small test case

test.c

/* Simple XCB application drawing a box in a window */
/* to compile it use :
   gcc -Wall x.c -lxcb
   */
#include <xcb/xcb.h>
#include <stdio.h>
#include <stdlib.h>

void xcb_set_window_rect(xcb_connection_t *conn, xcb_window_t window, int *r) {
	xcb_void_cookie_t cookie;
	cookie = xcb_configure_window(conn, window,
			XCB_CONFIG_WINDOW_X |
			XCB_CONFIG_WINDOW_Y |
			XCB_CONFIG_WINDOW_WIDTH |
			XCB_CONFIG_WINDOW_HEIGHT,
			r);
}
static void get_window_position(xcb_connection_t *c, xcb_window_t w, int *x, int *y, int *wi, int *he){
	xcb_query_tree_reply_t *tree = xcb_query_tree_reply(c, xcb_query_tree(c, w), NULL);
	xcb_get_geometry_reply_t *geo = xcb_get_geometry_reply(c, xcb_get_geometry(c, w), NULL);
	xcb_translate_coordinates_reply_t *t = xcb_translate_coordinates_reply(c, xcb_translate_coordinates(c, w, tree->root, geo->x, geo->y), NULL);
	*x = t->dst_x;
	*y = t->dst_y;
	*wi = geo->width;
	*he = geo->height;
	free(tree);
	free(geo);
	free(t);
}

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 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, 0,
			XCB_WINDOW_CLASS_INPUT_OUTPUT, s->root_visual,
			mask, values);

	/* map (show) the window */
	xcb_map_window(c, w);

	xcb_flush(c);

	xcb_motion_notify_event_t *te;
	/* event loop */
	int oldm[2]={0};
	int co[4]={200,200,100,100};
	xcb_set_window_rect(c, w, co);
	xcb_flush(c);
	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;
		}
		free(e);
		break;
	}
	for(;1;){
		int x,y,wi,he;
		get_window_position(c, w, co, co+1, co+2, co+3);
		xcb_set_window_rect(c, w, co);
		xcb_flush(c);
		usleep(500);
	}
	/* close connection to server */
	xcb_disconnect(c);

	return 0;
}