// gcc `pkg-config --libs xcb` main.c -o main

#include <stdio.h>

#include <stdlib.h>

#include <xcb/xcb.h>

xcb_connection_t *connection;

xcb_screen_t *screen;

xcb_window_t create_window() {

// http://www.x.org/releases/current/doc/xproto/x11protocol.html#requests:CreateWindow

// http://www.x.org/archive/current/doc/man/man3/xcb_create_window.3.xhtml

//

// N.B. xcb's order corresponds to the order of the wire.

// You can look at the protocol encoding: http://www.x.org/releases/current/doc/xproto/x11protocol.html#Encoding::Requests

uint32_t mask;

uint32_t values[2];

xcb_window_t window;

xcb_void_cookie_t cookie;

mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;

values[0] = screen->white_pixel;

values[1] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_KEY_PRESS;

window = xcb_generate_id(connection);

cookie = xcb_create_window(connection,

XCB_COPY_FROM_PARENT, window, screen->root,

0, 0, 640, 480,

0,

XCB_WINDOW_CLASS_INPUT_OUTPUT,

screen->root_visual,

mask, values);

xcb_map_window(connection, window);

return window;

}

xcb_gcontext_t create_graphics_context(xcb_window_t window) {

xcb_gcontext_t graphics_context;

uint32_t mask;

uint32_t values[2];

mask = XCB_GC_FOREGROUND | XCB_GC_GRAPHICS_EXPOSURES;

values[0] = screen->black_pixel;

values[1] = 0;

graphics_context = xcb_generate_id(connection);

xcb_create_gc(connection,

graphics_context, window,

mask, values);

return graphics_context;

}

void event_loop(xcb_window_t window, xcb_gcontext_t graphics_context) {

xcb_generic_event_t *event;

xcb_rectangle_t r = { 20, 20, 60, 60 };

while(event = xcb_wait_for_event(connection)) {

switch(event->response_type) {

case XCB_EXPOSE:

xcb_poly_fill_rectangle(connection, window, graphics_context, 1, &r);

xcb_flush(connection);

break;

case XCB_KEY_PRESS:

return;

}

}

}

int main(void) {

xcb_window_t window;

xcb_gcontext_t graphics_context;

connection = xcb_connect(NULL, NULL); // Callers need to use xcb_connection_has_error() to check for failure.

screen = xcb_setup_roots_iterator(xcb_get_setup(connection)).data;

window = create_window();

graphics_context = create_graphics_context(window);

xcb_flush(connection);

event_loop(window, graphics_context);

puts("bye!");

return EXIT_SUCCESS;

}