XCB

 /* einfache XCB-Applikation, die ein Rechteck in ein Fenster zeichnet.
    Kompilierbar beispielsweise mit: gcc -o xcbtest xcbtest.c -lxcb   */

 #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 };

                        /* Verbindung zum X-Server öffnen */
   if((c = xcb_connect(NULL,NULL)) == NULL) {
     printf("Cannot open display\n");
     exit(1);
   }
                        /* get the first screen */
   s = xcb_setup_roots_iterator( xcb_get_setup(c) ).data;

                        /* schwarzen Grafikkontext erzeugen */
   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);

                        /* Fenster erzeugen */
   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);

                        /* Anzeigen (einblenden, "map") des Fensters */
   xcb_map_window(c, w);

   xcb_flush(c);

                        /* event loop, Ereignisschleife */
   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:  /* beenden, wenn eine Taste gedrückt wird */
       done = 1;
       break;
     }
     free(e);
   }
                        /* Verbindung zum X-Server trennen */
   xcb_disconnect(c);

   return 0;
 }