XCB

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XCB
Developed by Jamey Sharp, Josh Triplett, Bart Massey
Latest release 1.1 / 4 November 2007
OS POSIX
Genre 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 is implemented as free software and 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. 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.

Contents

[edit] Aims

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 previous version used M4.) A tertiary aim is to repurpose these protocol descriptions for the creation of protocol documentation, further 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.)

[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.

[edit] References

[edit] External links

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