XCB

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XCB

Developer:	Jamey Sharp, Josh Triplett, Bart Massey
Latest release:	1.0 / 24 November 2006
OS:	POSIX
Use:	X Window core protocol development library
License:	MIT
Website:	xcb.freedesktop.org

In computing, XCB (X C Binding) is a C language binding for the X Window System. It aims to replace Xlib. The project was started in 2001 by Bart Massey.

Xlib/XCB provides application binary interface compatibility with both Xlib and XCB, providing an incremental porting path.

1 Aims of XCB
2 Example
3 References
4 External links

[edit] Aims of XCB

The main aims of XCB are:

reduction in library size and complexity;
direct access to the X11 protocol.

Secondary aims include making the C interface asynchronous, facilitating better multithreading and making extensions easier to implement (via XML protocol descriptions).

The core and extension protocol descriptions are in XML, with the C bindings created via XSLT. A tertiary aim is to repurpose these protocol descriptions for the creation of protocol documentation, further language bindings, and server-side stubs.

Massey has worked to prove XCB formally correct, using Z notation. (Xlib has long been known to contain errors.)

[edit] Example

/* Simple XCB application drawing a box in a window */

#include <xcb/xcb.h>
#include <stdio.h>
#include <stdlib.h>

int main()
{
  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 with the server */
  c = xcb_connect(NULL,NULL);
  if (xcb_connection_has_error(c)) {
    printf("Cannot open display\n");
    exit(1);
  }
                       /* 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);

  return 0;
}

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