display X clients operate in a single locale
for both X and the host processing environment.
They will configure the locale by calling three functions:
the host locale configuration function,
XSupportsLocale,
and
XSetLocaleModifiers.

The semantics of certain categories of X internationalization capabilities
can be configured by setting modifiers.
Modifiers are named by implementation-dependent and locale-specific strings.
The only standard use for this capability at present
is selecting one of several styles of keyboard input method.

To configure Xlib locale modifiers for the current locale, use
XSetLocaleModifiers.

char *XSetLocaleModifiers(char *modifier_list);

modifier_list

Specifies the modifiers.

The
XSetLocaleModifiers
function sets the X modifiers for the current locale setting.
The modifier_list argument is a null-terminated string of the form
“{@category=value}”, that is,
having zero or more concatenated “@category=value”
entries, where category is a category name
and value is the (possibly empty) setting for that category.
The values are encoded in the current locale.
Category names are restricted to the POSIX Portable Filename Character Set.

The local host X locale modifiers announcer (on POSIX-compliant systems,
the XMODIFIERS environment variable) is appended to the modifier_list to
provide default values on the local host.
If a given category appears more than once in the list,
the first setting in the list is used.
If a given category is not included in the full modifier list,
the category is set to an implementation-dependent default
for the current locale.
An empty value for a category explicitly specifies the
implementation-dependent default.

If the function is successful, it returns a pointer to a string.
The contents of the string are such that a subsequent call with that string
(in the same locale) will restore the modifiers to the same settings.
If modifier_list is a NULL pointer,
XSetLocaleModifiers
also returns a pointer to such a string,
and the current locale modifiers are not changed.

If invalid values are given for one or more modifier categories supported by
the locale, a NULL pointer is returned, and none of the
current modifiers are changed.

At program startup,
the modifiers that are in effect are unspecified until
the first successful call to set them. Whenever the locale is changed, the
modifiers that are in effect become unspecified until the next successful call
to set them.
Clients should always call
XSetLocaleModifiers
with a non-NULL modifier_list after setting the locale
before they call any locale-dependent Xlib routine.

The only standard modifier category currently defined is “im”,
which identifies the desired input method.
The values for input method are not standardized.
A single locale may use multiple input methods,
switching input method under user control.
The modifier may specify the initial input method in effect
or an ordered list of input methods.
Multiple input methods may be specified in a single im value string
in an implementation-dependent manner.

The returned modifiers string is owned by Xlib and should not be modified or
freed by the client.
It may be freed by Xlib after the current locale or modifiers are changed.
Until freed, it will not be modified by Xlib.

The recommended procedure for clients initializing their locale and modifiers
is to obtain locale and modifier announcers separately from
one of the following prioritized sources:

A command line option
A resource
The empty string ("")

The first of these that is defined should be used.
Note that when a locale command line option or locale resource is defined,
the effect should be to set all categories to the specified locale,
overriding any category-specific settings in the local host environment.

Locale and Modifier Dependencies

The internationalized Xlib functions operate in the current locale
configured by the host environment and X locale modifiers set by
XSetLocaleModifiers
or in the locale and modifiers configured at the time
some object supplied to the function was created.
For each locale-dependent function,
the following table describes the locale (and modifiers) dependency:

Locale from	Affects the Function	In
Locale Query/Configuration:
`setlocale`	`XSupportsLocale`	Locale queried
`setlocale`	`XSetLocaleModifiers`	Locale modified
Resources:
`setlocale`	`XrmGetFileDatabase` `XrmGetStringDatabase`	Locale of XrmDatabase
XrmDatabase	`XrmPutFileDatabase` `XrmLocaleOfDatabase`	Locale of XrmDatabase
Setting Standard Properties:
`setlocale`	`XmbSetWMProperties`	Encoding of supplied/returned text (some WM_ property text in environment locale)
`setlocale`	`XmbTextPropertyToTextList` `XwcTextPropertyToTextList` `XmbTextListToTextProperty` `XwcTextListToTextProperty`	Encoding of supplied/returned text
Text Input:
`setlocale`	`XOpenIM`	XIM input method selection
	`XRegisterIMInstantiateCallback`	XIM selection
	`XUnregisterIMInstantiateCallback`	XIM selection
XIM	`XCreateIC`	XIC input method configuration
XIM	`XLocaleOfIM`, and so on	Queried locale
XIC	`XmbLookupString`	Keyboard layout
XIC	`XwcLookupString`	Encoding of returned text
Text Drawing:
`setlocale`	`XOpenOM`	XOM output method selection
`setlocale`	`XCreateFontSet`	Charsets of fonts in XFontSet
XOM	`XCreateOC`	XOC output method configuration
XOM	`XLocaleOfOM`, and so on	Queried locale
XFontSet	`XmbDrawText`,	Locale of supplied text
	`XwcDrawText`, and so on	Locale of supplied text
	`XExtentsOfFontSet`, and so on `XmbTextExtents`, `XwcTextExtents`, and so on	Locale-dependent metrics
Xlib Errors:
`setlocale`	`XGetErrorDatabaseText`, `XGetErrorText`, and so on	Locale of error message

Clients may assume that a locale-encoded text string returned
by an X function can be passed to a C library routine, or vice versa,
if the locale is the same at the two calls.

All text strings processed by internationalized Xlib functions are assumed
to begin in the initial state of the encoding of the locale, if the encoding
is state-dependent.

All Xlib functions behave as if they do not change the current locale
or X modifier setting.
(This means that if they do change locale or call
XSetLocaleModifiers
with a non-NULL argument, they must save and restore the current state on
entry and exit.)
Also, Xlib functions on implementations that conform to the ANSI C library do
not alter the global state associated with the ANSI C functions
mblen,
mbtowc,
wctomb,
and
strtok.

Variable Argument Lists

Various functions in this chapter have arguments that conform
to the ANSI C variable argument list calling convention.
Each function denoted with an argument of the form “...” takes
a variable-length list of name and value pairs,
where each name is a string and each value is of type
XPointer.
A name argument that is NULL identifies the end of the list.

A variable-length argument list may contain a nested list.
If the name
XNVaNestedList
is specified in place of an argument name,
then the following value is interpreted as an
XVaNestedList
value that specifies a list of values logically inserted into the
original list at the point of declaration.
A NULL identifies the end of a nested list.

To allocate a nested variable argument list dynamically, use
XVaCreateNestedList.

XVaNestedList XVaCreateNestedList(int dummy);

dummy	Specifies an unused argument (required by ANSI C).
...	Specifies the variable length argument list(Al.

The
XVaCreateNestedList
function allocates memory and copies its arguments into
a single list pointer,
which may be used as a value for arguments requiring a list value.
Any entries are copied as specified.
Data passed by reference is not copied;
the caller must ensure data remains valid for the lifetime
of the nested list.
The list should be freed using
XFree
when it is no longer needed.

Output Methods

This section provides discussions of the following X Output Method
(XOM) topics:

Output method overview
Output method functions
Output method values
Output context functions
Output context values
Creating and freeing a font set
Obtaining font set metrics
Drawing text using font sets

Output Method Overview

Locale-dependent text may include one or more text components, each of
which may require different fonts and character set encodings.
In some languages, each component might have a different
drawing direction, and some components might contain
context-dependent characters that change shape based on
relationships with neighboring characters.

When drawing such locale-dependent text, some locale-specific
knowledge is required;
for example, what fonts are required to draw the text,
how the text can be separated into components, and which
fonts are selected to draw each component.
Further, when bidirectional text must be drawn,
the internal representation order of the text must be changed
into the visual representation order to be drawn.

An X Output Method provides a functional interface so that clients
do not have to deal directly with such locale-dependent details.
Output methods provide the following capabilities:

Creating a set of fonts required to draw locale-dependent text.
Drawing locale-dependent text with a font set without the caller
needing to be aware of locale dependencies.
Obtaining the escapement and extents in pixels of locale-dependent text.
Determining if bidirectional or context-dependent drawing is required
in a specific locale with a specific font set.

Two different abstractions are used in the representation of
the output method for clients.

The abstraction used to communicate with an output method
is an opaque data structure represented by the
XOM
data type.
The abstraction for representing the state of a particular output thread
is called an output context.
The Xlib representation of an output context is an
XOC,
which is compatible with
XFontSet
in terms of its functional interface, but is
a broader, more generalized abstraction.

Output Method Functions

To open an output method, use
XOpenOM.

XOM XOpenOM(Display *display, XrmDatabase db, char *res_name, char *res_class);

display	Specifies the connection to the X server.
db	Specifies a pointer to the resource database.
res_name	Specifies the full resource name of the application.
res_class	Specifies the full class name of the application.

The
XOpenOM
function opens an output method
matching the current locale and modifiers specification.
The current locale and modifiers are bound to the output method
when
XOpenOM
is called.
The locale associated with an output method cannot be changed.

The specific output method to which this call will be routed
is identified on the basis of the current locale and modifiers.
XOpenOM
will identify a default output method corresponding to the
current locale.
That default can be modified using
XSetLocaleModifiers
to set the output method modifier.

The db argument is the resource database to be used by the output method
for looking up resources that are private to the output method.
It is not intended that this database be used to look
up values that can be set as OC values in an output context.
If db is NULL,
no database is passed to the output method.

The res_name and res_class arguments specify the resource name
and class of the application.
They are intended to be used as prefixes by the output method
when looking up resources that are common to all output contexts
that may be created for this output method.
The characters used for resource names and classes must be in the
X Portable Character Set.
The resources looked up are not fully specified
if res_name or res_class is NULL.

The res_name and res_class arguments are not assumed to exist beyond
the call to
XOpenOM.
The specified resource database is assumed to exist for the lifetime
of the output method.

XOpenOM
returns NULL if no output method could be opened.

To close an output method, use
XCloseOM.

Status XCloseOM(XOM om);

om	Specifies the output method.

The
XCloseOM
function closes the specified output method.

To set output method attributes, use
XSetOMValues.

char *XSetOMValues(XOM om);

om	Specifies the output method.
...	Specifies the variable-length argument list to set XOM values.

The
XSetOMValues
function presents a variable argument list programming interface
for setting properties or features of the specified output method.
This function returns NULL if it succeeds;
otherwise,
it returns the name of the first argument that could not be obtained.

No standard arguments are currently defined by Xlib.

To query an output method, use
XGetOMValues.

char *XGetOMValues(XOM om);

om	Specifies the output method.
...	Specifies the variable-length argument list to get XOM values.

The
XGetOMValues
function presents a variable argument list programming interface
for querying properties or features of the specified output method.
This function returns NULL if it succeeds;
otherwise,
it returns the name of the first argument that could not be obtained.

To obtain the display associated with an output method, use
XDisplayOfOM.

Display *XDisplayOfOM(XOM om);

om	Specifies the output method.

The
XDisplayOfOM
function returns the display associated with the specified output method.

To get the locale associated with an output method, use
XLocaleOfOM.

char *XLocaleOfOM(XOM om);

om	Specifies the output method.

The
XLocaleOfOM
returns the locale associated with the specified output method.

X Output Method Values

The following table describes how XOM values are interpreted by an
output method.
The first column lists the XOM values. The second column indicates
how each of the XOM values are treated by a particular output style.

The following key applies to this table.

Key	Explanation
G	This value may be read using `XGetOMValues`.

XOM Value	Key
XNRequiredCharSet	G
XNQueryOrientation	G
XNDirectionalDependentDrawing	G
XNContextualDrawing	G

Required Char Set

The
XNRequiredCharSet
argument returns the list of charsets that are required for loading the fonts
needed for the locale.
The value of the argument is a pointer to a structure of type
XOMCharSetList.

The
XOMCharSetList
structure is defined as follows:


typedef struct {
     int    charset_count;
     char   **charset_list;
} XOMCharSetList;

The charset_list member is a list of one or more null-terminated
charset names, and the charset_count member is the number of
charset names.

The required charset list is owned by Xlib and should not be modified or
freed by the client.
It will be freed by a call to
XCloseOM
with the associated
XOM.
Until freed, its contents will not be modified by Xlib.

Query Orientation

The
XNQueryOrientation
argument returns the global orientation of text when drawn.
Other than
XOMOrientation_LTR_TTB,
the set of orientations supported is locale-dependent.
The value of the argument is a pointer to a structure of type
XOMOrientation.
Clients are responsible for freeing the
XOMOrientation
structure by using
XFree;
this also frees the contents of the structure.


typedef struct {
     int          num_orientation;
     XOrientation *orientation;     /* Input Text description */
} XOMOrientation;

typedef enum {
     XOMOrientation_LTR_TTB,
     XOMOrientation_RTL_TTB,     
     XOMOrientation_TTB_LTR,
     XOMOrientation_TTB_RTL,
     XOMOrientation_Context
} XOrientation;

The possible value for XOrientation may be:

XOMOrientation_LTR_TTB
left-to-right, top-to-bottom global orientation
XOMOrientation_RTL_TTB
right-to-left, top-to-bottom global orientation
XOMOrientation_TTB_LTR
top-to-bottom, left-to-right global orientation
XOMOrientation_TTB_RTL
top-to-bottom, right-to-left global orientation
XOMOrientation_Context
contextual global orientation

Directional Dependent Drawing

The
XNDirectionalDependentDrawing
argument indicates whether the text rendering functions
implement implicit handling of directional text. If this value
is
True,
the output method has knowledge of directional
dependencies and reorders text as necessary when
rendering text. If this value is
False,
the output method does not implement any directional text
handling, and all character directions are assumed to be left-to-right.

Regardless of the rendering order of characters,
the origins of all characters are on the primary draw direction side
of the drawing origin.

This OM value presents functionality identical to the
XDirectionalDependentDrawing
function.

Context Dependent Drawing

The
XNContextualDrawing
argument indicates whether the text rendering functions
implement implicit context-dependent drawing. If this value is
True,
the output method has knowledge of context dependencies and
performs character shape editing, combining glyphs to present
a single character as necessary. The actual shape editing is
dependent on the locale implementation and the font set used.

This OM value presents functionality identical to the
XContextualDrawing
function.

Output Context Functions

An output context is an abstraction that contains both the data
required by an output method and the information required
to display that data.
There can be multiple output contexts for one output method.
The programming interfaces for creating, reading, or modifying
an output context use a variable argument list.
The name elements of the argument lists are referred to as XOC values.
It is intended that output methods be controlled by these XOC values.
As new XOC values are created,
they should be registered with the X Consortium.
An
XOC
can be used anywhere an
XFontSet
can be used, and vice versa;
XFontSet
is retained for compatibility with previous releases.
The concepts of output methods and output contexts include broader,
more generalized abstraction than font set,
supporting complex and more intelligent text display, and dealing not only
with multiple fonts but also with context dependencies.
However,
XFontSet
is widely used in several interfaces, so
XOC
is defined as an upward compatible type of
XFontSet.

To create an output context, use
XCreateOC.

XOC XCreateOC(XOM om);

om	Specifies the output method.
...	Specifies the variable-length argument list to set XOC values.

The
XCreateOC
function creates an output context within the specified output method.

The base font names argument is mandatory at creation time, and
the output context will not be created unless it is provided.
All other output context values can be set later.

XCreateOC
returns NULL if no output context could be created.
NULL can be returned for any of the following reasons:

A required argument was not set.
A read-only argument was set.
An argument name is not recognized.
The output method encountered an output method implementation-dependent error.

XCreateOC
can generate a
BadAtom
error.

To destroy an output context, use
XDestroyOC.

void XDestroyOC(XOC oc);

oc	Specifies the output context.

The
XDestroyOC
function destroys the specified output context.

To get the output method associated with an output context, use
XOMOfOC.

XOM XOMOfOC(XOC oc);

oc	Specifies the output context.

The
XOMOfOC
function returns the output method associated with the
specified output context.

Xlib provides two functions for setting and reading output context values,
respectively,
XSetOCValues
and
XGetOCValues.
Both functions have a variable-length argument list.
In that argument list, any XOC value's name must be denoted
with a character string using the X Portable Character Set.

To set XOC values, use
XSetOCValues.

char *XSetOCValues(XOC oc);

oc	Specifies the output context.
...	Specifies the variable-length argument list to set XOC values.

The
XSetOCValues
function returns NULL if no error occurred;
otherwise,
it returns the name of the first argument that could not be set.
An argument might not be set for any of the following reasons:

The argument is read-only.
The argument name is not recognized.
An implementation-dependent error occurs.

Each value to be set must be an appropriate datum,
matching the data type imposed by the semantics of the argument.

XSetOCValues
can generate a
BadAtom
error.

To obtain XOC values, use
XGetOCValues.

char *XGetOCValues(XOC oc);

oc	Specifies the output context.
...	Specifies the variable-length argument list to get XOC values.

The
XGetOCValues
function returns NULL if no error occurred; otherwise,
it returns the name of the first argument that could not be obtained.
An argument might not be obtained for any of the following reasons:

The argument name is not recognized.
An implementation-dependent error occurs.

Each argument value
following a name must point to a location where the value is to be stored.

Output Context Values

The following table describes how XOC values are interpreted
by an output method.
The first column lists the XOC values.
The second column indicates the alternative interfaces that function
identically and are provided for compatibility with previous releases.
The third column indicates how each of the XOC values is treated.

The following keys apply to this table.

Key	Explanation
C	This value must be set with `XCreateOC`.
D	This value may be set using `XCreateOC`. If it is not set,a default is provided.
G	This value may be read using `XGetOCValues`.
S	This value must be set using `XSetOCValues`.

XOC Value	Alternative Interface	Key
BaseFontName	`XCreateFontSet`	C-G
MissingCharSet	`XCreateFontSet`	G
DefaultString	`XCreateFontSet`	G
Orientation	-	D-S-G
ResourceName	-	S-G
ResourceClass	-	S-G
FontInfo	`XFontsOfFontSet`	G
OMAutomatic	-	G

Base Font Name

The
XNBaseFontName
argument is a list of base font names that Xlib uses
to load the fonts needed for the locale.
The base font names are a comma-separated list. The string is null-terminated
and is assumed to be in the Host Portable Character Encoding;
otherwise, the result is implementation-dependent.
White space immediately on either side of a separating comma is ignored.

Use of XLFD font names permits Xlib to obtain the fonts needed for a
variety of locales from a single locale-independent base font name.
The single base font name should name a family of fonts whose members
are encoded in the various charsets needed by the locales of interest.

An XLFD base font name can explicitly name a charset needed for the locale.
This allows the user to specify an exact font for use with a charset required
by a locale, fully controlling the font selection.

If a base font name is not an XLFD name,
Xlib will attempt to obtain an XLFD name from the font properties
for the font.
If Xlib is successful, the
XGetOCValues
function will return this XLFD name instead of the client-supplied name.

This argument must be set at creation time
and cannot be changed.
If no fonts exist for any of the required charsets,
or if the locale definition in Xlib requires that a font exist
for a particular charset and a font is not found for that charset,
XCreateOC
returns NULL.

When querying for the
XNBaseFontName
XOC value,
XGetOCValues
returns a null-terminated string identifying the base font names that
Xlib used to load the fonts needed for the locale.
This string is owned by Xlib and should not be modified or freed by
the client.
The string will be freed by a call to
XDestroyOC
with the associated
XOC.
Until freed, the string contents will not be modified by Xlib.

Missing CharSet

The
XNMissingCharSet
argument returns the list of required charsets that are missing from the
font set.
The value of the argument is a pointer to a structure of type
XOMCharSetList.

If fonts exist for all of the charsets required by the current locale,
charset_list is set to NULL and charset_count is set to zero.
If no fonts exist for one or more of the required charsets,
charset_list is set to a list of one or more null-terminated charset names
for which no fonts exist, and charset_count is set to the number of
missing charsets.
The charsets are from the list of the required charsets for
the encoding of the locale and do not include any charsets to which Xlib
may be able to remap a required charset.

The missing charset list is owned by Xlib and should not be modified or
freed by the client.
It will be freed by a call to
XDestroyOC
with the associated
XOC.
Until freed, its contents will not be modified by Xlib.

Default String

When a drawing or measuring function is called with an
XOC
that has missing charsets, some characters in the locale will not be
drawable.
The
XNDefaultString
argument returns a pointer to a string that represents the glyphs
that are drawn with this
XOC
when the charsets of the available fonts do not include all glyphs
required to draw a character.
The string does not necessarily consist of valid characters
in the current locale and is not necessarily drawn with
the fonts loaded for the font set,
but the client can draw or measure the default glyphs
by including this string in a string being drawn or measured with the
XOC.

If the
XNDefaultString
argument returned the empty string (""),
no glyphs are drawn and the escapement is zero.
The returned string is null-terminated.
It is owned by Xlib and should not be modified or freed by the client.
It will be freed by a call to
XDestroyOC
with the associated
XOC.
Until freed, its contents will not be modified by Xlib.

Orientation

The
XNOrientation
argument specifies the current orientation of text when drawn. The value of
this argument is one of the values returned by the
XGetOMValues
function with the
XNQueryOrientation
argument specified in the
XOrientation
list.
The value of the argument is of type
XOrientation.
When
XNOrientation
is queried, the value specifies the current orientation.
When
XNOrientation
is set, a value is used to set the current orientation.

When
XOMOrientation_Context
is set, the text orientation of the
text is determined according to an implementation-defined method
(for example, ISO 6429 control sequences), and the initial text orientation for
locale-dependent Xlib functions is assumed to
be
XOMOrientation_LTR_TTB.

The
XNOrientation
value does not change the prime drawing direction
for Xlib drawing functions.

Resource Name and Class

The
XNResourceName
and
XNResourceClass
arguments are strings that specify the full name and class
used by the client to obtain resources for the display of the output context.
These values should be used as prefixes for name and class
when looking up resources that may vary according to the output context.
If these values are not set,
the resources will not be fully specified.

It is not intended that values that can be set as XOM values be
set as resources.

When querying for the
XNResourceName
or
XNResourceClass
XOC value,
XGetOCValues
returns a null-terminated string.
This string is owned by Xlib and should not be modified or freed by
the client.
The string will be freed by a call to
XDestroyOC
with the associated
XOC
or when the associated value is changed via
XSetOCValues.
Until freed, the string contents will not be modified by Xlib.

Font Info

The
XNFontInfo
argument specifies a list of one or more
XFontStruct
structures
and font names for the fonts used for drawing by the given output context.
The value of the argument is a pointer to a structure of type
XOMFontInfo.


typedef struct {
     int         num_font;
     XFontStruct **font_struct_list;
     char        **font_name_list;
} XOMFontInfo;

A list of pointers to the
XFontStruct
structures is returned to font_struct_list.
A list of pointers to null-terminated, fully-specified font name strings
in the locale of the output context is returned to font_name_list.
The font_name_list order corresponds to the font_struct_list order.
The number of
XFontStruct
structures and font names is returned to num_font.

Because it is not guaranteed that a given character will be imaged using a
single font glyph,
there is no provision for mapping a character or default string
to the font properties, font ID, or direction hint for the font
for the character.
The client may access the
XFontStruct
list to obtain these values for all the fonts currently in use.

Xlib does not guarantee that fonts are loaded from the server
at the creation of an
XOC.
Xlib may choose to cache font data, loading it only as needed to draw text
or compute text dimensions.
Therefore, existence of the per_char metrics in the
XFontStruct
structures in the
XFontStructSet
is undefined.
Also, note that all properties in the
XFontStruct
structures are in the STRING encoding.

The client must not free the
XOMFontInfo
struct itself; it will be freed when the
XOC
is closed.

OM Automatic

The
XNOMAutomatic
argument returns whether the associated output context was created by
XCreateFontSet
or not. Because the
XFreeFontSet
function not only destroys the output context but also closes the implicit
output method associated with it,
XFreeFontSet
should be used with any output context created by
XCreateFontSet.
However, it is possible that a client does not know how the output context
was created.
Before a client destroys the output context,
it can query whether
XNOMAutomatic
is set to determine whether
XFreeFontSet
or
XDestroyOC
should be used to destroy the output context.

Creating and Freeing a Font Set

Xlib international text drawing is done using a set of one or more fonts,
as needed for the locale of the text.
Fonts are loaded according to a list of base font names
supplied by the client and the charsets required by the locale.
The
XFontSet
is an opaque type representing the state of a particular output thread
and is equivalent to the type
XOC.

The
XCreateFontSet
function is a convenience function for creating an output context using
only default values. The returned
XFontSet
has an implicitly created
XOM.
This
XOM
has an OM value
XNOMAutomatic
automatically set to
True
so that the output context self indicates whether it was created by
XCreateOC
or
XCreateFontSet.

XFontSet XCreateFontSet(Display *display, char *base_font_name_list, char ***missing_charset_list_return, int *missing_charset_count_return, char **def_string_return);

display	Specifies the connection to the X server.
base_font_name_list	Specifies the base font names.
missing_charset_list_return	Returns the missing charsets.
missing_charset_count_return	Returns the number of missing charsets.
def_string_return	Returns the string drawn for missing charsets.

The
XCreateFontSet
function creates a font set for the specified display.
The font set is bound to the current locale when
XCreateFontSet
is called.
The font set may be used in subsequent calls to obtain font
and character information and to image text in the locale of the font set.

The base_font_name_list argument is a list of base font names
that Xlib uses to load the fonts needed for the locale.
The base font names are a comma-separated list.
The string is null-terminated
and is assumed to be in the Host Portable Character Encoding;
otherwise, the result is implementation-dependent.
White space immediately on either side of a separating comma is ignored.

If a base font name is not an XLFD name,
Xlib will attempt to obtain an XLFD name from the font properties
for the font.
If this action is successful in obtaining an XLFD name, the
XBaseFontNameListOfFontSet
function will return this XLFD name instead of the client-supplied name.

Xlib uses the following algorithm to select the fonts
that will be used to display text with the
XFontSet.

For each font charset required by the locale,
the base font name list is searched for the first appearance of one
of the following cases that names a set of fonts that exist at the server:

The first XLFD-conforming base font name that specifies the required
charset or a superset of the required charset in its
CharSetRegistry
and
CharSetEncoding
fields.
The implementation may use a base font name whose specified charset
is a superset of the required charset, for example,
an ISO8859-1 font for an ASCII charset.
The first set of one or more XLFD-conforming base font names
that specify one or more charsets that can be remapped to support the
required charset.
The Xlib implementation may recognize various mappings
from a required charset to one or more other charsets
and use the fonts for those charsets.
For example, JIS Roman is ASCII with tilde and backslash replaced
by yen and overbar;
Xlib may load an ISO8859-1 font to support this character set
if a JIS Roman font is not available.
The first XLFD-conforming font name or the first non-XLFD font name
for which an XLFD font name can be obtained, combined with the
required charset (replacing the
CharSetRegistry
and
CharSetEncoding
fields in the XLFD font name).
As in case 1,
the implementation may use a charset that is a superset
of the required charset.
The first font name that can be mapped in some implementation-dependent
manner to one or more fonts that support imaging text in the charset.

For example, assume that a locale required the charsets:

ISO8859-1
JISX0208.1983
JISX0201.1976
GB2312-1980.0

The user could supply a base_font_name_list that explicitly specifies the
charsets, ensuring that specific fonts are used if they exist.
For example:

"-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-240-JISX0208.1983-0,\\
-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-120-JISX0201.1976-0,\\
-GB-Fixed-Medium-R-Normal--26-180-100-100-C-240-GB2312-1980.0,\\
-Adobe-Courier-Bold-R-Normal--25-180-75-75-M-150-ISO8859-1"

Alternatively, the user could supply a base_font_name_list
that omits the charsets,
letting Xlib select font charsets required for the locale.
For example:

"-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-240,\\
-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-120,\\
-GB-Fixed-Medium-R-Normal--26-180-100-100-C-240,\\
-Adobe-Courier-Bold-R-Normal--25-180-100-100-M-150"

Alternatively, the user could simply supply a single base font name
that allows Xlib to select from all available fonts
that meet certain minimum XLFD property requirements.
For example:

"-*-*-*-R-Normal--*-180-100-100-*-*"

If
XCreateFontSet
is unable to create the font set,
either because there is insufficient memory or because the current locale
is not supported,
XCreateFontSet
returns NULL, missing_charset_list_return is set to NULL,
and missing_charset_count_return
is set to zero.
If fonts exist for all of the charsets required by the current locale,
XCreateFontSet
returns a valid
XFontSet,
missing_charset_list_return is set to NULL,
and missing_charset_count_return is set to zero.

If no font exists for one or more of the required charsets,
XCreateFontSet
sets missing_charset_list_return to a
list of one or more null-terminated charset names for which no font exists
and sets missing_charset_count_return to the number of missing fonts.
The charsets are from the list of the required charsets for
the encoding of the locale and do not include any charsets to which Xlib
may be able to remap a required charset.

If no font exists for any of the required charsets
or if the locale definition in Xlib requires that a font exist
for a particular charset and a font is not found for that charset,
XCreateFontSet
returns NULL.
Otherwise,
XCreateFontSet
returns a valid
XFontSet
to font_set.

When an Xmb/wc drawing or measuring function is called with an
XFontSet
that has missing charsets, some characters in the locale will not be
drawable.
If def_string_return is non-NULL,
XCreateFontSet
returns a pointer to a string that represents the glyphs
that are drawn with this
XFontSet
when the charsets of the available fonts do not include all font glyphs
required to draw a codepoint.
The string does not necessarily consist of valid characters
in the current locale and is not necessarily drawn with
the fonts loaded for the font set,
but the client can draw and measure the default glyphs
by including this string in a string being drawn or measured with the
XFontSet.

If the string returned to def_string_return is the empty string (""),
no glyphs are drawn, and the escapement is zero.
The returned string is null-terminated.
It is owned by Xlib and should not be modified or freed by the client.
It will be freed by a call to
XFreeFontSet
with the associated
XFontSet.
Until freed, its contents will not be modified by Xlib.

The client is responsible for constructing an error message from the
missing charset and default string information and may choose to continue
operation in the case that some fonts did not exist.

The returned
XFontSet
and missing charset list should be freed with
XFreeFontSet
and
XFreeStringList,
respectively.
The client-supplied base_font_name_list may be freed
by the client after calling
XCreateFontSet.

To obtain a list of
XFontStruct
structures and full font names given an
XFontSet,
use
XFontsOfFontSet.

int XFontsOfFontSet(XFontSet font_set, XFontStruct ***font_struct_list_return, char ***font_name_list_return);

font_set	Specifies the font set.
font_struct_list_return	Returns the list of font structs.
font_name_list_return	Returns the list of font names.

The
XFontsOfFontSet
function returns a list of one or more
XFontStructs
and font names for the fonts used by the Xmb and Xwc layers
for the given font set.
A list of pointers to the
XFontStruct
structures is returned to font_struct_list_return.
A list of pointers to null-terminated, fully specified font name strings
in the locale of the font set is returned to font_name_list_return.
The font_name_list order corresponds to the font_struct_list order.
The number of
XFontStruct
structures and font names is returned as the value of the function.

Xlib does not guarantee that fonts are loaded from the server
at the creation of an
XFontSet.
Xlib may choose to cache font data, loading it only as needed to draw text
or compute text dimensions.
Therefore, existence of the per_char metrics in the
XFontStruct
structures in the
XFontStructSet
is undefined.
Also, note that all properties in the
XFontStruct
structures are in the STRING encoding.

The
XFontStruct
and font name lists are owned by Xlib
and should not be modified or freed by the client.
They will be freed by a call to
XFreeFontSet
with the associated
XFontSet.
Until freed, their contents will not be modified by Xlib.

To obtain the base font name list and the selected font name list given an
XFontSet,
use
XBaseFontNameListOfFontSet.

char *XBaseFontNameListOfFontSet(XFontSet font_set);

font_set

Specifies the font set.

The
XBaseFontNameListOfFontSet
function returns the original base font name list supplied
by the client when the
XFontSet
was created.
A null-terminated string containing a list of
comma-separated font names is returned
as the value of the function.
White space may appear immediately on either side of separating commas.

If
XCreateFontSet
obtained an XLFD name from the font properties for the font specified
by a non-XLFD base name, the
XBaseFontNameListOfFontSet
function will return the XLFD name instead of the non-XLFD base name.

The base font name list is owned by Xlib and should not be modified or
freed by the client.
It will be freed by a call to
XFreeFontSet
with the associated
XFontSet.
Until freed, its contents will not be modified by Xlib.

To obtain the locale name given an
XFontSet,
use
XLocaleOfFontSet.

char *XLocaleOfFontSet(XFontSet font_set);

font_set

Specifies the font set.

The
XLocaleOfFontSet
function
returns the name of the locale bound to the specified
XFontSet,
as a null-terminated string.

The returned locale name string is owned by Xlib
and should not be modified or freed by the client.
It may be freed by a call to
XFreeFontSet
with the associated
XFontSet.
Until freed, it will not be modified by Xlib.

The
XFreeFontSet
function is a convenience function for freeing an output context.
XFreeFontSet
also frees its associated
XOM
if the output context was created by
XCreateFontSet.

void XFreeFontSet(Display *display, XFontSet font_set);

display	Specifies the connection to the X server.
font_set	Specifies the font set.

The
XFreeFontSet
function frees the specified font set.
The associated base font name list, font name list,
XFontStruct
list, and
XFontSetExtents,
if any, are freed.

Obtaining Font Set Metrics

Metrics for the internationalized text drawing functions
are defined in terms of a primary draw direction,
which is the default direction in which the character origin advances
for each succeeding character in the string.
The Xlib interface is currently defined to support only a left-to-right
primary draw direction.
The drawing origin is the position passed to the drawing function
when the text is drawn.
The baseline is a line drawn through the drawing origin parallel
to the primary draw direction.
Character ink is the pixels painted in the foreground color
and does not include interline or intercharacter spacing
or image text background pixels.

The drawing functions are allowed to implement implicit text
directionality control, reversing the order in which characters are
rendered along the primary draw direction in response to locale-specific
lexical analysis of the string.

Regardless of the character rendering order,
the origins of all characters are on the primary draw direction side
of the drawing origin.
The screen location of a particular character image may be determined with
XmbTextPerCharExtents
or
XwcTextPerCharExtents.

The drawing functions are allowed to implement context-dependent
rendering, where the glyphs drawn for a string are not simply a
concatenation of the glyphs that represent each individual character.
A string of two characters drawn with
XmbDrawString
may render differently than if the two characters
were drawn with separate calls to
XmbDrawString.
If the client appends or inserts a character
in a previously drawn string,
the client may need to redraw some adjacent characters
to obtain proper rendering.

To find out about direction-dependent rendering, use
XDirectionalDependentDrawing.

Bool XDirectionalDependentDrawing(XFontSet font_set);

font_set

Specifies the font set.

The
XDirectionalDependentDrawing
function returns
True
if the drawing functions implement implicit text directionality;
otherwise, it returns
False.

To find out about context-dependent rendering, use
XContextualDrawing.

Bool XContextualDrawing(XFontSet font_set);

font_set

Specifies the font set.

The
XContextualDrawing
function returns
True
if text drawn with the font set might include context-dependent drawing;
otherwise, it returns
False.

To find out about context-dependent or direction-dependent rendering, use
XContextDependentDrawing.

Bool XContextDependentDrawing(XFontSet font_set);

font_set

Specifies the font set.

The
XContextDependentDrawing
function returns
True
if the drawing functions implement implicit text directionality or
if text drawn with the font_set might include context-dependent drawing;
otherwise, it returns
False.

The drawing functions do not interpret newline, tab, or other control
characters.
The behavior when nonprinting characters other than space are drawn
is implementation-dependent.
It is the client's responsibility to interpret control characters
in a text stream.

The maximum character extents for the fonts that are used by the text
drawing layers can be accessed by the
XFontSetExtents
structure:


typedef struct {
     XRectangle max_ink_extent;     /* over all drawable characters */
     XRectangle max_logical_extent; /* over all drawable characters */
} XFontSetExtents;

The
XRectangle
structures used to return font set metrics are the usual Xlib screen-oriented
rectangles
with x, y giving the upper left corner, and width and height always positive.

The max_ink_extent member gives the maximum extent, over all drawable characters, of
the rectangles that bound the character glyph image drawn in the
foreground color, relative to a constant origin.
See
XmbTextExtents
and
XwcTextExtents
for detailed semantics.

The max_logical_extent member gives the maximum extent,
over all drawable characters, of the rectangles
that specify minimum spacing to other graphical features,
relative to a constant origin.
Other graphical features drawn by the client, for example,
a border surrounding the text, should not intersect this rectangle.
The max_logical_extent member should be used to compute minimum
interline spacing and the minimum area that must be allowed
in a text field to draw a given number of arbitrary characters.

Due to context-dependent rendering,
appending a given character to a string may change
the string's extent by an amount other than that character's
individual extent.

The rectangles for a given character in a string can be obtained from
XmbTextPerCharExtents
or
XwcTextPerCharExtents.

To obtain the maximum extents structure given an
XFontSet,
use
XExtentsOfFontSet.

XFontSetExtents *XExtentsOfFontSet(XFontSet font_set);

font_set

Specifies the font set.

The
XExtentsOfFontSet
function returns an
XFontSetExtents
structure for the fonts used by the Xmb and Xwc layers
for the given font set.

The
XFontSetExtents
structure is owned by Xlib and should not be modified
or freed by the client.
It will be freed by a call to
XFreeFontSet
with the associated
XFontSet.
Until freed, its contents will not be modified by Xlib.

To obtain the escapement in pixels of the specified text as a value,
use
XmbTextEscapement
or
XwcTextEscapement.

int XmbTextEscapement(XFontSet font_set, char *string, int num_bytes);

int XwcTextEscapement(XFontSet font_set, wchar_t *string, int num_wchars);

font_set	Specifies the font set.
string	Specifies the character string.
num_bytes	Specifies the number of bytes in the string argument.
num_wchars	Specifies the number of characters in the string argument.

The
XmbTextEscapement
and
XwcTextEscapement
functions return the escapement in pixels of the specified string as a value,
using the fonts loaded for the specified font set.
The escapement is the distance in pixels in the primary draw
direction from the drawing origin to the origin of the next character to
be drawn, assuming that the rendering of the next character is not
dependent on the supplied string.

Regardless of the character rendering order,
the escapement is always positive.

To obtain the overall_ink_return and overall_logical_return arguments,
the overall bounding box of the string's image, and a logical bounding box,
use
XmbTextExtents
or
XwcTextExtents.

int XmbTextExtents(XFontSet font_set, char *string, int num_bytes, XRectangle *overall_ink_return, XRectangle *overall_logical_return);

int XwcTextExtents(XFontSet font_set, wchar_t *string, int num_wchars, XRectangle *overall_ink_return, XRectangle *overall_logical_return);

font_set	Specifies the font set.
string	Specifies the character string.
num_bytes	Specifies the number of bytes in the string argument.
num_wchars	Specifies the number of characters in the string argument.
overall_ink_return	Returns the overall ink dimensions.
overall_logical_return	Returns the overall logical dimensions.

The
XmbTextExtents
and
XwcTextExtents
functions set the components of the specified overall_ink_return and
overall_logical_return
arguments to the overall bounding box of the string's image
and a logical bounding box for spacing purposes, respectively.
They return the value returned by
XmbTextEscapement
or
XwcTextEscapement.
These metrics are relative to the drawing origin of the string,
using the fonts loaded for the specified font set.

If the overall_ink_return argument is non-NULL,
it is set to the bounding box of the string's character ink.
The overall_ink_return for a nondescending, horizontally drawn
Latin character is conventionally entirely above the baseline;
that is, overall_ink_return.height <= -overall_ink_return.y.
The overall_ink_return for a nonkerned character
is entirely at, and to the right of, the origin;
that is, overall_ink_return.x >= 0.
A character consisting of a single pixel at the origin would set
overall_ink_return fields y = 0, x = 0, width = 1, and height = 1.

If the overall_logical_return argument is non-NULL,
it is set to the bounding box that provides minimum spacing
to other graphical features for the string.
Other graphical features, for example, a border surrounding the text,
should not intersect this rectangle.

When the
XFontSet
has missing charsets,
metrics for each unavailable character are taken
from the default string returned by
XCreateFontSet
so that the metrics represent the text as it will actually be drawn.
The behavior for an invalid codepoint is undefined.

To determine the effective drawing origin for a character in a drawn string,
the client should call
XmbTextPerCharExtents
on the entire string, then on the character,
and subtract the x values of the returned
rectangles for the character.
This is useful to redraw portions of a line of text
or to justify words, but for context-dependent rendering,
the client should not assume that it can redraw the character by itself
and get the same rendering.

To obtain per-character information for a text string,
use
XmbTextPerCharExtents
or
XwcTextPerCharExtents.

Status XmbTextPerCharExtents(XFontSet font_set, char *string, int num_bytes, XRectangle *ink_array_return, XRectangle *logical_array_return, int array_size, int *num_chars_return, XRectangle *overall_ink_return, XRectangle *overall_logical_return);

Status XwcTextPerCharExtents(XFontSet font_set, wchar_t *string, int num_wchars, XRectangle *ink_array_return, XRectangle *logical_array_return, int array_size, int *num_chars_return, XRectangle *overall_ink_return, XRectangle *overall_logical_return);

font_set	Specifies the font set.
string	Specifies the character string.
num_bytes	Specifies the number of bytes in the string argument.
num_wchars	Specifies the number of characters in the string argument.
ink_array_return	Returns the ink dimensions for each character.
logical_array_return	Returns the logical dimensions for each character.
array_size	Specifies the size of ink_array_return and logical_array_return. The caller must pass in arrays of this size.
num_chars_return	Returns the number of characters in the string argument.
overall_ink_return	Returns the overall ink dimensions.
overall_logical_return	Returns the overall logical dimensions.

The
XmbTextPerCharExtents
and
XwcTextPerCharExtents
functions return the text dimensions of each character of the specified text,
using the fonts loaded for the specified font set.
Each successive element of ink_array_return and logical_array_return
is set to the successive character's drawn metrics,
relative to the drawing origin of the string and one
rectangle
for each character in the supplied text string.
The number of elements of ink_array_return and logical_array_return
that have been set is returned to num_chars_return.

Each element of ink_array_return is set to the bounding box
of the corresponding character's drawn foreground color.
Each element of logical_array_return is set to the bounding box
that provides minimum spacing to other graphical features
for the corresponding character.
Other graphical features should not intersect any of the
logical_array_return rectangles.

Note that an
XRectangle
represents the effective drawing dimensions of the character,
regardless of the number of font glyphs that are used to draw
the character or the direction in which the character is drawn.
If multiple characters map to a single character glyph,
the dimensions of all the
XRectangles
of those characters are the same.

When the
XFontSet
has missing charsets, metrics for each unavailable
character are taken from the default string returned by
XCreateFontSet
so that the metrics represent the text as it will actually be drawn.
The behavior for an invalid codepoint is undefined.

If the array_size is too small for the number of characters in the
supplied text, the functions return zero
and num_chars_return is set to the number of rectangles required.
Otherwise, the functions return a nonzero value.

If the overall_ink_return or overall_logical_return argument is non-NULL,
XmbTextPerCharExtents
and
XwcTextPerCharExtents
return the maximum extent of the string's metrics to overall_ink_return
or overall_logical_return, as returned by
XmbTextExtents
or
XwcTextExtents.

Drawing Text Using Font Sets

The functions defined in this section
draw text at a specified location in a drawable.
They are similar to the functions
XDrawText,
XDrawString,
and
XDrawImageString
except that they work with font sets instead of single fonts
and interpret the text based on the locale of the font set
instead of treating the bytes of the string as direct font indexes.
See section 8.6 for details
of the use of Graphics Contexts (GCs)
and possible protocol errors.
If a
BadFont
error is generated,
characters prior to the offending character may have been drawn.

The text is drawn using the fonts loaded for the specified font set;
the font in the GC is ignored and may be modified by the functions.
No validation that all fonts conform to some width rule is performed.

The text functions
XmbDrawText
and
XwcDrawText
use the following structures:


typedef struct {
     char     *chars;    /* pointer to string */
     int      nchars;    /* number of bytes */
     int      delta;     /* pixel delta between strings */
     XFontSet font_set;  /* fonts, None means don't change */
} XmbTextItem;


typedef struct {
     wchar_t *chars;     /* pointer to wide char string */
     int nchars;     /* number of wide characters */
     int delta;     /* pixel delta between strings */
     XFontSet font_set;     /* fonts, None means don't change */
} XwcTextItem;

To draw text using multiple font sets in a given drawable, use
XmbDrawText
or
XwcDrawText.

void XmbDrawText(Display *display, Drawable d, GC gc, int x, int y, XmbTextItem *items, int nitems);

void XwcDrawText(Display *display, Drawable d, GC gc, int x, int y, XwcTextItem *items, int nitems);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
x
y	Specify the x and y coordinates of the position in the new parent window.
items	Specifies an array of text items.
nitems	Specifies the number of text items in the array.

The
XmbDrawText
and
XwcDrawText
functions allow complex spacing and font set shifts between text strings.
Each text item is processed in turn, with the origin of a text
element advanced in the primary draw direction by the escapement of the
previous text item.
A text item delta specifies an additional escapement of the text item
drawing origin in the primary draw direction.
A font_set member other than
None
in an item causes the font set to be used for this and subsequent text items
in the text_items list.
Leading text items with a font_set member set to
None
will not be drawn.

XmbDrawText
and
XwcDrawText
do not perform any context-dependent rendering between text segments.
Clients may compute the drawing metrics by passing each text segment to
XmbTextExtents
and
XwcTextExtents
or
XmbTextPerCharExtents
and
XwcTextPerCharExtents.
When the
XFontSet
has missing charsets, each unavailable character is drawn
with the default string returned by
XCreateFontSet.
The behavior for an invalid codepoint is undefined.

To draw text using a single font set in a given drawable, use
XmbDrawString
or
XwcDrawString.

void XmbDrawString(Display *display, Drawable d, XFontSet font_set, GC gc, int x, int y, char *string, int num_bytes);

void XwcDrawString(Display *display, Drawable d, XFontSet font_set, GC gc, int x, int y, wchar_t *string, int num_wchars);

display	Specifies the connection to the X server.
d	Specifies the drawable.
font_set	Specifies the font set.
gc	Specifies the GC.
x
y	Specify the x and y coordinates of the position in the new parent window.
string	Specifies the character string.
num_bytes	Specifies the number of bytes in the string argument.
num_wchars	Specifies the number of characters in the string argument.

The
XmbDrawString
and
XwcDrawString
functions draw the specified text with the foreground pixel.
When the
XFontSet
has missing charsets, each unavailable character is drawn
with the default string returned by
XCreateFontSet.
The behavior for an invalid codepoint is undefined.

To draw image text using a single font set in a given drawable, use
XmbDrawImageString
or
XwcDrawImageString.

void XmbDrawImageString(Display *display, Drawable d, XFontSet font_set, GC gc, int x, int y, char *string, int num_bytes);

void XwcDrawImageString(Display *display, Drawable d, XFontSet font_set, GC gc, int x, int y, wchar_t *string, int num_wchars);

display	Specifies the connection to the X server.
d	Specifies the drawable.
font_set	Specifies the font set.
gc	Specifies the GC.
x
y	Specify the x and y coordinates of the position in the new parent window.
string	Specifies the character string.
num_bytes	Specifies the number of bytes in the string argument.
num_wchars	Specifies the number of characters in the string argument.

The
XmbDrawImageString
and
XwcDrawImageString
functions fill a destination rectangle with the background pixel defined
in the GC and then paint the text with the foreground pixel.
The filled rectangle is the rectangle returned to overall_logical_return by
XmbTextExtents
or
XwcTextExtents
for the same text and
XFontSet.

When the
XFontSet
has missing charsets, each unavailable character is drawn
with the default string returned by
XCreateFontSet.
The behavior for an invalid codepoint is undefined.

Input Methods

This section provides discussions of the following X Input Method
(XIM) topics:

Input method overview
Input method management
Input method functions
Input method values
Input context functions
Input context values
Input method callback semantics
Event filtering
Getting keyboard input
Input method conventions

Input Method Overview

This section provides definitions for terms and concepts used
for internationalized text input and a brief overview of the
intended use of the mechanisms provided by Xlib.

A large number of languages in the world use alphabets
consisting of a small set of symbols (letters) to form words.
To enter text into a computer in an alphabetic language,
a user usually has a keyboard on which there exist key symbols corresponding
to the alphabet.
Sometimes, a few characters of an alphabetic language are missing
on the keyboard.
Many computer users who speak a Latin-alphabet-based language
only have an English-based keyboard.
They need to hit a combination of keystrokes
to enter a character that does not exist directly on the keyboard.
A number of algorithms have been developed for entering such characters.
These are known as European input methods, compose input methods,
or dead-key input methods.

Japanese is an example of a language with a phonetic symbol set,
where each symbol represents a specific sound.
There are two phonetic symbol sets in Japanese: Katakana and Hiragana.
In general,
Katakana is used for words that are of foreign origin,
and Hiragana is used for writing native Japanese words.
Collectively, the two systems are called Kana.
Each set consists of 48 characters.

Korean also has a phonetic symbol set, called Hangul.
Each of the 24 basic phonetic symbols (14 consonants and 10 vowels)
represents a specific sound.
A syllable is composed of two or three parts:
the initial consonants, the vowels, and the optional last consonants.
With Hangul,
syllables can be treated as the basic units on which text processing is done.
For example,
a delete operation may work on a phonetic symbol or a syllable.
Korean code sets include several thousands of these syllables.
A user types the phonetic symbols that make up the syllables of the words
to be entered.
The display may change as each phonetic symbol is entered.
For example,
when the second phonetic symbol of a syllable is entered,
the first phonetic symbol may change its shape and size.
Likewise, when the third phonetic symbol is entered,
the first two phonetic symbols may change their shape and size.

Not all languages rely solely on alphabetic or phonetic systems.
Some languages, including Japanese and Korean, employ an
ideographic writing system.
In an ideographic system, rather than taking a small set of
symbols and combining them in different ways to create words,
each word consists of one unique symbol (or, occasionally, several symbols).
The number of symbols can be very large:
approximately 50,000 have been identified in Hanzi,
the Chinese ideographic system.

Two major aspects of ideographic systems impact their use with computers.
First, the standard computer character sets in Japan, China, and Korea
include roughly 8,000 characters,
while sets in Taiwan have between 15,000 and 30,000 characters.
This makes it necessary to use more than one byte to represent a character.
Second, it obviously is impractical to have a keyboard that includes
all of a given language's ideographic symbols.
Therefore, a mechanism is required for entering characters
so that a keyboard with a reasonable number of keys can be used.
Those input methods are usually based on phonetics,
but there also exist methods based on the graphical properties of
characters.

In Japan, both Kana and the ideographic system Kanji are used.
In Korea, Hangul and sometimes the ideographic system Hanja are used.
Now consider entering ideographs in Japan, Korea, China, and Taiwan.

In Japan, either Kana or English characters are typed and then a region
is selected (sometimes automatically) for conversion to Kanji.
Several Kanji characters may have the same phonetic representation.
If that is the case with the string entered,
a menu of characters is presented and
the user must choose the appropriate one.
If no choice is necessary or a preference has been established,
the input method does the substitution directly.
When Latin characters are converted to Kana or Kanji,
it is called a romaji conversion.

In Korea, it is usually acceptable to keep Korean text in Hangul form,
but some people may choose to write Hanja-originated words in Hanja
rather than in Hangul.
To change Hangul to Hanja,
the user selects a region for conversion
and then follows the same basic method as that described for Japanese.

Probably because there are well-accepted phonetic writing systems
for Japanese and Korean,
computer input methods in these countries for entering ideographs
are fairly standard.
Keyboard keys have both English characters and phonetic symbols
engraved on them, and the user can switch between the two sets.

The situation is different for Chinese.
While there is a phonetic system called Pinyin promoted by authorities,
there is no consensus for entering Chinese text.
Some vendors use a phonetic decomposition (Pinyin or another),
others use ideographic decomposition of Chinese words,
with various implementations and keyboard layouts.
There are about 16 known methods, none of which is a clear standard.

Also, there are actually two ideographic sets used:
Traditional Chinese (the original written Chinese)
and Simplified Chinese.
Several years ago,
the People's Republic of China launched a campaign to simplify
some ideographic characters and eliminate redundancies altogether.
Under the plan,
characters would be streamlined every five years.
Characters have been revised several times now,
resulting in the smaller, simpler set that makes up Simplified Chinese.

Input Method Architecture

As shown in the previous section,
there are many different input methods in use today,
each varying with language, culture, and history.
A common feature of many input methods is that the user may type
multiple keystrokes to compose a single character (or set
of characters).
The process of composing characters from keystrokes is called
preediting.
It may require complex algorithms and large dictionaries
involving substantial computer resources.

Input methods may require one or more areas in which to show the
feedback of the actual keystrokes, to propose disambiguation to the
user, to list dictionaries, and so on.
The input method areas of concern are as follows:

The status area is a logical extension of the
LEDs that exist on the physical keyboard.
It is a window that is intended to present the internal state
of the input method that is critical to the user.
The status area may consist of text data and bitmaps or some combination.
The preedit area displays the
intermediate text for those languages that are composing prior to
the client handling the data.
The auxiliary area is used for pop-up menus and customizing
dialogs that may be required for an input method.
There may be multiple auxiliary areas for an input method.
Auxiliary areas are managed by the input method independent of the client.
Auxiliary areas are assumed to be separate dialogs,
which are maintained by the input method.

There are various user interaction styles used for preediting.
The ones supported by Xlib are as follows:

For on-the-spot input methods,
preediting data will be displayed directly in the application window.
Application data is moved to allow preedit data to appear
at the point of insertion.
Over-the-spot preediting means that the data is displayed in
a preedit window that is placed over the point of insertion.
Off-the-spot preediting means that the preedit window is
inside the application window but not at the point of insertion.
Often, this type of window is placed at the bottom of the application window.
Root-window preediting refers to input methods that use a preedit
window that is the child of
RootWindow.

It would require a lot of computing resources if portable applications
had to include input methods for all the languages in the world.
To avoid this,
a goal of the Xlib design is to allow an application
to communicate with an input method placed in a separate process.
Such a process is called an input server.
The server to which the application should connect is dependent on
the environment when the application is started up,
that is, the user language and the actual encoding to be used for it.
The input method connection is said to be locale-dependent.
It is also user-dependent.
For a given language, the user can choose, to some extent,
the user interface style of input method (if choice is possible among
several).

Using an input server implies communication overhead,
but applications can be migrated without relinking.
Input methods can be implemented either as a
stub communicating to an input server or as a local library.

An input method may be based on a front-end or a back-end
architecture.
In a front-end architecture,
there are two separate connections to the X server:
keystrokes go directly from the X server to the input method on
one connection and other events to the regular client connection.
The input method is then acting as a filter and sends composed strings
to the client.
A front-end architecture requires synchronization between the
two connections to avoid lost key events or locking issues.

In a back-end architecture,
a single X server connection is used.
A dispatching mechanism must decide on this channel to delegate appropriate
keystrokes to the input method.
For instance,
it may retain a Help keystroke for its own purpose.
In the case where the input method is a separate process (that is, a server),
there must be a special communication protocol between the back-end client
and the input server.

A front-end architecture introduces synchronization issues
and a filtering mechanism for noncharacter keystrokes
(Function keys, Help, and so on).
A back-end architecture sometimes implies more communication overhead
and more process switching.
If all three processes (X server, input server, client)
are running on a single workstation,
there are two process switches for each keystroke in a back-end
architecture,
but there is only one in a front-end architecture.

The abstraction used by a client to communicate with an input method
is an opaque data structure represented by the
XIM
data type.
This data structure is returned by the
XOpenIM
function, which opens an input method on a given display.
Subsequent operations on this data structure encapsulate all communication
between client and input method.
There is no need for an X client to use any networking library
or natural language package to use an input method.

A single input server may be used for one or more languages,
supporting one or more encoding schemes.
But the strings returned from an input method will always be encoded
in the (single) locale associated with the
XIM
object.

Input Contexts

Xlib provides the ability to manage a multi-threaded state for text input.
A client may be using multiple windows,
each window with multiple text entry areas,
and the user possibly switching among them at any time.
The abstraction for representing the state of a particular input thread
is called an input context.
The Xlib representation of an input context is an
XIC.

An input context is the abstraction retaining the state, properties,
and semantics of communication between a client and an input method.
An input context is a combination of an input method, a locale
specifying the encoding of the character strings to be returned,
a client window, internal state information,
and various layout or appearance characteristics.
The input context concept somewhat matches for input the graphics context
abstraction defined for graphics output.

One input context belongs to exactly one input method.
Different input contexts may be associated with the same input method,
possibly with the same client window.
An
XIC
is created with the
XCreateIC
function, providing an
XIM
argument and affiliating the input context to the input method
for its lifetime.
When an input method is closed with
XCloseIM,
all of its affiliated input contexts should not be used any more
(and should preferably be destroyed before closing the input method).

Considering the example of a client window with multiple text entry areas,
the application programmer could, for example, choose to implement as follows:

As many input contexts are created as text entry areas, and the client
will get the input accumulated on each context each time it looks up
in that context.
A single context is created for a top-level window in the application.
If such a window contains several text entry areas,
each time the user moves to another text entry area,
the client has to indicate changes in the context.

A range of choices can be made by application designers to use
either a single or multiple input contexts,
according to the needs of their application.

Getting Keyboard Input

To obtain characters from an input method,
a client must call the function
XmbLookupString
or
XwcLookupString
with an input context created from that input method.
Both a locale and display are bound to an input method when it is opened,
and an input context inherits this locale and display.
Any strings returned by
XmbLookupString
or
XwcLookupString
will be encoded in that locale.

Focus Management

For each text entry area in which the
XmbLookupString
or
XwcLookupString
functions are used,
there will be an associated input context.

When the application focus moves to a text entry area,
the application must set the input context focus to the
input context associated with that area.
The input context focus is set by calling
XSetICFocus
with the appropriate input context.

Also, when the application focus moves out of a text entry area, the
application should unset the focus for the associated input context
by calling
XUnsetICFocus.
As an optimization, if
XSetICFocus
is called successively on two different input contexts,
setting the focus on the second
will automatically unset the focus on the first.

To set and unset the input context focus correctly,
it is necessary to track application-level focus changes.
Such focus changes do not necessarily correspond to X server focus changes.

If a single input context
is being used to do input for
multiple text entry areas, it will also be necessary
to set the focus window of the
input context whenever the focus window changes
(see section 13.5.6.3).

Geometry Management

In most input method architectures
(on-the-spot being the notable exception),
the input method will perform the display of its own data.
To provide better visual locality,
it is often desirable to have the input method areas embedded within a client.
To do this,
the client may need to allocate space for an input method.
Xlib provides support that allows the size and position of input method
areas to be provided by a client.
The input method areas that are supported for geometry management
are the status area and the preedit area.

The fundamental concept on which geometry management for input method windows
is based is the proper division of responsibilities between the
client (or toolkit) and the input method.
The division of responsibilities is as follows:

The client is responsible for the geometry of the input method window.
The input method is responsible for the contents of the input method window.

An input method is able to suggest a size to the client,
but it cannot suggest a placement.
Also the input method can only suggest a size.
It does not determine the size,
and it must accept the size it is given.

Before a client provides geometry management for an input method,
it must determine if geometry management is needed.
The input method indicates the need for geometry management
by setting
XIMPreeditArea
or
XIMStatusArea
in its
XIMStyles
value returned by
XGetIMValues.
When a client has decided that it will provide geometry management
for an input method,
it indicates that decision by setting the
XNInputStyle
value in the
XIC.

After a client has established with the input method
that it will do geometry management,
the client must negotiate the geometry with the input method.
The geometry is negotiated by the following steps:

The client suggests an area to the input method by setting the
XNAreaNeeded
value for that area.
If the client has no constraints for the input method,
it either will not suggest an area or will set the width and height to zero.
Otherwise, it will set one of the values.
The client will get the XIC value
XNAreaNeeded.
The input method will return its suggested size in this value.
The input method should pay attention to any constraints suggested
by the client.
The client sets the XIC value
XNArea
to inform the input method of the geometry of its window.
The client should try to honor the geometry requested by the input method.
The input method must accept this geometry.

Clients doing geometry management must be aware that setting other
XIC values may affect the geometry desired by an input method.
For example,
XNFontSet
and
XNLineSpace
may change the geometry desired by the input method.

The table of XIC values
(see section 13.5.6)
indicates the values that can cause the desired geometry to change
when they are set.
It is the responsibility of the client to renegotiate the geometry
of the input method window when it is needed.

In addition,
a geometry management callback is provided
by which an input method can initiate a geometry change.

Event Filtering

A filtering mechanism is provided to allow input methods
to capture X events transparently to clients.
It is expected that toolkits (or clients) using
XmbLookupString
or
XwcLookupString
will call this filter at some point in the event processing mechanism
to make sure that events needed by an input method can be filtered
by that input method.

If there were no filter,
a client could receive and discard events that are necessary
for the proper functioning of an input method.
The following provides a few examples of such events:

Expose events on preedit window in local mode.
Events may be used by an input method to communicate with an input server.
Such input server protocol-related events have to be intercepted
if one does not want to disturb client code.
Key events can be sent to a filter before they are bound
to translations such as those the X Toolkit Intrinsics library provides.

Clients are expected to get the XIC value
XNFilterEvents
and augment the event mask for the client window with that event mask.
This mask may be zero.

Callbacks

When an on-the-spot input method is implemented,
only the client can insert or delete preedit data in place
and possibly scroll existing text.
This means that the echo of the keystrokes has to be achieved
by the client itself, tightly coupled with the input method logic.

When the user enters a keystroke,
the client calls
XmbLookupString
or
XwcLookupString.
At this point, in the on-the-spot case,
the echo of the keystroke in the preedit has not yet been done.
Before returning to the client logic that handles the input characters,
the look-up function
must call the echoing logic to insert the new keystroke.
If the keystrokes entered so far make up a character,
the keystrokes entered need to be deleted,
and the composed character will be returned.
Hence, what happens is that, while being called by client code,
the input method logic has to call back to the client before it returns.
The client code, that is, a callback procedure,
is called from the input method logic.

There are a number of cases where the input method logic has to
call back the client.
Each of those cases is associated with a well-defined callback action.
It is possible for the client to specify, for each input context,
what callback is to be called for each action.

There are also callbacks provided for feedback of status information
and a callback to initiate a geometry request for an input method.

Visible Position Feedback Masks

In the on-the-spot input style, there is a problem when
attempting to draw preedit strings that are longer than the
available space. Once the display area is exceeded, it is not
clear how best to display the preedit string.
The visible position feedback masks of
XIMText
help resolve this problem by allowing the input method to specify hints that
indicate the essential portions of the preedit string.
For example, such hints can help developers implement
scrolling of a long preedit string within a short preedit display area.

Preedit String Management

As highlighted before, the input method architecture provides
preediting, which supports a type of preprocessor input composition.
In this case, composition consists of interpreting a sequence
of key events and returning a committed string via
XmbLookupString
or
XwcLookupString.
This provides the basics for input methods.

In addition to preediting based on key events, a general framework
is provided to give a client that desires it more advanced preediting based
on the text within the client. This framework is called
string conversion and is provided using XIC values.
The fundamental concept of string conversion
is to allow the input method to manipulate the client's
text independent of any user preediting operation.

The need for string conversion is based on
language needs and input method capabilities.
The following are some examples of string conversion:

Transliteration conversion provides language-specific conversions
within the input method.
In the case of Korean input, users wish to convert a Hangul string
into a Hanja string while in preediting, after preediting,
or in other situations (for example, on a selected string).
The conversion is triggered when the user
presses a Hangul-to-Hanja key sequence (which may be input method specific).
Sometimes the user may want to invoke the conversion after finishing
preediting or on a user-selected string.
Thus, the string to be converted is in an application buffer, not in
the preedit area of the input method. The string conversion services
allow the client to request this transliteration conversion from the
input method.
There are many other transliteration conversions defined for
various languages, for example, Kana-to-Kanji conversion in Japanese.

The key to remember is that transliteration conversions are triggered
at the request of the user and returned to the client
immediately without affecting the preedit area of the input method.
Reconversion of a previously committed string or
a selected string is supported by many input methods as a
convenience to the user.
For example, a user tends to mistype the commit key while
preediting. In that case, some input methods provide a special
key sequence to request a “reconvert” operation on the
committed string, similiar to the undo facility provided by most
text editors.
Another example is where the user is proofreading a document
that has some misconversions from preediting and wants to correct
the misconverted text. Such reconversion is again triggered
by the user invoking some special action, but reconversions should
not affect the state of the preedit area.
Context-sensitive conversion is required for some languages
and input methods that need to retrieve text that surrounds the
current spot location (cursor position) of the client's buffer.
Such text is needed when the preediting operation depends on
some surrounding characters (usually preceding the spot location).
For example,
in Thai language input, certain character sequences may be invalid and
the input method may want to check whether characters constitute a
valid word. Input methods that do such context-dependent
checking need to retrieve the characters surrounding the current
cursor position to obtain complete words.

Unlike other conversions, this conversion is not explicitly
requested by the user.
Input methods that provide such context-sensitive conversion
continuously need to request context from the client, and any change
in the context of the spot location may affect such conversions.
The client's context would be needed if the user moves the cursor
and starts editing again.

For this reason, an input method supporting this type of conversion
should take notice of when the client calls
XmbResetIC
or
XwcResetIC,
which is usually an indication of a context change.

Context-sensitive conversions just need a copy of the client's text,
while other conversions replace the client's text with new text
to achieve the reconversion or transliteration. Yet in all
cases the result of a conversion, either immediately or via preediting,
is returned by the
XmbLookupString
and
XwcLookupString
functions.

String conversion support is dependent on the availability of the
XNStringConversion
or
XNStringConversionCallback
XIC values.
Because the input method may not support string conversions,
clients have to query the availability of string conversion
operations by checking the supported XIC values list by calling
XGetIMValues
with the
XNQueryICValuesList
IM value.

The difference between these two values is whether the
conversion is invoked by the client or the input method.
The
XNStringConversion
XIC value is used by clients to request
a string conversion from the input method. The client
is responsible for determining which events are used
to trigger the string conversion and whether the string to be
converted should be copied or deleted. The type of conversion
is determined by the input method; the client can only
pass the string to be converted. The client is guaranteed that
no
XNStringConversionCallback
will be issued when this value is set; thus, the client need
only set one of these values.

The
XNStringConversionCallback
XIC value is used by the client to notify the input method that
it will accept requests from the input method for string conversion.
If this value is set,
it is the input method's responsibility to determine which
events are used to trigger the string conversion.
When such events occur, the input method issues a call to the
client-supplied procedure to retrieve the string to be converted. The client's
callback procedure is notified whether to copy or delete the string and
is provided with hints as to the amount of text needed.
The
XIMStringConversionCallbackStruct
specifies which text should be passed back to the input method.

Finally, the input method may call the client's
XNStringConversionCallback
procedure multiple times if the string returned from the callback is
not sufficient to perform a successful conversion. The arguments
to the client's procedure allow the input method to define a
position (in character units) relative to the client's cursor position
and the size of the text needed. By varying the position and size of
the desired text in subsequent callbacks, the input method can retrieve
additional text.

Input Method Management

The interface to input methods might appear to be simply creating
an input method
(XOpenIM)
and freeing an input method
(XCloseIM).
However, input methods may
require complex communication with input method servers (IM servers),
for example:

If the X server, IM server, and X clients are started asynchronously,
some clients may attempt to connect to the IM server before it is
fully operational, and fail.
Therefore, some mechanism is needed to allow clients to detect when an IM
server has started.

It is up to clients to decide what should be done when an IM server is
not available (for example, wait, or use some other IM server).

Some input methods may allow the underlying IM server to be switched.
Such customization may be desired without restarting the entire client.

To support management of input methods in these cases, the following
functions are provided:

`XRegisterIMInstantiateCallback`	This function allows clients to register a callback procedure to be called when Xlib detects that an IM server is up and available.
`XOpenIM`	A client calls this function as a result of the callback procedure being called.
`XSetIMValues`, `XSetICValues`	These functions use the XIM and XIC values, XNDestroyCallback, to allow a client to register a callback procedure to be called when Xlib detects that an IM server that was associated with an opened input method is no longer available. In addition, this function can be used to switch IM servers for those input methods that support such functionality. The IM value for switching IM servers is implementation-dependent; see the description below about switching IM servers.
`XUnregisterIMInstantiateCallback`	This function removes a callback procedure registered by the client.

Input methods that support switching of IM servers may exhibit some
side-effects:

The input method will ensure that any new IM server supports any of the
input styles being used by input contexts already associated with the
input method.
However, the list of supported input styles may be different.

Geometry management requests on previously created input contexts
may be initiated by the new IM server.

Hot Keys

Some clients need to guarantee which keys can be used to escape from the
input method, regardless of the input method state;
for example, the client-specific Help key or the keys to move the
input focus.
The HotKey mechanism allows clients
to specify a set of keys for this purpose. However, the input
method might not allow clients to specify hot keys.
Therefore, clients have to query support of hot keys by checking the
supported XIC values list by calling
XGetIMValues
with the
XNQueryICValuesList
IM value.
When the hot keys specified conflict with the key bindings of the
input method, hot keys take precedence over the key bindings of the input
method.

Preedit State Operation

An input method may have several internal states, depending on its
implementation and the locale. However, one state that is
independent of locale and implementation is whether the input method
is currently performing a preediting operation.
Xlib provides the ability for an application to manage the preedit state
programmatically. Two methods are provided for
retrieving the preedit state of an input context.
One method is to query the state by calling
XGetICValues
with the
XNPreeditState
XIC value.
Another method is to receive notification whenever
the preedit state is changed. To receive such notification,
an application needs to register a callback by calling
XSetICValues
with the
XNPreeditStateNotifyCallback
XIC value.
In order to change the preedit state programmatically, an application
needs to call
XSetICValues
with
XNPreeditState.

Availability of the preedit state is input method dependent. The input
method may not provide the ability to set the state or to
retrieve the state programmatically. Therefore, clients have to
query availability of preedit state operations by checking the
supported XIC values list by calling
XGetIMValues
with the
XNQueryICValuesList
IM value.

Input Method Functions

To open a connection, use
XOpenIM.

XIM XOpenIM(Display *display, XrmDatabase db, char *res_name, char *res_class);

display	Specifies the connection to the X server.
db	Specifies a pointer to the resource database.
res_name	Specifies the full resource name of the application.
res_class	Specifies the full class name of the application.

The
XOpenIM
function opens an input method,
matching the current locale and modifiers specification.
Current locale and modifiers are bound to the input method at opening time.
The locale associated with an input method cannot be changed dynamically.
This implies that the strings returned by
XmbLookupString
or
XwcLookupString,
for any input context affiliated with a given input method,
will be encoded in the locale current at the time the input method is opened.

The specific input method to which this call will be routed
is identified on the basis of the current locale.
XOpenIM
will identify a default input method corresponding to the
current locale.
That default can be modified using
XSetLocaleModifiers
for the input method modifier.

The db argument is the resource database to be used by the input method
for looking up resources that are private to the input method.
It is not intended that this database be used to look
up values that can be set as IC values in an input context.
If db is NULL,
no database is passed to the input method.

The res_name and res_class arguments specify the resource name
and class of the application.
They are intended to be used as prefixes by the input method
when looking up resources that are common to all input contexts
that may be created for this input method.
The characters used for resource names and classes must be in the
X Portable Character Set.
The resources looked up are not fully specified
if res_name or res_class is NULL.

The res_name and res_class arguments are not assumed to exist beyond
the call to
XOpenIM.
The specified resource database is assumed to exist for the lifetime
of the input method.

XOpenIM
returns NULL if no input method could be opened.

To close a connection, use
XCloseIM.

Status XCloseIM(XIM im);

im	Specifies the input method.

The
XCloseIM
function closes the specified input method.

To set input method attributes, use
XSetIMValues.

char *XSetIMValues(XIM im);

im	Specifies the input method.
...	Specifies the variable-length argument list to set XIM values.

The
XSetIMValues
function presents a variable argument list programming interface
for setting attributes of the specified input method.
It returns NULL if it succeeds;
otherwise,
it returns the name of the first argument that could not be set.
Xlib does not attempt to set arguments from the supplied list that
follow the failed argument;
all arguments in the list preceding the failed argument have been set
correctly.

To query an input method, use
XGetIMValues.

char *XGetIMValues(XIM im);

im	Specifies the input method.
...	Specifies the variable length argument list to get XIM values.

The
XGetIMValues
function presents a variable argument list programming interface
for querying properties or features of the specified input method.
This function returns NULL if it succeeds;
otherwise,
it returns the name of the first argument that could not be obtained.

Each XIM value argument (following a name) must point to
a location where the XIM value is to be stored.
That is, if the XIM value is of type T,
the argument must be of type T*.
If T itself is a pointer type,
then
XGetIMValues
allocates memory to store the actual data,
and the client is responsible for freeing this data by calling
XFree
with the returned pointer.

To obtain the display associated with an input method, use
XDisplayOfIM.

Display *XDisplayOfIM(XIM im);

im	Specifies the input method.

The
XDisplayOfIM
function returns the display associated with the specified input method.

To get the locale associated with an input method, use
XLocaleOfIM.

char *XLocaleOfIM(XIM im);

im	Specifies the input method.

The
XLocaleOfIM
function returns the locale associated with the specified input method.

To register an input method instantiate callback, use
XRegisterIMInstantiateCallback.

Bool XRegisterIMInstantiateCallback(Display *display, XrmDatabase db, char *res_name, char *res_class, XIMProc callback, XPointer *client_data);

display	Specifies the connection to the X server.
db	Specifies a pointer to the resource database.
res_name	Specifies the full resource name of the application.
res_class	Specifies the full class name of the application.
callback	Specifies a pointer to the input method instantiate callback.
client_data	Specifies the additional client data.

The
XRegisterIMInstantiateCallback
function registers a callback to be invoked whenever a new input method
becomes available for the specified display that matches the current
locale and modifiers.

The function returns
True
if it succeeds; otherwise, it returns
False.

The generic prototype is as follows:

void IMInstantiateCallback(Display *display, XPointer client_data, XPointer call_data);

display	Specifies the connection to the X server.
client_data	Specifies the additional client data.
call_data	Not used for this callback and always passed as NULL.

To unregister an input method instantiation callback, use
XUnregisterIMInstantiateCallback.

Bool XUnregisterIMInstantiateCallback(Display *display, XrmDatabase db, char *res_name, char *res_class, XIMProc callback, XPointer *client_data);

display	Specifies the connection to the X server.
db	Specifies a pointer to the resource database.
res_name	Specifies the full resource name of the application.
res_class	Specifies the full class name of the application.
callback	Specifies a pointer to the input method instantiate callback.
client_data	Specifies the additional client data.

The
XUnregisterIMInstantiateCallback
function removes an input method instantiation callback previously
registered.
The function returns
True
if it succeeds; otherwise, it returns
False.

Input Method Values

The following table describes how XIM values are interpreted
by an input method.
The first column lists the XIM values.
The second column indicates how each of the XIM values
are treated by that input style.

The following keys apply to this table.

Key	Explanation
D	This value may be set using `XSetIMValues`. If it is not set, a default is provided.
S	This value may be set using `XSetIMValues`.
G	This value may be read using `XGetIMValues`.

XIM Value	Key
XNQueryInputStyle	G
XNResourceName	D-S-G
XNResourceClass	D-S-G
XNDestroyCallback	D-S-G
XNQueryIMValuesList	G
XNQueryICValuesList	G
XNVisiblePosition	G
XNR6PreeditCallback	D-S-G

XNR6PreeditCallback
is obsolete and its use is not recommended
(see section 13.5.4.6).

Query Input Style

A client should always query the input method to determine which input
styles are supported.
The client should then find an input style it is capable of supporting.

If the client cannot find an input style that it can support,
it should negotiate with the user the continuation of the program
(exit, choose another input method, and so on).

The argument value must be a pointer to a location
where the returned value will be stored.
The returned value is a pointer to a structure of type
XIMStyles.
Clients are responsible for freeing the
XIMStyles
structure.
To do so, use
XFree.

The
XIMStyles
structure is defined as follows:

typedef unsigned long XIMStyle;


#define     XIMPreeditArea             0x0001L
#define     XIMPreeditCallbacks        0x0002L
#define     XIMPreeditPosition         0x0004L
#define     XIMPreeditNothing          0x0008L
#define     XIMPreeditNone             0x0010L

#define     XIMStatusArea              0x0100L
#define     XIMStatusCallbacks         0x0200L
#define     XIMStatusNothing           0x0400L
#define     XIMStatusNone              0x0800L

typedef struct {
      unsigned short count_styles;
      XIMStyle * supported_styles;
} XIMStyles;

An
XIMStyles
structure contains the number of input styles supported
in its count_styles field.
This is also the size of the supported_styles array.

The supported styles is a list of bitmask combinations,
which indicate the combination of styles for each of the areas supported.
These areas are described later.
Each element in the list should select one of the bitmask values for
each area.
The list describes the complete set of combinations supported.
Only these combinations are supported by the input method.

The preedit category defines what type of support is provided
by the input method for preedit information.

XIMPreeditArea	If chosen, the input method would require the client to provide some area values for it to do its preediting. Refer to XIC values XNArea and XNAreaNeeded.
XIMPreeditPosition	If chosen, the input method would require the client to provide positional values. Refer to XIC values XNSpotLocation and XNFocusWindow.
XIMPreeditCallbacks	If chosen, the input method would require the client to define the set of preedit callbacks. Refer to XIC values XNPreeditStartCallback, XNPreeditDoneCallback, XNPreeditDrawCallback, and XNPreeditCaretCallback.
XIMPreeditNothing	If chosen, the input method can function without any preedit values.
XIMPreeditNone	The input method does not provide any preedit feedback. Any preedit value is ignored. This style is mutually exclusive with the other preedit styles.

The status category defines what type of support is provided
by the input method for status information.

XIMStatusArea	The input method requires the client to provide some area values for it to do its status feedback. See XNArea and XNAreaNeeded.
XIMStatusCallbacks	The input method requires the client to define the set of status callbacks, XNStatusStartCallback, XNStatusDoneCallback, and XNStatusDrawCallback.
XIMStatusNothing	The input method can function without any status values.
XIMStatusNone	The input method does not provide any status feedback. If chosen, any status value is ignored. This style is mutually exclusive with the other status styles.

Resource Name and Class

The
XNResourceName
and
XNResourceClass
arguments are strings that specify the full name and class
used by the input method.
These values should be used as prefixes for the name and class
when looking up resources that may vary according to the input method.
If these values are not set,
the resources will not be fully specified.

It is not intended that values that can be set as XIM values be
set as resources.

Destroy Callback

The
XNDestroyCallback
argument is a pointer to a structure of type
XIMCallback.
XNDestroyCallback
is triggered when an input method stops its service for any reason.
After the callback is invoked, the input method is closed and the
associated input context(s) are destroyed by Xlib.
Therefore, the client should not call
XCloseIM
or
XDestroyIC.

The generic prototype of this callback function is as follows:

void DestroyCallback(XIM im, XPointer client_data, XPointer call_data);

im	Specifies the input method.
client_data	Specifies the additional client data.
call_data	Not used for this callback and always passed as NULL.

A DestroyCallback is always called with a NULL call_data argument.

Query IM/IC Values List

XNQueryIMValuesList
and
XNQueryICValuesList
are used to query about XIM and XIC values supported by the input method.

The argument value must be a pointer to a location where the returned
value will be stored. The returned value is a pointer to a structure
of type
XIMValuesList.
Clients are responsible for freeing the
XIMValuesList
structure.
To do so, use
XFree.

The
XIMValuesList
structure is defined as follows:


typedef struct {
     unsigned short count_values;
     char **supported_values;
} XIMValuesList;

Visible Position

The
XNVisiblePosition
argument indicates whether the visible position masks of
XIMFeedback
in
XIMText
are available.

The argument value must be a pointer to a location where the returned
value will be stored. The returned value is of type
Bool.
If the returned value is
True,
the input method uses the visible position masks of
XIMFeedback
in
XIMText;
otherwise, the input method does not use the masks.

Because this XIM value is optional, a client should call
XGetIMValues
with argument
XNQueryIMValuesList
before using this argument.
If the
XNVisiblePosition
does not exist in the IM values list returned from
XNQueryIMValuesList,
the visible position masks of
XIMFeedback
in
XIMText
are not used to indicate the visible position.

Preedit Callback Behavior

The
XNR6PreeditCallback
argument originally included in the X11R6 specification has been
deprecated.\(dg

During formulation of the X11R6 specification, the behavior of
the R6 PreeditDrawCallbacks was going to differ significantly from
that of the R5 callbacks.
Late changes to the specification converged the R5 and R6 behaviors,
eliminating the need for
XNR6PreeditCallback.
Unfortunately, this argument was not removed from the R6 specification
before it was published.

The
XNR6PreeditCallback
argument indicates whether the behavior of preedit callbacks regarding
XIMPreeditDrawCallbackStruct
values follows Release 5 or Release 6 semantics.

The value is of type
Bool.
When querying for
XNR6PreeditCallback,
if the returned value is
True,
the input method uses the Release 6 behavior;
otherwise, it uses the Release 5 behavior.
The default value is
False.
In order to use Release 6 semantics, the value of
XNR6PreeditCallback
must be set to
True.

Because this XIM value is optional, a client should call
XGetIMValues
with argument
XNQueryIMValuesList
before using this argument.
If the
XNR6PreeditCallback
does not exist in the IM values list returned from
XNQueryIMValuesList,
the PreeditCallback behavior is Release 5 semantics.

Input Context Functions

An input context is an abstraction that is used to contain both the data
required (if any) by an input method and the information required
to display that data.
There may be multiple input contexts for one input method.
The programming interfaces for creating, reading, or modifying
an input context use a variable argument list.
The name elements of the argument lists are referred to as XIC values.
It is intended that input methods be controlled by these XIC values.
As new XIC values are created,
they should be registered with the X Consortium.

To create an input context, use
XCreateIC.

XIC XCreateIC(XIM im);

im	Specifies the input method.
...	Specifies the variable length argument list to set XIC values.

The
XCreateIC
function creates a context within the specified input method.

Some of the arguments are mandatory at creation time, and
the input context will not be created if those arguments are not provided.
The mandatory arguments are the input style and the set of text callbacks
(if the input style selected requires callbacks).
All other input context values can be set later.

XCreateIC
returns a NULL value if no input context could be created.
A NULL value could be returned for any of the following reasons:

A required argument was not set.
A read-only argument was set (for example,
XNFilterEvents).
The argument name is not recognized.
The input method encountered an input method implementation-dependent error.

XCreateIC
can generate
BadAtom,
BadColor,
BadPixmap,
and
BadWindow
errors.

To destroy an input context, use
XDestroyIC.

void XDestroyIC(XIC ic);

ic	Specifies the input context.

XDestroyIC
destroys the specified input context.

To communicate to and synchronize with input method
for any changes in keyboard focus from the client side,
use
XSetICFocus
and
XUnsetICFocus.

void XSetICFocus(XIC ic);

ic	Specifies the input context.

The
XSetICFocus
function allows a client to notify an input method that the focus window
attached to the specified input context has received keyboard focus.
The input method should take action to provide appropriate feedback.
Complete feedback specification is a matter of user interface policy.

Calling
XSetICFocus
does not affect the focus window value.

void XUnsetICFocus(XIC ic);

ic	Specifies the input context.

The
XUnsetICFocus
function allows a client to notify an input method that the specified input context
has lost the keyboard focus and that no more input is expected on the focus window
attached to that input context.
The input method should take action to provide appropriate feedback.
Complete feedback specification is a matter of user interface policy.

Calling
XUnsetICFocus
does not affect the focus window value;
the client may still receive
events from the input method that are directed to the focus window.

To reset the state of an input context to its initial state, use
XmbResetIC
or
XwcResetIC.

char *XmbResetIC(XIC ic);

wchar_t *XwcResetIC(XIC ic);

ic	Specifies the input context.

When
XNResetState
is set to
XIMInitialState,
XmbResetIC
and
XwcResetIC
reset an input context to its initial state;
when
XNResetState
is set to
XIMPreserveState,
the current input context state is preserved.
In both cases, any input pending on that context is deleted.
The input method is required to clear the preedit area, if any,
and update the status accordingly.
Calling
XmbResetIC
or
XwcResetIC
does not change the focus.

The return value of
XmbResetIC
is its current preedit string as a multibyte string.
If there is any preedit text drawn or visible to the user,
then these procedures must return a non-NULL string.
If there is no visible preedit text,
then it is input method implementation-dependent
whether these procedures return a non-NULL string or NULL.

The client should free the returned string by calling
XFree.

To get the input method associated with an input context, use
XIMOfIC.

XIM XIMOfIC(XIC ic);

ic	Specifies the input context.

The
XIMOfIC
function returns the input method associated with the specified input context.

Xlib provides two functions for setting and reading XIC values, respectively,
XSetICValues
and
XGetICValues.
Both functions have a variable-length argument list.
In that argument list, any XIC value's name must be denoted
with a character string using the X Portable Character Set.

To set XIC values, use
XSetICValues.

char *XSetICValues(XIC ic);

ic	Specifies the input context.
...	Specifies the variable length argument list to set XIC values.

The
XSetICValues
function returns NULL if no error occurred;
otherwise,
it returns the name of the first argument that could not be set.
An argument might not be set for any of the following reasons:

The argument is read-only (for example,
XNFilterEvents).
The argument name is not recognized.
An implementation-dependent error occurs.

Each value to be set must be an appropriate datum,
matching the data type imposed by the semantics of the argument.

XSetICValues
can generate
BadAtom,
BadColor,
BadCursor,
BadPixmap,
and
BadWindow
errors.

To obtain XIC values, use
XGetICValues.

char *XGetICValues(XIC ic);

ic	Specifies the input context.
...	Specifies the variable length argument list to get XIC values.

The
XGetICValues
function returns NULL if no error occurred; otherwise,
it returns the name of the first argument that could not be obtained.
An argument could not be obtained for any of the following reasons:

The argument name is not recognized.
The input method encountered an implementation-dependent error.

Each IC attribute value argument (following a name) must point to
a location where the IC value is to be stored.
That is, if the IC value is of type T,
the argument must be of type T*.
If T itself is a pointer type,
then
XGetICValues
allocates memory to store the actual data,
and the client is responsible for freeing this data by calling
XFree
with the returned pointer.
The exception to this rule is for an IC value of type
XVaNestedList
(for preedit and status attributes).
In this case, the argument must also be of type
XVaNestedList.
Then, the rule of changing type T to T* and freeing the allocated data
applies to each element of the nested list.

Input Context Values

The following tables describe how XIC values are interpreted
by an input method depending on the input style chosen by the
user.

The first column lists the XIC values.
The second column indicates which values are involved in affecting,
negotiating, and setting the geometry of the input method windows.
The subentries under the third column indicate the different
input styles that are supported.
Each of these columns indicates how each of the XIC values
are treated by that input style.

The following keys apply to these tables.

Key	Explanation
C	This value must be set with `XCreateIC`.
D	This value may be set using `XCreateIC`.> If it is not set,> a default is provided.
G	This value may be read using `XGetICValues`.
GN	This value may cause geometry negotiation when its value is set by means of `XCreateIC` or `XSetICValues`.
GR	This value will be the response of the input method when any GN value is changed.
GS	This value will cause the geometry of the input method window to be set.
O	This value must be set once and only once. It need not be set at create time.
S	This value may be set with `XSetICValues`.
Ignored	This value is ignored by the input method for the given input style.

XIC Value	Geometry Mangement	Preedit Callback	Preedit Position	Input Style Preedit Area	Preedit Nothing	Preedit None
Input Style		C-G	C-G	C-G	C-G	C-G
Client Window		O-G	O-G	O-G	O-G	Ignored
Focus Window	GN	D-S-G	D-S-G	D-S-G	D-S-G	Ignored
Resource Name		Ignored	D-S-G	D-S-G	D-S-G	Ignored
Resource Class		Ignored	D-S-G	D-S-G	D-S-G	Ignored
Geometry Callback		Ignored	Ignored	D-S-G	Ignored	Ignored
Filter Events		G	G	G	G	Ignored
Destroy Callback		D-S-G	D-S-G	D-S-G	D-S-G	D-S-G
String Conversion Callback		S-G	S-G	S-G	S-G	S-G
String Conversion		D-S-G	D-S-G	D-S-G	D-S-G	D-S-G
Reset State		D-S-G	D-S-G	D-S-G	D-S-G	Ignored
HotKey		S-G	S-G	S-G	S-G	Ignored
HotKeyState		D-S-G	D-S-G	D-S-G	D-S-G	Ignored
`Preedit`
Area	GS	Ignored	D-S-G	D-S-G	Ignored	Ignored
Area Needed	GN-GR	Ignored	Ignored	S-G	Ignored	Ignored
Spot Location		Ignored	D-S-G	Ignored	Ignored	Ignored
Colormap		Ignored	D-S-G	D-S-G	D-S-G	Ignored
Foreground		Ignored	D-S-G	D-S-G	D-S-G	Ignored
Background		Ignored	D-S-G	D-S-G	D-S-G	Ignored
Background Pixmap		Ignored	D-S-G	D-S-G	D-S-G	Ignored
Font Set	GN	Ignored	D-S-G	D-S-G	D-S-G	Ignored
Line Spacing	GN	Ignored	D-S-G	D-S-G	D-S-G	Ignored
Cursor		Ignored	D-S-G	D-S-G	D-S-G	Ignored
Preedit State		D-S-G	D-S-G	D-S-G	D-S-G	Ignored
Preedit State Notify Callback		S-G	S-G	S-G	S-G	Ignored
Preedit Callbacks		C-S-G	Ignored	Ignored	Ignored	Ignored

XIC Value	Geomentry Management	Status Callback	Status Area	Status Nothing	Status None
Input Style		C-G	C-G	C-G	C-G
Client Window		O-G	O-G	O-G	Ignored
Focus Window	GN	D-S-G	D-S-G	D-S-G	Ignored
Resource Name		Ignored	D-S-G	D-S-G	Ignored
Resource Class		Ignored	D-S-G	D-S-G	Ignored
Geometry Callback		Ignored	D-S-G	Ignored	Ignored
Filter Events		G	G	G	G
Status
Area	GS	Ignored	D-S-G	Ignored	Ignored
Area Needed	GN-GR	Ignored	S-G	Ignored	Ignored
Colormap		Ignored	D-S-G	D-S-G	Ignored
Foreground		Ignored	D-S-G	D-S-G	Ignored
Background		Ignored	D-S-G	D-S-G	Ignored
Background Pixmap		Ignored	D-S-G	D-S-G	Ignored
Font Set	GN	Ignored	D-S-G	D-S-G	Ignored
Line Spacing	GN	Ignored	D-S-G	D-S-G	Ignored
Cursor		Ignored	D-S-G	D-S-G	Ignored
Status Callbacks		C-S-G	Ignored	Ignored	Ignored

Input Style

The
XNInputStyle
argument specifies the input style to be used.
The value of this argument must be one of the values returned by the
XGetIMValues
function with the
XNQueryInputStyle
argument specified in the supported_styles list.

Note that this argument must be set at creation time
and cannot be changed.

Client Window

The
XNClientWindow
argument specifies to the input method the client window in
which the input method
can display data or create subwindows.
Geometry values for input method areas are given with respect to the client
window.
Dynamic change of client window is not supported.
This argument may be set only once and
should be set before any input is done using this input context.
If it is not set,
the input method may not operate correctly.

If an attempt is made to set this value a second time with
XSetICValues,
the string
XNClientWindow
will be returned by
XSetICValues,
and the client window will not be changed.

If the client window is not a valid window ID on the display
attached to the input method,
a
BadWindow
error can be generated when this value is used by the input method.

Focus Window

The
XNFocusWindow
argument specifies the focus window.
The primary purpose of the
XNFocusWindow
is to identify the window that will receive the key event when input
is composed.
In addition, the input method may possibly affect the focus window
as follows:

Select events on it
Send events to it
Modify its properties
Grab the keyboard within that window

The associated value must be of type
Window.
If the focus window is not a valid window ID on the display
attached to the input method,
a
BadWindow
error can be generated when this value is used by the input method.

When this XIC value is left unspecified,
the input method will use the client window as the default focus window.

Resource Name and Class

The
XNResourceName
and
XNResourceClass
arguments are strings that specify the full name and class
used by the client to obtain resources for the client window.
These values should be used as prefixes for name and class
when looking up resources that may vary according to the input context.
If these values are not set,
the resources will not be fully specified.

It is not intended that values that can be set as XIC values be
set as resources.

Geometry Callback

The
XNGeometryCallback
argument is a structure of type
XIMCallback
(see section 13.5.6.13.12).

The
XNGeometryCallback
argument specifies the geometry callback that a client can set.
This callback is not required for correct operation of either
an input method or a client.
It can be set for a client whose user interface policy permits
an input method to request the dynamic change of that input
method's window.
An input method that does dynamic change will need to filter any
events that it uses to initiate the change.

Filter Events

The
XNFilterEvents
argument returns the event mask that an input method needs
to have selected for.
The client is expected to augment its own event mask
for the client window with this one.

This argument is read-only, is set by the input method at create time,
and is never changed.

The type of this argument is
unsigned
long.
Setting this value will cause an error.

Destroy Callback

The
XNDestroyCallback
argument is a pointer to a structure of type
XIMCallback
(see section 13.5.6.13.12).
This callback is triggered when the input method
stops its service for any reason; for example, when a connection to an IM
server is broken. After the destroy callback is called,
the input context is destroyed and the input method is closed.
Therefore, the client should not call
XDestroyIC
and
XCloseIM.

String Conversion Callback

The
XNStringConversionCallback
argument is a structure of type
XIMCallback
(see section 13.5.6.13.12).

The
XNStringConversionCallback
argument specifies a string conversion callback. This callback
is not required for correct operation of
either the input method or the client. It can be set by a client
to support string conversions that may be requested
by the input method. An input method that does string conversions
will filter any events that it uses to initiate the conversion.

Because this XIC value is optional, a client should call
XGetIMValues
with argument
XNQueryICValuesList
before using this argument.

String Conversion

The
XNStringConversion
argument is a structure of type
XIMStringConversionText.

The
XNStringConversion
argument specifies the string to be converted by an input method.
This argument is not required for correct operation of either
the input method or the client.

String conversion facilitates the manipulation of text independent
of preediting.
It is essential for some input methods and clients to manipulate
text by performing context-sensitive conversion,
reconversion, or transliteration conversion on it.

Because this XIC value is optional, a client should call
XGetIMValues
with argument
XNQueryICValuesList
before using this argument.

The
XIMStringConversionText
structure is defined as follows:

typedef struct _XIMStringConversionText {
     unsigned short              length;
     XIMStringConversionFeedback *feedback;
     Bool                        encoding_is_wchar;
     union {
          char     *mbs;
          wchar_t  *wcs;
     } string;
} XIMStringConversionText;

typedef unsigned long XIMStringConversionFeedback;

The feedback member is reserved for future use. The text to be
converted is defined by the string and length members. The length
is indicated in characters. To prevent the library from freeing memory
pointed to by an uninitialized pointer, the client should set the feedback
element to NULL.

Reset State

The
XNResetState
argument specifies the state the input context will return to after calling
XmbResetIC
or
XwcResetIC.

The XIC state may be set to its initial state, as specified by the
XNPreeditState
value when
XCreateIC
was called, or it may be set to preserve the current state.

The valid masks for
XIMResetState
are as follows:

typedef unsigned long XIMResetState;

#define XIMInitialState  (1L)
#define XIMPreserveState (1L<<1)

If
XIMInitialState
is set, then
XmbResetIC
and
XwcResetIC
will return to the initial
XNPreeditState
state of the XIC.

If
XIMPreserveState
is set, then
XmbResetIC
and
XwcResetIC
will preserve the current state of the XIC.

If
XNResetState
is left unspecified, the default is
XIMInitialState.

XIMResetState
values other than those specified above will default to
XIMInitialState.

Because this XIC value is optional, a client should call
XGetIMValues
with argument
XNQueryICValuesList
before using this argument.

Hot Keys

The
XNHotKey
argument specifies the hot key list to the XIC.
The hot key list is a pointer to the structure of type
XIMHotKeyTriggers,
which specifies the key events that must be received
without any interruption of the input method.
For the hot key list set with this argument to be utilized, the client
must also set
XNHotKeyState
to
XIMHotKeyStateON.

Because this XIC value is optional, a client should call
XGetIMValues
with argument
XNQueryICValuesList
before using this functionality.

The value of the argument is a pointer to a structure of type
XIMHotKeyTriggers.

If an event for a key in the hot key list is found, then the process will
receive the event and it will be processed inside the client.


typedef struct {
     KeySym keysym;
     unsigned int modifier;
     unsigned int modifier_mask;
} XIMHotKeyTrigger;

typedef struct {
     int num_hot_key;
     XIMHotKeyTrigger *key;
} XIMHotKeyTriggers;

The combination of modifier and modifier_mask are used to represent one of
three states for each modifier:
either the modifier must be on, or the modifier must be off, or the modifier
is a ``don't care'' - it may be on or off.
When a modifier_mask bit is set to 0, the state of the associated modifier
is ignored when evaluating whether the key is hot or not.

Modifier Bit	Mask Bit	Meaning
0	1	The modifier must be off.
1	1	The modifier must be on.
n/a	0	Do not care if the modifier is on or off.

Hot Key State

The
XNHotKeyState
argument specifies the hot key state of the input method.
This is usually used to switch the input method between hot key
operation and normal input processing.

The value of the argument is a pointer to a structure of type
XIMHotKeyState .

typedef unsigned long XIMHotKeyState;

#define XIMHotKeyStateON            (0x0001L)
#define XIMHotKeyStateOFF           (0x0002L)

If not specified, the default is
XIMHotKeyStateOFF.

Preedit and Status Attributes

The
XNPreeditAttributes
and
XNStatusAttributes
arguments specify to an input method the attributes to be used for the
preedit and status areas,
if any.
Those attributes are passed to
XSetICValues
or
XGetICValues
as a nested variable-length list.
The names to be used in these lists are described in the following sections.

Area

The value of the
XNArea
argument must be a pointer to a structure of type
XRectangle.
The interpretation of the
XNArea
argument is dependent on the input method style that has been set.

If the input method style is
XIMPreeditPosition,
XNArea
specifies the clipping region within which preediting will take place.
If the focus window has been set,
the coordinates are assumed to be relative to the focus window.
Otherwise, the coordinates are assumed to be relative to the client window.
If neither has been set,
the results are undefined.

If
XNArea
is not specified, is set to NULL, or is invalid,
the input method will default the clipping region
to the geometry of the
XNFocusWindow.
If the area specified is NULL or invalid,
the results are undefined.

If the input style is
XIMPreeditArea
or
XIMStatusArea,
XNArea
specifies the geometry provided by the client to the input method.
The input method may use this area to display its data,
either preedit or status depending on the area designated.
The input method may create a window as a child of the client window
with dimensions that fit the
XNArea.
The coordinates are relative to the client window.
If the client window has not been set yet,
the input method should save these values
and apply them when the client window is set.
If
XNArea
is not specified, is set to NULL, or is invalid,
the results are undefined.

Area Needed

When set, the
XNAreaNeeded
argument specifies the geometry suggested by the client for this area
(preedit or status).
The value associated with the argument must be a pointer to a
structure of type
XRectangle.
Note that the x, y values are not used
and that nonzero values for width or height are the constraints
that the client wishes the input method to respect.

When read, the
XNAreaNeeded
argument specifies the preferred geometry desired by the input method
for the area.

This argument is only valid if the input style is
XIMPreeditArea
or
XIMStatusArea.
It is used for geometry negotiation between the client and the input method
and has no other effect on the input method
(see section 13.5.1.5).

Spot Location

The
XNSpotLocation
argument specifies to the input method the coordinates of the spot
to be used by an input method executing with
XNInputStyle
set to
XIMPreeditPosition.
When specified to any input method other than
XIMPreeditPosition,
this XIC value is ignored.

The x coordinate specifies the position where the next character
would be inserted.
The y coordinate is the position of the baseline used
by the current text line in the focus window.
The x and y coordinates are relative to the focus window, if it has been set;
otherwise, they are relative to the client window.
If neither the focus window nor the client window has been set,
the results are undefined.

The value of the argument is a pointer to a structure of type
XPoint.

Colormap

Two different arguments can be used to indicate what colormap the input method
should use to allocate colors, a colormap ID, or a standard colormap name.

The
XNColormap
argument is used to specify a colormap ID.
The argument value is of type
Colormap.
An invalid argument may generate a
BadColor
error when it is used by the input method.

The
XNStdColormap
argument is used to indicate the name of the standard colormap
in which the input method should allocate colors.
The argument value is an
Atom
that should be a valid atom for calling
XGetRGBColormaps.
An invalid argument may generate a
BadAtom
error when it is used by the input method.

If the colormap is left unspecified,
the client window colormap becomes the default.

Foreground and Background

The
XNForeground
and
XNBackground
arguments specify the foreground and background pixel, respectively.
The argument value is of type
unsigned
long.
It must be a valid pixel in the input method colormap.

If these values are left unspecified,
the default is determined by the input method.

Background Pixmap

The
XNBackgroundPixmap
argument specifies a background pixmap to be used as the background of the
window.
The value must be of type
Pixmap.
An invalid argument may generate a
BadPixmap
error when it is used by the input method.

If this value is left unspecified,
the default is determined by the input method.

Font Set

The
XNFontSet
argument specifies to the input method what font set is to be used.
The argument value is of type
XFontSet.

If this value is left unspecified,
the default is determined by the input method.

Line Spacing

The
XNLineSpace
argument specifies to the input method what line spacing is to be used
in the preedit window if more than one line is to be used.
This argument is of type
int.

If this value is left unspecified,
the default is determined by the input method.

Cursor

The
XNCursor
argument specifies to the input method what cursor is to be used
in the specified window.
This argument is of type
Cursor.

An invalid argument may generate a
BadCursor
error when it is used by the input method.
If this value is left unspecified,
the default is determined by the input method.

Preedit State

The
XNPreeditState
argument specifies the state of input preediting for the input method.
Input preediting can be on or off.

The valid mask names for
XNPreeditState
are as follows:

typedef unsigned long XIMPreeditState;

#define XIMPreeditUnknown    0L
#define XIMPreeditEnable     1L
#define XIMPreeditDisable    (1L<<1)

If a value of
XIMPreeditEnable
is set, then input preediting is turned on by the input method.

If a value of
XIMPreeditDisable
is set, then input preediting is turned off by the input method.

If
XNPreeditState
is left unspecified, then the state will be implementation-dependent.

When
XNResetState
is set to
XIMInitialState,
the
XNPreeditState
value specified at the creation time will be reflected as the initial state for
XmbResetIC
and
XwcResetIC.

Because this XIC value is optional, a client should call
XGetIMValues
with argument
XNQueryICValuesList
before using this argument.

Preedit State Notify Callback

The preedit state notify callback is triggered by the input method
when the preediting state has changed.
The value of the
XNPreeditStateNotifyCallback
argument is a pointer to a structure of type
XIMCallback.
The generic prototype is as follows:

void PreeditStateNotifyCallback(XIC ic, XPointer client_data, XIMPreeditStateNotifyCallbackStruct *call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Specifies the current preedit state.

The
XIMPreeditStateNotifyCallbackStruct
structure is defined as follows:


typedef struct _XIMPreeditStateNotifyCallbackStruct {
     XIMPreeditState state;
} XIMPreeditStateNotifyCallbackStruct;

Because this XIC value is optional, a client should call
XGetIMValues
with argument
XNQueryICValuesList
before using this argument.

Preedit and Status Callbacks

A client that wants to support the input style
XIMPreeditCallbacks
must provide a set of preedit callbacks to the input method.
The set of preedit callbacks is as follows:

XNPreeditStartCallback	This is called when the input method starts preedit.
XNPreeditDoneCallback	This is called when the input method stops preedit.
XNPreeditDrawCallback	This is called when a number of preedit keystrokes should be echoed.
XNPreeditCaretCallback	This is called to move the text insertion point within the preedit string.

A client that wants to support the input style
XIMStatusCallbacks
must provide a set of status callbacks to the input method.
The set of status callbacks is as follows:

XNStatusStartCallback	This is called when the input method initializes the status area.
XNStatusDoneCallback	This is called when the input method no longer needs the status area.
XNStatusDrawCallback	This is called when updating of the status area is required.

The value of any status or preedit argument is a pointer
to a structure of type
XIMCallback.


typedef void (*XIMProc)();

typedef struct {
     XPointer client_data;
     XIMProc callback;
} XIMCallback;

Each callback has some particular semantics and will carry the data
that expresses the environment necessary to the client
into a specific data structure.
This paragraph only describes the arguments to be used to set
the callback.

Setting any of these values while doing preedit
may cause unexpected results.

Input Method Callback Semantics

XIM callbacks are procedures defined by clients or text drawing packages
that are to be called from the input method when selected events occur.
Most clients will use a text editing package or a toolkit
and, hence, will not need to define such callbacks.
This section defines the callback semantics, when they are triggered,
and what their arguments are.
This information is mostly useful for X toolkit implementors.

Callbacks are mostly provided so that clients (or text editing
packages) can implement on-the-spot preediting in their own window.
In that case,
the input method needs to communicate and synchronize with the client.
The input method needs to communicate changes in the preedit window
when it is under control of the client.
Those callbacks allow the client to initialize the preedit area,
display a new preedit string,
move the text insertion point during preedit,
terminate preedit, or update the status area.

All callback procedures follow the generic prototype:

void CallbackPrototype(XIC ic, XPointer client_data, SomeType call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Specifies data specific to the callback.

The call_data argument is a structure that expresses the arguments needed
to achieve the semantics;
that is,
it is a specific data structure appropriate to the callback.
In cases where no data is needed in the callback,
this call_data argument is NULL.
The client_data argument is a closure that has been initially specified
by the client when specifying the callback and passed back.
It may serve, for example, to inherit application context in the callback.

The following paragraphs describe the programming semantics
and specific data structure associated with the different reasons.

Geometry Callback

The geometry callback is triggered by the input method
to indicate that it wants the client to negotiate geometry.
The generic prototype is as follows:

void GeometryCallback(XIC ic, XPointer client_data, XPointer call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Not used for this callback and always passed as NULL.

The callback is called with a NULL call_data argument.

Destroy Callback

The destroy callback is triggered by the input method
when it stops service for any reason.
After the callback is invoked, the input context will be freed by Xlib.
The generic prototype is as follows:

void DestroyCallback(XIC ic, XPointer client_data, XPointer call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Not used for this callback and always passed as NULL.

The callback is called with a NULL call_data argument.

String Conversion Callback

The string conversion callback is triggered by the input method
to request the client to return the string to be converted. The
returned string may be either a multibyte or wide character string,
with an encoding matching the locale bound to the input context.
The callback prototype is as follows:

void StringConversionCallback(XIC ic, XPointer client_data, XIMStringConversionCallbackStruct *call_data);

ic	Specifies the input method.
client_data	Specifies the additional client data.
call_data	Specifies the amount of the string to be converted.

The callback is passed an
XIMStringConversionCallbackStruct
structure in the call_data argument.
The text member is an
XIMStringConversionText
structure (see section 13.5.6.9)
to be filled in by the client
and describes the text to be sent to the input method.
The data pointed to by the
string and feedback elements of the
XIMStringConversionText
structure will be freed using
XFree
by the input method
after the callback returns. So the client should not point to
internal buffers that are critical to the client.
Similarly, because the feedback element is currently reserved for future
use, the client should set feedback to NULL to prevent the library from
freeing memory at some random location due to an uninitialized pointer.

The
XIMStringConversionCallbackStruct
structure is defined as follows:

typedef struct _XIMStringConversionCallbackStruct {
     XIMStringConversionPosition position;          
     XIMCaretDirection direction;
     short factor;
     XIMStringConversionOperation operation;
     XIMStringConversionText *text;
} XIMStringConversionCallbackStruct;

typedef short XIMStringConversionPosition;

typedef unsigned short XIMStringConversionOperation;

#define XIMStringConversionSubstitution       (0x0001)
#define XIMStringConversionRetrieval          (0x0001)

XIMStringConversionPosition
specifies the starting position of the string to be returned
in the
XIMStringConversionText
structure. The value identifies a position, in units of characters,
relative to the client's cursor position in the client's buffer.

The ending position of the text buffer is determined by
the direction and factor members. Specifically, it is the character position
relative to the starting point as defined by the
XIMCaretDirection.
The factor member of
XIMStringConversionCallbackStruct
specifies the number of
XIMCaretDirection
positions to be applied. For example, if the direction specifies
XIMLineEnd
and factor is 1, then all characters from the starting position to
the end of the current display line are returned. If the direction
specifies
XIMForwardChar
or
XIMBackwardChar,
then the factor specifies a relative position, indicated in characters,
from the starting position.

XIMStringConversionOperation
specifies whether the string to be converted should be
deleted (substitution) or copied (retrieval) from the client's
buffer. When the
XIMStringConversionOperation
is
XIMStringConversionSubstitution,
the client must delete the string to be converted from its own buffer.
When the
XIMStringConversionOperation
is
XIMStringConversionRetrieval,
the client must not delete the string to be converted from its buffer.
The substitute operation is typically used for reconversion and
transliteration conversion,
while the retrieval operation is typically used for context-sensitive
conversion.

Preedit State Callbacks

When the input method turns preediting on or off, a
PreeditStartCallback
or
PreeditDoneCallback
callback is triggered to let the toolkit do the setup
or the cleanup for the preedit region.

int PreeditStartCallback(XIC ic, XPointer client_data, XPointer call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Not used for this callback and always passed as NULL.

When preedit starts on the specified input context,
the callback is called with a NULL call_data argument.
PreeditStartCallback
will return the maximum size of the preedit string.
A positive number indicates the maximum number of bytes allowed
in the preedit string,
and a value of -1 indicates there is no limit.

void PreeditDoneCallback(XIC ic, XPointer client_data, XPointer call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Not used for this callback and always passed as NULL.

When preedit stops on the specified input context,
the callback is called with a NULL call_data argument.
The client can release the data allocated by
PreeditStartCallback.

PreeditStartCallback
should initialize appropriate data needed for
displaying preedit information and for handling further
PreeditDrawCallback
calls.
Once
PreeditStartCallback
is called, it will not be called again before
PreeditDoneCallback
has been called.

Preedit Draw Callback

This callback is triggered to draw and insert, delete or replace,
preedit text in the preedit region.
The preedit text may include unconverted input text such as Japanese Kana,
converted text such as Japanese Kanji characters, or characters of both kinds.
That string is either a multibyte or wide character string,
whose encoding matches the locale bound to the input context.
The callback prototype
is as follows:

void PreeditDrawCallback(XIC ic, XPointer client_data, XIMPreeditDrawCallbackStruct *call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Specifies the preedit drawing information.

The callback is passed an
XIMPreeditDrawCallbackStruct
structure in the call_data argument.
The text member of this structure contains the text to be drawn.
After the string has been drawn,
the caret should be moved to the specified location.

The
XIMPreeditDrawCallbackStruct
structure is defined as follows:


typedef struct _XIMPreeditDrawCallbackStruct {
     int caret;     /* Cursor offset within preedit string */
     int chg_first;     /* Starting change position */
     int chg_length;     /* Length of the change in character count */
     XIMText *text;
} XIMPreeditDrawCallbackStruct;

The client must keep updating a buffer of the preedit text
and the callback arguments referring to indexes in that buffer.
The call_data fields have specific meanings according to the operation,
as follows:

To indicate text deletion,
the call_data member specifies a NULL text field.
The text to be deleted is then the current text in the buffer
from position chg_first (starting at zero) on a character length
of chg_length.
When text is non-NULL,
it indicates insertion or replacement of text in the buffer.
The chg_length member
identifies the number of characters in the current preedit buffer
that are affected by this call.
A positive chg_length indicates that chg_length number of characters, starting
at chg_first, must be deleted or must be replaced by text, whose length is
specified in the
XIMText
structure.
A chg_length value of zero indicates that text must be inserted
right at the position specified by chg_first.
A value of zero for chg_first specifies the first character in the buffer.
chg_length and chg_first combine to identify the modification required to
the preedit buffer; beginning at chg_first, replace chg_length number of
characters with the text in the supplied
XIMText
structure. For example, suppose the preedit buffer contains the string "ABCDE".
```
Text:      A B C D E
          ^ ^ ^ ^ ^ ^
CharPos:  0 1 2 3 4 5
```
The CharPos in the diagram shows the location of the character position
relative to the character.
If the value of chg_first is 1 and the value of chg_length is 3, this
says to replace 3 characters beginning at character position 1 with the
string in the
XIMText
structure.
Hence, BCD would be replaced by the value in the structure.
Though chg_length and chg_first are both signed integers they will
never have a negative value.
The caret member
identifies the character position before which the cursor should
be placed - after modification to the preedit buffer has been completed.
For example, if caret is zero, the cursor is at
the beginning of the buffer. If the caret is one, the cursor is between
the first and second character.

typedef struct _XIMText {
     unsigned short length;
     XIMFeedback * feedback;
     Bool encoding_is_wchar; 
     union {
          char * multi_byte;
          wchar_t * wide_char;
     } string; 
} XIMText;

The text string passed is actually a structure specifying as follows:

The length member is the text length in characters.
The encoding_is_wchar member is a value that indicates
if the text string is encoded in wide character or multibyte format.
The text string may be passed either as multibyte or as wide character;
the input method controls in which form data is passed.
The client's
callback routine must be able to handle data passed in either form.
The string member is the text string.
The feedback member indicates rendering type for each character in the
string member.
If string is NULL (indicating that only highlighting of the existing
preedit buffer should be updated), feedback points to length highlight
elements that should be applied to the existing preedit buffer, beginning
at chg_first.

The feedback member expresses the types of rendering feedback
the callback should apply when drawing text.
Rendering of the text to be drawn is specified either in generic ways
(for example, primary, secondary) or in specific ways (reverse, underline).
When generic indications are given,
the client is free to choose the rendering style.
It is necessary, however, that primary and secondary be mapped
to two distinct rendering styles.

If an input method wants to control display of the preedit string, an
input method can indicate the visibility hints using feedbacks in
a specific way.
The
XIMVisibleToForward,
XIMVisibleToBackword,
and
XIMVisibleToCenter
masks are exclusively used for these visibility hints.
The
XIMVisibleToForward
mask
indicates that the preedit text is preferably displayed in the
primary draw direction from the
caret position in the preedit area forward.
The
XIMVisibleToBackword
mask
indicates that the preedit text is preferably displayed from
the caret position in the preedit area backward, relative to the primary
draw direction.
The
XIMVisibleToCenter
mask
indicates that the preedit text is preferably displayed with
the caret position in the preedit area centered.

The insertion point of the preedit string could exist outside of
the visible area when visibility hints are used.
Only one of the
masks
is valid for the entire preedit string, and only one character
can hold one of these feedbacks for a given input context at one time.
This feedback may be OR'ed together with another highlight (such as
XIMReverse).
Only the most recently set feedback is valid, and any previous
feedback is automatically canceled. This is a hint to the client, and
the client is free to choose how to display the preedit string.

The feedback member also specifies how rendering of the text argument
should be performed.
If the feedback is NULL,
the callback should apply the same feedback as is used for the surrounding
characters in the preedit buffer; if chg_first is at a highlight boundary,
the client can choose which of the two highlights to use.
If feedback is not NULL, feedback specifies an array defining the
rendering for each
character of the string, and the length of the array is thus length.

If an input method wants to indicate that it is only updating the feedback of
the preedit text without changing the content of it,
the
XIMText
structure will contain a NULL value for the string field,
the number of characters affected (relative to chg_first)
will be in the length field,
and the feedback field will point to an array of
XIMFeedback.

Each element in the feedback array is a bitmask represented by a value of type
XIMFeedback.
The valid mask names are as follows:

typedef unsigned long XIMFeedback;

#define     XIMReverse                     1L
#define     XIMUnderline                   (1L<<1)
#define     XIMHighlight                   (1L<<2)
#define     XIMPrimary                     (1L<<5)*
#define     XIMSecondary                   (1L<<6)*
#define     XIMTertiary                    (1L<<7)*
#define     XIMVisibleToForward            (1L<<8)
#define     XIMVisibleToBackward           (1L<<9)
#define     XIMVisibleToCenter               (1L<<10)

*† The values for XIMPrimary, XIMSecondary, and XIMTertiary were incorrectly defined in
the R5 specification. The X Consortium’s X11R5 implementation correctly
implemented the values for these highlights. The value of these highlights has
been corrected in this specification to agree with the values in the
Consortium’s X11R5 and X11R6 implementations.

Characters drawn with the
XIMReverse
highlight should be drawn by swapping the foreground and background colors
used to draw normal, unhighlighted characters.
Characters drawn with the
XIMUnderline
highlight should be underlined.
Characters drawn with the
XIMHighlight,
XIMPrimary,
XIMSecondary,
and
XIMTertiary
highlights should be drawn in some unique manner that must be different
from
XIMReverse
and
XIMUnderline.

The values for
XIMPrimary,
XIMSecondary,
and
XIMTertiary
were incorrectly defined in the R5 specification.
The X Consortium's X11R5
implementation correctly implemented the values for these highlights.
The value of these highlights has been corrected in this specification
to agree with the values in the Consortium's X11R5 and X11R6 implementations.

Preedit Caret Callback

An input method may have its own navigation keys to allow the user
to move the text insertion point in the preedit area
(for example, to move backward or forward).
Consequently, input method needs to indicate to the client that it
should move the text insertion point.
It then calls the PreeditCaretCallback.

void PreeditCaretCallback(XIC ic, XPointer client_data, XIMPreeditCaretCallbackStruct *call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Specifies the preedit caret information.

The input method will trigger PreeditCaretCallback
to move the text insertion point during preedit.
The call_data argument contains a pointer to an
XIMPreeditCaretCallbackStruct
structure,
which indicates where the caret should be moved.
The callback must move the insertion point to its new location
and return, in field position, the new offset value from the initial position.

The
XIMPreeditCaretCallbackStruct
structure is defined as follows:


typedef struct _XIMPreeditCaretCallbackStruct {
     int position;     /* Caret offset within preedit string */
     XIMCaretDirection direction;     /* Caret moves direction */
     XIMCaretStyle style;     /* Feedback of the caret */
} XIMPreeditCaretCallbackStruct;

The
XIMCaretStyle
structure is defined as follows:


typedef enum {
     XIMIsInvisible,     /* Disable caret feedback */ 
     XIMIsPrimary,     /* UI defined caret feedback */
     XIMIsSecondary,     /* UI defined caret feedback */
} XIMCaretStyle;

The
XIMCaretDirection
structure is defined as follows:


typedef enum {
     XIMForwardChar, XIMBackwardChar,
     XIMForwardWord, XIMBackwardWord,
     XIMCaretUp, XIMCaretDown,
     XIMNextLine, XIMPreviousLine,
     XIMLineStart, XIMLineEnd, 
     XIMAbsolutePosition,
     XIMDontChange,
 } XIMCaretDirection;

These values are defined as follows:

`XIMForwardChar`	Move the caret forward one character position.
`XIMBackwardChar`	Move the caret backward one character position.
`XIMForwardWord`	Move the caret forward one word.
`XIMBackwardWord`	Move the caret backward one word.
`XIMCaretUp`	Move the caret up one line keeping the current horizontal offset.
`XIMCaretDown`	Move the caret down one line keeping the current horizontal offset.
`XIMPreviousLine`	Move the caret to the beginning of the previous line.
`XIMNextLine`	Move the caret to the beginning of the next line.
`XIMLineStart`	Move the caret to the beginning of the current display line that contains the caret.
`XIMLineEnd`	Move the caret to the end of the current display line that contains the caret.
`XIMAbsolutePosition`	The callback must move to the location specified by the position field of the callback data, indicated in characters, starting from the beginning of the preedit text. Hence, a value of zero means move back to the beginning of the preedit text.
`XIMDontChange`	The caret position does not change.

Status Callbacks

An input method may communicate changes in the status of an input context
(for example, created, destroyed, or focus changes) with three status
callbacks: StatusStartCallback, StatusDoneCallback, and StatusDrawCallback.

When the input context is created or gains focus,
the input method calls the StatusStartCallback callback.

void StatusStartCallback(XIC ic, XPointer client_data, XPointer call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Not used for this callback and always passed as NULL.

The callback should initialize appropriate data for displaying status
and for responding to StatusDrawCallback calls.
Once StatusStartCallback is called,
it will not be called again before StatusDoneCallback has been called.

When an input context
is destroyed or when it loses focus, the input method calls StatusDoneCallback.

void StatusDoneCallback(XIC ic, XPointer client_data, XPointer call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Not used for this callback and always passed as NULL.

The callback may release any data allocated on
StatusStart.

When an input context status has to be updated, the input method calls
StatusDrawCallback.

void StatusDrawCallback(XIC ic, XPointer client_data, XIMStatusDrawCallbackStruct *call_data);

ic	Specifies the input context.
client_data	Specifies the additional client data.
call_data	Specifies the status drawing information.

The callback should update the status area by either drawing a string
or imaging a bitmap in the status area.

The
XIMStatusDataType
and
XIMStatusDrawCallbackStruct
structures are defined as follows:


typedef enum {
     XIMTextType,
     XIMBitmapType,
} XIMStatusDataType;

typedef struct _XIMStatusDrawCallbackStruct {
     XIMStatusDataType type;
     union {
          XIMText *text;
          Pixmap  bitmap;
     } data;
} XIMStatusDrawCallbackStruct;

The feedback styles
XIMVisibleToForward,
XIMVisibleToBackword,
and
XIMVisibleToCenter
are not relevant and will not appear in the
XIMFeedback
element of the
XIMText
structure.

Event Filtering

Xlib provides the ability for an input method
to register a filter internal to Xlib.
This filter is called by a client (or toolkit) by calling
XFilterEvent
after calling
XNextEvent.
Any client that uses the
XIM
interface should call
XFilterEvent
to allow input methods to process their events without knowledge
of the client's dispatching mechanism.
A client's user interface policy may determine the priority
of event filters with respect to other event-handling mechanisms
(for example, modal grabs).

Clients may not know how many filters there are, if any,
and what they do.
They may only know if an event has been filtered on return of
XFilterEvent.
Clients should discard filtered events.

To filter an event, use
XFilterEvent.

Bool XFilterEvent(XEvent *event, Window w);

event	Specifies the event to filter.
w	Specifies the window for which the filter is to be applied.

If the window argument is
None,
XFilterEvent
applies the filter to the window specified in the
XEvent
structure.
The window argument is provided so that layers above Xlib
that do event redirection can indicate to which window an event
has been redirected.

If
XFilterEvent
returns
True,
then some input method has filtered the event,
and the client should discard the event.
If
XFilterEvent
returns
False,
then the client should continue processing the event.

If a grab has occurred in the client and
XFilterEvent
returns
True,
the client should ungrab the keyboard.

Getting Keyboard Input

To get composed input from an input method,
use
XmbLookupString
or
XwcLookupString.

int XmbLookupString(XIC ic, XKeyPressedEvent *event, char *buffer_return, int bytes_buffer, KeySym *keysym_return, Status *status_return);

int XwcLookupString(XIC ic, XKeyPressedEvent *event, wchar_t *buffer_return, int wchars_buffer, KeySym *keysym_return, Status *status_return);

ic	Specifies the input context.
event	Specifies the key event to be used.
buffer_return	Returns a multibyte string or wide character string (if any) from the input method.
bytes_buffer
wchars_buffer	Specifies space available in the return buffer.
keysym_return	Returns the KeySym computed from the event if this argument is not NULL.
status_return	Returns a value indicating what kind of data is returned.

The
XmbLookupString
and
XwcLookupString
functions return the string from the input method specified
in the buffer_return argument.
If no string is returned,
the buffer_return argument is unchanged.

The KeySym into which the KeyCode from the event was mapped is returned
in the keysym_return argument if it is non-NULL and the status_return
argument indicates that a KeySym was returned.
If both a string and a KeySym are returned,
the KeySym value does not necessarily correspond to the string returned.

XmbLookupString
returns the length of the string in bytes, and
XwcLookupString
returns the length of the string in characters.
Both
XmbLookupString
and
XwcLookupString
return text in the encoding of the locale bound to the input method
of the specified input context.

Each string returned by
XmbLookupString
and
XwcLookupString
begins in the initial state of the encoding of the locale
(if the encoding of the locale is state-dependent).

Note

To insure proper input processing,
it is essential that the client pass only
KeyPress
events to
XmbLookupString
and
XwcLookupString.
Their behavior when a client passes a
KeyRelease
event is undefined.

Clients should check the status_return argument before
using the other returned values.
These two functions both return a value to status_return
that indicates what has been returned in the other arguments.
The possible values returned are:

XBufferOverflow	The input string to be returned is too large for the supplied buffer_return. The required size (`XmbLookupString` in bytes; `XwcLookupString` in characters) is returned as the value of the function, and the contents of buffer_return and keysym_return are not modified. The client should recall the function with the same event and a buffer of adequate size to obtain the string.
XLookupNone	No consistent input has been composed so far. The contents of buffer_return and keysym_return are not modified, and the function returns zero.
XLookupChars	Some input characters have been composed. They are placed in the buffer_return argument, and the string length is returned as the value of the function. The string is encoded in the locale bound to the input context. The content of the keysym_return argument is not modified.
XLookupKeySym	A KeySym has been returned instead of a string and is returned in keysym_return. The content of the buffer_return argument is not modified, and the function returns zero.
XLookupBoth	Both a KeySym and a string are returned; XLookupChars and XLookupKeySym occur simultaneously.

It does not make any difference if the input context passed as an argument to
XmbLookupString
and
XwcLookupString
is the one currently in possession of the focus or not.
Input may have been composed within an input context before it lost the focus,
and that input may be returned on subsequent calls to
XmbLookupString
or
XwcLookupString
even though it does not have any more keyboard focus.

Input Method Conventions

The input method architecture is transparent to the client.
However, clients should respect a number of conventions in order
to work properly.
Clients must also be aware of possible effects of synchronization
between input method and library in the case of a remote input server.

Client Conventions

A well-behaved client (or toolkit) should first query the input method style.
If the client cannot satisfy the requirements of the supported styles
(in terms of geometry management or callbacks),
it should negotiate with the user continuation of the program
or raise an exception or error of some sort.

Synchronization Conventions

A
KeyPress
event with a KeyCode of zero is used exclusively as a
signal that an input method has composed input that can be returned by
XmbLookupString
or
XwcLookupString.
No other use is made of a
KeyPress
event with KeyCode of zero.

Such an event may be generated by either a front-end
or a back-end input method in an implementation-dependent manner.
Some possible ways to generate this event include:

A synthetic event sent by an input method server
An artificial event created by a input method filter and pushed
onto a client's event queue
A
KeyPress
event whose KeyCode value is modified by an input method filter

When callback support is specified by the client,
input methods will not take action unless they explicitly
called back the client and obtained no response
(the callback is not specified or returned invalid data).

String Constants

The following symbols for string constants are defined in
<X11/Xlib.h>.
Although they are shown here with particular macro definitions,
they may be implemented as macros, as global symbols, or as a
mixture of the two. The string pointer value itself
is not significant; clients must not assume that inequality of two
values implies inequality of the actual string data.

#define XNVaNestedList                       "XNVaNestedList"
#define XNSeparatorofNestedList              "separatorofNestedList"
#define XNQueryInputStyle                    "queryInputStyle"
#define XNClientWindow                       "clientWindow"
#define XNInputStyle                         "inputStyle"
#define XNFocusWindow                        "focusWindow"
#define XNResourceName                       "resourceName"
#define XNResourceClass                      "resourceClass"
#define XNGeometryCallback                   "geometryCallback"
#define XNDestroyCallback                    "destroyCallback"
#define XNFilterEvents                       "filterEvents"
#define XNPreeditStartCallback               "preeditStartCallback"
#define XNPreeditDoneCallback                "preeditDoneCallback"
#define XNPreeditDrawCallback                "preeditDrawCallback"
#define XNPreeditCaretCallback               "preeditCaretCallback"
#define XNPreeditStateNotifyCallback         "preeditStateNotifyCallback"
#define XNPreeditAttributes                  "preeditAttributes"
#define XNStatusStartCallback                "statusStartCallback"
#define XNStatusDoneCallback                 "statusDoneCallback"
#define XNStatusDrawCallback                 "statusDrawCallback"
#define XNStatusAttributes                   "statusAttributes"
#define XNArea                               "area"
#define XNAreaNeeded                         "areaNeeded"
#define XNSpotLocation                       "spotLocation"
#define XNColormap                           "colorMap"
#define XNStdColormap                        "stdColorMap"
#define XNForeground                         "foreground"
#define XNBackground                         "background"
#define XNBackgroundPixmap                   "backgroundPixmap"
#define XNFontSet                            "fontSet"
#define XNLineSpace                          "lineSpace"
#define XNCursor                             "cursor"
#define XNQueryIMValuesList                  "queryIMValuesList"
#define XNQueryICValuesList                  "queryICValuesList"
#define XNStringConversionCallback           "stringConversionCallback"
#define XNStringConversion                   "stringConversion"
#define XNResetState                         "resetState"
#define XNHotKey                             "hotkey"
#define XNHotKeyState                        "hotkeyState"
#define XNPreeditState                       "preeditState"
#define XNVisiblePosition                    "visiblePosition"
#define XNR6PreeditCallbackBehavior          "r6PreeditCallback"
#define XNRequiredCharSet                    "requiredCharSet"
#define XNQueryOrientation                   "queryOrientation"
#define XNDirectionalDependentDrawing        "directionalDependentDrawing"
#define XNContextualDrawing                  "contextualDrawing"
#define XNBaseFontName                       "baseFontName"
#define XNMissingCharSet                     "missingCharSet"
#define XNDefaultString                      "defaultString"
#define XNOrientation                        "orientation"
#define XNFontInfo                           "fontInfo"
#define XNOMAutomatic                        "omAutomatic"

Chapter 14. Inter-Client Communication Functions

Table of Contents

The Inter-Client Communication Conventions Manual,
hereafter referred to as the ICCCM,
details the X Consortium approved conventions that govern inter-client communications. These
conventions ensure peer-to-peer client cooperation in the use of selections, cut buffers, and shared
resources as well as client cooperation with window and session managers. For further information,
see the Inter-Client Communication Conventions Manual.

Xlib provides a number of standard properties and programming interfaces that are ICCCM
compliant. The predefined atoms for some of these properties are defined in the <X11/Xatom.h>
header file, where to avoid name conflicts with user symbols their #define name has an XA_ prefix.
For further information about atoms and properties,
see section 4.3.

Xlib’s selection and cut buffer mechanisms provide the primary programming interfaces by which
peer client applications communicate with each other
(see sections 4.5 and
16.6). The functions
discussed in this chapter provide the primary programming interfaces by which client applications
communicate with their window and session managers as well as share standard colormaps.

The standard properties that are of special interest for communicating with window and session
managers are:

Name	Type	Format	Description
WM_CLASS	STRING	8	Set by application programs to allow window and session managers to obtain the application’s resources from the resource database.
WM_CLIENT_MACHINE	TEXT		The string name of the machine on which the client application is running.
WM_COLORMAP_WINDOWS	WINDOWS	32	The list of window IDs that may need a different colormap from that of their top-level window.
WM_COMMAND	TEXT		The command and arguments, null separated, used to invoke the application.
WM_HINTS	WM_HINTS	32	Additional hints set by the client for use by the window manager. The C type of this property is XWMHints.
WM_ICON_NAME	TEXT		The name to be used in an icon.
WM_ICON_SIZE	WM_ICON_SIZE	32	The window manager may set this property on the root window to specify the icon sizes it supports. The C type of this property is XIconSize.
WM_NAME	TEXT		The name of the application.
WM_NORMAL_HINTS	WM_NORMAL_HINTS	32	Size hints for a window in its normal state. The C type of this property is XSizeHints.
WM_PROTOCOLS	ATOM	32	List of atoms that identify the communications protocols between the client and window manager in which the client is willing to participate.
WM_STATE	WM_STATE	32	Intended for communication between window and session managers only.
WM_TRANSIENT_FOR	WINDOW	32	Set by application programs to indicate to the window manager that a transient top-level window, such as a dialog box.

The remainder of this chapter discusses:

Client to window manager communication
Client to session manager communication
Standard colormaps

Client to Window Manager Communication

This section discusses how to:

Manipulate top-level windows
Convert string lists
Set and read text properties
Set and read the WM_NAME property
Set and read the WM_ICON_NAME property
Set and read the WM_HINTS property
Set and read the WM_NORMAL_HINTS property
Set and read the WM_CLASS property
Set and read the WM_TRANSIENT_FOR property
Set and read the WM_PROTOCOLS property
Set and read the WM_COLORMAP_WINDOWS property
Set and read the WM_ICON_SIZE property
Use window manager convenience functions

Manipulating Top-Level Windows

Xlib provides functions that you can use to change the visibility or size
of top-level windows (that is, those that were created as children
of the root window).
Note that the subwindows that you create are ignored by window managers.
Therefore,
you should use the basic window functions described in
chapter 3
to manipulate your application's subwindows.

To request that a top-level window be iconified, use
XIconifyWindow.

Status XIconifyWindow(Display *display, Window w, int screen_number);

display	Specifies the connection to the X server.
w	Specifies the window.
screen_number	Specifies the appropriate screen number on the host server.

The
XIconifyWindow
function sends a WM_CHANGE_STATE
ClientMessage
event with a format of 32 and a first data element of
IconicState
(as described in section 4.1.4 of the
Inter-Client Communication Conventions Manual)
and a window of w
to the root window of the specified screen
with an event mask set to
SubstructureNotifyMask |
SubstructureRedirectMask.
Window managers may elect to receive this message and
if the window is in its normal state,
may treat it as a request to change the window's state from normal to iconic.
If the WM_CHANGE_STATE property cannot be interned,
XIconifyWindow
does not send a message and returns a zero status.
It returns a nonzero status if the client message is sent successfully;
otherwise, it returns a zero status.

To request that a top-level window be withdrawn, use
XWithdrawWindow.

Status XWithdrawWindow(Display *display, Window w, int screen_number);

display	Specifies the connection to the X server.
w	Specifies the window.
screen_number	Specifies the appropriate screen number on the host server.

The
XWithdrawWindow
function unmaps the specified window
and sends a synthetic
UnmapNotify
event to the root window of the specified screen.
Window managers may elect to receive this message
and may treat it as a request to change the window's state to withdrawn.
When a window is in the withdrawn state,
neither its normal nor its iconic representations is visible.
It returns a nonzero status if the
UnmapNotify
event is successfully sent;
otherwise, it returns a zero status.

XWithdrawWindow
can generate a
BadWindow
error.

To request that a top-level window be reconfigured, use
XReconfigureWMWindow.

Status XReconfigureWMWindow(Display *display, Window w, int screen_number, unsigned int value_mask, XWindowChanges *values);

display	Specifies the connection to the X server.
w	Specifies the window.
screen_number	Specifies the appropriate screen number on the host server.
value_mask	Specifies which values are to be set using information in the values structure. This mask is the bitwise inclusive OR of the valid configure window values bits.
values	Specifies the XWindowChanges structure.

The
XReconfigureWMWindow
function issues a
ConfigureWindow
request on the specified top-level window.
If the stacking mode is changed and the request fails with a
BadMatch
error,
the error is trapped by Xlib and a synthetic
ConfigureRequestEvent
containing the same configuration parameters is sent to the root
of the specified window.
Window managers may elect to receive this event
and treat it as a request to reconfigure the indicated window.
It returns a nonzero status if the request or event is successfully sent;
otherwise, it returns a zero status.

XReconfigureWMWindow
can generate
BadValue
and
BadWindow
errors.

Converting String Lists

Many of the text properties allow a variety of types and formats.
Because the data stored in these properties are not
simple null-terminated strings, an
XTextProperty
structure is used to describe the encoding, type, and length of the text
as well as its value.
The
XTextProperty
structure contains:


typedef struct {
	unsigned char *value;	/* property data */
	Atom encoding;	/* type of property */
	int format;	/* 8, 16, or 32 */
	unsigned long nitems;	/* number of items in value */
} XTextProperty;

Xlib provides functions to convert localized text to or from encodings
that support the inter-client communication conventions for text.
In addition, functions are provided for converting between lists of pointers
to character strings and text properties in the STRING encoding.

The functions for localized text return a signed integer error status
that encodes
Success
as zero, specific error conditions as negative numbers, and partial conversion
as a count of unconvertible characters.

#define #XNoMemory           -1
#define #XLocaleNotSupported -2
#define #XConverterNotFound  -3

typedef enum {
	XStringStyle,		/* STRING */
	XCompoundTextStyle,	/* COMPOUND_TEXT */
	XTextStyle,		/* text in owner's encoding (current locale) */
	XStdICCTextStyle	/* STRING, else COMPOUND_TEXT */
} XICCEncodingStyle;

To convert a list of text strings to an
XTextProperty
structure, use
XmbTextListToTextProperty
or
XwcTextListToTextProperty.

int XmbTextListToTextProperty(Display *display, char **list, int count, XICCEncodingStyle style, XTextProperty *text_prop_return);

int XwcTextListToTextProperty(Display *display, wchar_t **list, int count, XICCEncodingStyle style, XTextProperty *text_prop_return);

display	Specifies the connection to the X server.
list	Specifies a list of null-terminated character strings.
count	Specifies the number of strings specified.
style	Specifies the manner in which the property is encoded.
text_prop_return	Returns the XTextProperty structure.

The
XmbTextListToTextProperty
and
XwcTextListToTextProperty
functions set the specified
XTextProperty
value to a set of null-separated elements representing the concatenation
of the specified list of null-terminated text strings.
A final terminating null is stored at the end of the value field
of text_prop_return but is not included in the nitems member.

The functions set the encoding field of text_prop_return to an
Atom
for the specified display
naming the encoding determined by the specified style
and convert the specified text list to this encoding for storage in
the text_prop_return value field.
If the style
XStringStyle
or
XCompoundTextStyle
is specified,
this encoding is “STRING” or “COMPOUND_TEXT”, respectively.
If the style
XTextStyle
is specified,
this encoding is the encoding of the current locale.
If the style
XStdICCTextStyle
is specified,
this encoding is “STRING” if the text is fully convertible to STRING,
else “COMPOUND_TEXT”.

If insufficient memory is available for the new value string,
the functions return
XNoMemory.
If the current locale is not supported,
the functions return
XLocaleNotSupported.
In both of these error cases,
the functions do not set text_prop_return.

To determine if the functions are guaranteed not to return
XLocaleNotSupported,
use
XSupportsLocale.

If the supplied text is not fully convertible to the specified encoding,
the functions return the number of unconvertible characters.
Each unconvertible character is converted to an implementation-defined and
encoding-specific default string.
Otherwise, the functions return
Success.
Note that full convertibility to all styles except
XStringStyle
is guaranteed.

To free the storage for the value field, use
XFree.

To obtain a list of text strings from an
XTextProperty
structure, use
XmbTextPropertyToTextList
or
XwcTextPropertyToTextList.

int XmbTextPropertyToTextList(Display *display, XTextProperty *text_prop, char ***list_return, int *count_return);

int XwcTextPropertyToTextList(Display *display, XTextProperty *text_prop, wchar_t ***list_return, int *count_return);

display	Specifies the connection to the X server.
text_prop	Specifies the XTextProperty structure to be used.
list_return	Returns a list of null-terminated character strings.
count_return	Returns the number of strings.

The
XmbTextPropertyToTextList
and
XwcTextPropertyToTextList
functions return a list of text strings in the current locale representing the
null-separated elements of the specified
XTextProperty
structure.
The data in text_prop must be format 8.

Multiple elements of the property (for example, the strings in a disjoint
text selection) are separated by a null byte.
The contents of the property are not required to be null-terminated;
any terminating null should not be included in text_prop.nitems.

If insufficient memory is available for the list and its elements,
XmbTextPropertyToTextList
and
XwcTextPropertyToTextList
return
XNoMemory.
If the current locale is not supported,
the functions return
XLocaleNotSupported.
Otherwise, if the encoding field of text_prop is not convertible
to the encoding of the current locale,
the functions return
XConverterNotFound.
For supported locales,
existence of a converter from COMPOUND_TEXT, STRING
or the encoding of the current locale is guaranteed if
XSupportsLocale
returns
True
for the current locale (but the actual text
may contain unconvertible characters).
Conversion of other encodings is implementation-dependent.
In all of these error cases,
the functions do not set any return values.

Otherwise,
XmbTextPropertyToTextList
and
XwcTextPropertyToTextList
return the list of null-terminated text strings to list_return
and the number of text strings to count_return.

If the value field of text_prop is not fully convertible to the encoding of
the current locale,
the functions return the number of unconvertible characters.
Each unconvertible character is converted to a string in the
current locale that is specific to the current locale.
To obtain the value of this string,
use
XDefaultString.
Otherwise,
XmbTextPropertyToTextList
and
XwcTextPropertyToTextList
return
Success.

To free the storage for the list and its contents returned by
XmbTextPropertyToTextList,
use
XFreeStringList.
To free the storage for the list and its contents returned by
XwcTextPropertyToTextList,
use
XwcFreeStringList.

To free the in-memory data associated with the specified
wide character string list, use
XwcFreeStringList.

void XwcFreeStringList(wchar_t **list);

list

Specifies the list of strings to be freed.

The
XwcFreeStringList
function frees memory allocated by
XwcTextPropertyToTextList.

To obtain the default string for text conversion in the current locale,
use

char *XDefaultString(void);

The
XDefaultString
function returns the default string used by Xlib for text conversion
(for example, in
XmbTextPropertyToTextList).
The default string is the string in the current locale that is output
when an unconvertible character is found during text conversion.
If the string returned by
XDefaultString
is the empty string (""),
no character is output in the converted text.
XDefaultString
does not return NULL.

The string returned by
XDefaultString
is independent of the default string for text drawing;
see
XCreateFontSet
to obtain the default string for an
XFontSet.

The behavior when an invalid codepoint is supplied to any Xlib function is
undefined.

The returned string is null-terminated.
It is owned by Xlib and should not be modified or freed by the client.
It may be freed after the current locale is changed.
Until freed, it will not be modified by Xlib.

To set the specified list of strings in the STRING encoding to a
XTextProperty
structure, use
XStringListToTextProperty.

Status XStringListToTextProperty(char **list, int count, XTextProperty *text_prop_return);

list	Specifies a list of null-terminated character strings.
count	Specifies the number of strings.
text_prop_return	Returns the XTextProperty structure.

The
XStringListToTextProperty
function sets the specified
XTextProperty
to be of type STRING (format 8) with a value representing the
concatenation of the specified list of null-separated character strings.
An extra null byte (which is not included in the nitems member)
is stored at the end of the value field of text_prop_return.
The strings are assumed (without verification) to be in the STRING encoding.
If insufficient memory is available for the new value string,
XStringListToTextProperty
does not set any fields in the
XTextProperty
structure and returns a zero status.
Otherwise, it returns a nonzero status.
To free the storage for the value field, use
XFree.

To obtain a list of strings from a specified
XTextProperty
structure in the STRING encoding, use
XTextPropertyToStringList.

Status XTextPropertyToStringList(XTextProperty *text_prop, char ***list_return, int *count_return);

text_prop	Specifies the XTextProperty structure to be used.
list_return	Returns a list of null-terminated character strings.
count_return	Returns the number of strings.

The
XTextPropertyToStringList
function returns a list of strings representing the null-separated elements
of the specified
XTextProperty
structure.
The data in text_prop must be of type STRING and format 8.
Multiple elements of the property
(for example, the strings in a disjoint text selection)
are separated by NULL (encoding 0).
The contents of the property are not null-terminated.
If insufficient memory is available for the list and its elements,
XTextPropertyToStringList
sets no return values and returns a zero status.
Otherwise, it returns a nonzero status.
To free the storage for the list and its contents, use
XFreeStringList.

To free the in-memory data associated with the specified string list, use
XFreeStringList.

void XFreeStringList(char **list);

list

Specifies the list of strings to be freed.

The
XFreeStringList
function releases memory allocated by
XmbTextPropertyToTextList
and
XTextPropertyToStringList
and the missing charset list allocated by
XCreateFontSet.

Setting and Reading Text Properties

Xlib provides two functions that you can use to set and read
the text properties for a given window.
You can use these functions to set and read those properties of type TEXT
(WM_NAME, WM_ICON_NAME, WM_COMMAND, and WM_CLIENT_MACHINE).
In addition,
Xlib provides separate convenience functions that you can use to set each
of these properties.
For further information about these convenience functions,
see sections
14.1.4,
14.1.5,
14.2.1, and
14.2.2,
respectively.

To set one of a window's text properties, use
XSetTextProperty.

void XSetTextProperty(Display *display, Window w, XTextProperty *text_prop, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
text_prop	Specifies the XTextProperty structure to be used.
property	Specifies the property name.

The
XSetTextProperty
function replaces the existing specified property for the named window
with the data, type, format, and number of items determined
by the value field, the encoding field, the format field,
and the nitems field, respectively, of the specified
XTextProperty
structure.
If the property does not already exist,
XSetTextProperty
sets it for the specified window.

XSetTextProperty
can generate
BadAlloc,
BadAtom,
BadValue,
and
BadWindow
errors.

To read one of a window's text properties, use
XGetTextProperty.

Status XGetTextProperty(Display *display, Window w, XTextProperty *text_prop_return, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
text_prop_return	Returns the XTextProperty structure.
property	Specifies the property name.

The
XGetTextProperty
function reads the specified property from the window
and stores the data in the returned
XTextProperty
structure.
It stores the data in the value field,
the type of the data in the encoding field,
the format of the data in the format field,
and the number of items of data in the nitems field.
An extra byte containing null (which is not included in the nitems member)
is stored at the end of the value field of text_prop_return.
The particular interpretation of the property's encoding
and data as text is left to the calling application.
If the specified property does not exist on the window,
XGetTextProperty
sets the value field to NULL,
the encoding field to
None,
the format field to zero,
and the nitems field to zero.

If it was able to read and store the data in the
XTextProperty
structure,
XGetTextProperty
returns a nonzero status;
otherwise, it returns a zero status.

XGetTextProperty
can generate
BadAtom
and
BadWindow
errors.

Setting and Reading the WM_NAME Property

Xlib provides convenience functions that you can use to set and read
the WM_NAME property for a given window.

To set a window's WM_NAME property with the supplied convenience function, use
XSetWMName.

void XSetWMName(Display *display, Window w, XTextProperty *text_prop);

display	Specifies the connection to the X server.
w	Specifies the window.
text_prop	Specifies the XTextProperty structure to be used.

The
XSetWMName
convenience function calls
XSetTextProperty
to set the WM_NAME property.

To read a window's WM_NAME property with the supplied convenience function, use
XGetWMName.

Status XGetWMName(Display *display, Window w, XTextProperty *text_prop_return);

display	Specifies the connection to the X server.
w	Specifies the window.
text_prop_return	Returns the XTextProperty structure.

The
XGetWMName
convenience function calls
XGetTextProperty
to obtain the WM_NAME property.
It returns a nonzero status on success;
otherwise, it returns a zero status.

The following two functions have been superseded by
XSetWMName
and
XGetWMName,
respectively.
You can use these additional convenience functions
for window names that are encoded as STRING properties.

To assign a name to a window, use
XStoreName.

XStoreName(Display *display, Window w, char *window_name);

display	Specifies the connection to the X server.
w	Specifies the window.
window_name	Specifies the window name, which should be a null-terminated string.

The
XStoreName
function assigns the name passed to window_name to the specified window.
A window manager can display the window name in some prominent
place, such as the title bar, to allow users to identify windows easily.
Some window managers may display a window's name in the window's icon,
although they are encouraged to use the window's icon name
if one is provided by the application.
If the string is not in the Host Portable Character Encoding,
the result is implementation-dependent.

XStoreName
can generate
BadAlloc
and
BadWindow
errors.

To get the name of a window, use
XFetchName.

Status XFetchName(Display *display, Window w, char **window_name_return);

display	Specifies the connection to the X server.
w	Specifies the window.
window_name_return	Returns the window name, which is a null-terminated string.

The
XFetchName
function returns the name of the specified window.
If it succeeds,
it returns a nonzero status;
otherwise, no name has been set for the window,
and it returns zero.
If the WM_NAME property has not been set for this window,
XFetchName
sets window_name_return to NULL.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned string is in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
When finished with it, a client must free
the window name string using
XFree.

XFetchName
can generate a
BadWindow
error.

Setting and Reading the WM_ICON_NAME Property

Xlib provides convenience functions that you can use to set and read
the WM_ICON_NAME property for a given window.

To set a window's WM_ICON_NAME property,
use
XSetWMIconName.

void XSetWMIconName(Display *display, Window w, XTextProperty *text_prop);

display	Specifies the connection to the X server.
w	Specifies the window.
text_prop	Specifies the XTextProperty structure to be used.

The
XSetWMIconName
convenience function calls
XSetTextProperty
to set the WM_ICON_NAME property.

To read a window's WM_ICON_NAME property,
use
XGetWMIconName.

Status XGetWMIconName(Display *display, Window w, XTextProperty *text_prop_return);

display	Specifies the connection to the X server.
w	Specifies the window.
text_prop_return	Returns the XTextProperty structure.

The
XGetWMIconName
convenience function calls
XGetTextProperty
to obtain the WM_ICON_NAME property.
It returns a nonzero status on success;
otherwise, it returns a zero status.

The next two functions have been superseded by
XSetWMIconName
and
XGetWMIconName,
respectively.
You can use these additional convenience functions
for window names that are encoded as STRING properties.

To set the name to be displayed in a window's icon, use
XSetIconName.

XSetIconName(Display *display, Window w, char *icon_name);

display	Specifies the connection to the X server.
w	Specifies the window.
icon_name	Specifies the icon name, which should be a null-terminated string.

If the string is not in the Host Portable Character Encoding,
the result is implementation-dependent.
XSetIconName
can generate
BadAlloc
and
BadWindow
errors.

To get the name a window wants displayed in its icon, use
XGetIconName.

Status XGetIconName(Display *display, Window w, char **icon_name_return);

display	Specifies the connection to the X server.
w	Specifies the window.
icon_name_return	Returns the window's icon name, which is a null-terminated string.

The
XGetIconName
function returns the name to be displayed in the specified window's icon.
If it succeeds, it returns a nonzero status; otherwise,
if no icon name has been set for the window,
it returns zero.
If you never assigned a name to the window,
XGetIconName
sets icon_name_return to NULL.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned string is in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
When finished with it, a client must free
the icon name string using
XFree.

XGetIconName
can generate a
BadWindow
error.

Setting and Reading the WM_HINTS Property

Xlib provides functions that you can use to set and read
the WM_HINTS property for a given window.
These functions use the flags and the
XWMHints
structure, as defined in the
<X11/Xutil.h>

header file.

To allocate an
XWMHints
structure, use
XAllocWMHints.

XWMHints *XAllocWMHints(void);

The
XAllocWMHints
function allocates and returns a pointer to an
XWMHints
structure.
Note that all fields in the
XWMHints
structure are initially set to zero.
If insufficient memory is available,
XAllocWMHints
returns NULL.
To free the memory allocated to this structure,
use
XFree.

The
XWMHints
structure contains:

/* Window manager hints mask bits */

#define         InputHint             (1L<<0)
#define         StateHint             (1L<<1)
#define         IconPixmapHint        (1L<<2)
#define         IconWindowHint        (1L<<3)
#define         IconPositionHint      (1L<<4)
#define         IconMaskHint          (1L<<5)
#define         WindowGroupHint       (1L<<6)
#define         UrgencyHint           (1L<<8)
#define         AllHints              (InputHint|StateHint|IconPixmapHint|
                                       IconWIndowHint|IconPositionHint|
                                       IconMaskHint|WindowGroupHint)


/* Values */

typedef struct {
	long flags;	        /* marks which fields in this structure are defined */
	Bool input;	        /* does this application rely on the window manager to
			           get keyboard input? */
	int initial_state;	/* see below */
	Pixmap icon_pixmap;	/* pixmap to be used as icon */
	Window icon_window;	/* window to be used as icon */
	int icon_x, icon_y;	/* initial position of icon */
	Pixmap icon_mask;	/* pixmap to be used as mask for icon_pixmap */
	XID window_group;	/* id of related window group */
	/* this structure may be extended in the future */
} XWMHints;

The input member is used to communicate to the window manager the input focus
model used by the application.
Applications that expect input but never explicitly set focus to any
of their subwindows (that is, use the push model of focus management),
such as X Version 10 style applications that use real-estate
driven focus, should set this member to
True.
Similarly, applications
that set input focus to their subwindows only when it is given to their
top-level window by a window manager should also set this member to
True.
Applications that manage their own input focus by explicitly setting
focus to one of their subwindows whenever they want keyboard input
(that is, use the pull model of focus management) should set this member to
False.
Applications that never expect any keyboard input also should set this member
to
False.

Pull model window managers should make it possible for push model
applications to get input by setting input focus to the top-level windows of
applications whose input member is
True.
Push model window managers should
make sure that pull model applications do not break them
by resetting input focus to
PointerRoot
when it is appropriate (for example, whenever an application whose
input member is
False
sets input focus to one of its subwindows).

The definitions for the initial_state flag are:

#define      WithdrawnState 0
#define      NormalState    1   /* most applications start this way */
#define      IconicState    3   /* application wants to start as an icon */

The icon_mask specifies which pixels of the icon_pixmap should be used as the
icon.
This allows for nonrectangular icons.
Both icon_pixmap and icon_mask must be bitmaps.
The icon_window lets an application provide a window for use as an icon
for window managers that support such use.
The window_group lets you specify that this window belongs to a group
of other windows.
For example, if a single application manipulates multiple
top-level windows, this allows you to provide enough
information that a window manager can iconify all of the windows
rather than just the one window.

The
UrgencyHint
flag, if set in the flags field, indicates that the client deems the window
contents to be urgent, requiring the timely response of the user. The
window manager will make some effort to draw the user's attention to this
window while this flag is set. The client must provide some means by which the
user can cause the urgency flag to be cleared (either mitigating
the condition that made the window urgent or merely shutting off the alarm)
or the window to be withdrawn.

To set a window's WM_HINTS property, use
XSetWMHints.

XSetWMHints(Display *display, Window w, XWMHints *wmhints);

display	Specifies the connection to the X server.
w	Specifies the window.
wmhints	Specifies the XWMHints structure to be used.

The
XSetWMHints
function sets the window manager hints that include icon information and location,
the initial state of the window, and whether the application relies on the
window manager to get keyboard input.

XSetWMHints
can generate
BadAlloc
and
BadWindow
errors.

To read a window's WM_HINTS property, use
XGetWMHints.

XWMHints *XGetWMHints(Display *display, Window w);

display	Specifies the connection to the X server.
w	Specifies the window.

The
XGetWMHints
function reads the window manager hints and
returns NULL if no WM_HINTS property was set on the window
or returns a pointer to an
XWMHints
structure if it succeeds.
When finished with the data,
free the space used for it by calling
XFree.

XGetWMHints
can generate a
BadWindow
error.

Setting and Reading the WM_NORMAL_HINTS Property

Xlib provides functions that you can use to set or read
the WM_NORMAL_HINTS property for a given window.
The functions use the flags and the
XSizeHints
structure, as defined in the
<X11/Xutil.h>

header file.

The size of the
XSizeHints
structure may grow in future releases, as new components are
added to support new ICCCM features.
Passing statically allocated instances of this structure into
Xlib may result in memory corruption when running against a
future release of the library.
As such, it is recommended that only dynamically allocated
instances of the structure be used.

To allocate an
XSizeHints
structure, use
XAllocSizeHints.

XSizeHints *XAllocSizeHints(void);

The
XAllocSizeHints
function allocates and returns a pointer to an
XSizeHints
structure.
Note that all fields in the
XSizeHints
structure are initially set to zero.
If insufficient memory is available,
XAllocSizeHints
returns NULL.
To free the memory allocated to this structure,
use
XFree.

The
XSizeHints
structure contains:

/* Size hints mask bits */

#define           USPosition         (1L<<0)  /* user specified x,y */
#define           USSize             (1L<<1)  /* user specified width,height */
#define           PPosition          (1L<<2)  /* program specified posistion */
#define           PSize              (1L<<3)  /* program specified size */
#define           PMinSize           (1L<<4)  /* program specified minimum size */
#define           PMaxSize           (1L<<5)  /* program specified maximum size */
#define           PResizeInc         (1L<<5)  /* program specified resize increments */
#define           PAspect            (1L<<6)  /* program specified min and max aspect ratios */
#define           PBaseSize          (1L<<8)
#define           PWinGravity        (1L<<9)
#define           PAllHints          (PPosition|Psize|
                                      PMinSize|PMaxSize|
                                      PResizeInc|PAspect)


/* Values */

typedef struct {
	long flags;	        /* marks which fields in this structure are defined */
	int x, y;	        /* Obsolete */
	int width, height;	/* Obsolete */
	int min_width, min_height;
	int max_width, max_height;
	int width_inc, height_inc;
	struct {
	       int x;	        /* numerator */
	       int y;	        /* denominator */
	} min_aspect, max_aspect;
	int base_width, base_height;
	int win_gravity;
	/* this structure may be extended in the future */
} XSizeHints;

The x, y, width, and height members are now obsolete
and are left solely for compatibility reasons.
The min_width and min_height members specify the
minimum window size that still allows the application to be useful.
The max_width and max_height members specify the maximum window size.
The width_inc and height_inc members define an arithmetic progression of
sizes (minimum to maximum) into which the window prefers to be resized.
The min_aspect and max_aspect members are expressed
as ratios of x and y,
and they allow an application to specify the range of aspect
ratios it prefers.
The base_width and base_height members define the desired size of the window.
The window manager will interpret the position of the window
and its border width to position the point of the outer rectangle
of the overall window specified by the win_gravity member.
The outer rectangle of the window includes any borders or decorations
supplied by the window manager.
In other words,
if the window manager decides to place the window where the client asked,
the position on the parent window's border named by the win_gravity
will be placed where the client window would have been placed
in the absence of a window manager.

Note that use of the
PAllHints
macro is highly discouraged.

To set a window's WM_NORMAL_HINTS property, use
XSetWMNormalHints.

void XSetWMNormalHints(Display *display, Window w, XSizeHints *hints);

display	Specifies the connection to the X server.
w	Specifies the window.
hints	Specifies the size hints for the window in its normal state.

The
XSetWMNormalHints
function replaces the size hints for the WM_NORMAL_HINTS property
on the specified window.
If the property does not already exist,
XSetWMNormalHints
sets the size hints for the WM_NORMAL_HINTS property on the specified window.
The property is stored with a type of WM_SIZE_HINTS and a format of 32.

XSetWMNormalHints
can generate
BadAlloc
and
BadWindow
errors.

To read a window's WM_NORMAL_HINTS property, use
XGetWMNormalHints.

Status XGetWMNormalHints(Display *display, Window w, XSizeHints *hints_return, long *supplied_return);

display	Specifies the connection to the X server.
w	Specifies the window.
hints_return	Returns the size hints for the window in its normal state.
supplied_return	Returns the hints that were supplied by the user.

The
XGetWMNormalHints
function returns the size hints stored in the WM_NORMAL_HINTS property
on the specified window.
If the property is of type WM_SIZE_HINTS, is of format 32,
and is long enough to contain either an old (pre-ICCCM)
or new size hints structure,
XGetWMNormalHints
sets the various fields of the
XSizeHints
structure, sets the supplied_return argument to the list of fields
that were supplied by the user (whether or not they contained defined values),
and returns a nonzero status.
Otherwise, it returns a zero status.

If
XGetWMNormalHints
returns successfully and a pre-ICCCM size hints property is read,
the supplied_return argument will contain the following bits:

(USPosition|USSize|PPosition|PSize|PMinSize|
 PMaxSize|PResizeInc|PAspect)

If the property is large enough to contain the base size
and window gravity fields as well,
the supplied_return argument will also contain the following bits:

PBaseSize|PWinGravity

XGetWMNormalHints
can generate a
BadWindow
error.

To set a window's WM_SIZE_HINTS property, use
XSetWMSizeHints.

void XSetWMSizeHints(Display *display, Window w, XSizeHints *hints, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
hints	Specifies the XSizeHints structure to be used.
property	Specifies the property name.

The
XSetWMSizeHints
function replaces the size hints for the specified property
on the named window.
If the specified property does not already exist,
XSetWMSizeHints
sets the size hints for the specified property
on the named window.
The property is stored with a type of WM_SIZE_HINTS and a format of 32.
To set a window's normal size hints,
you can use the
XSetWMNormalHints
function.

XSetWMSizeHints
can generate
BadAlloc,
BadAtom,
and
BadWindow
errors.

To read a window's WM_SIZE_HINTS property, use
XGetWMSizeHints.

Status XGetWMSizeHints(Display *display, Window w, XSizeHints *hints_return, long *supplied_return, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
hints_return	Returns the XSizeHints structure.
supplied_return	Returns the hints that were supplied by the user.
property	Specifies the property name.

The
XGetWMSizeHints
function returns the size hints stored in the specified property
on the named window.
If the property is of type WM_SIZE_HINTS, is of format 32,
and is long enough to contain either an old (pre-ICCCM)
or new size hints structure,
XGetWMSizeHints
sets the various fields of the
XSizeHints
structure, sets the supplied_return argument to the
list of fields that were supplied by the user
(whether or not they contained defined values),
and returns a nonzero status.
Otherwise, it returns a zero status.
To get a window's normal size hints,
you can use the
XGetWMNormalHints
function.

If
XGetWMSizeHints
returns successfully and a pre-ICCCM size hints property is read,
the supplied_return argument will contain the following bits:

(USPosition|USSize|PPosition|PSize|PMinSize|
 PMaxSize|PResizeInc|PAspect)

If the property is large enough to contain the base size
and window gravity fields as well,
the supplied_return argument will also contain the following bits:

PBaseSize|PWinGravity

XGetWMSizeHints
can generate
BadAtom
and
BadWindow
errors.

Setting and Reading the WM_CLASS Property

Xlib provides functions that you can use to set and get
the WM_CLASS property for a given window.
These functions use the
XClassHint
structure, which is defined in the
<X11/Xutil.h>

header file.

To allocate an
XClassHint
structure, use
XAllocClassHint.

XClassHint *XAllocClassHint(void);

The
XAllocClassHint
function allocates and returns a pointer to an
XClassHint
structure.
Note that the pointer fields in the
XClassHint
structure are initially set to NULL.
If insufficient memory is available,
XAllocClassHint
returns NULL.
To free the memory allocated to this structure,
use
XFree.

The
XClassHint
contains:


typedef struct {
	char *res_name;
	char *res_class;
} XClassHint;

The res_name member contains the application name,
and the res_class member contains the application class.
Note that the name set in this property may differ from the name set as WM_NAME.
That is, WM_NAME specifies what should be displayed in the title bar and,
therefore, can contain temporal information (for example, the name of
a file currently in an editor's buffer).
On the other hand,
the name specified as part of WM_CLASS is the formal name of the application
that should be used when retrieving the application's resources from the
resource database.

To set a window's WM_CLASS property, use
XSetClassHint.

XSetClassHint(Display *display, Window w, XClassHint *class_hints);

display	Specifies the connection to the X server.
w	Specifies the window.
class_hints	Specifies the XClassHint structure that is to be used.

The
XSetClassHint
function sets the class hint for the specified window.
If the strings are not in the Host Portable Character Encoding,
the result is implementation-dependent.

XSetClassHint
can generate
BadAlloc
and
BadWindow
errors.

To read a window's WM_CLASS property, use
XGetClassHint.

Status XGetClassHint(Display *display, Window w, XClassHint *class_hints_return);

display	Specifies the connection to the X server.
w	Specifies the window.
class_hints_return	Returns the XClassHint structure.

The
XGetClassHint
function returns the class hint of the specified window to the members
of the supplied structure.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
It returns a nonzero status on success;
otherwise, it returns a zero status.
To free res_name and res_class when finished with the strings,
use
XFree
on each individually.

XGetClassHint
can generate a
BadWindow
error.

Setting and Reading the WM_TRANSIENT_FOR Property

Xlib provides functions that you can use to set and read
the WM_TRANSIENT_FOR property for a given window.

To set a window's WM_TRANSIENT_FOR property, use
XSetTransientForHint.

XSetTransientForHint(Display *display, Window w, Window prop_window);

display	Specifies the connection to the X server.
w	Specifies the window.
prop_window	Specifies the window that the WM_TRANSIENT_FOR property is to be set to.

The
XSetTransientForHint
function sets the WM_TRANSIENT_FOR property of the specified window to the
specified prop_window.

XSetTransientForHint
can generate
BadAlloc
and
BadWindow
errors.

To read a window's WM_TRANSIENT_FOR property, use
XGetTransientForHint.

Status XGetTransientForHint(Display *display, Window w, Window *prop_window_return);

display	Specifies the connection to the X server.
w	Specifies the window.
prop_window_return	Returns the WM_TRANSIENT_FOR property of the specified window.

The
XGetTransientForHint
function returns the WM_TRANSIENT_FOR property for the specified window.
It returns a nonzero status on success;
otherwise, it returns a zero status.

XGetTransientForHint
can generate a
BadWindow
error.

Setting and Reading the WM_PROTOCOLS Property

Xlib provides functions that you can use to set and read
the WM_PROTOCOLS property for a given window.

To set a window's WM_PROTOCOLS property, use
XSetWMProtocols.

Status XSetWMProtocols(Display *display, Window w, Atom *protocols, int count);

display	Specifies the connection to the X server.
w	Specifies the window.
protocols	Specifies the list of protocols.
count	Specifies the number of protocols in the list.

The
XSetWMProtocols
function replaces the WM_PROTOCOLS property on the specified window
with the list of atoms specified by the protocols argument.
If the property does not already exist,
XSetWMProtocols
sets the WM_PROTOCOLS property on the specified window
to the list of atoms specified by the protocols argument.
The property is stored with a type of ATOM and a format of 32.
If it cannot intern the WM_PROTOCOLS atom,
XSetWMProtocols
returns a zero status.
Otherwise, it returns a nonzero status.

XSetWMProtocols
can generate
BadAlloc
and
BadWindow
errors.

To read a window's WM_PROTOCOLS property, use
XGetWMProtocols.

Status XGetWMProtocols(Display *display, Window w, Atom **protocols_return, int *count_return);

display	Specifies the connection to the X server.
w	Specifies the window.
protocols_return	Returns the list of protocols.
count_return	Returns the number of protocols in the list.

The
XGetWMProtocols
function returns the list of atoms stored in the WM_PROTOCOLS property
on the specified window.
These atoms describe window manager protocols in which the owner
of this window is willing to participate.
If the property exists, is of type ATOM, is of format 32,
and the atom WM_PROTOCOLS can be interned,
XGetWMProtocols
sets the protocols_return argument to a list of atoms,
sets the count_return argument to the number of elements in the list,
and returns a nonzero status.
Otherwise, it sets neither of the return arguments
and returns a zero status.
To release the list of atoms, use
XFree.

XGetWMProtocols
can generate a
BadWindow
error.

Setting and Reading the WM_COLORMAP_WINDOWS Property

Xlib provides functions that you can use to set and read
the WM_COLORMAP_WINDOWS property for a given window.

To set a window's WM_COLORMAP_WINDOWS property, use
XSetWMColormapWindows.

Status XSetWMColormapWindows(Display *display, Window w, Window *colormap_windows, int count);

display	Specifies the connection to the X server.
w	Specifies the window.
colormap_windows	Specifies the list of windows.
count	Specifies the number of windows in the list.

The
XSetWMColormapWindows
function replaces the WM_COLORMAP_WINDOWS property on the specified
window with the list of windows specified by the colormap_windows argument.
If the property does not already exist,
XSetWMColormapWindows
sets the WM_COLORMAP_WINDOWS property on the specified
window to the list of windows specified by the colormap_windows argument.
The property is stored with a type of WINDOW and a format of 32.
If it cannot intern the WM_COLORMAP_WINDOWS atom,
XSetWMColormapWindows
returns a zero status.
Otherwise, it returns a nonzero status.

XSetWMColormapWindows
can generate
BadAlloc
and
BadWindow
errors.

To read a window's WM_COLORMAP_WINDOWS property, use
XGetWMColormapWindows.

Status XGetWMColormapWindows(Display *display, Window w, Window **colormap_windows_return, int *count_return);

display	Specifies the connection to the X server.
w	Specifies the window.
colormap_windows_return	Returns the list of windows.
count_return	Returns the number of windows in the list.

The
XGetWMColormapWindows
function returns the list of window identifiers stored
in the WM_COLORMAP_WINDOWS property on the specified window.
These identifiers indicate the colormaps that the window manager
may need to install for this window.
If the property exists, is of type WINDOW, is of format 32,
and the atom WM_COLORMAP_WINDOWS can be interned,
XGetWMColormapWindows
sets the windows_return argument to a list of window identifiers,
sets the count_return argument to the number of elements in the list,
and returns a nonzero status.
Otherwise, it sets neither of the return arguments
and returns a zero status.
To release the list of window identifiers, use
XFree.

XGetWMColormapWindows
can generate a
BadWindow
error.

Setting and Reading the WM_ICON_SIZE Property

Xlib provides functions that you can use to set and read
the WM_ICON_SIZE property for a given window.
These functions use the
XIconSize

structure, which is defined in the
<X11/Xutil.h>

header file.

To allocate an
XIconSize
structure, use
XAllocIconSize.

XIconSize *XAllocIconSize(void);

The
XAllocIconSize
function allocates and returns a pointer to an
XIconSize
structure.
Note that all fields in the
XIconSize
structure are initially set to zero.
If insufficient memory is available,
XAllocIconSize
returns NULL.
To free the memory allocated to this structure,
use
XFree.

The
XIconSize
structure contains:


typedef struct {
	int min_width, min_height;
	int max_width, max_height;
	int width_inc, height_inc;
} XIconSize;

The width_inc and height_inc members define an arithmetic progression of
sizes (minimum to maximum) that represent the supported icon sizes.

To set a window's WM_ICON_SIZE property, use
XSetIconSizes.

XSetIconSizes(Display *display, Window w, XIconSize *size_list, int count);

display	Specifies the connection to the X server.
w	Specifies the window.
size_list	Specifies the size list.
count	Specifies the number of items in the size list.

The
XSetIconSizes
function is used only by window managers to set the supported icon sizes.

XSetIconSizes
can generate
BadAlloc
and
BadWindow
errors.

To read a window's WM_ICON_SIZE property, use
XGetIconSizes.

Status XGetIconSizes(Display *display, Window w, XIconSize **size_list_return, int *count_return);

display	Specifies the connection to the X server.
w	Specifies the window.
size_list_return	Returns the size list.
count_return	Returns the number of items in the size list.

The
XGetIconSizes
function returns zero if a window manager has not set icon sizes;
otherwise, it returns nonzero.
XGetIconSizes
should be called by an application that
wants to find out what icon sizes would be most appreciated by the
window manager under which the application is running.
The application
should then use
XSetWMHints
to supply the window manager with an icon pixmap or window in one of the
supported sizes.
To free the data allocated in size_list_return, use
XFree.

XGetIconSizes
can generate a
BadWindow
error.

Using Window Manager Convenience Functions

The
XmbSetWMProperties
function stores the standard set of window manager properties,
with text properties in standard encodings
for internationalized text communication.
The standard window manager properties for a given window are
WM_NAME, WM_ICON_NAME, WM_HINTS, WM_NORMAL_HINTS, WM_CLASS,
WM_COMMAND, WM_CLIENT_MACHINE, and WM_LOCALE_NAME.

void XmbSetWMProperties(Display *display, Window w, char *window_name, char *icon_name, char *argv[], int argc, XSizeHints *normal_hints, XWMHints *wm_hints, XClassHint *class_hints);

display	Specifies the connection to the X server.
w	Specifies the window.
window_name	Specifies the window name, which should be a null-terminated string.
icon_name	Specifies the icon name, which should be a null-terminated string.
argv	Specifies the application's argument list.
argc	Specifies the number of arguments.
hints	Specifies the size hints for the window in its normal state.
wm_hints	Specifies the XWMHints structure to be used.
class_hints	Specifies the XClassHint structure to be used.

The
XmbSetWMProperties
convenience function provides a simple programming interface
for setting those essential window properties that are used
for communicating with other clients
(particularly window and session managers).

If the window_name argument is non-NULL,
XmbSetWMProperties
sets the WM_NAME property.
If the icon_name argument is non-NULL,
XmbSetWMProperties
sets the WM_ICON_NAME property.
The window_name and icon_name arguments are null-terminated strings
in the encoding of the current locale.
If the arguments can be fully converted to the STRING encoding,
the properties are created with type “STRING”;
otherwise, the arguments are converted to Compound Text,
and the properties are created with type “COMPOUND_TEXT”.

If the normal_hints argument is non-NULL,
XmbSetWMProperties
calls
XSetWMNormalHints,
which sets the WM_NORMAL_HINTS property
(see section 14.1.7).
If the wm_hints argument is non-NULL,
XmbSetWMProperties
calls
XSetWMHints,
which sets the WM_HINTS property
(see section 14.1.6).

If the argv argument is non-NULL,
XmbSetWMProperties
sets the WM_COMMAND property from argv and argc.
An argc of zero indicates a zero-length command.

The hostname of the machine is stored using
XSetWMClientMachine
(see section 14.2.2).

If the class_hints argument is non-NULL,
XmbSetWMProperties
sets the WM_CLASS property.
If the res_name member in the
XClassHint
structure is set to the NULL pointer and the RESOURCE_NAME
environment variable is set,
the value of the environment variable is substituted for res_name.
If the res_name member is NULL,
the environment variable is not set, and argv and argv[0] are set,
then the value of argv[0], stripped of any directory prefixes,
is substituted for res_name.

It is assumed that the supplied class_hints.res_name and argv,
the RESOURCE_NAME environment variable, and the hostname of the machine
are in the encoding of the locale announced for the LC_CTYPE category
(on POSIX-compliant systems, the LC_CTYPE, else LANG environment variable).
The corresponding WM_CLASS, WM_COMMAND, and WM_CLIENT_MACHINE properties
are typed according to the local host locale announcer.
No encoding conversion is performed prior to storage in the properties.

For clients that need to process the property text in a locale,
XmbSetWMProperties
sets the WM_LOCALE_NAME property to be the name of the current locale.
The name is assumed to be in the Host Portable Character Encoding
and is converted to STRING for storage in the property.

XmbSetWMProperties
can generate
BadAlloc
and
BadWindow
errors.

To set a window's standard window manager properties
with strings in client-specified encodings, use
XSetWMProperties.
The standard window manager properties for a given window are
WM_NAME, WM_ICON_NAME, WM_HINTS, WM_NORMAL_HINTS, WM_CLASS,
WM_COMMAND, and WM_CLIENT_MACHINE.

void XSetWMProperties(Display *display, Window w, XTextProperty *window_name, XTextProperty *icon_name, char **argv, int argc, XSizeHints *normal_hints, XWMHints *wm_hints, XClassHint *class_hints);

display	Specifies the connection to the X server.
w	Specifies the window.
window_name	Specifies the window name, which should be a null-terminated string.
icon_name	Specifies the icon name, which should be a null-terminated string.
argv	Specifies the application's argument list.
argc	Specifies the number of arguments.
normal_hints	Specifies the size hints for the window in its normal state.
wm_hints	Specifies the XWMHints structure to be used.
class_hints	Specifies the XClassHint structure to be used.

The
XSetWMProperties
convenience function provides a single programming interface
for setting those essential window properties that are used
for communicating with other clients (particularly window and session
managers).

If the window_name argument is non-NULL,
XSetWMProperties
calls
XSetWMName,
which, in turn, sets the WM_NAME property
(see section 14.1.4).
If the icon_name argument is non-NULL,
XSetWMProperties
calls
XSetWMIconName,
which sets the WM_ICON_NAME property
(see section 14.1.5).
If the argv argument is non-NULL,
XSetWMProperties
calls
XSetCommand,
which sets the WM_COMMAND property
(see section 14.2.1).
Note that an argc of zero is allowed to indicate a zero-length command.
Note also that the hostname of this machine is stored using
XSetWMClientMachine
(see section 14.2.2).

If the normal_hints argument is non-NULL,
XSetWMProperties
calls
XSetWMNormalHints,
which sets the WM_NORMAL_HINTS property
(see section 14.1.7).
If the wm_hints argument is non-NULL,
XSetWMProperties
calls
XSetWMHints,
which sets the WM_HINTS property
(see section 14.1.6).

If the class_hints argument is non-NULL,
XSetWMProperties
calls
XSetClassHint,
which sets the WM_CLASS property
(see section 14.1.8).
If the res_name member in the
XClassHint
structure is set to the NULL pointer and the RESOURCE_NAME environment
variable is set,
then the value of the environment variable is substituted for res_name.
If the res_name member is NULL,
the environment variable is not set,
and argv and argv[0] are set,
then the value of argv[0], stripped of
any directory prefixes, is substituted for res_name.

XSetWMProperties
can generate
BadAlloc
and
BadWindow
errors.

Client to Session Manager Communication

This section discusses how to:

Set and read the WM_COMMAND property
Set and read the WM_CLIENT_MACHINE property

Setting and Reading the WM_COMMAND Property

Xlib provides functions that you can use to set and read
the WM_COMMAND property for a given window.

To set a window's WM_COMMAND property, use
XSetCommand.

XSetCommand(Display *display, Window w, char **argv, int argc);

display	Specifies the connection to the X server.
w	Specifies the window.
argv	Specifies the application's argument list.
argc	Specifies the number of arguments.

The
XSetCommand
function sets the command and arguments used to invoke the
application.
(Typically, argv is the argv array of your main program.)
If the strings are not in the Host Portable Character Encoding,
the result is implementation-dependent.

XSetCommand
can generate
BadAlloc
and
BadWindow
errors.

To read a window's WM_COMMAND property, use
XGetCommand.

Status XGetCommand(Display *display, Window w, char ***argv_return, int *argc_return);

display	Specifies the connection to the X server.
w	Specifies the window.
argv_return	Returns the application's argument list.
argc_return	Returns the number of arguments returned.

The
XGetCommand
function reads the WM_COMMAND property from the specified window
and returns a string list.
If the WM_COMMAND property exists,
it is of type STRING and format 8.
If sufficient memory can be allocated to contain the string list,
XGetCommand
fills in the argv_return and argc_return arguments
and returns a nonzero status.
Otherwise, it returns a zero status.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
To free the memory allocated to the string list, use
XFreeStringList.

Setting and Reading the WM_CLIENT_MACHINE Property

Xlib provides functions that you can use to set and read
the WM_CLIENT_MACHINE property for a given window.

To set a window's WM_CLIENT_MACHINE property, use
XSetWMClientMachine.

void XSetWMClientMachine(Display *display, Window w, XTextProperty *text_prop);

display	Specifies the connection to the X server.
w	Specifies the window.
text_prop	Specifies the XTextProperty structure to be used.

The
XSetWMClientMachine
convenience function calls
XSetTextProperty
to set the WM_CLIENT_MACHINE property.

To read a window's WM_CLIENT_MACHINE property, use
XGetWMClientMachine.

Status XGetWMClientMachine(Display *display, Window w, XTextProperty *text_prop_return);

display	Specifies the connection to the X server.
w	Specifies the window.
text_prop_return	Returns the XTextProperty structure.

The
XGetWMClientMachine
convenience function performs an
XGetTextProperty
on the WM_CLIENT_MACHINE property.
It returns a nonzero status on success;
otherwise, it returns a zero status.

Standard Colormaps

Applications with color palettes, smooth-shaded drawings, or digitized
images demand large numbers of colors.
In addition, these applications often require an efficient mapping
from color triples to pixel values that display the appropriate colors.

As an example, consider a three-dimensional display program that wants
to draw a smoothly shaded sphere.
At each pixel in the image of the sphere,
the program computes the intensity and color of light
reflected back to the viewer.
The result of each computation is a triple of red, green, and blue (RGB)
coefficients in the range 0.0 to 1.0.
To draw the sphere, the program needs a colormap that provides a
large range of uniformly distributed colors.
The colormap should be arranged so that the program can
convert its RGB triples into pixel values very quickly,
because drawing the entire sphere requires many such
conversions.

On many current workstations,
the display is limited to 256 or fewer colors.
Applications must allocate colors carefully,
not only to make sure they cover the entire range they need
but also to make use of as many of the available colors as possible.
On a typical X display,
many applications are active at once.
Most workstations have only one hardware look-up table for colors,
so only one application colormap can be installed at a given time.
The application using the installed colormap is displayed correctly,
and the other applications go technicolor and are
displayed with false colors.

As another example, consider a user who is running an
image processing program to display earth-resources data.
The image processing program needs a colormap set up with 8 reds,
8 greens, and 4 blues, for a total of 256 colors.
Because some colors are already in use in the default colormap,
the image processing program allocates and installs a new colormap.

The user decides to alter some of the colors in the image
by invoking a color palette program to mix and choose colors.
The color palette program also needs a
colormap with eight reds, eight greens, and four blues, so just like
the image processing program, it must allocate and
install a new colormap.

Because only one colormap can be installed at a time,
the color palette may be displayed incorrectly
whenever the image processing program is active.
Conversely, whenever the palette program is active,
the image may be displayed incorrectly.
The user can never match or compare colors in the palette and image.
Contention for colormap resources can be reduced if applications
with similar color needs share colormaps.

The image processing program and the color palette program
could share the same colormap if there existed a convention that described
how the colormap was set up.
Whenever either program was active,
both would be displayed correctly.

The standard colormap properties define a set of commonly used
colormaps.
Applications that share these colormaps and conventions display
true colors more often and provide a better interface to the user.

Standard colormaps allow applications to share commonly used color
resources.
This allows many applications to be displayed in true colors
simultaneously, even when each application needs an entirely filled
colormap.

Several standard colormaps are described in this section.
Usually, a window manager creates these colormaps.
Applications should use the standard colormaps if they already exist.

To allocate an
XStandardColormap
structure, use
XAllocStandardColormap.

XStandardColormap *XAllocStandardColormap(void);

The
XAllocStandardColormap
function allocates and returns a pointer to an
XStandardColormap
structure.
Note that all fields in the
XStandardColormap
structure are initially set to zero.
If insufficient memory is available,
XAllocStandardColormap
returns NULL.
To free the memory allocated to this structure,
use
XFree.

The
XStandardColormap
structure contains:

/* Hints */

#define       ReeaseByFreeingColormap  ((XID)1L)

/* Values */

typedef struct {
	Colormap colormap;
	unsigned long red_max;
	unsigned long red_mult;
	unsigned long green_max;
	unsigned long green_mult;
	unsigned long blue_max;
	unsigned long blue_mult;
	unsigned long base_pixel;
	VisualID visualid;
	XID killid;
} XStandardColormap;

The colormap member is the colormap created by the
XCreateColormap
function.
The red_max, green_max, and blue_max members give the maximum
red, green, and blue values, respectively.
Each color coefficient ranges from zero to its max, inclusive.
For example,
a common colormap allocation is 3/3/2 (3 planes for red, 3
planes for green, and 2 planes for blue).
This colormap would have red_max = 7, green_max = 7,
and blue_max = 3.
An alternate allocation that uses only 216 colors is red_max = 5,
green_max = 5, and blue_max = 5.

The red_mult, green_mult, and blue_mult members give the
scale factors used to compose a full pixel value.
(See the discussion of the base_pixel members for further information.)
For a 3/3/2 allocation, red_mult might be 32,
green_mult might be 4, and blue_mult might be 1.
For a 6-colors-each allocation, red_mult might be 36,
green_mult might be 6, and blue_mult might be 1.

The base_pixel member gives the base pixel value used to
compose a full pixel value.
Usually, the base_pixel is obtained from a call to the
XAllocColorPlanes
function.
Given integer red, green, and blue coefficients in their appropriate
ranges, one then can compute a corresponding pixel value by
using the following expression:


(r * red_mult + g * green_mult + b * blue_mult + base_pixel) & 0xFFFFFFFF

For
GrayScale
colormaps,
only the colormap, red_max, red_mult,
and base_pixel members are defined.
The other members are ignored.
To compute a
GrayScale
pixel value, use the following expression:


(gray * red_mult + base_pixel) & 0xFFFFFFFF

Negative multipliers can be represented by converting the 2's
complement representation of the multiplier into an unsigned long and
storing the result in the appropriate _mult field.
The step of masking by 0xFFFFFFFF effectively converts the resulting
positive multiplier into a negative one.
The masking step will take place automatically on many machine architectures,
depending on the size of the integer type used to do the computation.

The visualid member gives the ID number of the visual from which the
colormap was created.
The killid member gives a resource ID that indicates whether
the cells held by this standard colormap are to be released
by freeing the colormap ID or by calling the
XKillClient
function on the indicated resource.
(Note that this method is necessary for allocating out of an existing colormap.)

The properties containing the
XStandardColormap
information have
the type RGB_COLOR_MAP.

The remainder of this section discusses standard colormap properties and atoms
as well as how to manipulate standard colormaps.

Standard Colormap Properties and Atoms

Several standard colormaps are available.
Each standard colormap is defined by a property,
and each such property is identified by an atom.
The following list names the atoms and describes the colormap
associated with each one.
The
<X11/Xatom.h>

header file contains the definitions for each of the following atoms,
which are prefixed with XA_.

RGB_DEFAULT_MAP	This atom names a property. The value of the property is an array of XStandardColormap structures. Each entry in the array describes an RGB subset of the default color map for the Visual specified by visual_id. Some applications only need a few RGB colors and may be able to allocate them from the system default colormap. This is the ideal situation because the fewer colormaps that are active in the system the more applications are displayed with correct colors at all times. A typical allocation for the RGB_DEFAULT_MAP on 8-plane displays is 6 reds, 6 greens, and 6 blues. This gives 216 uniformly distributed colors (6 intensities of 36 different hues) and still leaves 40 elements of a 256-element colormap available for special-purpose colors for text, borders, and so on.
RGB_BEST_MAP	This atom names a property. The value of the property is an XStandardColormap. The property defines the best RGB colormap available on the screen. (Of course, this is a subjective evaluation.) Many image processing and three-dimensional applications need to use all available colormap cells and to distribute as many perceptually distinct colors as possible over those cells. This implies that there may be more green values available than red, as well as more green or red than blue. For an 8-plane PseudoColor visual, RGB_BEST_MAP is likely to be a 3/3/2 allocation. For a 24-plane DirectColor visual, RGB_BEST_MAP is normally an 8/8/8 allocation.
RGB_RED_MAP,RGB_GREEN_MAP,RGB_BLUE_MAP	These atoms name properties. The value of each property is an XStandardColormap. The properties define all-red, all-green, and all-blue colormaps, respectively. These maps are used by applications that want to make color-separated images. For example, a user might generate a full-color image on an 8-plane display both by rendering an image three times (once with high color resolution in red, once with green, and once with blue) and by multiply exposing a single frame in a camera.
RGB_GRAY_MAP	This atom names a property. The value of the property is an XStandardColormap. The property describes the best GrayScale colormap available on the screen. As previously mentioned, only the colormap, red_max, red_mult, and base_pixel members of the XStandardColormap structure are used for GrayScale colormaps.

Setting and Obtaining Standard Colormaps

Xlib provides functions that you can use to set and obtain an
XStandardColormap
structure.

To set an
XStandardColormap
structure, use
XSetRGBColormaps.

void XSetRGBColormaps(Display *display, Window w, XStandardColormap *std_colormap, int count, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
std_colormap	Specifies the XStandardColormap structure to be used.
count	Specifies the number of colormaps.
property	Specifies the property name.

The
XSetRGBColormaps
function replaces the RGB colormap definition in the specified property
on the named window.
If the property does not already exist,
XSetRGBColormaps
sets the RGB colormap definition in the specified property
on the named window.
The property is stored with a type of RGB_COLOR_MAP and a format of 32.
Note that it is the caller's responsibility to honor the ICCCM
restriction that only RGB_DEFAULT_MAP contain more than one definition.

The
XSetRGBColormaps
function usually is only used by window or session managers.
To create a standard colormap,
follow this procedure:

Open a new connection to the same server.
Grab the server.
See if the property is on the property list of the root window for the screen.
If the desired property is not present:
Create a colormap (unless you are using the default colormap of the screen).
Determine the color characteristics of the visual.
Allocate cells in the colormap (or create it with
AllocAll).
Call
XStoreColors
to store appropriate color values in the colormap.
Fill in the descriptive members in the
XStandardColormap
structure.
Attach the property to the root window.
Use
XSetCloseDownMode
to make the resource permanent.
Ungrab the server.

XSetRGBColormaps
can generate
BadAlloc,
BadAtom,
and
BadWindow
errors.

To obtain the
XStandardColormap
structure associated with the specified property, use
XGetRGBColormaps.

Status XGetRGBColormaps(Display *display, Window w, XStandardColormap **std_colormap_return, int *count_return, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
std_colormap_return	Returns the XStandardColormap structure.
count_return	Returns the number of colormaps.
property	Specifies the property name.

The
XGetRGBColormaps
function returns the RGB colormap definitions stored
in the specified property on the named window.
If the property exists, is of type RGB_COLOR_MAP, is of format 32,
and is long enough to contain a colormap definition,
XGetRGBColormaps
allocates and fills in space for the returned colormaps
and returns a nonzero status.
If the visualid is not present,
XGetRGBColormaps
assumes the default visual for the screen on which the window is located;
if the killid is not present,
None
is assumed, which indicates that the resources cannot be released.
Otherwise,
none of the fields are set, and
XGetRGBColormaps
returns a zero status.
Note that it is the caller's responsibility to honor the ICCCM
restriction that only RGB_DEFAULT_MAP contain more than one definition.

XGetRGBColormaps
can generate
BadAtom
and
BadWindow
errors.

Chapter 15. Resource Manager Functions

Table of Contents

Resource File SyntaxResource Manager Matching RulesQuarksCreating and Storing DatabasesMerging Resource DatabasesLooking Up ResourcesStoring into a Resource DatabaseEnumerating Database EntriesParsing Command Line Options

A program often needs a variety of options in the X environment
(for example, fonts, colors, icons, and cursors).
Specifying all of these options on the command line is awkward
because users may want to customize many aspects of the program
and need a convenient way to establish these customizations as
the default settings.
The resource manager is provided for this purpose.
Resource specifications are usually stored in human-readable files
and in server properties.

The resource manager is a database manager with a twist.
In most database systems,
you perform a query using an imprecise specification,
and you get back a set of records.
The resource manager, however, allows you to specify a large
set of values with an imprecise specification, to query the database
with a precise specification, and to get back only a single value.
This should be used by applications that need to know what the
user prefers for colors, fonts, and other resources.
It is this use as a database for dealing with X resources that
inspired the name "Resource Manager,"
although the resource manager can be and is used in other ways.

For example,
a user of your application may want to specify
that all windows should have a blue background
but that all mail-reading windows should have a red background.
With well-engineered and coordinated applications,
a user can define this information using only two lines of specifications.

As an example of how the resource manager works,
consider a mail-reading application called xmh.
Assume that it is designed so that it uses a
complex window hierarchy all the way down to individual command buttons,
which may be actual small subwindows in some toolkits.
These are often called objects or widgets.
In such toolkit systems,
each user interface object can be composed of other objects
and can be assigned a name and a class.
Fully qualified names or classes can have arbitrary numbers of component names,
but a fully qualified name always has the same number of component names as a
fully qualified class.
This generally reflects the structure of the application as composed
of these objects, starting with the application itself.

For example, the xmh mail program has a name "xmh" and is one
of a class of "Mail" programs.
By convention, the first character of class components is capitalized,
and the first letter of name components is in lowercase.
Each name and class finally has an attribute
(for example, "foreground" or "font").
If each window is properly assigned a name and class,
it is easy for the user to specify attributes of any portion
of the application.

At the top level,
the application might consist of a paned window (that is, a window divided
into several sections) named "toc".
One pane of the paned window is a button box window named "buttons"
and is filled with command buttons.
One of these command buttons is used to incorporate
new mail and has the name "incorporate".
This window has a fully qualified name, "xmh.toc.buttons.incorporate",
and a fully qualified class, "Xmh.Paned.Box.Command".
Its fully qualified name is the name of its parent, "xmh.toc.buttons",
followed by its name, "incorporate".
Its class is the class of its parent, "Xmh.Paned.Box",
followed by its particular class, "Command".
The fully qualified name of a resource is
the attribute's name appended to the object's fully qualified
name, and the fully qualified class is its class appended to the object's
class.

The incorporate button might need the following resources:
Title string,
Font,
Foreground color for its inactive state,
Background color for its inactive state,
Foreground color for its active state, and
Background color for its active state.
Each resource is considered
to be an attribute of the button and, as such, has a name and a class.
For example, the foreground color for the button in
its active state might be named "activeForeground",
and its class might be "Foreground".

When an application looks up a resource (for example, a color),
it passes the complete name and complete class of the resource
to a look-up routine.
The resource manager compares this complete specification
against the incomplete specifications of entries in the resource
database, finds the best match, and returns the corresponding
value for that entry.

The definitions for the resource manager are contained in
<X11/Xresource.h>.

Resource File Syntax

The syntax of a resource file is a sequence of resource lines
terminated by newline characters or the end of the file.
The syntax of an individual resource line is:


ResourceLine     =     Comment | IncludeFile | ResourceSpec | <empty line>
Comment     =     "!" {<any character except null or newline>}
IncludeFile     =     "#" WhiteSpace "include" WhiteSpace FileName WhiteSpace
FileName     =     <valid filename for operating system>
ResourceSpec     =     WhiteSpace ResourceName WhiteSpace ":" WhiteSpace Value
ResourceName     =     [Binding] {Component Binding} ComponentName
Binding     =     "." | "*"
WhiteSpace     =     {<space> | <horizontal tab>}
Component     =     "?" | ComponentName
ComponentName     =     NameChar {NameChar}
NameChar     =     "a"-"z" | "A"-"Z" | "0"-"9" | "_" | "-"
Value     =     {<any character except null or unescaped newline>}

Elements separated by vertical bar (|) are alternatives.
Curly braces ({......}) indicate zero or more repetitions
of the enclosed elements.
Square brackets ([......]) indicate that the enclosed element is optional.
Quotes ("......") are used around literal characters.

IncludeFile lines are interpreted by replacing the line with the
contents of the specified file.
The word "include" must be in lowercase.
The file name is interpreted relative to the directory of the file in
which the line occurs (for example, if the file name contains no
directory or contains a relative directory specification).

If a ResourceName contains a contiguous sequence of two or more Binding
characters, the sequence will be replaced with a single ".." character
if the sequence contains only ".." characters;
otherwise, the sequence will be replaced with a single "*" character.

A resource database never contains more than one entry for a given
ResourceName. If a resource file contains multiple lines with the
same ResourceName, the last line in the file is used.

Any white space characters before or after the name or colon in a ResourceSpec
are ignored.
To allow a Value to begin with white space,
the two-character sequence "\\space" (backslash followed by space)
is recognized and replaced by a space character,
and the two-character sequence "\\tab"
(backslash followed by horizontal tab)
is recognized and replaced by a horizontal tab character.
To allow a Value to contain embedded newline characters,
the two-character sequence "\\n" is recognized and replaced by a
newline character.
To allow a Value to be broken across multiple lines in a text file,
the two-character sequence "\\newline"
(backslash followed by newline) is
recognized and removed from the value.
To allow a Value to contain arbitrary character codes,
the four-character sequence "\\nnn",
where each n is a digit character in the range of "0"-"7",
is recognized and replaced with a single byte that contains
the octal value specified by the sequence.
Finally, the two-character sequence "\newline" is recognized
and replaced with a single backslash.

As an example of these sequences,
the following resource line contains a value consisting of four
characters: a backslash, a null, a "z", and a newline:

magic.values: \magic.values: \\000\
z\n
0\
z\n

Resource Manager Matching Rules

The algorithm for determining which resource database entry
matches a given query is the heart of the resource manager.
All queries must fully specify the name and class of the desired resource
(use of the characters "*" and "?" is not permitted).
The library supports up to 100 components in a full name or class.
Resources are stored in the database with only partially specified
names and classes, using pattern matching constructs.
An asterisk (*) is a loose binding and is used to represent any number
of intervening components, including none.
A period (.) is a tight binding and is used to separate immediately
adjacent components.
A question mark (?) is used to match any single component name or class.
A database entry cannot end in a loose binding;
the final component (which cannot be the character "?") must be specified.
The lookup algorithm searches the database for the entry that most
closely matches (is most specific for) the full name and class being queried.
When more than one database entry matches the full name and class,
precedence rules are used to select just one.

The full name and class are scanned from left to right (from highest
level in the hierarchy to lowest), one component at a time.
At each level, the corresponding component and/or binding of each
matching entry is determined, and these matching components and
bindings are compared according to precedence rules.
Each of the rules is applied at each level before moving to the next level,
until a rule selects a single entry over all others.
The rules, in order of precedence, are:

An entry that contains a matching component (whether name, class,
or the character "?")
takes precedence over entries that elide the level (that is, entries
that match the level in a loose binding).
An entry with a matching name takes precedence over both
entries with a matching class and entries that match using the character "?".
An entry with a matching class takes precedence over
entries that match using the character "?".
An entry preceded by a tight binding takes precedence over entries
preceded by a loose binding.

To illustrate these rules,
consider the following resource database entries:


xmh*Paned*activeForeground:     red     (entry A)
*incorporate.Foreground:     blue     (entry B)
xmh.toc*Command*activeForeground:     green     (entry C)
xmh.toc*?.Foreground:     white     (entry D)
xmh.toc*Command.activeForeground:     black     (entry E)

Consider a query for the resource:


xmh.toc.messagefunctions.incorporate.activeForeground     (name)
Xmh.Paned.Box.Command.Foreground     (class)

At the first level (xmh, Xmh), rule 1 eliminates entry B.
At the second level (toc, Paned), rule 2 eliminates entry A.
At the third level (messagefunctions, Box), no entries are eliminated.
At the fourth level (incorporate, Command), rule 2 eliminates entry D.
At the fifth level (activeForeground, Foreground), rule 3 eliminates entry C.

Quarks

Most uses of the resource manager involve defining names,
classes, and representation types as string constants.
However, always referring to strings in the resource manager can be slow,
because it is so heavily used in some toolkits.
To solve this problem,
a shorthand for a string is used in place of the string
in many of the resource manager functions.
Simple comparisons can be performed rather than string comparisons.
The shorthand name for a string is called a quark and is the
type
XrmQuark.
On some occasions,
you may want to allocate a quark that has no string equivalent.

A quark is to a string what an atom is to a string in the server,
but its use is entirely local to your application.

To allocate a new quark, use
XrmUniqueQuark.

XrmQuark XrmUniqueQuark(void);

The
XrmUniqueQuark
function allocates a quark that is guaranteed not to represent any string that
is known to the resource manager.

Each name, class, and representation type is typedef'd as an
XrmQuark.

typedef int XrmQuark, *XrmQuarkList;
typedef XrmQuark XrmName;
typedef XrmQuark XrmClass;
typedef XrmQuark XrmRepresentation;
#define NULLQUARK ((XrmQuark) 0)

Lists are represented as null-terminated arrays of quarks.
The size of the array must be large enough for the number of components used.

typedef XrmQuarkList XrmNameList;
typedef XrmQuarkList XrmClassList;

To convert a string to a quark, use
XrmStringToQuark
or
XrmPermStringToQuark.

#define XrmStringToName(string) XrmStringToQuark(string)
#define XrmStringToClass(string) XrmStringToQuark(string)
#define XrmStringToRepresentation(string) XrmStringToQuark(string)

XrmQuark XrmStringToQuark(char *string);

string

Specifies the string for which a quark(Ql is to be allocated.

These functions can be used to convert from string to quark representation.
If the string is not in the Host Portable Character Encoding,
the conversion is implementation-dependent.
The string argument to
XrmStringToQuark
need not be permanently allocated storage.
XrmPermStringToQuark
is just like
XrmStringToQuark,
except that Xlib is permitted to assume the string argument is permanently
allocated,
and, hence, that it can be used as the value to be returned by
XrmQuarkToString.

For any given quark, if
XrmStringToQuark
returns a non-NULL value,
all future calls will return the same value (identical address).

To convert a quark to a string, use
XrmQuarkToString.

#define XrmNameToString(name)  XrmQuarkToString(name)
#define XrmClassToString(class)  XrmQuarkToString(name)
#define XrmRepresentationToString(type)  XrmQuarkToString(type)

char *XrmQuarkToString(XrmQuark quark);

quark

Specifies the quark for which the equivalent string is desired.

These functions can be used to convert from quark representation to string.
The string pointed to by the return value must not be modified or freed.
The returned string is byte-for-byte equal to the original
string passed to one of the string-to-quark routines.
If no string exists for that quark,
XrmQuarkToString
returns NULL.
For any given quark, if
XrmQuarkToString
returns a non-NULL value,
all future calls will return the same value (identical address).

To convert a string with one or more components to a quark list, use
XrmStringToQuarkList.

#define XrmStringToNameList(str,name)  XrmStringToQuarkList((str), (name))
#define XrmStringToClassList(str,class)  XrmStringToQuarkList((str), (class))

void XrmStringToQuarkList(char *string, XrmQuarkList quarks_return);

string	Specifies the string for which a quark list is to be allocated.
quarks_return	Returns the list of quarks. The caller must allocate sufficient space for the quarks list before calling `XrmStringToQuarkList`.

The
XrmStringToQuarkList
function converts the null-terminated string (generally a fully qualified name)
to a list of quarks.
Note that the string must be in the valid ResourceName format
(see section 15.1).
If the string is not in the Host Portable Character Encoding,
the conversion is implementation-dependent.

A binding list is a list of type
XrmBindingList
and indicates if components of name or class lists are bound tightly or loosely
(that is, if wildcarding of intermediate components is specified).

typedef enum {XrmBindTightly, XrmBindLoosely} XrmBinding, *XrmBindingList;

XrmBindTightly
indicates that a period separates the components, and
XrmBindLoosely
indicates that an asterisk separates the components.

To convert a string with one or more components to a binding list
and a quark list, use
XrmStringToBindingQuarkList.

XrmStringToBindingQuarkList(char *string, XrmBindingList bindings_return, XrmQuarkList quarks_return);

string	Specifies the string for which a quark list is to be allocated.
bindings_return	Returns the binding list. The caller must allocate sufficient space for the binding list before calling `XrmStringToBindingQuarkList`.
quarks_return	Returns the list of quarks. The caller must allocate sufficient space for the quarks list before calling `XrmStringToBindingQuarkList`.

Component names in the list are separated by a period or
an asterisk character.
The string must be in the format of a valid ResourceName
(see section 15.1).
If the string does not start with a period or an asterisk,
a tight binding is assumed.
For example, the string “*a.b*c” becomes:


quarks:       a         b         c
bindings:     loose     tight     loose

Creating and Storing Databases

A resource database is an opaque type,
XrmDatabase.
Each database value is stored in an
XrmValue
structure.
This structure consists of a size, an address, and a representation type.
The size is specified in bytes.
The representation type is a way for you to store data tagged by some
application-defined type (for example, the strings “font” or “color”).
It has nothing to do with the C data type or with its class.
The
XrmValue
structure is defined as:


typedef struct {
     unsigned int size;
     XPointer addr;
} XrmValue, *XrmValuePtr;

To initialize the resource manager, use
XrmInitialize.

void XrmInitialize(void XrmInitialize(\|));

To retrieve a database from disk, use
XrmGetFileDatabase.

XrmDatabase XrmGetFileDatabase(char *filename);

filename

Specifies the resource database file name.

The
XrmGetFileDatabase
function opens the specified file,
creates a new resource database, and loads it with the specifications
read in from the specified file.
The specified file should contain a sequence of entries in valid ResourceLine
format (see section 15.1);
the database that results from reading a file
with incorrect syntax is implementation-dependent.
The file is parsed in the current locale,
and the database is created in the current locale.
If it cannot open the specified file,
XrmGetFileDatabase
returns NULL.

To store a copy of a database to disk, use
XrmPutFileDatabase.

void XrmPutFileDatabase(XrmDatabase database, char *stored_db);

database	Specifies the database that is to be used.
stored_db	Specifies the file name for the stored database.

The
XrmPutFileDatabase
function stores a copy of the specified database in the specified file.
Text is written to the file as a sequence of entries in valid
ResourceLine format
(see section 15.1).
The file is written in the locale of the database.
Entries containing resource names that are not in the Host Portable Character
Encoding or containing values that are not in the encoding of the database
locale, are written in an implementation-dependent manner.
The order in which entries are written is implementation-dependent.
Entries with representation types other than “String” are ignored.

To obtain a pointer to the screen-independent resources of a display, use
XResourceManagerString.

char *XResourceManagerString(Display *display);

display

Specifies the connection to the X server.

The
XResourceManagerString
function returns the RESOURCE_MANAGER property from the server's root
window of screen zero, which was returned when the connection was opened using
XOpenDisplay.
The property is converted from type STRING to the current locale.
The conversion is identical to that produced by
XmbTextPropertyToTextList
for a single element STRING property.
The returned string is owned by Xlib and should not be freed by the client.
The property value must be in a format that is acceptable to
XrmGetStringDatabase.
If no property exists, NULL is returned.

To obtain a pointer to the screen-specific resources of a screen, use
XScreenResourceString.

char *XScreenResourceString(Screen *screen);

screen

Specifies the screen.

The
XScreenResourceString
function returns the SCREEN_RESOURCES property from the root window of the
specified screen.
The property is converted from type STRING to the current locale.
The conversion is identical to that produced by
XmbTextPropertyToTextList
for a single element STRING property.
The property value must be in a format that is acceptable to
XrmGetStringDatabase.
If no property exists, NULL is returned.
The caller is responsible for freeing the returned string by using
XFree.

To create a database from a string, use
XrmGetStringDatabase.

XrmDatabase XrmGetStringDatabase(char *data);

data

Specifies the database contents using a string.

The
XrmGetStringDatabase
function creates a new database and stores the resources specified
in the specified null-terminated string.
XrmGetStringDatabase
is similar to
XrmGetFileDatabase
except that it reads the information out of a string instead of out of a file.
The string should contain a sequence of entries in valid ResourceLine
format (see section 15.1)
terminated by a null character;
the database that results from using a string
with incorrect syntax is implementation-dependent.
The string is parsed in the current locale,
and the database is created in the current locale.

To obtain the locale name of a database, use
XrmLocaleOfDatabase.

char *XrmLocaleOfDatabase(XrmDatabase database);

database

Specifies the resource database.

The
XrmLocaleOfDatabase
function returns the name of the locale bound to the specified
database, as a null-terminated string.
The returned locale name string is owned by Xlib and should not be
modified or freed by the client.
Xlib is not permitted to free the string until the database is destroyed.
Until the string is freed,
it will not be modified by Xlib.

To destroy a resource database and free its allocated memory, use
XrmDestroyDatabase.

void XrmDestroyDatabase(XrmDatabase database);

database

Specifies the resource database.

If database is NULL,
XrmDestroyDatabase
returns immediately.

To associate a resource database with a display, use
XrmSetDatabase.

void XrmSetDatabase(Display *display, XrmDatabase database);

display	Specifies the connection to the X server.
database	Specifies the resource database.

The
XrmSetDatabase
function associates the specified resource database (or NULL)
with the specified display.
The database previously associated with the display (if any) is not destroyed.
A client or toolkit may find this function convenient for retaining a database
once it is constructed.

To get the resource database associated with a display, use
XrmGetDatabase.

XrmDatabase XrmGetDatabase(Display *display);

display

Specifies the connection to the X server.

The
XrmGetDatabase
function returns the database associated with the specified display.
It returns NULL if a database has not yet been set.

Merging Resource Databases

To merge the contents of a resource file into a database, use
XrmCombineFileDatabase.

Status XrmCombineFileDatabase(char *filename, XrmDatabase *target_db, Bool override);

filename	Specifies the resource database file name.
target_db	Specifies the resource database into which the source database is to be merged.
override	Specifies whether source entries override target ones.

The
XrmCombineFileDatabase
function merges the contents of a resource file into a database.
If the same specifier is used for an entry in both the file and
the database,
the entry in the file will replace the entry in the database
if override is
True;
otherwise, the entry in the file is discarded.
The file is parsed in the current locale.
If the file cannot be read,
a zero status is returned;
otherwise, a nonzero status is returned.
If target_db contains NULL,
XrmCombineFileDatabase
creates and returns a new database to it.
Otherwise, the database pointed to by target_db is not destroyed by the merge.
The database entries are merged without changing values or types,
regardless of the locale of the database.
The locale of the target database is not modified.

To merge the contents of one database into another database, use
XrmCombineDatabase.

void XrmCombineDatabase(XrmDatabase source_db, XrmDatabase *target_db, Bool override);

source_db	Specifies the resource database that is to be merged into the target database.
target_db	Specifies the resource database into which the source database is to be merged.
override	Specifies whether source entries override target ones.

The
XrmCombineDatabase
function merges the contents of one database into another.
If the same specifier is used for an entry in both databases,
the entry in the source_db will replace the entry in the target_db
if override is
True;
otherwise, the entry in source_db is discarded.
If target_db contains NULL,
XrmCombineDatabase
simply stores source_db in it.
Otherwise, source_db is destroyed by the merge, but the database pointed
to by target_db is not destroyed.
The database entries are merged without changing values or types,
regardless of the locales of the databases.
The locale of the target database is not modified.

To merge the contents of one database into another database with override
semantics, use
XrmMergeDatabases.

void XrmMergeDatabases(XrmDatabase source_db, XrmDatabase *target_db);

source_db	Specifies the resource database that is to be merged into the target database.
target_db	Specifies the resource database into which the source database is to be merged.

Calling the
XrmMergeDatabases
function is equivalent to calling the
XrmCombineDatabase
function with an override argument of
True.

Looking Up Resources

To retrieve a resource from a resource database, use
XrmGetResource,
XrmQGetResource,
or
XrmQGetSearchResource.

Bool XrmGetResource(XrmDatabase database, char *str_name, char *str_class, char **str_type_return, XrmValue *value_return);

database	Specifies the database that is to be used.
str_name	Specifies the fully qualified name of the value being retrieved (as a string).
str_class	Specifies the fully qualified class of the value being retrieved (as a string).
str_type_return	Returns the representation type of the destination (as a string).
value_return	Returns the value in the database.

Bool XrmQGetResource(XrmDatabase database, XrmNameList quark_name, XrmClassList quark_class, XrmRepresentation *quark_type_return, XrmValue *value_return);

database	Specifies the database that is to be used.
quark_name	Specifies the fully qualified name of the value being retrieved (as a quark).
quark_class	Specifies the fully qualified class of the value being retrieved (as a quark).
quark_type_return	Returns the representation type of the destination (as a quark).
value_return	Returns the value in the database.

The
XrmGetResource
and
XrmQGetResource
functions retrieve a resource from the specified database.
Both take a fully qualified name/class pair, a destination
resource representation, and the address of a value
(size/address pair).
The value and returned type point into database memory;
therefore, you must not modify the data.

The database only frees or overwrites entries on
XrmPutResource,
XrmQPutResource,
or
XrmMergeDatabases.
A client that is not storing new values into the database or
is not merging the database should be safe using the address passed
back at any time until it exits.
If a resource was found, both
XrmGetResource
and
XrmQGetResource
return
True;
otherwise, they return
False.

Most applications and toolkits do not make random probes
into a resource database to fetch resources.
The X toolkit access pattern for a resource database is quite stylized.
A series of from 1 to 20 probes is made with only the
last name/class differing in each probe.
The
XrmGetResource
function is at worst a
2n algorithm,
where n is the length of the name/class list.
This can be improved upon by the application programmer by prefetching a list
of database levels that might match the first part of a name/class list.

To obtain a list of database levels, use
XrmQGetSearchList.

Bool XrmQGetSearchResource(XrmDatabase database, XrmNameList names, XrmClassList classes, XrmSearchList list_return, int list_length);

database	Specifies the database that is to be used.
names	Specifies a list of resource names.
classes	Specifies a list of resource classes.
list_return	Returns a search list for further use. The caller must allocate sufficient space for the list before calling `XrmQGetSearchList`.
list_length	Specifies the number of entries (not the byte size) allocated for list_return.

The
XrmQGetSearchList
function takes a list of names and classes
and returns a list of database levels where a match might occur.
The returned list is in best-to-worst order and
uses the same algorithm as
XrmGetResource
for determining precedence.
If list_return was large enough for the search list,
XrmQGetSearchList
returns
True;
otherwise, it returns
False.

The size of the search list that the caller must allocate is
dependent upon the number of levels and wildcards in the resource specifiers
that are stored in the database.
The worst case length is
3n,
where n is the number of name or class
components in names or classes.

When using
XrmQGetSearchList
followed by multiple probes for resources with a common name and class prefix,
only the common prefix should be specified in the name and class list to
XrmQGetSearchList.

To search resource database levels for a given resource, use
XrmQGetSearchResource.

Bool XrmQGetSearchResource(XrmSearchList list, XrmName name, XrmClass class, XrmRepresentation *type_return, XrmValue *value_return);

list	Specifies the search list returned by `XrmQGetSearchList`.
name	Specifies the resource name.
class	Specifies the resource class.
type_return	Returns data representation type.
value_return	Returns the value in the database.

The
XrmQGetSearchResource
function searches the specified database levels for the resource
that is fully identified by the specified name and class.
The search stops with the first match.
XrmQGetSearchResource
returns
True
if the resource was found;
otherwise, it returns
False.

A call to
XrmQGetSearchList
with a name and class list containing all but the last component
of a resource name followed by a call to
XrmQGetSearchResource
with the last component name and class returns the same database entry as
XrmGetResource
and
XrmQGetResource
with the fully qualified name and class.

Storing into a Resource Database

To store resources into the database, use
XrmPutResource
or
XrmQPutResource.
Both functions take a partial resource specification, a
representation type, and a value.
This value is copied into the specified database.

void XrmPutResource(XrmDatabase *database, char *specifier, char *type, XrmValue *value);

database	Specifies the resource database.
specifier	Specifies a complete or partial specification of the resource.
type	Specifies the type of the resource.
value	Specifies the value of the resource, which is specified as a string.

If database contains NULL,
XrmPutResource
creates a new database and returns a pointer to it.
XrmPutResource
is a convenience function that calls
XrmStringToBindingQuarkList
followed by:

XrmQPutResource(database, bindings, quarks, XrmStringToQuark(type), value)

If the specifier and type are not in the Host Portable Character Encoding,
the result is implementation-dependent.
The value is stored in the database without modification.

void XrmQPutResource(XrmDatabase *database, XrmBindingList bindings, XrmQuarkList quarks, XrmRepresentation type, XrmValue *value);

database	Specifies the resource database.
bindings	Specifies a list of bindings.
quarks	Specifies the complete or partial name or the class list of the resource.
type	Specifies the type of the resource.
value	Specifies the value of the resource, which is specified as a string.

If database contains NULL,
XrmQPutResource
creates a new database and returns a pointer to it.
If a resource entry with the identical bindings and quarks already
exists in the database, the previous type and value are replaced by the new
specified type and value.
The value is stored in the database without modification.

To add a resource that is specified as a string, use
XrmPutStringResource.

void XrmPutStringResource(XrmDatabase *database, char *specifier, char *value);

database	Specifies the resource database.
specifier	Specifies a complete or partial specification of the resource.
value	Specifies the value of the resource, which is specified as a string.

If database contains NULL,
XrmPutStringResource
creates a new database and returns a pointer to it.
XrmPutStringResource
adds a resource with the specified value to the specified database.
XrmPutStringResource
is a convenience function that first calls
XrmStringToBindingQuarkList
on the specifier and then calls
XrmQPutResource,
using a “String” representation type.
If the specifier is not in the Host Portable Character Encoding,
the result is implementation-dependent.
The value is stored in the database without modification.

To add a string resource using quarks as a specification, use
XrmQPutStringResource.

void XrmQPutStringResource(XrmDatabase *database, XrmBindingList bindings, XrmQuarkList quarks, char *value);

database	Specifies the resource database.
bindings	Specifies a list of bindings.
quarks	Specifies the complete or partial name or the class list of the resource.
value	Specifies the value of the resource, which is specified as a string.

If database contains NULL,
XrmQPutStringResource
creates a new database and returns a pointer to it.
XrmQPutStringResource
is a convenience routine that constructs an
XrmValue
for the value string (by calling
strlen
to compute the size) and
then calls
XrmQPutResource,
using a “String” representation type.
The value is stored in the database without modification.

To add a single resource entry that is specified as a string that contains
both a name and a value, use
XrmPutLineResource.

void XrmPutLineResource(XrmDatabase *database, char *line);

database	Specifies the resource database.
line	Specifies the resource name and value pair as a single string.

If database contains NULL,
XrmPutLineResource
creates a new database and returns a pointer to it.
XrmPutLineResource
adds a single resource entry to the specified database.
The line should be in valid ResourceLine format
(see section 15.1)
terminated by a newline or null character;
the database that results from using a string
with incorrect syntax is implementation-dependent.
The string is parsed in the locale of the database.
If the
ResourceName
is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Note that comment lines are not stored.

Enumerating Database Entries

To enumerate the entries of a database, use
XrmEnumerateDatabase.

#define       XrmEnumAllLevels       0
#define       XrmEnumOneLevel        0

Bool XrmEnumerateDatabase(XrmDatabase database, XrmNameList name_prefix, XrmClassList class_prefix, int mode, Bool (*proc)(), XPointer arg);

database	Specifies the resource database.
name_prefix	Specifies the resource name prefix.
class_prefix	Specifies the resource class prefix.
mode	Specifies the number of levels to enumerate.
proc	Specifies the procedure that is to be called for each matching entry.
arg	Specifies the user-supplied argument that will be passed to the procedure.

The
XrmEnumerateDatabase
function calls the specified procedure for each resource in the database
that would match some completion of the given name/class resource prefix.
The order in which resources are found is implementation-dependent.
If mode is
XrmEnumOneLevel,
a resource must match the given name/class prefix with
just a single name and class appended. If mode is
XrmEnumAllLevels,
the resource must match the given name/class prefix with one or more names and
classes appended.
If the procedure returns
True,
the enumeration terminates and the function returns
True.
If the procedure always returns
False,
all matching resources are enumerated and the function returns
False.

The procedure is called with the following arguments:


(*proc)(database, bindings, quarks, type, value, arg)
     XrmDatabase *database;
     XrmBindingList bindings;
     XrmQuarkList quarks;
     XrmRepresentation *type;
     XrmValue *value;
     XPointer arg;

The bindings and quarks lists are terminated by
NULLQUARK.
Note that pointers
to the database and type are passed, but these values should not be modified.

The procedure must not modify the database.
If Xlib has been initialized for threads, the procedure is called with
the database locked and the result of a call by the procedure to any
Xlib function using the same database is not defined.

Parsing Command Line Options

The
XrmParseCommand
function can be used to parse the command line arguments to a program
and modify a resource database with selected entries from the command line.


typedef enum {
     XrmoptionNoArg,     /* Value is specified in XrmOptionDescRec.value */
     XrmoptionIsArg,     /* Value is the option string itself */
     XrmoptionStickyArg,     /* Value is characters immediately following option */
     XrmoptionSepArg,     /* Value is next argument in argv */
     XrmoptionResArg,     /* Resource and value in next argument in argv */
     XrmoptionSkipArg,     /* Ignore this option and the next argument in argv */
     XrmoptionSkipLine,     /* Ignore this option and the rest of argv */
     XrmoptionSkipNArgs     /* Ignore this option and the next
          \ \ \ XrmOptionDescRec.value arguments in argv */
} XrmOptionKind;

Note that
XrmoptionSkipArg
is equivalent to
XrmoptionSkipNArgs
with the
XrmOptionDescRec.value
field containing the value one.
Note also that the value zero for
XrmoptionSkipNArgs
indicates that only the option itself is to be skipped.


typedef struct {
     char *option;     /* Option specification string in argv              */
     char *specifier;     /* Binding and resource name (sans application name)    */
     XrmOptionKind argKind;     /* Which style of option it is         */
     XPointer value;     /* Value to provide if XrmoptionNoArg or 
          \ \ \ XrmoptionSkipNArgs   */
} XrmOptionDescRec, *XrmOptionDescList;

To load a resource database from a C command line, use
XrmParseCommand.

void XrmParseCommand(XrmDatabase *database, XrmOptionDescList table, int table_count, char *name, int *argc_in_out, char **argv_in_out);

database	Specifies the resource database.
table	Specifies the table of command line arguments to be parsed.
table_count	Specifies the number of entries in the table.
name	Specifies the application name.
argc_in_out	Specifies the number of arguments and returns the number of remaining arguments.
argv_in_out	Specifies the command line arguments and returns the remaining arguments.

The
XrmParseCommand
function parses an (argc, argv) pair according to the specified option table,
loads recognized options into the specified database with type “String,”
and modifies the (argc, argv) pair to remove all recognized options.
If database contains NULL,
XrmParseCommand
creates a new database and returns a pointer to it.
Otherwise, entries are added to the database specified.
If a database is created, it is created in the current locale.

The specified table is used to parse the command line.
Recognized options in the table are removed from argv,
and entries are added to the specified resource database
in the order they occur in argv.
The table entries contain information on the option string,
the option name, the style of option,
and a value to provide if the option kind is
XrmoptionNoArg.
The option names are compared byte-for-byte to arguments in argv,
independent of any locale.
The resource values given in the table are stored in the resource database
without modification.
All resource database entries are created
using a “String” representation type.
The argc argument specifies the number of arguments in argv
and is set on return to the remaining number of arguments that were not parsed.
The name argument should be the name of your application
for use in building the database entry.
The name argument is prefixed to the resourceName in the option table
before storing a database entry.
The name argument is treated as a single component, even if it
has embedded periods.
No separating (binding) character is inserted,
so the table must contain either a period (.) or an asterisk (*)
as the first character in each resourceName entry.
To specify a more completely qualified resource name,
the resourceName entry can contain multiple components.
If the name argument and the resourceNames are not in the
Host Portable Character Encoding,
the result is implementation-dependent.

The following provides a sample option table:


static XrmOptionDescRec opTable[] = {
{"-background",     "*background",                 XrmoptionSepArg,    (XPointer) NULL},
{"-bd",             "*borderColor",                XrmoptionSepArg,    (XPointer) NULL},
{"-bg",             "*background",                 XrmoptionSepArg,    (XPointer) NULL},
{"-borderwidth",    "*TopLevelShell.borderWidth",  XrmoptionSepArg,    (XPointer) NULL},
{"-bordercolor",    "*borderColor",                XrmoptionSepArg,    (XPointer) NULL},
{"-bw",             "*TopLevelShell.borderWidth",  XrmoptionSepArg,    (XPointer) NULL},
{"-display",        ".display",                    XrmoptionSepArg,    (XPointer) NULL},
{"-fg",             "*foreground",                 XrmoptionSepArg,    (XPointer) NULL},
{"-fn",             "*font",                       XrmoptionSepArg,    (XPointer) NULL},
{"-font",           "*font",                       XrmoptionSepArg,    (XPointer) NULL},
{"-foreground",     "*foreground",                 XrmoptionSepArg,    (XPointer) NULL},
{"-geometry",       ".TopLevelShell.geometry",     XrmoptionSepArg,    (XPointer) NULL},
{"-iconic",         ".TopLevelShell.iconic",       XrmoptionNoArg,     (XPointer) "on"},
{"-name",           ".name",                       XrmoptionSepArg,    (XPointer) NULL},
{"-reverse",        "*reverseVideo",               XrmoptionNoArg,     (XPointer) "on"},
{"-rv",             "*reverseVideo",               XrmoptionNoArg,     (XPointer) "on"},
{"-synchronous",    "*synchronous",                XrmoptionNoArg,     (XPointer) "on"},
{"-title",          ".TopLevelShell.title",        XrmoptionSepArg,    (XPointer) NULL},
{"-xrm",            NULL,                          XrmoptionResArg,    (XPointer) NULL},
};

In this table, if the -background (or -bg) option is used to set
background colors, the stored resource specifier matches all
resources of attribute background.
If the -borderwidth option is used,
the stored resource specifier applies only to border width
attributes of class TopLevelShell (that is, outer-most windows, including
pop-up windows).
If the -title option is used to set a window name,
only the topmost application windows receive the resource.

When parsing the command line,
any unique unambiguous abbreviation for an option name in the table is
considered a match for the option.
Note that uppercase and lowercase matter.

Chapter 16. Application Utility Functions

Table of Contents

Using Keyboard Utility FunctionsKeySym Classification MacrosUsing Latin-1 Keyboard Event FunctionsAllocating Permanent StorageParsing the Window GeometryManipulating RegionsCreating, Copying, or Destroying RegionsMoving or Shrinking RegionsComputing with RegionsDetermining if Regions Are Empty or EqualLocating a Point or a Rectangle in a RegionUsing Cut BuffersDetermining the Appropriate Visual TypeManipulating ImagesManipulating BitmapsUsing the Context Manager

Once you have initialized the X system,
you can use the Xlib utility functions to:

Use keyboard utility functions
Use Latin-1 keyboard event functions
Allocate permanent storage
Parse the window geometry
Manipulate regions
Use cut buffers
Determine the appropriate visual type
Manipulate images
Manipulate bitmaps
Use the context manager

As a group,
the functions discussed in this chapter provide the functionality that
is frequently needed and that spans toolkits.
Many of these functions do not generate actual protocol requests to the server.

Using Keyboard Utility Functions

This section discusses mapping between KeyCodes and KeySyms,
classifying KeySyms, and mapping between KeySyms and string names.
The first three functions in this section operate on a cached copy of the
server keyboard mapping.
The first four KeySyms for each KeyCode
are modified according to the rules given in section 12.7.
To obtain the untransformed KeySyms defined for a key,
use the functions described in section 12.7.

To obtain a KeySym for the KeyCode of an event, use
XLookupKeysym.

KeySym XLookupKeysym(XKeyEvent *key_event, int index);

key_event	Specifies the KeyPress or KeyRelease event.
index	Specifies the index into the KeySyms list for the event's KeyCode.

The
XLookupKeysym
function uses a given keyboard event and the index you specified to return
the KeySym from the list that corresponds to the KeyCode member in the
XKeyPressedEvent
or
XKeyReleasedEvent
structure.
If no KeySym is defined for the KeyCode of the event,
XLookupKeysym
returns
NoSymbol.

To obtain a KeySym for a specific KeyCode, use
XKeycodeToKeysym.

KeySym XKeycodeToKeysym(Display *display, KeyCode keycode, int index);

display	Specifies the connection to the X server.
keycode	Specifies the KeyCode.
index	Specifies the element of KeyCode vector.

The
XKeycodeToKeysym
function uses internal Xlib tables
and returns the KeySym defined for the specified KeyCode and
the element of the KeyCode vector.
If no symbol is defined,
XKeycodeToKeysym
returns
NoSymbol.

To obtain a KeyCode for a key having a specific KeySym, use
XKeysymToKeycode.

KeyCode XKeysymToKeycode(Display *display, KeySym keysym);

display	Specifies the connection to the X server.
keysym	Specifies the KeySym that is to be searched for.

If the specified KeySym is not defined for any KeyCode,
XKeysymToKeycode
returns zero.

The mapping between KeyCodes and KeySyms is cached internal to Xlib.
When this information is changed at the server, an Xlib function must
be called to refresh the cache.
To refresh the stored modifier and keymap information, use
XRefreshKeyboardMapping.

XRefreshKeyboardMapping(XMappingEvent *event_map);

event_map

Specifies the mapping event that is to be used.

The
XRefreshKeyboardMapping
function refreshes the stored modifier and keymap information.
You usually call this function when a
MappingNotify
event with a request member of
MappingKeyboard
or
MappingModifier
occurs.
The result is to update Xlib's knowledge of the keyboard.

To obtain the uppercase and lowercase forms of a KeySym, use
XConvertCase.

void XConvertCase(KeySym keysym, KeySym *lower_return, KeySym *upper_return);

keysym	Specifies the KeySym that is to be converted.
lower_return	Returns the lowercase form of keysym, or keysym.
upper_return	Returns the uppercase form of keysym, or keysym.

The
XConvertCase
function returns the uppercase and lowercase forms of the specified Keysym,
if the KeySym is subject to case conversion;
otherwise, the specified KeySym is returned to both lower_return and
upper_return.
Support for conversion of other than Latin and Cyrillic KeySyms is
implementation-dependent.

KeySyms have string names as well as numeric codes.
To convert the name of the KeySym to the KeySym code, use
XStringToKeysym.

KeySym XStringToKeysym(char *string);

string

Specifies the name of the KeySym that is to be converted.

Standard KeySym names are obtained from
<X11/keysymdef.h>

by removing the XK_ prefix from each name.
KeySyms that are not part of the Xlib standard also may be obtained
with this function.
The set of KeySyms that are available in this manner
and the mechanisms by which Xlib obtains them is implementation-dependent.

If the KeySym name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
If the specified string does not match a valid KeySym,
XStringToKeysym
returns
NoSymbol.

To convert a KeySym code to the name of the KeySym, use
XKeysymToString.

char *XKeysymToString(KeySym keysym);

keysym

Specifies the KeySym that is to be converted.

The returned string is in a static area and must not be modified.
The returned string is in the Host Portable Character Encoding.
If the specified KeySym is not defined,
XKeysymToString
returns a NULL.

KeySym Classification Macros

You may want to test if a KeySym is, for example,
on the keypad or on one of the function keys.
You can use KeySym macros to perform the following tests.

IsCursorKey(keysym)

keysym

Specifies the KeySym that is to be tested.

Returns
True
if the specified KeySym is a cursor key.

IsFunctionKey(keysym)

keysym

Specifies the KeySym that is to be tested.

Returns
True
if the specified KeySym is a function key.

IsKeypadKey(keysym)

keysym

Specifies the KeySym that is to be tested.

Returns
True
if the specified KeySym is a standard keypad key.

IsPrivateKeypadKey(keysym)

keysym

Specifies the KeySym that is to be tested.

Returns
True
if the specified KeySym is a vendor-private keypad key.

IsMiscFunctionKey(keysym)

keysym

Specifies the KeySym that is to be tested.

Returns
True
if the specified KeySym is a miscellaneous function key.

IsModifierKey(keysym)

keysym

Specifies the KeySym that is to be tested.

Returns
True
if the specified KeySym is a modifier key.

IsPFKey(keysym)

keysym

Specifies the KeySym that is to be tested.

Returns
True
if the specified KeySym is a PF key.

Using Latin-1 Keyboard Event Functions

Chapter 13
describes internationalized text input facilities,
but sometimes it is expedient to write an application that
only deals with Latin-1 characters and ASCII controls,
so Xlib provides a simple function for that purpose.
XLookupString
handles the standard modifier semantics described in section 12.7.
This function does not use any of the input method facilities
described in chapter 13 and does not depend on the current locale.

To map a key event to an ISO Latin-1 string, use
XLookupString.

int XLookupString(XKeyEvent *event_struct, char *buffer_return, int bytes_buffer, KeySym *keysym_return, XComposeStatus *status_in_out);

event_struct	Specifies the key event structure to be used. You can pass XKeyPressedEvent or XKeyReleasedEvent.
buffer_return	Returns the translated characters.
bytes_buffer	Specifies the length of the buffer. No more than bytes_buffer of translation are returned.
keysym_return	Returns the KeySym computed from the event if this argument is not NULL.
status_in_out	Specifies or returns the XComposeStatus structure or NULL.

The
XLookupString
function translates a key event to a KeySym and a string.
The KeySym is obtained by using the standard interpretation of the
Shift,
Lock,
group, and numlock modifiers as defined in the X Protocol specification.
If the KeySym has been rebound (see
XRebindKeysym),
the bound string will be stored in the buffer.
Otherwise, the KeySym is mapped, if possible, to an ISO Latin-1 character
or (if the Control modifier is on) to an ASCII control character,
and that character is stored in the buffer.
XLookupString
returns the number of characters that are stored in the buffer.

If present (non-NULL),
the
XComposeStatus
structure records the state,
which is private to Xlib,
that needs preservation across calls to
XLookupString
to implement compose processing.
The creation of
XComposeStatus
structures is implementation-dependent;
a portable program must pass NULL for this argument.

XLookupString
depends on the cached keyboard information mentioned in the
previous section, so it is necessary to use
XRefreshKeyboardMapping
to keep this information up-to-date.

To rebind the meaning of a KeySym for
XLookupString,
use
XRebindKeysym.

XRebindKeysym(Display *display, KeySym keysym, KeySym list[ ], int mod_count, unsignedchar *string, int num_bytes);

display	Specifies the connection to the X server.
keysym	Specifies the KeySym that is to be rebound.
list	Specifies the KeySyms to be used as modifiers.
mod_count	Specifies the number of modifiers in the modifier list.
string	Specifies the string that is copied and will be returned by `XLookupString`.
num_bytes	Specifies the number of bytes in the string argument.

The
XRebindKeysym
function can be used to rebind the meaning of a KeySym for the client.
It does not redefine any key in the X server but merely
provides an easy way for long strings to be attached to keys.
XLookupString
returns this string when the appropriate set of
modifier keys are pressed and when the KeySym would have been used for
the translation.
No text conversions are performed;
the client is responsible for supplying appropriately encoded strings.
Note that you can rebind a KeySym that may not exist.

Allocating Permanent Storage

To allocate some memory you will never give back, use
Xpermalloc.

char *Xpermalloc(unsigned int size);

The
Xpermalloc
function allocates storage that can never be freed for the life of the
program. The memory is allocated with alignment for the C type double.
This function may provide some performance and space savings over
the standard operating system memory allocator.

Parsing the Window Geometry

To parse standard window geometry strings, use
XParseGeometry.

int XParseGeometry(char *parsestring, int *x_return, int *y_return, unsigned int *width_return, unsigned int *height_return);

parsestring	Specifies the string you want to parse.
x_return
y_return	Return the x and y offsets.
width_return
height_return	Return the width and height determined.

By convention,
X applications use a standard string to indicate window size and placement.
XParseGeometry
makes it easier to conform to this standard because it allows you
to parse the standard window geometry.
Specifically, this function lets you parse strings of the form:

[=][<width>{xX}<height>][{+-}<xoffset>{+-}<yoffset>]

The fields map into the arguments associated with this function.
(Items enclosed in < > are integers, items in [ ] are optional, and
items enclosed in { } indicate “choose one of.”
Note that the brackets should not appear in the actual string.)
If the string is not in the Host Portable Character Encoding,
the result is implementation-dependent.

The
XParseGeometry
function returns a bitmask that indicates which of the four values (width,
height, xoffset, and yoffset) were actually found in the string
and whether the x and y values are negative.
By convention, −0 is not equal to +0, because the user needs to
be able to say “position the window relative to the right or bottom edge.”
For each value found, the corresponding argument is updated.
For each value not found, the argument is left unchanged.
The bits are represented by
XValue,
YValue,
WidthValue,
HeightValue,
XNegative,
or
YNegative
and are defined in
<X11/Xutil.h>.

They will be set whenever one of the values is defined
or one of the signs is set.

If the function returns either the
XValue
or
YValue
flag,
you should place the window at the requested position.

To construct a window's geometry information, use
XWMGeometry.

int XWMGeometry(Display *display, int screen, char *user_geom, char *def_geom, unsigned int bwidth, XSizeHints *hints, int *x_return, int *y_return, int *width_return, int *height_return, int *gravity_return);

display	Specifies the connection to the X server.
screen	Specifies the screen.
user_geom	Specifies the user-specified geometry or NULL.
def_geom	Specifies the application's default geometry or NULL.
bwidth	Specifies the border width.
hints	Specifies the size hints for the window in its normal state.
x_return
y_return	Return the x and y offsets.
width_return
height_return	Return the width and height determined.
gravity_return	Returns the window gravity.

The
XWMGeometry
function combines any geometry information (given in the format used by
XParseGeometry)
specified by the user and by the calling program with size hints
(usually the ones to be stored in WM_NORMAL_HINTS) and returns the position,
size, and gravity
(NorthWestGravity,
NorthEastGravity,
SouthEastGravity,
or
SouthWestGravity)
that describe the window.
If the base size is not set in the
XSizeHints
structure,
the minimum size is used if set.
Otherwise, a base size of zero is assumed.
If no minimum size is set in the hints structure,
the base size is used.
A mask (in the form returned by
XParseGeometry)
that describes which values came from the user specification
and whether or not the position coordinates are relative
to the right and bottom edges is returned.
Note that these coordinates will have already been accounted for
in the x_return and y_return values.

Note that invalid geometry specifications can cause a width or height
of zero to be returned.
The caller may pass the address of the hints win_gravity field
as gravity_return to update the hints directly.

Manipulating Regions

Regions are arbitrary sets of pixel locations.
Xlib provides functions for manipulating regions.
The opaque type
Region
is defined in
<X11/Xutil.h>.

Xlib provides functions that you can use to manipulate regions.
This section discusses how to:

Create, copy, or destroy regions
Move or shrink regions
Compute with regions
Determine if regions are empty or equal
Locate a point or rectangle in a region

Creating, Copying, or Destroying Regions

To create a new empty region, use
XCreateRegion.

Region XCreateRegion(void);

To generate a region from a polygon, use
XPolygonRegion.

Region XPolygonRegion(XPoint points[], int n, int fill_rule);

points	Specifies an array of points.
n	Specifies the number of points in the polygon.
fill_rule	Specifies the fill-rule you want to set for the specified GC. You can pass EvenOddRule or WindingRule.

The
XPolygonRegion
function returns a region for the polygon defined by the points array.
For an explanation of fill_rule,
see
XCreateGC.

To set the clip-mask of a GC to a region, use
XSetRegion.

XSetRegion(Display *display, GC gc, Region r);

display	Specifies the connection to the X server.
gc	Specifies the GC.
r	Specifies the region.

The
XSetRegion
function sets the clip-mask in the GC to the specified region.
The region is specified relative to the drawable's origin.
The resulting GC clip origin is implementation-dependent.
Once it is set in the GC,
the region can be destroyed.

To deallocate the storage associated with a specified region, use
XDestroyRegion.

XDestroyRegion(Region r);

r	Specifies the region.

Moving or Shrinking Regions

To move a region by a specified amount, use
XOffsetRegion.

XOffsetRegion(Region r, int dx, int dy);

r	Specifies the region.
dx
dy	Specify the x and y coordinates, which define the amount you want to move the specified region.

To reduce a region by a specified amount, use
XShrinkRegion.

XShrinkRegion(Region r, int dx, int dy);

r	Specifies the region.
dx
dy	Specify the x and y coordinates, which define the amount you want to shrink the specified region.

Positive values shrink the size of the region,
and negative values expand the region.

Computing with Regions

To generate the smallest rectangle enclosing a region, use
XClipBox.

XClipBox(Region r, XRectangle *rect_return);

r	Specifies the region.
rect_return	Returns the smallest enclosing rectangle.

The
XClipBox
function returns the smallest rectangle enclosing the specified region.

To compute the intersection of two regions, use
XIntersectRegion.

XIntersectRegion(Region sra, Region srb, Region dr_return);

sra
srb	Specify the two regions with which you want to perform the computation.
dr_return	Returns the result of the computation.

To compute the union of two regions, use
XUnionRegion.

XUnionRegion(Region sra, Region srb, Region dr_return);

sra
srb	Specify the two regions with which you want to perform the computation.
dr_return	Returns the result of the computation.

To create a union of a source region and a rectangle, use
XUnionRectWithRegion.

XUnionRectWithRegion(XRectangle *rectangle, Region src_region, Region dest_region_return);

rectangle	Specifies the rectangle.
src_region	Specifies the source region to be used.
dest_region_return	Returns the destination region.

The
XUnionRectWithRegion
function updates the destination region from a union of the specified rectangle
and the specified source region.

To subtract two regions, use
XSubtractRegion.

XSubtractRegion(Region sra, Region srb, Region dr_return);

sra
srb	Specify the two regions with which you want to perform the computation.
dr_return	Returns the result of the computation.

The
XSubtractRegion
function subtracts srb from sra and stores the results in dr_return.

To calculate the difference between the union and intersection
of two regions, use
XXorRegion.

XXorRegion(Region sra, Region srb, Region dr_return);

sra
srb	Specify the two regions with which you want to perform the computation.
dr_return	Returns the result of the computation.

Determining if Regions Are Empty or Equal

To determine if the specified region is empty, use
XEmptyRegion.

Bool XEmptyRegion(Region r);

r	Specifies the region.

The
XEmptyRegion
function returns
True
if the region is empty.

To determine if two regions have the same offset, size, and shape, use
XEqualRegion.

Bool XEqualRegion(Region r1, Region r2);

r1
r2	Specify the two regions.

The
XEqualRegion
function returns
True
if the two regions have the same offset, size, and shape.

Locating a Point or a Rectangle in a Region

To determine if a specified point resides in a specified region, use
XPointInRegion.

Bool XPointInRegion(Region r, int x, int y);

r	Specifies the region.
x
y	Specify the x and y coordinates, which define the point.

The
XPointInRegion
function returns
True
if the point (x, y) is contained in the region r.

To determine if a specified rectangle is inside a region, use
XRectInRegion.

int XRectInRegion(Region r, int x, int y, unsigned int width, unsigned int height);

r	Specifies the region.
x
y	Specify the x and y coordinates, which define the coordinates of the upper-left corner of the rectangle.
width
height	Specify the width and height, which define the rectangle.

The
XRectInRegion
function returns
RectangleIn
if the rectangle is entirely in the specified region,
RectangleOut
if the rectangle is entirely out of the specified region,
and
RectanglePart
if the rectangle is partially in the specified region.

Using Cut Buffers

Xlib provides functions to manipulate cut buffers,
a very simple form of cut-and-paste inter-client communication.
Selections are a much more powerful and useful mechanism for
interchanging data between client
(see section 4.5)
and generally should be used instead of cut buffers.

Cut buffers are implemented as properties on the first root window
of the display.
The buffers can only contain text, in the STRING encoding.
The text encoding is not changed by Xlib when fetching or storing.
Eight buffers are provided
and can be accessed as a ring or as explicit buffers (numbered 0 through 7).

To store data in cut buffer 0, use
XStoreBytes.

XStoreBytes(Display *display, char *bytes, int nbytes);

display	Specifies the connection to the X server.
bytes	Specifies the bytes, which are not necessarily ASCII or null-terminated.
nbytes	Specifies the number of bytes to be stored.

The data can have embedded null characters
and need not be null-terminated.
The cut buffer's contents can be retrieved later by
any client calling
XFetchBytes.

XStoreBytes
can generate a
BadAlloc
error.

To store data in a specified cut buffer, use
XStoreBuffer.

XStoreBuffer(Display *display, char *bytes, int nbytes, int buffer);

display	Specifies the connection to the X server.
bytes	Specifies the bytes, which are not necessarily ASCII or null-terminated.
nbytes	Specifies the number of bytes to be stored.
buffer	Specifies the buffer in which you want to store the bytes.

If an invalid buffer is specified, the call has no effect.
The data can have embedded null characters
and need not be null-terminated.

XStoreBuffer
can generate a
BadAlloc
error.

To return data from cut buffer 0, use
XFetchBytes.

char *XFetchBytes(Display *display, int *nbytes_return);

display	Specifies the connection to the X server.
nbytes_return	Returns the number of bytes in the buffer.

The
XFetchBytes
function
returns the number of bytes in the nbytes_return argument,
if the buffer contains data.
Otherwise, the function
returns NULL and sets nbytes to 0.
The appropriate amount of storage is allocated and the pointer returned.
The client must free this storage when finished with it by calling
XFree.

To return data from a specified cut buffer, use
XFetchBuffer.

char *XFetchBuffer(Display *display, int *nbytes_return, int buffer);

display	Specifies the connection to the X server.
nbytes_return	Returns the number of bytes in the buffer.
buffer	Specifies the buffer from which you want the stored data returned.

The
XFetchBuffer
function returns zero to the nbytes_return argument
if there is no data in the buffer or if an invalid
buffer is specified.

To rotate the cut buffers, use
XRotateBuffers.

XRotateBuffers(Display *display, int rotate);

display	Specifies the connection to the X server.
rotate	Specifies how much to rotate the cut buffers.

The
XRotateBuffers
function rotates the cut
buffers, such that buffer 0 becomes buffer n,
buffer 1 becomes n + 1 mod 8, and so on.
This cut buffer numbering is global to the display.
Note that
XRotateBuffers
generates
BadMatch
errors if any of the eight buffers have not been created.

Determining the Appropriate Visual Type

A single display can support multiple screens.
Each screen can have several different visual types supported
at different depths.
You can use the functions described in this section to determine
which visual to use for your application.

The functions in this section use the visual information masks and the
XVisualInfo
structure,
which is defined in
<X11/Xutil.h>

and contains:

/* Visual information mask bits */


#define   VisualNoMask                 0x0
#define   VisualIDMask                 0x1
#define   VisualScreenMask             0x2
#define   VisualDepthMask              0x4
#define   VisualClassMask              0x8
#define   VisualRedMaskMask            0x10
#define   VisualGreenMaskMask          0x20
#define   VisualBlueMaskMask           0x40
#define   VisualColormapSizeMask       0x80
#define   VisualBitsPerRGBMask         0x100
#define   VisualAllMask                0x1FF


/* Values */

typedef struct {
     Visual *visual;
     VisualID visualid;
     int screen;
     unsigned int depth;
     int class;
     unsigned long red_mask;
     unsigned long green_mask;
     unsigned long blue_mask;
     int colormap_size;
     int bits_per_rgb;
} XVisualInfo;

To obtain a list of visual information structures that match a specified
template, use
XGetVisualInfo.

XVisualInfo *XGetVisualInfo(Display *display, long vinfo_mask, XVisualInfo *vinfo_template, int *nitems_return);

display	Specifies the connection to the X server.
vinfo_mask	Specifies the visual mask value.
vinfo_template	Specifies the visual attributes that are to be used in matching the visual structures.
nitems_return	Returns the number of matching visual structures.

The
XGetVisualInfo
function returns a list of visual structures that have attributes
equal to the attributes specified by vinfo_template.
If no visual structures match the template using the specified vinfo_mask,
XGetVisualInfo
returns a NULL.
To free the data returned by this function, use
XFree.

To obtain the visual information that matches the specified depth and
class of the screen, use
XMatchVisualInfo.

Status XMatchVisualInfo(Display *display, int screen, int depth, int class, XVisualInfo *vinfo_return);

display	Specifies the connection to the X server.
screen	Specifies the screen.
depth	Specifies the depth of the screen.
class	Specifies the class of the screen.
vinfo_return	Returns the matched visual information.

The
XMatchVisualInfo
function returns the visual information for a visual that matches the specified
depth and class for a screen.
Because multiple visuals that match the specified depth and class can exist,
the exact visual chosen is undefined.
If a visual is found,
XMatchVisualInfo
returns nonzero and the information on the visual to vinfo_return.
Otherwise, when a visual is not found,
XMatchVisualInfo
returns zero.

Manipulating Images

Xlib provides several functions that perform basic operations on images.
All operations on images are defined using an
XImage
structure,
as defined in
<X11/Xlib.h>.

Because the number of different types of image formats can be very large,
this hides details of image storage properly from applications.

This section describes the functions for generic operations on images.
Manufacturers can provide very fast implementations of these for the
formats frequently encountered on their hardware.
These functions are neither sufficient nor desirable to use for general image
processing.
Rather, they are here to provide minimal functions on screen format
images.
The basic operations for getting and putting images are
XGetImage
and
XPutImage.

Note that no functions have been defined, as yet, to read and write images
to and from disk files.

The
XImage
structure describes an image as it exists in the client's memory.
The user can request that some of the members such as height, width,
and xoffset be changed when the image is sent to the server.
Note that bytes_per_line in concert with offset can be used to
extract a subset of the image.
Other members (for example, byte order, bitmap_unit, and so forth)
are characteristics of both the image and the server.
If these members
differ between the image and the server,
XPutImage
makes the appropriate conversions.
The first byte of the first line of
plane n must be located at the address (data + (n * height * bytes_per_line)).
For a description of the
XImage
structure,
see section 8.7.

To allocate an
XImage
structure and initialize it with image format values from a display, use
XCreateImage.

XImage *XCreateImage(Display *display, Visual *visual, unsigned int depth, int format, int offset, char *data, unsigned int width, unsigned int height, int bitmap_pad, int bytes_per_line);

display	Specifies the connection to the X server.
visual	Specifies the Visual structure.
depth	Specifies the depth of the image.
format	Specifies the format for the image. You can pass XYBitmap, XYPixmap, or ZPixmap.
offset	Specifies the number of pixels to ignore at the beginning of the scanline.
data	Specifies the image data.
width	Specifies the width of the image, in pixels.
height	Specifies the height of the image, in pixels.
bitmap_pad	Specifies the quantum of a scanline (8, 16, or 32). In other words, the start of one scanline is separated in client memory from the start of the next scanline by an integer multiple of this many bits.
bytes_per_line	Specifies the number of bytes in the client image between the start of one scanline and the start of the next.

The
XCreateImage
function allocates the memory needed for an
XImage
structure for the
specified display but does not allocate space for the image itself.
Rather, it initializes the structure byte-order, bit-order, and bitmap-unit
values from the display and returns a pointer to the
XImage
structure.
The red, green, and blue mask values are defined for Z format images only
and are derived from the
Visual
structure passed in.
Other values also are passed in.
The offset permits the rapid displaying of the image without requiring each
scanline to be shifted into position.
If you pass a zero value in bytes_per_line,
Xlib assumes that the scanlines are contiguous
in memory and calculates the value of bytes_per_line itself.

Note that when the image is created using
XCreateImage,
XGetImage,
or
XSubImage,
the destroy procedure that the
XDestroyImage
function calls frees both the image structure
and the data pointed to by the image structure.

The basic functions used to get a pixel, set a pixel, create a subimage,
and add a constant value to an image are defined in the image object.
The functions in this section are really macro invocations of the functions
in the image object and are defined in
<X11/Xutil.h>.

To obtain a pixel value in an image, use
XGetPixel.

unsigned long XGetPixel(XImage *ximage, int x, int y);

ximage	Specifies the image.
x
y	Specify the x and y coordinates.

The
XGetPixel
function returns the specified pixel from the named image.
The pixel value is returned in normalized format (that is,
the least significant byte of the long is the least significant byte
of the pixel).
The image must contain the x and y coordinates.

To set a pixel value in an image, use
XPutPixel.

XPutPixel(XImage *ximage, int x, int y, unsigned long pixel);

ximage	Specifies the image.
x
y	Specify the x and y coordinates.
pixel	Specifies the new pixel value.

The
XPutPixel
function overwrites the pixel in the named image with the specified pixel value.
The input pixel value must be in normalized format
(that is, the least significant byte of the long is the least significant
byte of the pixel).
The image must contain the x and y coordinates.

To create a subimage, use
XSubImage.

XImage *XSubImage(XImage *ximage, int x, int y, unsigned int subimage_width, unsigned int subimage_height);

ximage	Specifies the image.
x
y	Specify the x and y coordinates.
subimage_width	Specifies the width of the new subimage, in pixels.
subimage_height	Specifies the height of the new subimage, in pixels.

The
XSubImage
function creates a new image that is a subsection of an existing one.
It allocates the memory necessary for the new
XImage
structure
and returns a pointer to the new image.
The data is copied from the source image,
and the image must contain the rectangle defined by x, y, subimage_width,
and subimage_height.

To increment each pixel in an image by a constant value, use
XAddPixel.

XAddPixel(XImage *ximage, long value);

ximage	Specifies the image.
value	Specifies the constant value that is to be added.

The
XAddPixel
function adds a constant value to every pixel in an image.
It is useful when you have a base pixel value from allocating
color resources and need to manipulate the image to that form.

To deallocate the memory allocated in a previous call to
XCreateImage,
use
XDestroyImage.

XDestroyImage(XImage *ximage);

ximage

Specifies the image.

The
XDestroyImage
function deallocates the memory associated with the
XImage
structure.

Note that when the image is created using
XCreateImage,
XGetImage,
or
XSubImage,
the destroy procedure that this macro calls
frees both the image structure and the data pointed to by the image structure.

Manipulating Bitmaps

Xlib provides functions that you can use to read a bitmap from a file,
save a bitmap to a file, or create a bitmap.
This section describes those functions that transfer bitmaps to and
from the client's file system, thus allowing their reuse in a later
connection (for example, from an entirely different client or to a
different display or server).

The X version 11 bitmap file format is:

#define name_width width
#define name_height height
#define name_x_hot x
#define name_y_hot y
static unsigned char name_bits[] = { 0xNN,... }

The lines for the variables ending with _x_hot and _y_hot suffixes are optional
because they are present only if a hotspot has been defined for this bitmap.
The lines for the other variables are required.
The word “unsigned” is optional;
that is, the type of the _bits array can be “char” or “unsigned char”.
The _bits array must be large enough to contain the size bitmap.
The bitmap unit is 8.

To read a bitmap from a file and store it in a pixmap, use
XReadBitmapFile.

int XReadBitmapFile(Display *display, Drawable d, char *filename, unsigned int *width_return, unsigned int *height_return, Pixmap *bitmap_return, int *x_hot_return, int *y_hot_return);

display	Specifies the connection to the X server.
d	Specifies the drawable that indicates the screen.
filename	Specifies the file name to use. The format of the file name is operating-system dependent.
width_return
height_return	Return the width and height values of the read in bitmap file.
bitmap_return	Returns the bitmap that is created.
x_hot_return
y_hot_return	Return the hotspot coordinates.

The
XReadBitmapFile
function reads in a file containing a bitmap.
The file is parsed in the encoding of the current locale.
The ability to read other than the standard format
is implementation-dependent.
If the file cannot be opened,
XReadBitmapFile
returns
BitmapOpenFailed.
If the file can be opened but does not contain valid bitmap data,
it returns
BitmapFileInvalid.
If insufficient working storage is allocated,
it returns
BitmapNoMemory.
If the file is readable and valid,
it returns
BitmapSuccess.

XReadBitmapFile
returns the bitmap's height and width, as read
from the file, to width_return and height_return.
It then creates a pixmap of the appropriate size,
reads the bitmap data from the file into the pixmap,
and assigns the pixmap to the caller's variable bitmap.
The caller must free the bitmap using
XFreePixmap
when finished.
If name_x_hot and name_y_hot exist,
XReadBitmapFile
returns them to x_hot_return and y_hot_return;
otherwise, it returns −1,−1.

XReadBitmapFile
can generate
BadAlloc,
BadDrawable,
and
BadGC
errors.

To read a bitmap from a file and return it as data, use
XReadBitmapFileData.

int XReadBitmapFileData(char *filename, unsigned int *width_return, unsigned int *height_return, unsignedchar *data_return, int *x_hot_return, int *y_hot_return);

filename	Specifies the file name to use. The format of the file name is operating-system dependent.
width_return
height_return	Return the width and height values of the read in bitmap file.
data_return	Returns the bitmap data.
x_hot_return
y_hot_return	Return the hotspot coordinates.

The
XReadBitmapFileData
function reads in a file containing a bitmap, in the same manner as
XReadBitmapFile,
but returns the data directly rather than creating a pixmap in the server.
The bitmap data is returned in data_return; the client must free this
storage when finished with it by calling
XFree.
The status and other return values are the same as for
XReadBitmapFile.

To write out a bitmap from a pixmap to a file, use
XWriteBitmapFile.

int XWriteBitmapFile(Display *display, char *filename, Pixmap bitmap, unsigned int width, unsigned int height, int x_hot, int y_hot);

display	Specifies the connection to the X server.
filename	Specifies the file name to use. The format of the file name is operating-system dependent.
bitmap	Specifies the bitmap.
width
height	Specify the width and height.
x_hot
y_hot	Specify where to place the hotspot coordinates (or −1,−1 if none are present) in the file.

The
XWriteBitmapFile
function writes a bitmap out to a file in the X Version 11 format.
The name used in the output file is derived from the file name
by deleting the directory prefix.
The file is written in the encoding of the current locale.
If the file cannot be opened for writing,
it returns
BitmapOpenFailed.
If insufficient memory is allocated,
XWriteBitmapFile
returns
BitmapNoMemory;
otherwise, on no error,
it returns
BitmapSuccess.
If x_hot and y_hot are not −1, −1,
XWriteBitmapFile
writes them out as the hotspot coordinates for the bitmap.

XWriteBitmapFile
can generate
BadDrawable
and
BadMatch
errors.

To create a pixmap and then store bitmap-format data into it, use
XCreatePixmapFromBitmapData.

Pixmap XCreatePixmapFromBitmapData(Display *display, Drawable d, char *data, unsigned int width, unsigned int height, unsigned long fg, unsigned long bg, unsigned int depth);

display	Specifies the connection to the X server.
d	Specifies the drawable that indicates the screen.
data	Specifies the data in bitmap format.
width
height	Specify the width and height.
fg
bg	Specify the foreground and background pixel values to use.
depth	Specifies the depth of the pixmap.

The
XCreatePixmapFromBitmapData
function creates a pixmap of the given depth and then does a bitmap-format
XPutImage
of the data into it.
The depth must be supported by the screen of the specified drawable,
or a
BadMatch
error results.

XCreatePixmapFromBitmapData
can generate
BadAlloc,
BadDrawable,
BadGC,
and
BadValue
errors.

To include a bitmap written out by
XWriteBitmapFile

in a program directly, as opposed to reading it in every time at run time, use
XCreateBitmapFromData.

Pixmap XCreateBitmapFromData(Display *display, Drawable d, char *data, unsigned int width, unsigned int height);

display	Specifies the connection to the X server.
d	Specifies the drawable that indicates the screen.
data	Specifies the location of the bitmap data.
width
height	Specify the width and height.

The
XCreateBitmapFromData
function allows you to include in your C program (using
#include)
a bitmap file that was written out by
XWriteBitmapFile
(X version 11 format only) without reading in the bitmap file.
The following example creates a gray bitmap:

#include "gray.bitmap"

Pixmap bitmap;
bitmap = XCreateBitmapFromData(display, window, gray_bits, gray_width, gray_height);

If insufficient working storage was allocated,
XCreateBitmapFromData
returns
None.
It is your responsibility to free the
bitmap using
XFreePixmap
when finished.

XCreateBitmapFromData
can generate
BadAlloc
and
BadGC
errors.

Using the Context Manager

The context manager provides a way of associating data with an X resource ID
(mostly typically a window) in your program.
Note that this is local to your program;
the data is not stored in the server on a property list.
Any amount of data in any number of pieces can be associated with a
resource ID,
and each piece of data has a type associated with it.
The context manager requires knowledge of the resource ID
and type to store or retrieve data.

Essentially, the context manager can be viewed as a two-dimensional,
sparse array: one dimension is subscripted by the X resource ID
and the other by a context type field.
Each entry in the array contains a pointer to the data.
Xlib provides context management functions with which you can
save data values, get data values, delete entries, and create a unique
context type.
The symbols used are in
<X11/Xutil.h>.

To save a data value that corresponds to a resource ID and context type, use
XSaveContext.

int XSaveContext(Display *display, XID rid, XContext context, XPointer data);

display	Specifies the connection to the X server.
rid	Specifies the resource ID with which the data is associated.
context	Specifies the context type to which the data belongs.
data	Specifies the data to be associated with the window and type.

If an entry with the specified resource ID and type already exists,
XSaveContext
overrides it with the specified context.
The
XSaveContext
function returns a nonzero error code if an error has occurred
and zero otherwise.
Possible errors are
XCNOMEM
(out of memory).

To get the data associated with a resource ID and type, use
XFindContext.

int XFindContext(Display *display, XID rid, XContext context, XPointer *data_return);

display	Specifies the connection to the X server.
rid	Specifies the resource ID with which the data is associated.
context	Specifies the context type to which the data belongs.
data_return	Returns the data.

Because it is a return value,
the data is a pointer.
The
XFindContext
function returns a nonzero error code if an error has occurred
and zero otherwise.
Possible errors are
XCNOENT
(context-not-found).

To delete an entry for a given resource ID and type, use
XDeleteContext.

int XDeleteContext(Display *display, XID rid, XContext context);

display	Specifies the connection to the X server.
rid	Specifies the resource ID with which the data is associated.
context	Specifies the context type to which the data belongs.

The
XDeleteContext
function deletes the entry for the given resource ID
and type from the data structure.
This function returns the same error codes that
XFindContext
returns if called with the same arguments.
XDeleteContext
does not free the data whose address was saved.

To create a unique context type that may be used in subsequent calls to
XSaveContext
and
XFindContext,
use
XUniqueContext.

XContext XUniqueContext(void);

Appendix A. Xlib Functions and Protocol Requests

This appendix provides two tables that relate to Xlib functions
and the X protocol.
The following table lists each Xlib function (in alphabetical order)
and the corresponding protocol request that it generates.

Table A.1. Protocol requests made by each Xlib function

Xlib Function	Protocol Request
`XActivateScreenSaver`	`ForceScreenSaver`
`XAddHost`	`ChangeHosts`
`XAddHosts`	`ChangeHosts`
`XAddToSaveSet`	`ChangeSaveSet`
`XAllocColor`	`AllocColor`
`XAllocColorCells`	`AllocColorCells`
`XAllocColorPlanes`	`AllocColorPlanes`
`XAllocNamedColor`	`AllocNamedColor`
`XAllowEvents`	`AllowEvents`
`XAutoRepeatOff`	`ChangeKeyboardControl`
`XAutoRepeatOn`	`ChangeKeyboardControl`
`XBell`	`Bell`
`XChangeActivePointerGrab`	`ChangeActivePointerGrab`
`XChangeGC`	`ChangeGC`
`XChangeKeyboardControl`	`ChangeKeyboardControl`
`XChangeKeyboardMapping`	`ChangeKeyboardMapping`
`XChangePointerControl`	`ChangePointerControl`
`XChangeProperty`	`ChangeProperty`
`XChangeSaveSet`	`ChangeSaveSet`
`XChangeWindowAttributes`	`ChangeWindowAttributes`
`XCirculateSubwindows`	`CirculateWindow`
`XCirculateSubwindowsDown`	`CirculateWindow`
`XCirculateSubwindowsUp`	`CirculateWindow`
`XClearArea`	`ClearArea`
`XClearWindow`	`ClearArea`
`XConfigureWindow`	`ConfigureWindow`
`XConvertSelection`	`ConvertSelection`
`XCopyArea`	`CopyArea`
`XCopyColormapAndFree`	`CopyColormapAndFree`
`XCopyGC`	`CopyGC`
`XCopyPlane`	`CopyPlane`
`XCreateBitmapFromData`	`CreateGC`
	`CreatePixmap`
	`FreeGC`
	`PutImage`
`XCreateColormap`	`CreateColormap`
`XCreateFontCursor`	`CreateGlyphCursor`
`XCreateGC`	`CreateGC`
`XCreateGlyphCursor`	`CreateGlyphCursor`
`XCreatePixmap`	`CreatePixmap`
`XCreatePixmapCursor`	`CreateCursor`
`XCreatePixmapFromData`	`CreateGC`
	`CreatePixmap`
	`FreeGC`
	`PutImage`
`XCreateSimpleWindow`	`CreateWindow`
`XCreateWindow`	`CreateWindow`
`XDefineCursor`	`ChangeWindowAttributes`
`XDeleteProperty`	`DeleteProperty`
`XDestroySubwindows`	`DestroySubwindows`
`XDestroyWindow`	`DestroyWindow`
`XDisableAccessControl`	`SetAccessControl`
`XDrawArc`	`PolyArc`
`XDrawArcs`	`PolyArc`
`XDrawImageString`	`ImageText8`
`XDrawImageString16`	`ImageText16`
`XDrawLine`	`PolySegment`
`XDrawLines`	`PolyLine`
`XDrawPoint`	`PolyPoint`
`XDrawPoints`	`PolyPoint`
`XDrawRectangle`	`PolyRectangle`
`XDrawRectangles`	`PolyRectangle`
`XDrawSegments`	`PolySegment`
`XDrawString`	`PolyText8`
`XDrawString16`	`PolyText16`
`XDrawText`	`PolyText8`
`XDrawText16`	`PolyText16`
`XEnableAccessControl`	`SetAccessControl`
`XFetchBytes`	`GetProperty`
`XFetchName`	`GetProperty`
`XFillArc`	`PolyFillArc`
`XFillArcs`	`PolyFillArc`
`XFillPolygon`	`FillPoly`
`XFillRectangle`	`PolyFillRectangle`
`XFillRectangles`	`PolyFillRectangle`
`XForceScreenSaver`	`ForceScreenSaver`
`XFreeColormap`	`FreeColormap`
`XFreeColors`	`FreeColors`
`XFreeCursor`	`FreeCursor`
`XFreeFont`	`CloseFont`
`XFreeGC`	`FreeGC`
`XFreePixmap`	`FreePixmap`
`XGetAtomName`	`GetAtomName`
`XGetClassHint`	`GetProperty`
`XGetFontPath`	`GetFontPath`
`XGetGeometry`	`GetGeometry`
`XGetIconName`	`GetProperty`
`XGetIconSizes`	`GetProperty`
`XGetImage`	`GetImage`
`XGetInputFocus`	`GetInputFocus`
`XGetKeyboardControl`	`GetKeyboardControl`
`XGetKeyboardMapping`	`GetKeyboardMapping`
`XGetModifierMapping`	`GetModifierMapping`
	`GetMotionEvents`
`XGetNormalHints`	`GetProperty`
`XGetPointerControl`	`GetPointerControl`
`XGetPointerMapping`	`GetPointerMapping`
`XGetRGBColormaps`	`GetProperty`
`XGetScreenSaver`	`GetScreenSaver`
`XGetSelectionOwner`	`GetSelectionOwner`
`XGetSizeHints`	`GetProperty`
`XGetTextProperty`	`GetProperty`
`XGetTransientForHint`	`GetProperty`
`XGetWMClientMachine`	`GetProperty`
`XGetWMColormapWindows`	`GetProperty`
`XGetWMColormapWindows`	`InternAtom`
`XGetWMHints`	`GetProperty`
`XGetWMIconName`	`GetProperty`
`XGetWMName`	`GetProperty`
`XGetWMNormalHints`	`GetProperty`
`XGetWMProtocols`	`GetProperty`
`XGetWMProtocols`	`InternAtom`
`XGetWMSizeHints`	`GetProperty`
`XGetWindowAttributes`	`GetWindowAttributes`
`XGetWindowAttributes`	`GetGeometry`
`XGetWindowProperty`	`GetProperty`
`XGetZoomHints`	`GetProperty`
`XGrabButton`	`GrabButton`
`XGrabKey`	`GrabKey`
`XGrabKeyboard`	`GrabKeyboard`
`XGrabPointer`	`GrabPointer`
`XGrabServer`	`GrabServer`
`XIconifyWindow`	`InternAtom`
`XIconifyWindow`	`SendEvent`
`XInitExtension`	`QueryExtension`
`XInstallColormap`	`InstallColormap`
`XInternAtom`	`InternAtom`
`XKillClient`	`KillClient`
`XListExtensions`	`ListExtensions`
`XListFonts`	`ListFonts`
`XListFontsWithInfo`	`ListFontsWithInfo`
`XListHosts`	`ListHosts`
`XListInstalledColormaps`	`ListInstalledColormaps`
`XListProperties`	`ListProperties`
`XLoadFont`	`OpenFont`
`XLoadQueryFont`	`OpenFont`
`XLoadQueryFont`	`QueryFont`
`XLookupColor`	`LookupColor`
`XLowerWindow`	`ConfigureWindow`
`XMapRaised`	`ConfigureWindow`
`XMapRaised`	`MapWindow`
`XMapSubwindows`	`MapSubwindows`
`XMapWindow`	`MapWindow`
`XMoveResizeWindow`	`ConfigureWindow`
`XMoveWindow`	`ConfigureWindow`
`XNoOp`	`NoOperation`
`XOpenDisplay`	`CreateGC`
`XParseColor`	`LookupColor`
`XPutImage`	`PutImage`
`XQueryBestCursor`	`QueryBestSize`
`XQueryBestSize`	`QueryBestSize`
`XQueryBestStipple`	`QueryBestSize`
`XQueryBestTile`	`QueryBestSize`
`XQueryColor`	`QueryColors`
`XQueryColors`	`QueryColors`
`XQueryExtension`	`QueryExtension`
`XQueryFont`	`QueryFont`
`XQueryKeymap`	`QueryKeymap`
`XQueryPointer`	`QueryPointer`
`XQueryTextExtents`	`QueryTextExtents`
`XQueryTextExtents16`	`QueryTextExtents`
`XQueryTree`	`QueryTree`
`XRaiseWindow`	`ConfigureWindow`
`XReadBitmapFile`	`CreateGC`
	`CreatePixmap`
	`FreeGC`
	`PutImage`
`XRecolorCursor`	`RecolorCursor`
`XReconfigureWMWindow`	`ConfigureWindow`
`XReconfigureWMWindow`	`SendEvent`
`XRemoveFromSaveSet`	`ChangeSaveSet`
`XRemoveHost`	`ChangeHosts`
`XRemoveHosts`	`ChangeHosts`
`XReparentWindow`	`ReparentWindow`
`XResetScreenSaver`	`ForceScreenSaver`
`XResizeWindow`	`ConfigureWindow`
`XRestackWindows`	`ConfigureWindow`
`XRotateBuffers`	`RotateProperties`
`XRotateWindowProperties`	`RotateProperties`
`XSelectInput`	`ChangeWindowAttributes`
`XSendEvent`	`SendEvent`
`XSetAccessControl`	`SetAccessControl`
`XSetArcMode`	`ChangeGC`
`XSetBackground`	`ChangeGC`
`XSetClassHint`	`ChangeProperty`
`XSetClipMask`	`ChangeGC`
`XSetClipOrigin`	`ChangeGC`
`XSetClipRectangles`	`SetClipRectangles`
`XSetCloseDownMode`	`SetCloseDownMode`
`XSetCommand`	`ChangeProperty`
`XSetDashes`	`SetDashes`
`XSetFillRule`	`ChangeGC`
`XSetFillStyle`	`ChangeGC`
`XSetFont`	`ChangeGC`
`XSetFontPath`	`SetFontPath`
`XSetForeground`	`ChangeGC`
`XSetFunction`	`ChangeGC`
`XSetGraphicsExposures`	`ChangeGC`
`XSetIconName`	`ChangeProperty`
`XSetIconSizes`	`ChangeProperty`
`XSetInputFocus`	`SetInputFocus`
`XSetLineAttributes`	`ChangeGC`
`XSetModifierMapping`	`SetModifierMapping`
`XSetNormalHints`	`ChangeProperty`
`XSetPlaneMask`	`ChangeGC`
`XSetPointerMapping`	`SetPointerMapping`
`XSetRGBColormaps`	`ChangeProperty`
`XSetScreenSaver`	`SetScreenSaver`
`XSetSelectionOwner`	`SetSelectionOwner`
`XSetSizeHints`	`ChangeProperty`
`XSetStandardProperties`	`ChangeProperty`
`XSetState`	`ChangeGC`
`XSetStipple`	`ChangeGC`
`XSetSubwindowMode`	`ChangeGC`
`XSetTextProperty`	`ChangeProperty`
`XSetTile`	`ChangeGC`
`XSetTransientForHint`	`ChangeProperty`
`XSetTSOrigin`	`ChangeGC`
`XSetWMClientMachine`	`ChangeProperty`
`XSetWMColormapWindows`	`ChangeProperty`
`XSetWMColormapWindows`	`InternAtom`
`XSetWMHints`	`ChangeProperty`
`XSetWMIconName`	`ChangeProperty`
`XSetWMName`	`ChangeProperty`
`XSetWMNormalHints`	`ChangeProperty`
`XSetWMProperties`	`ChangeProperty`
`XSetWMProtocols`	`ChangeProperty`
`XSetWMProtocols`	`InternAtom`
`XSetWMSizeHints`	`ChangeProperty`
`XSetWindowBackground`	`ChangeWindowAttributes`
`XSetWindowBackgroundPixmap`	`ChangeWindowAttributes`
`XSetWindowBorder`	`ChangeWindowAttributes`
`XSetWindowBorderPixmap`	`ChangeWindowAttributes`
`XSetWindowBorderWidth`	`ConfigureWindow`
`XSetWindowColormap`	`ChangeWindowAttributes`
`XSetZoomHints`	`ChangeProperty`
`XStoreBuffer`	`ChangeProperty`
`XStoreBytes`	`ChangeProperty`
`XStoreColor`	`StoreColors`
`XStoreColors`	`StoreColors`
`XStoreName`	`ChangeProperty`
`XStoreNamedColor`	`StoreNamedColor`
`XSync`	`GetInputFocus`
`XSynchronize`	`GetInputFocus`
`XTranslateCoordinates`	`TranslateCoordinates`
`XUndefineCursor`	`ChangeWindowAttributes`
`XUngrabButton`	`UngrabButton`
`XUngrabKey`	`UngrabKey`
`XUngrabKeyboard`	`UngrabKeyboard`
`XUngrabPointer`	`UngrabPointer`
`XUngrabServer`	`UngrabServer`
`XUninstallColormap`	`UninstallColormap`
`XUnloadFont`	`CloseFont`
`XUnmapSubwindows`	`UnmapSubwindows`
`XUnmapWindow`	`UnmapWindow`
`XWarpPointer`	`WarpPointer`
`XWithdrawWindow`	`SendEvent`
`XWithdrawWindow`	`UnmapWindow`

The following table lists each X protocol request (in alphabetical
order) and the Xlib functions that reference it.

Table A.2. Xlib functions which use each Protocol Request

Protocol Request	Xlib Function
`AllocColor`	`XAllocColor`
`AllocColorCells`	`XAllocColorCells`
`AllocColorPlanes`	`XAllocColorPlanes`
`AllocNamedColor`	`XAllocNamedColor`
`AllowEvents`	`XAllowEvents`
`Bell`	`XBell`
`ChangeActivePointerGrab`	`XChangeActivePointerGrab`
`ChangeGC`	`XChangeGC`
	`XSetArcMode`
	`XSetBackground`
	`XSetClipMask`
	`XSetClipOrigin`
	`XSetFillRule`
	`XSetFillStyle`
	`XSetFont`
	`XSetForeground`
	`XSetFunction`
	`XSetGraphicsExposures`
	`XSetLineAttributes`
	`XSetPlaneMask`
	`XSetState`
	`XSetStipple`
	`XSetSubwindowMode`
	`XSetTile`
	`XSetTSOrigin`
`ChangeHosts`	`XAddHost`
	`XAddHosts`
	`XRemoveHost`
	`XRemoveHosts`
`ChangeKeyboardControl`	`XAutoRepeatOff`
	`XAutoRepeatOn`
	`XChangeKeyboardControl`
`ChangeKeyboardMapping`	`XChangeKeyboardMapping`
`ChangePointerControl`	`XChangePointerControl`
`ChangeProperty`	`XChangeProperty`
	`XSetClassHint`
	`XSetCommand`
	`XSetIconName`
	`XSetIconSizes`
	`XSetNormalHints`
	`XSetRGBColormaps`
	`XSetSizeHints`
	`XSetStandardProperties`
	`XSetTextProperty`
	`XSetTransientForHint`
	`XSetWMClientMachine`
	`XSetWMColormapWindows`
	`XSetWMHints`
	`XSetWMIconName`
	`XSetWMName`
	`XSetWMNormalHints`
	`XSetWMProperties`
	`XSetWMProtocols`
	`XSetWMSizeHints`
	`XSetZoomHints`
	`XStoreBuffer`
	`XStoreBytes`
	`XStoreName`
`ChangeSaveSet`	`XAddToSaveSet`
	`XChangeSaveSet`
	`XRemoveFromSaveSet`
`ChangeWindowAttributes`	`XChangeWindowAttributes`
	`XDefineCursor`
	`XSelectInput`
	`XSetWindowBackground`
	`XSetWindowBackgroundPixmap`
	`XSetWindowBorder`
	`XSetWindowBorderPixmap`
	`XSetWindowColormap`
	`XUndefineCursor`
`CirculateWindow`	`XCirculateSubwindowsDown`
	`XCirculateSubwindowsUp`
	`XCirculateSubwindows`
`ClearArea`	`XClearArea`
`ClearArea`	`XClearWindow`
`CloseFont`	`XFreeFont`
`CloseFont`	`XUnloadFont`
`ConfigureWindow`	`XConfigureWindow`
	`XLowerWindow`
	`XMapRaised`
	`XMoveResizeWindow`
	`XMoveWindow`
	`XRaiseWindow`
	`XReconfigureWMWindow`
	`XResizeWindow`
	`XRestackWindows`
	`XSetWindowBorderWidth`
`ConvertSelection`	`XConvertSelection`
`CopyArea`	`XCopyArea`
`CopyColormapAndFree`	`XCopyColormapAndFree`
`CopyGC`	`XCopyGC`
`CopyPlane`	`XCopyPlane`
`CreateColormap`	`XCreateColormap`
`CreateCursor`	`XCreatePixmapCursor`
`CreateGC`	`XCreateGC`
	`XCreateBitmapFromData`
	`XCreatePixmapFromData`
	`XOpenDisplay`
	`XReadBitmapFile`
`CreateGlyphCursor`	`XCreateFontCursor`
`CreateGlyphCursor`	`XCreateGlyphCursor`
`CreatePixmap`	`XCreatePixmap`
	`XCreateBitmapFromData`
	`XCreatePixmapFromData`
	`XReadBitmapFile`
`CreateWindow`	`XCreateSimpleWindow`
`CreateWindow`	`XCreateWindow`
`DeleteProperty`	`XDeleteProperty`
`DestroySubwindows`	`XDestroySubwindows`
`DestroyWindow`	`XDestroyWindow`
`FillPoly`	`XFillPolygon`
`ForceScreenSaver`	`XActivateScreenSaver`
	`XForceScreenSaver`
	`XResetScreenSaver`
`FreeColormap`	`XFreeColormap`
`FreeColors`	`XFreeColors`
`FreeCursor`	`XFreeCursor`
`FreeGC`	`XFreeGC`
	`XCreateBitmapFromData`
	`XCreatePixmapFromData`
	`XReadBitmapFile`
`FreePixmap`	`XFreePixmap`
`GetAtomName`	`XGetAtomName`
`GetFontPath`	`XGetFontPath`
`GetGeometry`	`XGetGeometry`
`GetGeometry`	`XGetWindowAttributes`
`GetImage`	`XGetImage`
`GetInputFocus`	`XGetInputFocus`
	`XSync`
	`XSynchronize`
`GetKeyboardControl`	`XGetKeyboardControl`
`GetKeyboardMapping`	`XGetKeyboardMapping`
`GetModifierMapping`	`XGetModifierMapping`
`GetMotionEvents`
`GetPointerControl`	`XGetPointerControl`
`GetPointerMapping`	`XGetPointerMapping`
`GetProperty`	`XFetchBytes`
	`XFetchName`
	`XGetClassHint`
	`XGetIconName`
	`XGetIconSizes`
	`XGetNormalHints`
	`XGetRGBColormaps`
	`XGetSizeHints`
	`XGetTextProperty`
	`XGetTransientForHint`
	`XGetWMClientMachine`
	`XGetWMColormapWindows`
	`XGetWMHints`
	`XGetWMIconName`
	`XGetWMName`
	`XGetWMNormalHints`
	`XGetWMProtocols`
	`XGetWMSizeHints`
	`XGetWindowProperty`
	`XGetZoomHints`
`GetSelectionOwner`	`XGetSelectionOwner`
`GetWindowAttributes`	`XGetWindowAttributes`
`GrabButton`	`XGrabButton`
`GrabKey`	`XGrabKey`
`GrabKeyboard`	`XGrabKeyboard`
`GrabPointer`	`XGrabPointer`
`GrabServer`	`XGrabServer`
`ImageText8`	`XDrawImageString`
`ImageText16`	`XDrawImageString16`
`InstallColormap`	`XInstallColormap`
`InternAtom`	`XGetWMColormapWindows`
	`XGetWMProtocols`
	`XIconifyWindow`
	`XInternAtom`
	`XSetWMColormapWindows`
	`XSetWMProtocols`
`KillClient`	`XKillClient`
`ListExtensions`	`XListExtensions`
`ListFonts`	`XListFonts`
`ListFontsWithInfo`	`XListFontsWithInfo`
`ListHosts`	`XListHosts`
`ListInstalledColormaps`	`XListInstalledColormaps`
`ListProperties`	`XListProperties`
`LookupColor`	`XLookupColor`
`LookupColor`	`XParseColor`
`MapSubwindows`	`XMapSubwindows`
`MapWindow`	`XMapRaised`
`MapWindow`	`XMapWindow`
`NoOperation`	`XNoOp`
`OpenFont`	`XLoadFont`
`OpenFont`	`XLoadQueryFont`
`PolyArc`	`XDrawArc`
`PolyArc`	`XDrawArcs`
`PolyFillArc`	`XFillArc`
`PolyFillArc`	`XFillArcs`
`PolyFillRectangle`	`XFillRectangle`
`PolyFillRectangle`	`XFillRectangles`
`PolyLine`	`XDrawLines`
`PolyPoint`	`XDrawPoint`
`PolyPoint`	`XDrawPoints`
`PolyRectangle`	`XDrawRectangle`
`PolyRectangle`	`XDrawRectangles`
`PolySegment`	`XDrawLine`
`PolySegment`	`XDrawSegments`
`PolyText8`	`XDrawString`
`PolyText8`	`XDrawText`
`PolyText16`	`XDrawString16`
`PolyText16`	`XDrawText16`
`PutImage`	`XPutImage`
	`XCreateBitmapFromData`
	`XCreatePixmapFromData`
	`XReadBitmapFile`
`QueryBestSize`	`XQueryBestCursor`
	`XQueryBestSize`
	`XQueryBestStipple`
	`XQueryBestTile`
`QueryColors`	`XQueryColor`
`QueryColors`	`XQueryColors`
`QueryExtension`	`XInitExtension`
`QueryExtension`	`XQueryExtension`
`QueryFont`	`XLoadQueryFont`
`QueryFont`	`XQueryFont`
`QueryKeymap`	`XQueryKeymap`
`QueryPointer`	`XQueryPointer`
`QueryTextExtents`	`XQueryTextExtents`
`QueryTextExtents`	`XQueryTextExtents16`
`QueryTree`	`XQueryTree`
`RecolorCursor`	`XRecolorCursor`
`ReparentWindow`	`XReparentWindow`
`RotateProperties`	`XRotateBuffers`
`RotateProperties`	`XRotateWindowProperties`
`SendEvent`	`XIconifyWindow`
	`XReconfigureWMWindow`
	`XSendEvent`
	`XWithdrawWindow`
`SetAccessControl`	`XDisableAccessControl`
	`XEnableAccessControl`
	`XSetAccessControl`
`SetClipRectangles`	`XSetClipRectangles`
`SetCloseDownMode`	`XSetCloseDownMode`
`SetDashes`	`XSetDashes`
`SetFontPath`	`XSetFontPath`
`SetInputFocus`	`XSetInputFocus`
`SetModifierMapping`	`XSetModifierMapping`
`SetPointerMapping`	`XSetPointerMapping`
`SetScreenSaver`	`XGetScreenSaver`
`SetScreenSaver`	`XSetScreenSaver`
`SetSelectionOwner`	`XSetSelectionOwner`
`StoreColors`	`XStoreColor`
`StoreColors`	`XStoreColors`
`StoreNamedColor`	`XStoreNamedColor`
`TranslateCoordinates`	`XTranslateCoordinates`
`UngrabButton`	`XUngrabButton`
`UngrabKey`	`XUngrabKey`
`UngrabKeyboard`	`XUngrabKeyboard`
`UngrabPointer`	`XUngrabPointer`
`UngrabServer`	`XUngrabServer`
`UninstallColormap`	`XUninstallColormap`
`UnmapSubwindows`	`XUnmapSubWindows`
`UnmapWindow`	`XUnmapWindow`
`UnmapWindow`	`XWithdrawWindow`
`WarpPointer`	`XWarpPointer`

Appendix B. X Font Cursors

The following are the available cursors that can be used with
XCreateFontCursor.

#define XC_X_cursor 0                     #define XC_ll_angle 76
#define XC_arrow 2                        #define XC_lr_angle 78
#define XC_based_arrow_down 4             #define XC_man 80
#define XC_based_arrow_up 6               #define XC_middlebutton 82
#define XC_boat 8                         #define XC_mouse 84
#define XC_bogosity 10                    #define XC_pencil 86
#define XC_bottom_left_corner 12          #define XC_pirate 88
#define XC_bottom_right_corner 14         #define XC_plus 90
#define XC_bottom_side 16                 #define XC_question_arrow 92
#define XC_bottom_tee 18                  #define XC_right_ptr 94
#define XC_box_spiral 20                  #define XC_right_side 96
#define XC_center_ptr 22                  #define XC_right_tee 98
#define XC_circle 24                      #define XC_rightbutton 100
#define XC_clock 26                       #define XC_rtl_logo 102
#define XC_coffee_mug 28                  #define XC_sailboat 104
#define XC_cross 30                       #define XC_sb_down_arrow 106
#define XC_cross_reverse 32               #define XC_sb_h_double_arrow 108
#define XC_crosshair 34                   #define XC_sb_left_arrow 110
#define XC_diamond_cross 36               #define XC_sb_right_arrow 112
#define XC_dot 38                         #define XC_sb_up_arrow 114
#define XC_dot_box_mask 40                #define XC_sb_v_double_arrow 116
#define XC_double_arrow 42                #define XC_shuttle 118
#define XC_draft_large 44                 #define XC_sizing 120
#define XC_draft_small 46                 #define XC_spider 122
#define XC_draped_box 48                  #define XC_spraycan 124
#define XC_exchange 50                    #define XC_star 126
#define XC_fleur 52                       #define XC_target 128
#define XC_gobbler 54                     #define XC_tcross 130
#define XC_gumby 56                       #define XC_top_left_arrow 132
#define XC_hand1 58                       #define XC_top_left_corner 134
#define XC_hand2 60                       #define XC_top_right_corner 136
#define XC_heart 62                       #define XC_top_side 138
#define XC_icon 64                        #define XC_top_tee 140
#define XC_iron_cross 66                  #define XC_trek 142
#define XC_left_ptr 68                    #define XC_ul_angle 144
#define XC_left_side 70                   #define XC_umbrella 146
#define XC_left_tee 72                    #define XC_ur_angle 148
#define XC_leftbutton 74                  #define XC_watch 150
                                          #define XC_xterm 152

Appendix C. Extensions

Table of Contents

Basic Protocol Support RoutinesHooking into XlibHooks into the LibraryHooks onto Xlib Data StructuresGC CachingGraphics BatchingWriting Extension StubsRequests, Replies, and Xproto.hRequest FormatStarting to Write a Stub ProcedureLocking Data StructuresSending the Protocol Request and ArgumentsVariable Length ArgumentsRepliesSynchronous CallingAllocating and Deallocating MemoryPortability ConsiderationsDeriving the Correct Extension Opcode

Because X can evolve by extensions to the core protocol,
it is important that extensions not be perceived as second-class citizens.
At some point,
your favorite extensions may be adopted as additional parts of the
X Standard.

Therefore, there should be little to distinguish the use of an extension from
that of the core protocol.
To avoid having to initialize extensions explicitly in application programs,
it is also important that extensions perform lazy evaluations,
automatically initializing themselves when called for the first time.

This appendix describes techniques for writing extensions to Xlib that will
run at essentially the same performance as the core protocol requests.

Note

It is expected that a given extension to X consists of multiple
requests.
Defining 10 new features as 10 separate extensions is a bad practice.
Rather, they should be packaged into a single extension
and should use minor opcodes to distinguish the requests.

The symbols and macros used for writing stubs to Xlib are listed in
<X11/Xlibint.h>.

Basic Protocol Support Routines

The basic protocol requests for extensions are
XQueryExtension
and
XListExtensions.

Bool XQueryExtension(Display *display, char *name, int *major_opcode_return, int *first_event_return, int *first_error_return);

display	Specifies the connection to the X server.
name	Specifies the extension name.
major_opcode_return	Returns the major opcode.
first_event_return	Returns the first event code, if any.
first_error_return	Returns the first error code, if any.

The
XQueryExtension
function determines if the named extension is present.
If the extension is not present,
XQueryExtension
returns
False;
otherwise, it returns
True.
If the extension is present,
XQueryExtension
returns the major opcode for the extension to major_opcode_return;
otherwise,
it returns zero.
Any minor opcode and the request formats are specific to the
extension.
If the extension involves additional event types,
XQueryExtension
returns the base event type code to first_event_return;
otherwise,
it returns zero.
The format of the events is specific to the extension.
If the extension involves additional error codes,
XQueryExtension
returns the base error code to first_error_return;
otherwise,
it returns zero.
The format of additional data in the errors is specific to the extension.

If the extension name is not in the Host Portable Character Encoding
the result is implementation-dependent.
Uppercase and lowercase matter;
the strings “thing”, “Thing”, and “thinG”
are all considered different names.

char **XListExtensions(Display *display, int *nextensions_return);

display	Specifies the connection to the X server.
nextensions_return	Returns the number of extensions listed.

The
XListExtensions
function returns a list of all extensions supported by the server.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.

XFreeExtensionList(char **list);

list

Specifies the list of extension names.

The
XFreeExtensionList
function frees the memory allocated by
XListExtensions.

Hooking into Xlib

These functions allow you to hook into the library.
They are not normally used by application programmers but are used
by people who need to extend the core X protocol and
the X library interface.
The functions, which generate protocol requests for X, are typically
called stubs.

In extensions, stubs first should check to see if they have initialized
themselves on a connection.
If they have not, they then should call
XInitExtension
to attempt to initialize themselves on the connection.

If the extension needs to be informed of GC/font allocation or
deallocation or if the extension defines new event types,
the functions described here allow the extension to be
called when these events occur.

The
XExtCodes
structure returns the information from
XInitExtension
and is defined in
<X11/Xlib.h>:

typedef struct _XExtCodes {	/* public to extension, cannot be changed */
	int extension;		/* extension number */
	int major_opcode;	/* major op-code assigned by server */
	int first_event;	/* first event number for the extension */
	int first_error;	/* first error number for the extension */
} XExtCodes;

XExtCodes *XInitExtension(Display *display, char *name);

display	Specifies the connection to the X server.
name	Specifies the extension name.

The
XInitExtension
function determines if the named extension exists.
Then, it allocates storage for maintaining the
information about the extension on the connection,
chains this onto the extension list for the connection,
and returns the information the stub implementor will need to access
the extension.
If the extension does not exist,
XInitExtension
returns NULL.

If the extension name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Uppercase and lowercase matter;
the strings “thing”, “Thing”, and “thinG”
are all considered different names.

The extension number in the
XExtCodes
structure is
needed in the other calls that follow.
This extension number is unique only to a single connection.

XExtCodes *XAddExtension(Display *display);

display

Specifies the connection to the X server.

For local Xlib extensions, the
XAddExtension
function allocates the
XExtCodes
structure, bumps the extension number count,
and chains the extension onto the extension list.
(This permits extensions to Xlib without requiring server extensions.)

Hooks into the Library

These functions allow you to define procedures that are to be
called when various circumstances occur.
The procedures include the creation of a new GC for a connection,
the copying of a GC, the freeing of a GC, the creating and freeing of fonts,
the conversion of events defined by extensions to and from wire
format, and the handling of errors.

All of these functions return the previous procedure defined for this
extension.

int XESetCloseDisplay(Display *display, int extension, int (*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when the display is closed.

The
XESetCloseDisplay
function defines a procedure to be called whenever
XCloseDisplay
is called.
It returns any previously defined procedure, usually NULL.

When
XCloseDisplay
is called,
your procedure is called
with these arguments:

int (*proc)(Display *display, XExtCodes *codes);

int *XESetCreateGC(Display *display, int extension, int (*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when a GC is closed.

The
XESetCreateGC
function defines a procedure to be called whenever
a new GC is created.
It returns any previously defined procedure, usually NULL.

When a GC is created,
your procedure is called with these arguments:

int (*proc)(Display *display, GC gc, XExtCodes *codes);

int *XESetCopyGC(Display *display, int extension, int (*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when GC components are copied.

The
XESetCopyGC
function defines a procedure to be called whenever
a GC is copied.
It returns any previously defined procedure, usually NULL.

When a GC is copied,
your procedure is called with these arguments:

int (*proc)(Display *display, GC gc, XExtCodes *codes);

int *XESetFreeGC(Display *display, int extension, int (*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when a GC is freed.

The
XESetFreeGC
function defines a procedure to be called whenever
a GC is freed.
It returns any previously defined procedure, usually NULL.

When a GC is freed,
your procedure is called with these arguments:

int (*proc)(Display *display, GC gc, XExtCodes *codes);

int *XESetCreateFont(Display *display, int extension, int (*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when a font is created.

The
XESetCreateFont
function defines a procedure to be called whenever
XLoadQueryFont
and
XQueryFont
are called.
It returns any previously defined procedure, usually NULL.

When
XLoadQueryFont
or
XQueryFont
is called,
your procedure is called with these arguments:

int (*proc)(Display *display, XFontStruct *fs, XExtCodes *codes);

int *XESetFreeFont(Display *display, int extension, int (*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when a font is freed.

The
XESetFreeFont
function defines a procedure to be called whenever
XFreeFont
is called.
It returns any previously defined procedure, usually NULL.

When
XFreeFont
is called, your procedure is called with these arguments:

int (*proc)(Display *display, XFontStruct *fs, XExtCodes *codes);

The
XESetWireToEvent
and
XESetEventToWire
functions allow you to define new events to the library.
An
XEvent
structure always has a type code (type
int)
as the first component.
This uniquely identifies what kind of event it is.
The second component is always the serial number (type
unsigned
long)
of the last request processed by the server.
The third component is always a Boolean (type
Bool)
indicating whether the event came from a
SendEvent
protocol request.
The fourth component is always a pointer to the display
the event was read from.
The fifth component is always a resource ID of one kind or another,
usually a window, carefully selected to be useful to toolkit dispatchers.
The fifth component should always exist, even if
the event does not have a natural destination;
if there is no value
from the protocol to put in this component, initialize it to zero.

There is an implementation limit such that your host event
structure size cannot be bigger than the size of the
XEvent
union of structures.
There also is no way to guarantee that more than 24 elements or 96 characters
in the structure will be fully portable between machines.

int *XESetWireToEvent(Display *display, int event_number, Status (*proc)());

display	Specifies the connection to the X server.
event_number	Specifies the event code.
proc	Specifies the procedure to call when converting an event.

The
XESetWireToEvent
function defines a procedure to be called when an event
needs to be converted from wire format
(xEvent)
to host format
(XEvent).
The event number defines which protocol event number to install a
conversion procedure for.
XESetWireToEvent
returns any previously defined procedure.

You can replace a core event conversion function with one
of your own, although this is not encouraged.
It would, however, allow you to intercept a core event
and modify it before being placed in the queue or otherwise examined.

When Xlib needs to convert an event from wire format to host
format, your procedure is called with these arguments:

int (*proc)(Display *display, XEvent *re, xEvent *event);

Your procedure must return status to indicate if the conversion succeeded.
The re argument is a pointer to where the host format event should be stored,
and the event argument is the 32-byte wire event structure.
In the
XEvent
structure you are creating,
you must fill in the five required members of the event structure.
You should fill in the type member with the type specified for the
xEvent
structure.
You should copy all other members from the
xEvent
structure (wire format) to the
XEvent
structure (host format).
Your conversion procedure should return
True
if the event should be placed in the queue or
False
if it should not be placed in the queue.

To initialize the serial number component of the event, call
_XSetLastRequestRead
with the event and use the return value.

unsigned long_XSetLastRequestRead(Display *display, xGenericReply *rep);

display	Specifies the connection to the X server.
rep	Specifies the wire event structure.

The
_XSetLastRequestRead
function computes and returns a complete serial number from the partial
serial number in the event.

Status *XESetEventToWire(Display *display, int event_number, int (*proc)());

display	Specifies the connection to the X server.
event_number	Specifies the event code.
proc	Specifies the procedure to call when converting an event.

The
XESetEventToWire
function defines a procedure to be called when an event
needs to be converted from host format
(XEvent)
to wire format
(xEvent)
form.
The event number defines which protocol event number to install a
conversion procedure for.
XESetEventToWire
returns any previously defined procedure.
It returns zero if the conversion fails or nonzero otherwise.

When Xlib needs to convert an event from host format to wire format,
your procedure is called with these arguments:

int (*proc)(Display *display, XEvent *re, xEvent *event);

The re argument is a pointer to the host format event,
and the event argument is a pointer to where the 32-byte wire event
structure should be stored.
You should fill in the type with the type from the
XEvent
structure.
All other members then should be copied from the host format to the
xEvent
structure.

Bool *XESetWireToError(Display *display, int error_number, Bool (*proc)());

display	Specifies the connection to the X server.
error_number	Specifies the error code.
proc	Specifies the procedure to call when an error is received.

The
XESetWireToError
function defines a procedure to be called when an extension
error needs to be converted from wire format to host format.
The error number defines which protocol error code to install
the conversion procedure for.
XESetWireToError
returns any previously defined procedure.

Use this function for extension errors that contain additional error values
beyond those in a core X error, when multiple wire errors must be combined
into a single Xlib error, or when it is necessary to intercept an
X error before it is otherwise examined.

When Xlib needs to convert an error from wire format to host format,
the procedure is called with these arguments:

int (*proc)(Display *display, XErrorEvent *he, xError *we);

The he argument is a pointer to where the host format error should be stored.
The structure pointed at by he is guaranteed to be as large as an
XEvent
structure and so can be cast to a type larger than an
XErrorEvent
to store additional values.
If the error is to be completely ignored by Xlib
(for example, several protocol error structures will be combined into
one Xlib error),
then the function should return
False;
otherwise, it should return
True.

int *XESetError(Display *display, int extension, int (*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when an error is received.

Inside Xlib, there are times that you may want to suppress the
calling of the external error handling when an error occurs.
This allows status to be returned on a call at the cost of the call
being synchronous (though most such functions are query operations, in any
case, and are typically programmed to be synchronous).

When Xlib detects a protocol error in
_XReply,
it calls your procedure with these arguments:

int (*proc)(Display *display, xError *err, XExtCodes *codes, int *ret_code);

The err argument is a pointer to the 32-byte wire format error.
The codes argument is a pointer to the extension codes structure.
The ret_code argument is the return code you may want
_XReply
returned to.

If your procedure returns a zero value,
the error is not suppressed, and
the client's error handler is called.
(For further information,
see section 11.8.2.)
If your procedure returns nonzero,
the error is suppressed, and
_XReply
returns the value of ret_code.

char *XESetErrorString(Display *display, int extension, char *(*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call to obtain an error string.

The
XGetErrorText
function returns a string to the user for an error.
XESetErrorString
allows you to define a procedure to be called that
should return a pointer to the error message.
The following is an example.

int (*proc)(Display *display, int code, XExtCodes *codes, char *buffer, int nbytes);

Your procedure is called with the error code for every error detected.
You should copy nbytes of a null-terminated string containing the
error message into buffer.

void *XESetPrintErrorValues(Display *display, int extension, void (*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when an error is printed.

The
XESetPrintErrorValues
function defines a procedure to be called when an extension
error is printed, to print the error values.
Use this function for extension errors that contain additional error values
beyond those in a core X error.
It returns any previously defined procedure.

When Xlib needs to print an error,
the procedure is called with these arguments:

void (*proc)(Display *display, XErrorEvent *ev, void *fp);

The structure pointed at by ev is guaranteed to be as large as an
XEvent
structure and so can be cast to a type larger than an
XErrorEvent
to obtain additional values set by using
XESetWireToError.
The underlying type of the fp argument is system dependent;
on a POSIX-compliant system, fp should be cast to type FILE*.

int *XESetFlushGC(Display *display, int extension, int *(*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when a GC is flushed.

The procedure set by the
XESetFlushGC
function has the same interface as the procedure set by the
XESetCopyGC
function, but is called when a GC cache needs to be updated in the server.

int *XESetCopyGC(Display *display, int extension, int *(*proc)());

display	Specifies the connection to the X server.
extension	Specifies the extension number.
proc	Specifies the procedure to call when a buffer is flushed.

The
XESetBeforeFlush
function defines a procedure to be called when data is about to be
sent to the server. When data is about to be sent, your procedure is
called one or more times with these arguments:

void (*proc)(Display *display, XExtCodes *codes, char *data, long len);

The data argument specifies a portion of the outgoing data buffer,
and its length in bytes is specified by the len argument.
Your procedure must not alter the contents of the data and must not
do additional protocol requests to the same display.

Hooks onto Xlib Data Structures

Various Xlib data structures have provisions for extension procedures
to chain extension supplied data onto a list.
These structures are
GC,
Visual,
Screen,
ScreenFormat,
Display,
and
XFontStruct.
Because the list pointer is always the first member in the structure,
a single set of procedures can be used to manipulate the data
on these lists.

The following structure is used in the functions in this section
and is defined in
<X11/Xlib.h>

typedef struct _XExtData {
	int number;	/* number returned by XInitExtension */
	struct _XExtData *next;	/* next item on list of data for structure */
	int (*free_private)();	/* if defined,  called to free private */
	XPointer private_data;	/* data private to this extension. */
} XExtData;

When any of the data structures listed above are freed,
the list is walked, and the structure's free procedure (if any) is called.
If free is NULL,
then the library frees both the data pointed to by the private_data member
and the structure itself.

union {	Display *display;
	GC gc;
	Visual *visual;
	Screen *screen;
	ScreenFormat *pixmap_format;
	XFontStruct *font } XEDataObject;

XExtData **XEHeadOfExtensionList(XEDataObject object);

object

Specifies the object.

The
XEHeadOfExtensionList
function returns a pointer to the list of extension structures attached
to the specified object.
In concert with
XAddToExtensionList,
XEHeadOfExtensionList
allows an extension to attach arbitrary data to any of the structures
of types contained in
XEDataObject.

XAddToExtensionList(XExtData **structure, XExtData *ext_data);

structure	Specifies the extension list.
ext_data	Specifies the extension data structure to add.

The structure argument is a pointer to one of the data structures
enumerated above.
You must initialize ext_data->number with the extension number
before calling this function.

XExtData *XFindOnExtensionList(struct_XExtData **structure, int number);

structure	Specifies the extension list.
number	Specifies the extension number from `XInitExtension`.

The
XFindOnExtensionList
function returns the first extension data structure
for the extension numbered number.
It is expected that an extension will add at most one extension
data structure to any single data structure's extension data list.
There is no way to find additional structures.

The
XAllocID
macro, which allocates and returns a resource ID, is defined in
<X11/Xlib.h>.

XAllocID(Display *display);

display

Specifies the connection to the X server.

This macro is a call through the
Display
structure to an internal resource ID allocator.
It returns a resource ID that you can use when creating new resources.

The
XAllocIDs
macro allocates and returns an array of resource ID.

XAllocIDs(Display *display, XID *ids_return, int count);

display	Specifies the connection to the X server.
ids_return	Returns the resource IDs.
rep	Specifies the number of resource IDs requested.

This macro is a call through the
Display
structure to an internal resource ID allocator.
It returns resource IDs to the array supplied by the caller.
To correctly handle automatic reuse of resource IDs, you must call
XAllocIDs
when requesting multiple resource IDs. This call might generate
protocol requests.

GC Caching

GCs are cached by the library to allow merging of independent change
requests to the same GC into single protocol requests.
This is typically called a write-back cache.
Any extension procedure whose behavior depends on the contents of a GC
must flush the GC cache to make sure the server has up-to-date contents
in its GC.

The
FlushGC
macro checks the dirty bits in the library's GC structure and calls
_XFlushGCCache
if any elements have changed.
The
FlushGC
macro is defined as follows:

FlushGC(Display *display, GC gc);

display	Specifies the connection to the X server.
gc	Specifies the GC.

Note that if you extend the GC to add additional resource ID components,
you should ensure that the library stub sends the change request immediately.
This is because a client can free a resource immediately after
using it, so if you only stored the value in the cache without
forcing a protocol request, the resource might be destroyed before being
set into the GC.
You can use the
_XFlushGCCache
procedure
to force the cache to be flushed.
The
_XFlushGCCache
procedure
is defined as follows:

_XFlushGCCache(Display *display, GC gc);

display	Specifies the connection to the X server.
gc	Specifies the GC.

Graphics Batching

If you extend X to add more poly graphics primitives, you may be able to
take advantage of facilities in the library to allow back-to-back
single calls to be transformed into poly requests.
This may dramatically improve performance of programs that are not
written using poly requests.
A pointer to an
xReq,
called last_req in the display structure, is the last request being processed.
By checking that the last request
type, drawable, gc, and other options are the same as the new one
and that there is enough space left in the buffer, you may be able
to just extend the previous graphics request by extending the length
field of the request and appending the data to the buffer.
This can improve performance by five times or more in naive programs.
For example, here is the source for the
XDrawPoint
stub.
(Writing extension stubs is discussed in the next section.)

#include <X11/Xlibint.h>

/* precompute the maximum size of batching request allowed */

static int size = sizeof(xPolyPointReq) + EPERBATCH * sizeof(xPoint);

XDrawPoint(dpy, d, gc, x, y)
    register Display *dpy;
    Drawable d;
    GC gc;
    int x, y; /* INT16 */
{
    xPoint *point;
    LockDisplay(dpy);
    FlushGC(dpy, gc);
    {
    register xPolyPointReq *req = (xPolyPointReq *) dpy->last_req;
    /* if same as previous request, with same drawable, batch requests */
    if (
          (req->reqType == X_PolyPoint)
       && (req->drawable == d)
       && (req->gc == gc->gid)
       && (req->coordMode == CoordModeOrigin)
       && ((dpy->bufptr + sizeof (xPoint)) <= dpy->bufmax)
       && (((char *)dpy->bufptr - (char *)req) < size) ) {
         point = (xPoint *) dpy->bufptr;
         req->length += sizeof (xPoint) >> 2;
         dpy->bufptr += sizeof (xPoint);
         }

    else {
        GetReqExtra(PolyPoint, 4, req); /* 1 point = 4 bytes */
        req->drawable = d;
        req->gc = gc->gid;
        req->coordMode = CoordModeOrigin;
        point = (xPoint *) (req + 1);
        }
    point->x = x;
    point->y = y;
    }
    UnlockDisplay(dpy);
    SyncHandle();
}

To keep clients from generating very long requests that may monopolize the
server,
there is a symbol defined in
<X11/Xlibint.h>
of EPERBATCH on the number of requests batched.
Most of the performance benefit occurs in the first few merged requests.
Note that
FlushGC
is called before picking up the value of last_req,
because it may modify this field.

Writing Extension Stubs

All X requests always contain the length of the request,
expressed as a 16-bit quantity of 32 bit words.
This means that a single request can be no more than 256K bytes in
length.
Some servers may not support single requests of such a length.
The value of dpy->max_request_size contains the maximum length as
defined by the server implementation.
For further information,
see X Window System Protocol.

Requests, Replies, and Xproto.h

The
<X11/Xproto.h>
file contains three sets of definitions that
are of interest to the stub implementor:
request names, request structures, and reply structures.

You need to generate a file equivalent to
<X11/Xproto.h>
for your extension and need to include it in your stub procedure.
Each stub procedure also must include
<X11/Xlibint.h>.

The identifiers are deliberately chosen in such a way that, if the
request is called X_DoSomething, then its request structure is
xDoSomethingReq, and its reply is xDoSomethingReply.
The GetReq family of macros, defined in
<X11/Xlibint.h>,
takes advantage of this naming scheme.

For each X request,
there is a definition in
<X11/Xproto.h>
that looks similar to this:

#define X_DoSomething   42

In your extension header file,
this will be a minor opcode,
instead of a major opcode.

Request Format

Every request contains an 8-bit major opcode and a 16-bit length field
expressed in units of 4 bytes.
Every request consists of 4 bytes of header
(containing the major opcode, the length field, and a data byte) followed by
zero or more additional bytes of data.
The length field defines the total length of the request, including the header.
The length field in a request must equal the minimum length required to contain
the request.
If the specified length is smaller or larger than the required length,
the server should generate a
BadLength
error.
Unused bytes in a request are not required to be zero.
Extensions should be designed in such a way that long protocol requests
can be split up into smaller requests,
if it is possible to exceed the maximum request size of the server.
The protocol guarantees the maximum request size to be no smaller than
4096 units (16384 bytes).

Major opcodes 128 through 255 are reserved for extensions.
Extensions are intended to contain multiple requests,
so extension requests typically have an additional minor opcode encoded
in the second data byte in the request header,
but the placement and interpretation of this minor opcode as well as all
other fields in extension requests are not defined by the core protocol.
Every request is implicitly assigned a sequence number (starting with one)
used in replies, errors, and events.

Most protocol requests have a corresponding structure typedef in
<X11/Xproto.h>,
which looks like:

typedef struct _DoSomethingReq {
	CARD8 reqType;		/* X_DoSomething */
	CARD8 someDatum;	/* used differently in different requests */
	CARD16 length;		/* total # of bytes in request, divided by 4 */
	...
	/* request-specific data */
	...
} xDoSomethingReq;

If a core protocol request has a single 32-bit argument,
you need not declare a request structure in your extension header file.
Instead, such requests use the
xResourceReq
structure in
<X11/Xproto.h>.
This structure is used for any request whose single argument is a
Window,
Pixmap,
Drawable,
GContext,
Font,
Cursor,
Colormap,
Atom,
or
VisualID.

typedef struct _ResourceReq {
	CARD8 reqType;	/* the request type, e.g. X_DoSomething */
	BYTE pad;	/* not used */
	CARD16 length;	/* 2 (= total # of bytes in request, divided by 4) */
	CARD32 id;	/* the Window, Drawable, Font, GContext, etc. */
} xResourceReq;

If convenient,
you can do something similar in your extension header file.

In both of these structures,
the reqType field identifies the type of the request (for example,
X_MapWindow or X_CreatePixmap).
The length field tells how long the request is
in units of 4-byte longwords.
This length includes both the request structure itself and any
variable-length data, such as strings or lists, that follow the
request structure.
Request structures come in different sizes,
but all requests are padded to be multiples of four bytes long.

A few protocol requests take no arguments at all.
Instead, they use the
xReq
structure in
<X11/Xproto.h>,
which contains only a reqType and a length (and a pad byte).

If the protocol request requires a reply,
then
<X11/Xproto.h>
also contains a reply structure typedef:

typedef struct _DoSomethingReply {
	BYTE type;	/* always X_Reply */
	BYTE someDatum;	/* used differently in different requests */
	CARD16 sequenceNumber;	/* # of requests sent so far */
	CARD32 length;	/* # of additional bytes, divided by 4 */
	...
	/* request-specific data */
	...
} xDoSomethingReply;

Most of these reply structures are 32 bytes long.
If there are not that many reply values,
then they contain a sufficient number of pad fields
to bring them up to 32 bytes.
The length field is the total number of bytes in the request minus 32,
divided by 4.
This length will be nonzero only if:

The reply structure is followed by variable-length data,
such as a list or string.
The reply structure is longer than 32 bytes.

Only
GetWindowAttributesl,
QueryFont,
QueryKeymap,
and
GetKeyboardControl
have reply structures longer than 32 bytes in the core protocol.

A few protocol requests return replies that contain no data.
<X11/Xproto.h>
does not define reply structures for these.
Instead, they use the
xGenericReply
structure, which contains only a type, length,
and sequence number (and sufficient padding to make it 32 bytes long).

Starting to Write a Stub Procedure

An Xlib stub procedure should start like this:

#include "<X11/Xlibint.h>

XDoSomething (arguments, ... )
/* argument declarations */
{

register XDoSomethingReq *req;
...

If the protocol request has a reply,
then the variable declarations should include the reply structure for the request.
The following is an example:

xDoSomethingReply rep;

Locking Data Structures

To lock the display structure for systems that
want to support multithreaded access to a single display connection,
each stub will need to lock its critical section.
Generally, this section is the point from just before the appropriate GetReq
call until all arguments to the call have been stored into the buffer.
The precise instructions needed for this locking depend upon the machine
architecture.
Two calls, which are generally implemented as macros, have been provided.

LockDisplay(Display *display);

UnlockDisplay(Display *display);

display

Specifies the connection to the X server.

Sending the Protocol Request and Arguments

After the variable declarations,
a stub procedure should call one of four macros defined in
<X11/Xlibint.h>:
GetReq,
GetReqExtra,
GetResReq,
or
GetEmptyReq.
All of these macros take, as their first argument,
the name of the protocol request as declared in
<X11/Xproto.h>
except with X_ removed.
Each one declares a
Display
structure pointer,
called dpy, and a pointer to a request structure, called req,
which is of the appropriate type.
The macro then appends the request structure to the output buffer,
fills in its type and length field, and sets req to point to it.

If the protocol request has no arguments (for instance, X_GrabServer),
then use
GetEmptyReq.

GetEmptyReq (DoSomething, req);

If the protocol request has a single 32-bit argument (such as a
Pixmap,
Window,
Drawable,
Atom,
and so on),
then use
GetResReq.
The second argument to the macro is the 32-bit object.
X_MapWindow
is a good example.

GetResReq (DoSomething, rid, req);

The rid argument is the
Pixmap,
Window,
or other resource ID.

If the protocol request takes any other argument list,
then call
GetReq.
After the
GetReq,
you need to set all the other fields in the request structure,
usually from arguments to the stub procedure.

GetReq (DoSomething, req);
/* fill in arguments here */
req->arg1 = arg1;
req->arg2 = arg2;
...

A few stub procedures (such as
XCreateGC
and
XCreatePixmap)
return a resource ID to the caller but pass a resource ID as an argument
to the protocol request.
Such procedures use the macro
XAllocID
to allocate a resource ID from the range of IDs
that were assigned to this client when it opened the connection.

rid = req->rid = XAllocID();
...
return (rid);

Finally, some stub procedures transmit a fixed amount of variable-length
data after the request.
Typically, these procedures (such as
XMoveWindow
and
XSetBackground)
are special cases of more general functions like
XMoveResizeWindow
and
XChangeGC.
These procedures use
GetReqExtra,
which is the same as
GetReq
except that it takes an additional argument (the number of
extra bytes to allocate in the output buffer after the request structure).
This number should always be a multiple of four. Note that it is possible
for req to be set to NULL as a defensive measure if the requested length
exceeds the Xlib's buffer size (normally 16K).

Variable Length Arguments

Some protocol requests take additional variable-length data that
follow the
xDoSomethingReq
structure.
The format of this data varies from request to request.
Some requests require a sequence of 8-bit bytes,
others a sequence of 16-bit or 32-bit entities,
and still others a sequence of structures.

It is necessary to add the length of any variable-length data to the
length field of the request structure.
That length field is in units of 32-bit longwords.
If the data is a string or other sequence of 8-bit bytes,
then you must round the length up and shift it before adding:

req->length += (nbytes+3)>>2;

To transmit variable-length data, use the
Data
macros.
If the data fits into the output buffer,
then this macro copies it to the buffer.
If it does not fit, however,
the
Data
macro calls
_XSend,
which transmits first the contents of the buffer and then your data.
The
Data
macros take three arguments:
the display, a pointer to the beginning of the data,
and the number of bytes to be sent.

Data(display, (char *) data, nbytes);

Data16(display, (short *) data, nbytes);

Data32(display, (long *) data, nbytes);

Data,
Data16,
and
Data32
are macros that may use their last argument
more than once, so that argument should be a variable rather than
an expression such as “nitems*sizeof(item)”.
You should do that kind of computation in a separate statement before calling
them.
Use the appropriate macro when sending byte, short, or long data.

If the protocol request requires a reply,
then call the procedure
_XSend
instead of the
Data
macro.
_XSend
takes the same arguments, but because it sends your data immediately instead of
copying it into the output buffer (which would later be flushed
anyway by the following call on
_XReply),
it is faster.

Replies

If the protocol request has a reply,
then call
_XReply
after you have finished dealing with
all the fixed-length and variable-length arguments.
_XReply
flushes the output buffer and waits for an
xReply
packet to arrive.
If any events arrive in the meantime,
_XReply
places them in the queue for later use.

Status _XReply(Display *display, xReply *rep, int extra, Bool discard);

display	Specifies the connection to the X server.
rep	Specifies the reply structure.
extra	Specifies the number of 32-bit words expected after the replay.
discard	Specifies if any data beyond that specified in the extra argument should be discarded.

The
_XReply
function waits for a reply packet and copies its contents into the
specified rep.
_XReply
handles error and event packets that occur before the reply is received.
_XReply
takes four arguments:

A
Display
* structure
A pointer to a reply structure (which must be cast to an
xReply
*)
The number of additional 32-bit words (beyond
sizeof( xReply)
= 32 bytes)
in the reply structure
A Boolean that indicates whether
_XReply
is to discard any additional bytes
beyond those it was told to read

Because most reply structures are 32 bytes long,
the third argument is usually 0.
The only core protocol exceptions are the replies to
GetWindowAttributesl,
QueryFont,
QueryKeymap,
and
GetKeyboardControl,
which have longer replies.

The last argument should be
False
if the reply structure is followed
by additional variable-length data (such as a list or string).
It should be
True
if there is not any variable-length data.

This last argument is provided for upward-compatibility reasons
to allow a client to communicate properly with a hypothetical later
version of the server that sends more data than the client expected.
For example, some later version of
GetWindowAttributesl
might use a
larger, but compatible,
xGetWindowAttributesReply
that contains additional attribute data at the end.

_XReply
returns
True
if it received a reply successfully or
False
if it received any sort of error.

For a request with a reply that is not followed by variable-length
data, you write something like:

_XReply(display, (xReply *)&rep, 0, True);
*ret1 = rep.ret1;
*ret2 = rep.ret2;
*ret3 = rep.ret3;
...
UnlockDisplay(dpy);
SyncHandle();
return (rep.ret4);
}

If there is variable-length data after the reply,
change the
True
to
False,
and use the appropriate
_XRead
function to read the variable-length data.

_XRead(Display *display, char *data_return, long nbytes);

display	Specifies the connection to the X server.
data_return	Specifies the buffer.
nbytes	Specifies the number of bytes required.

The
_XRead
function reads the specified number of bytes into data_return.

_XRead16(Display *display, short *data_return, long nbytes);

display	Specifies the connection to the X server.
data_return	Specifies the buffer.
nbytes	Specifies the number of bytes required.

The
_XRead16
function reads the specified number of bytes,
unpacking them as 16-bit quantities,
into the specified array as shorts.

_XRead32(Display *display, long *data_return, long nbytes);

display	Specifies the connection to the X server.
data_return	Specifies the buffer.
nbytes	Specifies the number of bytes required.

The
_XRead32
function reads the specified number of bytes,
unpacking them as 32-bit quantities,
into the specified array as longs.

_XRead16Pad(Display *display, short *data_return, long nbytes);

display	Specifies the connection to the X server.
data_return	Specifies the buffer.
nbytes	Specifies the number of bytes required.

The
_XRead16Pad
function reads the specified number of bytes,
unpacking them as 16-bit quantities,
into the specified array as shorts.
If the number of bytes is not a multiple of four,
_XRead16Pad
reads and discards up to two additional pad bytes.

_XReadPad(Display *display, char *data_return, long nbytes);

display	Specifies the connection to the X server.
data_return	Specifies the buffer.
nbytes	Specifies the number of bytes required.

The
_XReadPad
function reads the specified number of bytes into data_return.
If the number of bytes is not a multiple of four,
_XReadPad
reads and discards up to three additional pad bytes.

Each protocol request is a little different.
For further information,
see the Xlib sources for examples.

Synchronous Calling

Each procedure should have a call, just before returning to the user,
to a macro called
SyncHandle.
If synchronous mode is enabled (see
XSynchronize),
the request is sent immediately.
The library, however, waits until any error the procedure could generate
at the server has been handled.

Allocating and Deallocating Memory

To support the possible reentry of these procedures,
you must observe several conventions when allocating and deallocating memory,
most often done when returning data to the user from the window
system of a size the caller could not know in advance
(for example, a list of fonts or a list of extensions).
The standard C library functions on many systems
are not protected against signals or other multithreaded uses.
The following analogies to standard I/O library functions
have been defined:

These should be used in place of any calls you would make to the normal
C library functions.

If you need a single scratch buffer inside a critical section
(for example, to pack and unpack data to and from the wire protocol),
the general memory allocators may be too expensive to use
(particularly in output functions, which are performance critical).
The following function returns a scratch buffer for use within a
critical section:

char *_XAllocScratch(Display *display, unsigned long nbytes);

display	Specifies the connection to the X server.
nbytes	Specifies the number of bytes required.

This storage must only be used inside of a critical section of your
stub. The returned pointer cannot be assumed valid after any call
that might permit another thread to execute inside Xlib. For example,
the pointer cannot be assumed valid after any use of the
GetReq
or
Data
families of macros,
after any use of
_XReply,
or after any use of the
_XSend
or
_XRead
families of functions.

The following function returns a scratch buffer for use across
critical sections:

char *_XAllocTemp(Display *display, unsigned long nbytes);

display	Specifies the connection to the X server.
nbytes	Specifies the number of bytes required.

This storage can be used across calls that might permit another thread to
execute inside Xlib. The storage must be explicitly returned to Xlib.
The following function returns the storage:

void _XFreeTemp(Display *display, char *buf, unsigned long nbytes);

display	Specifies the connection to the X server.
buf	Specifies the buffer to return.
nbytes	Specifies the size of the buffer.

You must pass back the same pointer and size that were returned by
_XAllocTemp.

Portability Considerations

Many machine architectures
do not correctly or efficiently access data at unaligned locations;
their compilers pad out structures to preserve this characteristic.
Many other machines capable of unaligned references pad inside of structures
as well to preserve alignment, because accessing aligned data is
usually much faster.
Because the library and the server use structures to access data at
arbitrary points in a byte stream,
all data in request and reply packets must be naturally aligned;
that is, 16-bit data starts on 16-bit boundaries in the request
and 32-bit data on 32-bit boundaries.
All requests must be a multiple of 32 bits in length to preserve
the natural alignment in the data stream.
You must pad structures out to 32-bit boundaries.
Pad information does not have to be zeroed unless you want to
preserve such fields for future use in your protocol requests,
but it is recommended to zero it to avoid inadvertant data leakage
and improve compressability.
Floating point varies radically between machines and should be
avoided completely if at all possible.

This code may run on machines with 16-bit ints.
So, if any integer argument, variable, or return value either can take
only nonnegative values or is declared as a
CARD16
in the protocol, be sure to declare it as
unsigned
int
and not as
int.
(This, of course, does not apply to Booleans or enumerations.)

Similarly,
if any integer argument or return value is declared
CARD32
in the protocol,
declare it as an
unsigned
long
and not as
int
or
long.
This also goes for any internal variables that may
take on values larger than the maximum 16-bit
unsigned
int.

The library has always assumed that a
char
is 8 bits, a
short
is 16 bits, an
int
is 16 or 32 bits, and a
long
is 32 bits.
Unfortunately, this assumption remains on machines where a long
can hold 64-bits, and many functions and structures require unnecessarily
large fields to avoid breaking compatibility with existing code. Special
care must be taken with arrays of values that are transmitted in the
protocol as CARD32 or INT32 but have to be converted to arrays of 64-bit
long when passed to or from client applications.

The
PackData
macro is a half-hearted attempt to deal with the possibility of 32 bit shorts.
However, much more work is needed to make this work properly.

Deriving the Correct Extension Opcode

The remaining problem a writer of an extension stub procedure faces that
the core protocol does not face is to map from the call to the proper
major and minor opcodes.
While there are a number of strategies,
the simplest and fastest is outlined below.

Declare an array of pointers, _NFILE long (this is normally found
in
<stdio.h>
and is the number of file descriptors supported on the system)
of type
XExtCodes.
Make sure these are all initialized to NULL.
When your stub is entered, your initialization test is just to use
the display pointer passed in to access the file descriptor and an index
into the array.
If the entry is NULL, then this is the first time you
are entering the procedure for this display.
Call your initialization procedure and pass to it the display pointer.
Once in your initialization procedure, call
XInitExtension;
if it succeeds, store the pointer returned into this array.
Make sure to establish a close display handler to allow you to zero the entry.
Do whatever other initialization your extension requires.
(For example, install event handlers and so on.)
Your initialization procedure would normally return a pointer to the
XExtCodes
structure for this extension, which is what would normally
be found in your array of pointers.
After returning from your initialization procedure,
the stub can now continue normally, because it has its major opcode safely
in its hand in the
XExtCodes
structure.

Appendix D. Compatibility Functions

Table of Contents

X Version 11 Compatibility FunctionsSetting Standard PropertiesSetting and Getting Window Sizing HintsGetting and Setting an XStandardColormap StructureParsing Window GeometryGetting the X Environment DefaultsX Version 10 Compatibility FunctionsDrawing and Filling Polygons and CurvesAssociating User Data with a Value

The X Version 11 and X Version 10 functions discussed in this appendix
are obsolete, have been superseded by newer X Version 11 functions,
and are maintained for compatibility reasons only.

X Version 11 Compatibility Functions

You can use the X Version 11 compatibility functions to:

Set standard properties
Set and get window sizing hints
Set and get an
XStandardColormap
structure
Parse window geometry
Get X environment defaults

Setting Standard Properties

To specify a minimum set of properties describing the simplest application,
use
XSetStandardProperties.
This function has been superseded by
XSetWMProperties
and sets all or portions of the
WM_NAME, WM_ICON_NAME, WM_HINTS, WM_COMMAND,
and WM_NORMAL_HINTS properties.

XSetStandardProperties(Display *display, Window w, char *window_name, char *icon_name, Pixmap icon_pixmap, char **argv, int argc, XSizeHints *hints);

display	Specifies the connection to the X server.
w	Specifies the window.
window_name	Specifies the window name, which should be a null-terminated string.
icon_name	Specifies the icon name, which should be a null-terminated string.
icon_pixmap	Specifies the bitmap that is to be used for the icon or None.
argv	Specifies the application's argument list.
argc	Specifies the number of arguments.
hints	Specifies a pointer to the size hints for the window in its normal state.

The
XSetStandardProperties
function provides a means by which simple applications set the
most essential properties with a single call.
XSetStandardProperties
should be used to give a window manager some information about
your program's preferences.
It should not be used by applications that need
to communicate more information than is possible with
XSetStandardProperties.
(Typically, argv is the argv array of your main program.)
If the strings are not in the Host Portable Character Encoding,
the result is implementation-dependent.

XSetStandardProperties
can generate
BadAlloc
and
BadWindow
errors.

Setting and Getting Window Sizing Hints

Xlib provides functions that you can use to set or get window sizing hints.
The functions discussed in this section use the flags and the
XSizeHints
structure, as defined in the
<X11/Xutil.h>

header file and use the WM_NORMAL_HINTS property.

To set the size hints for a given window in its normal state, use
XSetNormalHints.
This function has been superseded by
XSetWMNormalHints.

XSetNormalHints(Display *display, Window w, XSizeHints *hints);

display	Specifies the connection to the X server.
w	Specifies the window.
hints	Specifies a pointer to the size hints for the window in its normal state.

The
XSetNormalHints
function sets the size hints structure for the specified window.
Applications use
XSetNormalHints
to inform the window manager of the size
or position desirable for that window.
In addition,
an application that wants to move or resize itself should call
XSetNormalHints
and specify its new desired location and size
as well as making direct Xlib calls to move or resize.
This is because window managers may ignore redirected
configure requests, but they pay attention to property changes.

To set size hints,
an application not only must assign values to the appropriate members
in the hints structure but also must set the flags member of the structure
to indicate which information is present and where it came from.
A call to
XSetNormalHints
is meaningless, unless the flags member is set to indicate which members of
the structure have been assigned values.

XSetNormalHints
can generate
BadAlloc
and
BadWindow
errors.

To return the size hints for a window in its normal state, use
XGetNormalHints.
This function has been superseded by
XGetWMNormalHints.

Status XGetNormalHints(Display *display, Window w, XSizeHints *hints_return);

display	Specifies the connection to the X server.
w	Specifies the window.
hints_return	Returns the size hints for the window in its normal state.

The
XGetNormalHints
function returns the size hints for a window in its normal state.
It returns a nonzero status if it succeeds or zero if
the application specified no normal size hints for this window.

XGetNormalHints
can generate a
BadWindow
error.

The next two functions set and read the WM_ZOOM_HINTS property.

To set the zoom hints for a window, use
XSetZoomHints.
This function is no longer supported by the
Inter-Client Communication Conventions Manual.

XSetZoomHints(Display *display, Window w, XSizeHints *zhints);

display	Specifies the connection to the X server.
w	Specifies the window.
zhints	Specifies a pointer to the zoom hints.

Many window managers think of windows in one of three states:
iconic, normal, or zoomed.
The
XSetZoomHints
function provides the window manager with information for the window in the
zoomed state.

XSetZoomHints
can generate
BadAlloc
and
BadWindow
errors.

To read the zoom hints for a window, use
XGetZoomHints.
This function is no longer supported by the
Inter-Client Communication Conventions Manual.

Status XGetZoomHints(Display *display, Window w, XSizeHints *zhints_return);

display	Specifies the connection to the X server.
w	Specifies the window.
zhints_return	Returns the zoom hints.

The
XGetZoomHints
function returns the size hints for a window in its zoomed state.
It returns a nonzero status if it succeeds or zero if
the application specified no zoom size hints for this window.

XGetZoomHints
can generate a
BadWindow
error.

To set the value of any property of type WM_SIZE_HINTS, use
XSetSizeHints.
This function has been superseded by
XSetWMSizeHints.

XSetSizeHints(Display *display, Window w, XSizeHints *hints, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
hints	Specifies a pointer to the size hints.
property	Specifies the property name.

The
XSetSizeHints
function sets the
XSizeHints
structure for the named property and the specified window.
This is used by
XSetNormalHints
and
XSetZoomHints
and can be used to set the value of any property of type WM_SIZE_HINTS.
Thus, it may be useful if other properties of that type get defined.

XSetSizeHints
can generate
BadAlloc,
BadAtom,
and
BadWindow
errors.

To read the value of any property of type WM_SIZE_HINTS, use
XGetSizeHints.
This function has been superseded by
XGetWMSizeHints.

Status XGetSizeHints(Display *display, Window w, XSizeHints *hints_return, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
hints_return	Returns the size hints.
property	Specifies the property name.

The
XGetSizeHints
function returns the
XSizeHints
structure for the named property and the specified window.
This is used by
XGetNormalHints
and
XGetZoomHints.
It also can be used to retrieve the value of any property of type
WM_SIZE_HINTS.
Thus, it may be useful if other properties of that type get defined.
XGetSizeHints
returns a nonzero status if a size hint was defined
or zero otherwise.

XGetSizeHints
can generate
BadAtom
and
BadWindow
errors.

Getting and Setting an XStandardColormap Structure

To get the
XStandardColormap
structure associated with one of the described atoms, use
XGetStandardColormap.
This function has been superseded by
XGetRGBColormaps.

Status XGetStandardColormap(Display *display, Window w, XStandardColormap *colormap_return, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
colormap_return	Returns the colormap associated with the specified atom.
property	Specifies the property name.

The
XGetStandardColormap
function returns the colormap definition associated with the atom supplied
as the property argument.
XGetStandardColormap
returns a nonzero status if successful and zero otherwise.
For example,
to fetch the standard
GrayScale
colormap for a display,
you use
XGetStandardColormap
with the following syntax:

XGetStandardColormap(dpy, DefaultRootWindow(dpy), &cmap, XA_RGB_GRAY_MAP);

See section 14.3 for the
semantics of standard colormaps.

XGetStandardColormap
can generate
BadAtom
and
BadWindow
errors.

To set a standard colormap, use
XSetStandardColormap.
This function has been superseded by
XSetRGBColormaps.

XSetStandardColormap(Display *display, Window w, XStandardColormap *colormap, Atom property);

display	Specifies the connection to the X server.
w	Specifies the window.
colormap	Specifies the colormap.
property	Specifies the property name.

The
XSetStandardColormap
function usually is only used by window or session managers.

XSetStandardColormap
can generate
BadAlloc,
BadAtom,
BadDrawable,
and
BadWindow
errors.

Parsing Window Geometry

To parse window geometry given a user-specified position
and a default position, use
XGeometry.
This function has been superseded by
XWMGeometry.

int XGeometry(Display *display, int screen, char *position, char *default_position, unsigned int bwidth, unsigned int fwidth, unsigned int fheight, int xadder, int yadder, int *x_return, int *y_return, int *width_return, int *height_return);

display	Specifies the connection to the X server.
screen	Specifies the screen.
position
default_position	Specify the geometry specifications.
bwidth	Specifies the border width.
fheight
fwidth	Specify the font height and width in pixels (increment size).
xadder
yadder	Specify additional interior padding needed in the window.
x_return
y_return	Return the x and y offsets.
width_return
height_return	Return the width and height determined.

You pass in the border width (bwidth),
size of the increments fwidth and fheight
(typically font width and height),
and any additional interior space (xadder and yadder)
to make it easy to compute the resulting size.
The
XGeometry
function returns the position the window should be placed given a position and
a default position.
XGeometry
determines the placement of
a window using a geometry specification as specified by
XParseGeometry
and the additional information about the window.
Given a fully qualified default geometry specification and
an incomplete geometry specification,
XParseGeometry
returns a bitmask value as defined above in the
XParseGeometry
call,
by using the position argument.

The returned width and height will be the width and height specified
by default_position as overridden by any user-specified position.
They are not affected by fwidth, fheight, xadder, or yadder.
The x and y coordinates are computed by using the border width,
the screen width and height, padding as specified by xadder and yadder,
and the fheight and fwidth times the width and height from the
geometry specifications.

Getting the X Environment Defaults

The
XGetDefault
function provides a primitive interface to the resource manager facilities
discussed in chapter 15.
It is only useful in very simple applications.

char *XGetDefault(Display *display, char *program, char *option);

display	Specifies the connection to the X server.
program	Specifies the program name for the Xlib defaults (usually argv[0] of the main program).
option	Specifies the option name.

The
XGetDefault
function returns the value of the resource prog.option,
where prog is the program argument with the directory prefix removed
and option must be a single component.
Note that multilevel resources cannot be used with
XGetDefault.
The class "Program.Name" is always used for the resource lookup.
If the specified option name does not exist for this program,
XGetDefault
returns NULL.
The strings returned by
XGetDefault
are owned by Xlib and should not be modified or freed by the client.

If a database has been set with
XrmSetDatabase,
that database is used for the lookup.
Otherwise, a database is created
and is set in the display (as if by calling
XrmSetDatabase).
The database is created in the current locale.
To create a database,
XGetDefault
uses resources from the RESOURCE_MANAGER property on the root
window of screen zero.
If no such property exists,
a resource file in the user's home directory is used.
On a POSIX-conformant system,
this file is
"$HOME/.Xdefaults".

After loading these defaults,
XGetDefault
merges additional defaults specified by the XENVIRONMENT
environment variable.
If XENVIRONMENT is defined,
it contains a full path name for the additional resource file.
If XENVIRONMENT is not defined,
XGetDefault
looks for
"$HOME/.Xdefaults-name" ,
where name specifies the name of the machine on which the application
is running.

X Version 10 Compatibility Functions

You can use the X Version 10 compatibility functions to:

Draw and fill polygons and curves
Associate user data with a value

Drawing and Filling Polygons and Curves

Xlib provides functions that you can use to draw or fill
arbitrary polygons or curves.
These functions are provided mainly for compatibility with X Version 10
and have no server support.
That is, they call other Xlib functions, not the server directly.
Thus, if you just have straight lines to draw, using
XDrawLines

or
XDrawSegments

is much faster.

The functions discussed here provide all the functionality of the
X Version 10 functions
XDraw,

XDrawFilled,

XDrawPatterned,

XDrawDashed,

and
XDrawTiled.

They are as compatible as possible given X Version 11's new line-drawing
functions.
One thing to note, however, is that
VertexDrawLastPoint
is no longer supported.
Also, the error status returned is the opposite of what it was under
X Version 10 (this is the X Version 11 standard error status).
XAppendVertex
and
XClearVertexFlag
from X Version 10 also are not supported.

Just how the graphics context you use is set up actually
determines whether you get dashes or not, and so on.
Lines are properly joined if they connect and include
the closing of a closed figure (see
XDrawLines).
The functions discussed here fail (return zero) only if they run out of memory
or are passed a
Vertex
list that has a
Vertex
with
VertexStartClosed
set that is not followed by a
Vertex
with
VertexEndClosed
set.

To achieve the effects of the X Version 10
XDraw,

XDrawDashed,

and
XDrawPatterned,

use
XDraw.

#include <X11/X10.h>

Status XDraw(Display *display, Drawable d, GC gc, Vertex *vlist, int vcount);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
vlist	Specifies a pointer to the list of vertices that indicate what to draw.
vcount	Specifies how many vertices are in vlist.

The
XDraw
function draws an arbitrary polygon or curve.
The figure drawn is defined by the specified list of vertices (vlist).
The points are connected by lines as specified in the flags in the
vertex structure.

Each Vertex, as defined in
<X11/X10.h>,

is a structure with the following members:

typedef struct _Vertex {
	short x,y;
	unsigned short flags;
} Vertex;

The x and y members are the coordinates of the vertex
that are relative to either the upper left inside corner of the drawable
(if
VertexRelative
is zero) or the previous vertex (if
VertexRelative
is one).

The flags, as defined in
<X11/X10.h>,

are as follows:

VertexRelative     0x0001     /* else absolute */
VertexDontDraw     0x0002     /* else draw */
VertexCurved       0x0004     /* else straight */
VertexStartClosed  0x0008     /* else not */
VertexEndClosed    0x0010     /* else not */

If
VertexRelative
is not set,
the coordinates are absolute (that is, relative to the drawable's origin).
The first vertex must be an absolute vertex.
If
VertexDontDraw
is one,
no line or curve is drawn from the previous vertex to this one.
This is analogous to picking up the pen and moving to another place
before drawing another line.
If
VertexCurved
is one,
a spline algorithm is used to draw a smooth curve from the previous vertex
through this one to the next vertex.
Otherwise, a straight line is drawn from the previous vertex to this one.
It makes sense to set
VertexCurved
to one only if a previous and next vertex are both defined
(either explicitly in the array or through the definition of a closed
curve).
It is permissible for
VertexDontDraw
bits and
VertexCurved
bits both to be one.
This is useful if you want to define the previous point for the smooth curve
but do not want an actual curve drawing to start until this point.
If
VertexStartClosed
is one,
then this point marks the beginning of a closed curve.
This vertex must be followed later in the array by another vertex
whose effective coordinates are identical
and that has a
VertexEndClosed
bit of one.
The points in between form a cycle to determine predecessor
and successor vertices for the spline algorithm.

This function uses these GC components:
function, plane-mask, line-width, line-style, cap-style, join-style,
fill-style, subwindow-mode, clip-x-origin, clip-y-origin, and
clip-mask.
It also uses these GC mode-dependent components:
foreground, background, tile, stipple,
tile-stipple-x-origin, tile-stipple-y-origin, dash-offset, and dash-list.

To achieve the effects of the X Version 10
XDrawTiled

and
XDrawFilled,

use
XDrawFilled.

#include <X11/X10.h>

Status XDrawFilled(Display *display, Drawable d, GC gc, Vertex *vlist, int vcount);

display	Specifies the connection to the X server.
d	Specifies the drawable.
gc	Specifies the GC.
vlist	Specifies a pointer to the list of vertices that indicate what to draw.
vcount	Specifies how many vertices are in vlist.

The
XDrawFilled
function draws arbitrary polygons or curves and then fills them.

Associating User Data with a Value

These functions have been superseded by the context management functions
(see section 16.10).
It is often necessary to associate arbitrary information with resource IDs.
Xlib provides the
XAssocTable
functions that you can use to make such an association.

Application programs often need to be able to easily refer to
their own data structures when an event arrives.
The
XAssocTable
system provides users of the X library with a method
for associating their own data structures with X resources
(Pixmaps,
Fonts,
Windows,
and so on).

An
XAssocTable
can be used to type X resources.
For example, the user
may want to have three or four types of windows,
each with different properties.
This can be accomplished by associating each X window ID
with a pointer to a window property data structure defined by the
user.
A generic type has been defined in the X library for resource IDs.
It is called an XID.

There are a few guidelines that should be observed when using an
XAssocTable :

All XIDs are relative to the specified display.
Because of the hashing scheme used by the association mechanism,
the following rules for determining the size of a
XAssocTable
should be followed.
Associations will be made and looked up more
efficiently if the table size (number of buckets in the hashing
system) is a power of two and if there are not more than 8 XIDs per
bucket.

To return a pointer to a new
XAssocTable,
use
XCreateAssocTable.

XAssocTable *XCreateAssocTable(int size);

size

Specifies the number of buckets in the hash system of
XAssocTable.

The size argument specifies the number of buckets in the
hash system of
XAssocTable.
For reasons of efficiency the number of buckets
should be a power of two.
Some size suggestions might be: use 32 buckets per 100 objects,
and a reasonable maximum number of objects per buckets is 8.
If an error allocating memory for the
XAssocTable
occurs,
a NULL pointer is returned.

To create an entry in a given
XAssocTable,
use
XMakeAssoc.

XMakeAssoc(Display *display, XAssocTable *table, XID x_id, char *data);

display	Specifies the connection to the X server.
table	Specifies the assoc table.
x_id	Specifies the X resource ID.
data	Specifies the data to be associated with the X resource ID.

The
XMakeAssoc
function inserts data into an
XAssocTable
keyed on an XID.
Data is inserted into the table only once.
Redundant inserts are ignored.
The queue in each association bucket is sorted from the lowest XID to
the highest XID.

To obtain data from a given
XAssocTable,
use
XLookUpAssoc.

char *XLookUpAssoc(Display *display, XAssocTable *table, XID x_id);

display	Specifies the connection to the X server.
table	Specifies the assoc table.
x_id	Specifies the X resource ID.

The
XLookUpAssoc
function retrieves the data stored in an
XAssocTable
by its XID.
If an appropriately matching XID can be found in the table,
XLookUpAssoc
returns the data associated with it.
If the x_id cannot be found in the table,
it returns NULL.

To delete an entry from a given
XAssocTable,
use
XDeleteAssoc.

XDeleteAssoc(Display *display, XAssocTable *table, XID x_id);

display	Specifies the connection to the X server.
table	Specifies the assoc table.
x_id	Specifies the X resource ID.

The
XDeleteAssoc
function deletes an association in an
XAssocTable
keyed on its XID.
Redundant deletes (and deletes of nonexistent XIDs) are ignored.
Deleting associations in no way impairs the performance of an
XAssocTable.

To free the memory associated with a given
XAssocTable,
use
XDestroyAssocTable.

XDestroyAssocTable(XAssocTable *table);

table

Specifies the assoc table.

Glossary

Access control list

X maintains a list of hosts from which client programs can be run.
By default,
only programs on the local host and hosts specified in an initial list read
by the server can use the display.
This access control list can be changed by clients on the local host.
Some server implementations can also implement other authorization mechanisms
in addition to or in place of this mechanism.
The action of this mechanism can be conditional based on the authorization
protocol name and data received by the server at connection setup.

Active grab

A grab is active when the pointer or keyboard is actually owned by the
single grabbing client.

Ancestors

If W is an inferior of A, then A is an ancestor of W.

Atom

An atom is a unique ID corresponding to a string name.
Atoms are used to identify properties, types, and selections.

Background

An
InputOutput
window can have a background, which is defined as a pixmap.
When regions of the window have their contents lost
or invalidated,
the server automatically tiles those regions with the background.

Backing store

When a server maintains the contents of a window,
the pixels saved off-screen are known as a backing store.

Base font name

A font name used to select a family of fonts whose members may be encoded
in various charsets.
The
CharSetRegistry
and
CharSetEncoding
fields of an XLFD name identify the charset of the font.
A base font name may be a full XLFD name, with all fourteen '-' delimiters,
or an abbreviated XLFD name containing only the first 12 fields of an XLFD name,
up to but not including
CharSetRegistry,
with or without the thirteenth '-', or a non-XLFD name.
Any XLFD fields may contain wild cards.

When creating an
XFontSet,
Xlib accepts from the client a list of one or more base font names
which select one or more font families.
They are combined with charset names obtained from the encoding of the locale
to load the fonts required to render text.

Bit gravity

When a window is resized,
the contents of the window are not necessarily discarded.
It is possible to request that the server relocate the previous contents
to some region of the window (though no guarantees are made).
This attraction of window contents for some location of
a window is known as bit gravity.

Bit plane

When a pixmap or window is thought of as a stack of bitmaps,
each bitmap is called a bit plane or plane.

Bitmap

A bitmap is a pixmap of depth one.

Border

An
InputOutput
window can have a border of equal thickness on all four sides of the window.
The contents of the border are defined by a pixmap,
and the server automatically maintains the contents of the border.
Exposure events are never generated for border regions.

Button grabbing

Buttons on the pointer can be passively grabbed by a client.
When the button is pressed,
the pointer is then actively grabbed by the client.

Byte order

For image (pixmap/bitmap) data,
the server defines the byte order,
and clients with different native byte ordering must swap bytes as
necessary.
For all other parts of the protocol,
the client defines the byte order,
and the server swaps bytes as necessary.

Character

A member of a set of elements used for the organization,
control, or representation of text (ISO2022, as adapted by XPG3).
Note that in ISO2022 terms, a character is not bound to a coded value
until it is identified as part of a coded character set.

Character glyph

The abstract graphical symbol for a character.
Character glyphs may or may not map one-to-one to font glyphs,
and may be context-dependent, varying with the adjacent characters.
Multiple characters may map to a single character glyph.

Character set

A collection of characters.

Charset

An encoding with a uniform, state-independent mapping from characters
to codepoints.
A coded character set.

For display in X,
there can be a direct mapping from a charset to one font,
if the width of all characters in the charset is either one or two bytes.
A text string encoded in an encoding such as Shift-JIS cannot be passed
directly to the X server, because the text imaging requests accept only
single-width charsets (either 8 or 16 bits).
Charsets which meet these restrictions can serve as “font charsets”.
Font charsets strictly speaking map font indices to font glyphs,
not characters to character glyphs.

Note that a single font charset is sometimes used as the encoding of a locale,
for example, ISO8859-1.

Children

The children of a window are its first-level subwindows.

Class

Windows can be of different classes or types.
See the entries for
InputOnly
and
InputOutput
windows for further information about valid window types.

Client

An application program connects to the window system server by some
interprocess communication (IPC) path, such as a TCP connection or a
shared memory buffer.
This program is referred to as a client of the window system server.
More precisely,
the client is the IPC path itself.
A program with multiple paths open to the server is viewed as
multiple clients by the protocol.
Resource lifetimes are controlled by
connection lifetimes, not by program lifetimes.

Clipping region

In a graphics context,
a bitmap or list of rectangles can be specified
to restrict output to a particular region of the window.
The image defined by the bitmap or rectangles is called a clipping region.

Coded character

A character bound to a codepoint.

Coded character set

A set of unambiguous rules that establishes a character set
and the one-to-one relationship between each character of the set
and its bit representation.
(ISO2022, as adapted by XPG3)
A definition of a one-to-one mapping of a set of characters to a set of
codepoints.

Codepoint

The coded representation of a single character in a coded character set.

Colormap

A colormap consists of a set of entries defining color values.
The colormap associated with a window is used to display the contents of
the window; each pixel value indexes the colormap to produce an RGB value
that drives the guns of a monitor.
Depending on hardware limitations,
one or more colormaps can be installed at one time so
that windows associated with those maps display with true colors.

Connection

The IPC path between the server and client program is known as a connection.
A client program typically (but not necessarily) has one
connection to the server over which requests and events are sent.

Containment

A window contains the pointer if the window is viewable and the
hotspot of the cursor is within a visible region of the window or a
visible region of one of its inferiors.
The border of the window is included as part of the window for containment.
The pointer is in a window if the window contains the pointer
but no inferior contains the pointer.

Coordinate system

The coordinate system has X horizontal and Y vertical,
with the origin [0, 0] at the upper left.
Coordinates are integral and coincide with pixel centers.
Each window and pixmap has its own coordinate system.
For a window,
the origin is inside the border at the inside upper-left corner.

Cursor

A cursor is the visible shape of the pointer on a screen.
It consists of a hotspot, a source bitmap, a shape bitmap,
and a pair of colors.
The cursor defined for a window controls the visible
appearance when the pointer is in that window.

Depth

The depth of a window or pixmap is the number of bits per pixel it has.
The depth of a graphics context is the depth of the drawables it can be
used in conjunction with graphics output.

Device

Keyboards, mice, tablets, track-balls, button boxes, and so on are all
collectively known as input devices.
Pointers can have one or more buttons
(the most common number is three).
The core protocol only deals with two devices: the keyboard
and the pointer.

DirectColor

DirectColor
is a class of colormap in which a pixel value is decomposed into three
separate subfields for indexing.
The first subfield indexes an array to produce red intensity values.
The second subfield indexes a second array to produce blue intensity values.
The third subfield indexes a third array to produce green intensity values.
The RGB (red, green, and blue) values in the colormap entry can be
changed dynamically.

Display

A server, together with its screens and input devices, is called a display.
The Xlib
Display
structure contains all information about the particular display and its screens
as well as the state that Xlib needs to communicate with the display over a
particular connection.

Drawable

Both windows and pixmaps can be used as sources and destinations
in graphics operations.
These windows and pixmaps are collectively known as drawables.
However, an
InputOnly
window cannot be used as a source or destination in a
graphics operation.

Encoding

A set of unambiguous rules that establishes a character set
and a relationship between the characters and their representations.
The character set does not have to be fixed to a finite pre-defined set of
characters.
The representations do not have to be of uniform length.
Examples are an ISO2022 graphic set, a state-independent
or state-dependent combination of graphic sets, possibly including control
sets, and the X Compound Text encoding.

In X, encodings are identified by a string
which appears as: the
CharSetRegistry
and
CharSetEncoding
components of an XLFD
name; the name of a charset of the locale for which a font could not be
found; or an atom which identifies the encoding of a text property or
which names an encoding for a text selection target type.
Encoding names should be composed of characters from the X Portable
Character Set.

Escapement

The escapement of a string is the distance in pixels in the
primary draw direction from the drawing origin to the origin of the next
character (that is, the one following the given string) to be drawn.

Event

Clients are informed of information asynchronously by means of events.
These events can be either asynchronously generated from devices or
generated as side effects of client requests.
Events are grouped into types.
The server never sends an event to a client unless the
client has specifically asked to be informed of that type of event.
However, clients can force events to be sent to other clients.
Events are typically reported relative to a window.

Event mask

Events are requested relative to a window.
The set of event types a client requests relative to a window is described
by using an event mask.

Event propagation

Device-related events propagate from the source window to ancestor
windows until some client has expressed interest in handling that type
of event or until the event is discarded explicitly.

Event source

The deepest viewable window that the pointer is in is called
the source of a device-related event.

Event synchronization

There are certain race conditions possible when demultiplexing device
events to clients (in particular, deciding where pointer and keyboard
events should be sent when in the middle of window management
operations).
The event synchronization mechanism allows synchronous processing of
device events.

Exposure event

Servers do not guarantee to preserve the contents of windows when
windows are obscured or reconfigured.
Exposure events are sent to clients to inform them when contents of regions
of windows have been lost.

Extension

Named extensions to the core protocol can be defined to extend the system.
Extensions to output requests, resources, and event types are all possible
and expected.

Font

A font is an array of glyphs (typically characters).
The protocol does no translation or interpretation of character sets.
The client simply indicates values used to index the glyph array.
A font contains additional metric information to determine interglyph
and interline spacing.

Font glyph

The abstract graphical symbol for an index into a font.

Frozen events

Clients can freeze event processing during keyboard and pointer grabs.

GC is an abbreviation for graphics context.
See Graphics context.

Glyph

An identified abstract graphical symbol independent of any actual image.
(ISO/IEC/DIS 9541-1)
An abstract visual representation of a graphic character,
not bound to a codepoint.

Glyph image

An image of a glyph, as obtained from a glyph representation displayed
on a presentation surface.
(ISO/IEC/DIS 9541-1)

Grab

Keyboard keys, the keyboard, pointer buttons, the pointer,
and the server can be grabbed for exclusive use by a client.
In general,
these facilities are not intended to be used by normal applications
but are intended for various input and window managers to implement various
styles of user interfaces.

Graphics context

Various information for graphics output is stored in a graphics
context (GC), such as foreground pixel, background
pixel, line width, clipping region, and so on.
A graphics context can only
be used with drawables that have the same root and the same depth as
the graphics context.

Gravity

The contents of windows and windows themselves have a gravity,
which determines how the contents move when a window is resized.
See Bit gravity and
Window gravity.

GrayScale

GrayScale
can be viewed as a degenerate case of
PseudoColor,
in which the red, green, and blue values in any given colormap entry
are equal and thus, produce shades of gray.
The gray values can be changed dynamically.

Host Portable Character Encoding

The encoding of the X Portable Character Set on the host.
The encoding itself is not defined by this standard,
but the encoding must be the same in all locales supported by Xlib on the host.
If a string is said to be in the Host Portable Character Encoding,
then it only contains characters from the X Portable Character Set,
in the host encoding.

Hotspot

A cursor has an associated hotspot, which defines the point in the
cursor corresponding to the coordinates reported for the pointer.

Identifier

An identifier is a unique value associated with a resource
that clients use to name that resource.
The identifier can be used over any connection to name the resource.

Inferiors

The inferiors of a window are all of the subwindows nested below it:
the children, the children's children, and so on.

Input focus

The input focus is usually a window defining the scope for processing
of keyboard input.
If a generated keyboard event usually would be reported to this window
or one of its inferiors,
the event is reported as usual.
Otherwise, the event is reported with respect to the focus window.
The input focus also can be set such that all keyboard events are discarded
and such that the focus window is dynamically taken to be the root window
of whatever screen the pointer is on at each keyboard event.

Input manager

Control over keyboard input is typically provided by an input manager
client, which usually is part of a window manager.

InputOnly window

An
InputOnly
window is a window that cannot be used for graphics requests.
InputOnly
windows are invisible and are used to control such things as cursors,
input event generation, and grabbing.
InputOnly
windows cannot have
InputOutput
windows as inferiors.

InputOutput window

An
InputOutput
window is the normal kind of window that is used for both input and output.
InputOutput
windows can have both
InputOutput
and
InputOnly
windows as inferiors.

Internationalization

The process of making software adaptable to the requirements
of different native languages, local customs, and character string encodings.
Making a computer program adaptable to different locales
without program source modifications or recompilation.

ISO2022

ISO standard for code extension techniques for 7-bit and 8-bit coded
character sets.

Key grabbing

Keys on the keyboard can be passively grabbed by a client.
When the key is pressed,
the keyboard is then actively grabbed by the client.

Keyboard grabbing

A client can actively grab control of the keyboard, and key events
will be sent to that client rather than the client the events would
normally have been sent to.

Keysym

An encoding of a symbol on a keycap on a keyboard.

Latin-1

The coded character set defined by the ISO8859-1 standard.

Latin Portable Character Encoding

The encoding of the X Portable Character Set using the Latin-1 codepoints
plus ASCII control characters.
If a string is said to be in the Latin Portable Character Encoding,
then it only contains characters from the X Portable Character Set,
not all of Latin-1.

Locale

The international environment of a computer program defining the “localized”
behavior of that program at run-time.
This information can be established from one or more sets of localization data.
ANSI C defines locale-specific processing by C system library calls.
See ANSI C and the X/Open Portability Guide specifications for more details.
In this specification, on implementations that conform to the ANSI C library,
the “current locale” is the current setting of the LC_CTYPE
setlocale
category.
Associated with each locale is a text encoding. When text is processed
in the context of a locale, the text must be in the encoding of the locale.
The current locale affects Xlib in its:

Encoding and processing of input method text
Encoding of resource files and values
Encoding and imaging of text strings
Encoding and decoding for inter-client text communication

Locale name

The identifier used to select the desired locale for the host C library
and X library functions.
On ANSI C library compliant systems,
the locale argument to the
setlocale
function.

Localization

The process of establishing information within a computer system specific
to the operation of particular native languages, local customs
and coded character sets.
(XPG3)

Mapped

A window is said to be mapped if a map call has been performed on it.
Unmapped windows and their inferiors are never viewable or visible.

Modifier keys

Shift, Control, Meta, Super, Hyper, Alt, Compose, Apple, CapsLock,
ShiftLock, and similar keys are called modifier keys.

Monochrome

Monochrome is a special case of
StaticGray
in which there are only two colormap entries.

Multibyte

A character whose codepoint is stored in more than one byte;
any encoding which can contain multibyte characters;
text in a multibyte encoding.
The “char *” null-terminated string datatype in ANSI C.
Note that references in this document to multibyte strings
imply only that the strings may contain multibyte characters.

Obscure

A window is obscured if some other window obscures it.
A window can be partially obscured and so still have visible regions.
Window A obscures window B if both are viewable
InputOutput
windows, if A is higher in the global stacking order,
and if the rectangle defined by the outside
edges of A intersects the rectangle defined by the outside edges of B.
Note the distinction between obscures and occludes.
Also note that window borders are included in the calculation.

Occlude

A window is occluded if some other window occludes it.
Window A occludes window B if both are mapped,
if A is higher in the global stacking order,
and if the rectangle defined by the outside edges of A intersects the rectangle defined
by the outside edges of B.
Note the distinction between occludes and obscures.
Also note that window borders are included in the calculation
and that
InputOnly
windows never obscure other windows but can occlude other windows.

Padding

Some padding bytes are inserted in the data stream to maintain
alignment of the protocol requests on natural boundaries.
This increases ease of portability to some machine architectures.

Parent window

If C is a child of P, then P is the parent of C.

Passive grab

Grabbing a key or button is a passive grab.
The grab activates when the key or button is actually pressed.

Pixel value

A pixel is an N-bit value,
where N is the number of bit planes used in a particular window or pixmap
(that is, is the depth of the window or pixmap).
A pixel in a window indexes a colormap to derive an actual color to be
displayed.

Pixmap

A pixmap is a three-dimensional array of bits.
A pixmap is normally thought of as a two-dimensional array of pixels,
where each pixel can be a value from 0 to 2N-1,
and where N is the depth (z axis) of the pixmap.
A pixmap can also be thought of as a stack of N bitmaps.
A pixmap can only be used on the screen that it was created in.

Plane

When a pixmap or window is thought of as a stack of bitmaps, each
bitmap is called a plane or bit plane.

Plane mask

Graphics operations can be restricted to only affect a subset of bit
planes of a destination.
A plane mask is a bit mask describing which planes are to be modified.
The plane mask is stored in a graphics context.

Pointer

The pointer is the pointing device currently attached to the cursor
and tracked on the screens.

Pointer grabbing

A client can actively grab control of the pointer.
Then button and motion events will be sent to that client
rather than the client the events would normally have been sent to.

Pointing device

A pointing device is typically a mouse, tablet, or some other
device with effective dimensional motion.
The core protocol defines only one visible cursor,
which tracks whatever pointing device is attached as the pointer.

POSIX

Portable Operating System Interface, ISO/IEC 9945-1 (IEEE Std 1003.1).

POSIX Portable Filename Character Set

The set of 65 characters which can be used in naming files on a POSIX-compliant
host that are correctly processed in all locales.
The set is:

a..z A..Z 0..9 ._-

Property

Windows can have associated properties that consist of a name, a type,
a data format, and some data.
The protocol places no interpretation on properties.
They are intended as a general-purpose naming mechanism for clients.
For example, clients might use properties to share information such as resize
hints, program names, and icon formats with a window manager.

Property list

The property list of a window is the list of properties that have
been defined for the window.

PseudoColor

PseudoColor
is a class of colormap in which a pixel value indexes the colormap entry to
produce an independent RGB value;
that is, the colormap is viewed as an array of triples (RGB values).
The RGB values can be changed dynamically.

Rectangle

A rectangle specified by [x,y,w,h] has an infinitely thin
outline path with corners at [x,y], [x+w,y], [x+w,y+h], and [x, y+h].
When a rectangle is filled,
the lower-right edges are not drawn.
For example,
if w=h=0,
nothing would be drawn.
For w=h=1,
a single pixel would be drawn.

Redirecting control

Window managers (or client programs) may enforce window layout
policy in various ways.
When a client attempts to change the size or position of a window,
the operation may be redirected to a specified client
rather than the operation actually being performed.

Information requested by a client program using the X protocol
is sent back to the client with a reply.
Both events and replies are multiplexed on the same connection.
Most requests do not generate replies,
but some requests generate multiple replies.

Request

A command to the server is called a request.
It is a single block of data sent over a connection.

Resource

Windows, pixmaps, cursors, fonts, graphics contexts, and colormaps are
known as resources.
They all have unique identifiers associated with them for naming purposes.
The lifetime of a resource usually is bounded by the lifetime of the
connection over which the resource was created.

RGB values

RGB values are the red, green, and blue intensity values that are used
to define a color.
These values are always represented as 16-bit, unsigned numbers, with 0
the minimum intensity and 65535 the maximum intensity.
The X server scales these values to match the display hardware.

Root

The root of a pixmap or graphics context is the same as the root
of whatever drawable was used when the pixmap or GC was created.
The root of a window is the root window under which the window was created.

Root window

Each screen has a root window covering it.
The root window cannot be reconfigured or unmapped,
but otherwise it acts as a full-fledged window.
A root window has no parent.

Save set

The save set of a client is a list of other clients' windows that,
if they are inferiors of one of the client's windows at connection
close, should not be destroyed and that should be remapped
if currently unmapped.
Save sets are typically used by window managers to avoid
lost windows if the manager should terminate abnormally.

Scanline

A scanline is a list of pixel or bit values viewed as a horizontal
row (all values having the same y coordinate) of an image, with the
values ordered by increasing the x coordinate.

Scanline order

An image represented in scanline order contains scanlines ordered by
increasing the y coordinate.

Screen

A server can provide several independent screens,
which typically have physically independent monitors.
This would be the expected configuration when there is only a single keyboard
and pointer shared among the screens.
A
Screen
structure contains the information about that screen
and is linked to the
Display
structure.

Selection

A selection can be thought of as an indirect property with dynamic
type.
That is, rather than having the property stored in the X server,
it is maintained by some client (the owner).
A selection is global and is thought of as belonging to the user
and being maintained by clients,
rather than being private to a particular window subhierarchy
or a particular set of clients.
When a client asks for the contents of
a selection, it specifies a selection target type,
which can be used to control the transmitted representation of the contents.
For example, if the selection is “the last thing the user clicked on,”
and that is currently an image, then the target type might specify
whether the contents of the image should be sent in XY format or
Z format.

The target type can also be used to control the class of
contents transmitted; for example,
asking for the “looks” (fonts, line
spacing, indentation, and so forth) of a paragraph selection, rather than the
text of the paragraph.
The target type can also be used for other
purposes.
The protocol does not constrain the semantics.

Server

The server, which is also referred to as the X server,
provides the basic windowing mechanism.
It handles IPC connections from clients,
multiplexes graphics requests onto the screens,
and demultiplexes input back to the appropriate clients.

Server grabbing

The server can be grabbed by a single client for exclusive use.
This prevents processing of any requests from other client connections until
the grab is completed.
This is typically only a transient state for such things as rubber-banding,
pop-up menus, or executing requests indivisibly.

Shift sequence

ISO2022 defines control characters and escape sequences
which temporarily (single shift) or permanently (locking shift) cause a
different character set to be in effect (“invoking” a character set).

Sibling

Children of the same parent window are known as sibling windows.

Stacking order

Sibling windows, similar to sheets of paper on a desk,
can stack on top of each other.
Windows above both obscure and occlude lower windows.
The relationship between sibling windows is known as the stacking order.

State-dependent encoding

An encoding in which an invocation of a charset can apply to multiple
characters in sequence.
A state-dependent encoding begins in an “initial state”
and enters other “shift states” when specific “shift sequences”
are encountered in the byte sequence.
In ISO2022 terms,
this means use of locking shifts, not single shifts.

State-independent encoding

Any encoding in which the invocations of the charsets are fixed,
or span only a single character.
In ISO2022 terms,
this means use of at most single shifts, not locking shifts.

StaticColor

StaticColor
can be viewed as a degenerate case of
PseudoColor
in which the RGB values are predefined and read-only.

StaticGray

StaticGray
can be viewed as a degenerate case of
GrayScale
in which the gray values are predefined and read-only.
The values are typically linear or near-linear increasing ramps.

Status

Many Xlib functions return a success status.
If the function does not succeed,
however, its arguments are not disturbed.

Stipple

A stipple pattern is a bitmap that is used to tile a region to serve
as an additional clip mask for a fill operation with the foreground
color.

STRING encoding

Latin-1, plus tab and newline.

String Equivalence

Two ISO Latin-1 STRING8 values are considered equal if they are the same
length and if corresponding bytes are either equal or are equivalent as
follows: decimal values 65 to 90 inclusive (characters “A” to “Z”) are
pairwise equivalent to decimal values 97 to 122 inclusive
(characters “a” to “z”), decimal values 192 to 214 inclusive
(characters “A grave” to “O diaeresis”) are pairwise equivalent to decimal
values 224 to 246 inclusive (characters “a grave” to “o diaeresis”),
and decimal values 216 to 222 inclusive (characters “O oblique” to “THORN”)
are pairwise equivalent to decimal values 246 to 254 inclusive
(characters “o oblique” to “thorn”).

Tile

A pixmap can be replicated in two dimensions to tile a region.
The pixmap itself is also known as a tile.

Timestamp

A timestamp is a time value expressed in milliseconds.
It is typically the time since the last server reset.
Timestamp values wrap around (after about 49.7 days).
The server, given its current time is represented by timestamp T,
always interprets timestamps from clients by treating half
of the timestamp space as being earlier in time than T
and half of the timestamp space as being later in time than T.
One timestamp value, represented by the constant
CurrentTime,
is never generated by the server.
This value is reserved for use in requests to represent the current server time.

TrueColor

TrueColor
can be viewed as a degenerate case of
DirectColor
in which the subfields in the pixel value directly encode the corresponding RGB
values.
That is, the colormap has predefined read-only RGB values.
The values are typically linear or near-linear increasing ramps.

Type

A type is an arbitrary atom used to identify the interpretation of property
data.
Types are completely uninterpreted by the server.
They are solely for the benefit of clients.
X predefines type atoms for many frequently used types,
and clients also can define new types.

Viewable

A window is viewable if it and all of its ancestors are mapped.
This does not imply that any portion of the window is actually visible.
Graphics requests can be performed on a window when it is not
viewable, but output will not be retained unless the server is maintaining
backing store.

Visible

A region of a window is visible if someone looking at the screen can
actually see it; that is, the window is viewable and the region is not occluded
by any other window.

Whitespace

Any spacing character.
On implementations that conform to the ANSI C library,
whitespace is any character for which
isspace
returns true.

Window gravity

When windows are resized,
subwindows may be repositioned automatically relative to some position in the
window.
This attraction of a subwindow to some part of its parent is known
as window gravity.

Window manager

Manipulation of windows on the screen and much of the user interface
(policy) is typically provided by a window manager client.

X Portable Character Set

A basic set of 97 characters which are assumed to exist in all
locales supported by Xlib. This set contains the following characters:

a..z A..Z 0..9
!"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~
<space>, <tab>, and <newline>

This is the left/lower half (also called the G0 set)
of the graphic character set of ISO8859-1 plus <space>, <tab>, and <newline>.
It is also the set of graphic characters in 7-bit ASCII plus the same
three control characters.
The actual encoding of these characters on the host is system dependent;
see the Host Portable Character Encoding.

XLFD

The X Logical Font Description Conventions
that define a standard syntax for structured font names.

XY format

The data for a pixmap is said to be in XY format if it is organized as
a set of bitmaps representing individual bit planes with the planes
appearing from most-significant to least-significant bit order.

Z format

The data for a pixmap is said to be in Z format if it is organized as
a set of pixel values in scanline order.