A quick hack to test alpha values for XCB_CW_BORDER_PIXEL and XCB_CW_BACK_PIXEL

test_border_alpha.c

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

static void die(const char *msg)
{
	fputs(msg, stderr);
	exit(1);
}

static xcb_visualtype_t *draw_argb_visual(const xcb_screen_t *s)
{
	xcb_depth_iterator_t depth_iter = xcb_screen_allowed_depths_iterator(s);
	xcb_visualtype_iterator_t visual_iter;

	if(depth_iter.data)
		for(; depth_iter.rem; xcb_depth_next (&depth_iter))
			if(depth_iter.data->depth == 32)
				for(visual_iter = xcb_depth_visuals_iterator(depth_iter.data);
						visual_iter.rem; xcb_visualtype_next (&visual_iter))
					return visual_iter.data;

	return NULL;
}

static xcb_window_t create_window(xcb_connection_t *c, xcb_screen_t *s)
{
	xcb_window_t win;
	xcb_visualtype_t *visual = draw_argb_visual(s);
	xcb_colormap_t cmap;

	if (!visual)
		return XCB_NONE;

	cmap = xcb_generate_id(c);
	win = xcb_generate_id(c);
        xcb_create_colormap(c, XCB_COLORMAP_ALLOC_NONE, cmap, s->root, visual->visual_id);
	xcb_create_window(c, 32, win, s->root, 10, 10, 50, 50, 5, XCB_WINDOW_CLASS_INPUT_OUTPUT,
			visual->visual_id,
			XCB_CW_BACK_PIXEL | XCB_CW_BORDER_PIXEL | XCB_CW_OVERRIDE_REDIRECT | XCB_CW_EVENT_MASK | XCB_CW_COLORMAP,
			(const uint32_t [])
			{
			0xaaaaaaaa,
			0x88888888,
			1,
			XCB_EVENT_MASK_BUTTON_PRESS,
			cmap
			});
	xcb_free_colormap(c, cmap);

	return win;
}

static void event_loop(xcb_connection_t *c)
{
	xcb_generic_event_t *event;
	int done = 0;

	while (!done && (event = xcb_wait_for_event(c)) != NULL) {
		printf("Got event %d\n", event->response_type);
		if (event->response_type == XCB_BUTTON_PRESS) {
			puts("existing");
			done = 1;
		}
		free(event);
		xcb_flush(c);
	}
}

int main()
{
	const xcb_setup_t *setup;
	xcb_window_t win;
	xcb_connection_t *c;
	xcb_screen_t *s;

	c = xcb_connect(NULL, NULL);
	setup = xcb_get_setup(c);
	if (xcb_connection_has_error(c) || !setup)
		die("Could not connect");

	s = xcb_setup_roots_iterator(setup).data;
	win = create_window(c, s);
	if (!win)
		die("could not create window");

	xcb_map_window(c, win);
	xcb_flush(c);

	event_loop(c);
	if (xcb_connection_has_error(c))
		die("Connection has error?!");
	xcb_disconnect(c);
	return 0;
}