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. OverviewXCB 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.[2] The main goals of XCB are to:
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).[3] 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.[4] (Xlib has long been known to contain errors.[5]) Xlib compatibilityXlib/XCB provides application binary interface compatibility with both Xlib and XCB, providing an incremental porting path.[6] 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.[7][8] 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 <stdio.h>
#include <stdlib.h>
#include <xcb/xcb.h>
int main(void)
{
xcb_connection_t *c;
xcb_screen_t *s;
xcb_window_t w;
xcb_gcontext_t g;
xcb_generic_event_t *e;
uint32_t mask;
uint32_t values[2];
int done = 0;
xcb_rectangle_t r = { 20, 20, 60, 60 };
// open connection to the server
c = xcb_connect(NULL, NULL);
if (xcb_connection_has_error(c)) {
printf("Cannot open display\n");
exit(EXIT_FAILURE);
}
// get the first screen
s = xcb_setup_roots_iterator( xcb_get_setup(c) ).data;
// create black graphics context
g = xcb_generate_id(c);
w = s->root;
mask = XCB_GC_FOREGROUND | XCB_GC_GRAPHICS_EXPOSURES;
values[0] = s->black_pixel;
values[1] = 0;
xcb_create_gc(c, g, w, mask, values);
// create window
w = xcb_generate_id(c);
mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
values[0] = s->white_pixel;
values[1] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_KEY_PRESS;
xcb_create_window(c, s->root_depth, w, s->root,
10, 10, 100, 100, 1,
XCB_WINDOW_CLASS_INPUT_OUTPUT, s->root_visual,
mask, values);
// map (show) the window
xcb_map_window(c, w);
xcb_flush(c);
// event loop
while (!done && (e = xcb_wait_for_event(c))) {
switch (e->response_type & ~0x80) {
case XCB_EXPOSE: // draw or redraw the window
xcb_poly_fill_rectangle(c, w, g, 1, &r);
xcb_flush(c);
break;
case XCB_KEY_PRESS: // exit on key press
done = 1;
break;
}
free(e);
}
// close connection to server
xcb_disconnect(c);
exit(EXIT_SUCCESS);
}
The bitwise and operation XCB has a comparable, but slightly lower-level API than Xlib,[10] as can be seen with this example. Protocol descriptionCreators 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.[dubious – discuss] libxcb itself is implemented as a code generator and a tiny C stub of utility functions. An example: <xcb header="bigreq" extension-xname="BIG-REQUESTS"
extension-name="BigRequests" extension-multiword="true"
major-version="0" minor-version="0">
<request name="Enable" opcode="0">
<reply>
<pad bytes="1" />
<field type="CARD32" name="maximum_request_length" />
</reply>
</request>
</xcb>
LogoThe XCB logo was produced by Gearóid Molloy, author of the web comic Neko the Kitty, and donated to the project.[11] Other language bindings
Notes
References
External links
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