XCB

XCB (''X protocol C-language Binding'') is a library implementing the client side of the X11 display server protocol. XCB is written in the C programming language and distributed under the MIT License. The project was started in 2001 by Bart Massey and aims to replace Xlib.

Overview

XCB was designed as a smaller, modernized replacement for Xlib, previously the primary C library for communicating with the X window system, coinciding with a more complete overhaul of the X implementation that took place during the early 2000s. The main goals of XCB are to:
* reduce library size and complexity
* provide direct access to the X11 protocol

The required size reduction is achieved primarily by restricting XCB's scope to handling the X protocol and omitting Xlib functionality such as its extensive utility library, much of which saw little use by applications. This results in a factor thirty reduction of the compiled library size (as of 2004).
Secondary goals include making the C interface asynchronous, facilitating better multithreading and making it easier to implement extensions (via XML protocol descriptions).

The core and extension protocol descriptions are in XML, with a program written in Python creating the C bindings. (Previous versions used XSLT and M4.)

A further goal is to be able to use these protocol descriptions to create protocol documentation, more language bindings, and server-side stubs.

Massey and others have worked to prove key portions of XCB formally correct using Z notation. (Xlib has long been known to contain errors.)

Xlib compatibility

''Xlib/XCB'' provides application binary interface compatibility with both Xlib and XCB, providing an incremental porting path. Xlib/XCB uses the protocol layer of Xlib, but replaces the Xlib transport layer with XCB, and provides access to the underlying XCB connection for direct use of XCB. Xlib/XCB allows an application to open a single connection to the X display server and use both XCB and Xlib, possibly through a mixture of libraries designed for one or the other.

Example

// Simple XCB application for opening a window and drawing a box in it

// To compile it using GNU, use:
// gcc x.c -lxcb

#include
#include
#include

int main(void)

The bitwise and operation a->response_type & ~0x80 removes a bit that indicates where the event came from.

XCB has a comparable, but slightly lower-level API than Xlib, as can be seen with this example.

Protocol description

Creators of XCB have invented a specialized interface description language to model X11 protocol in language-neutral way and facilitate generation of bindings to other programming languages. libxcb itself is implemented as a code generator and a tiny C stub of utility functions.

An example:

Logo

The XCB logo was produced by Gearóid Molloy, author of the web comic ''Neko the Kitty'', and donated to the project.KittyLogo
(xcb.freedesktop.org)

Other language bindings

XCB.pm
- Perl module implementing bindings to XCB.

xpyb
- The Python binding to the X Window System using XCB. As of June 2013, it does not support Python 3. Provided by freedesktop.org.

xcffib
- Another Python binding which supports Python 2 & 3 as well as several more X extensions than xpyb.

Notes

References

*
*
*

External links

XCB wiki
(freedesktop.org)

XCB API referencetutorial



Further publications

The X New Developer’s Guide: Xlib and XCB

{{DEFAULTSORT:Xcb
C (programming language) libraries
Freedesktop.org
Freedesktop.org libraries
Software using the MIT license
X Window System