It's alive! XCB+Cairo drawing on a root window

mess/cairo-xcb.c

@@ -17,7 +17,14 @@
 void render(xcb_connection_t *connection, int wid, cairo_t *cr, int win_w, int win_h);
 void set_window_title(xcb_connection_t *connection, xcb_window_t wid, const char *title);
 
+bool get_window_geometry(xcb_connection_t *connection, xcb_window_t wid, xcb_rectangle_t *rect);
+bool get_window_name(xcb_connection_t *connection, xcb_window_t wid, char *name);
+bool get_window_attributes(xcb_connection_t *connection, xcb_window_t wid, xcb_get_window_attributes_reply_t *reply);
+
+xcb_window_t find_subwindow(xcb_connection_t *connection, xcb_window_t win, int w, int h);
+
 int main(void) {
+  char buffer[8192];
   xcb_connection_t *connection = xcb_connect(getenv("DISPLAY"), NULL);
   if (!connection) {
     fprintf(stderr, "xcb_connect() failed\n");
@@ -25,7 +32,6 @@ int main(void) {
   }
 
   xcb_screen_t *screen = xcb_setup_roots_iterator(xcb_get_setup(connection)).data;
-  xcb_window_t wid = xcb_generate_id(connection);
 
   xcb_visualtype_t *visual = NULL;
   {
@@ -44,19 +50,33 @@ int main(void) {
 found_visual: {}
   }
 
-  int win_w = 150, win_h = 150;
-  uint32_t mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK,
-           values[2] = {
+  xcb_window_t root = find_subwindow(connection, screen->root, -1, -1);
+  xcb_window_t parent = find_subwindow(connection, root, screen->width_in_pixels, screen->height_in_pixels);
+
+  printf("parent: 0x%08x\n", parent);
+
+  xcb_window_t wid = xcb_generate_id(connection);
+
+  int win_w = screen->width_in_pixels, win_h = screen->height_in_pixels;
+  uint32_t mask = XCB_CW_BACK_PIXEL | XCB_CW_BACKING_STORE | XCB_CW_OVERRIDE_REDIRECT | XCB_CW_EVENT_MASK,
+           values[] = {
              screen->white_pixel,
+             XCB_BACKING_STORE_ALWAYS,
+             1,
              XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_STRUCTURE_NOTIFY | XCB_EVENT_MASK_FOCUS_CHANGE
            };
-  xcb_create_window(connection,
-      XCB_COPY_FROM_PARENT,
-      wid, screen->root,
+  xcb_create_window(
+      connection,
+      XCB_COPY_FROM_PARENT, /* depth */
+      wid, parent,
       0, 0, win_w, win_h, 0,
       XCB_WINDOW_CLASS_INPUT_OUTPUT,
       screen->root_visual, mask, values);
 
+  {
+    const static uint32_t values[] = { XCB_STACK_MODE_BELOW };
+    xcb_configure_window(connection, wid, XCB_CONFIG_WINDOW_STACK_MODE, values);
+  }
   xcb_map_window(connection, wid);
   xcb_flush(connection);
 
@@ -66,7 +86,6 @@ found_visual: {}
   xcb_generic_event_t *event;
   bool running = true;
 
-  char buffer[8192];
   while (running) {
     while (running && (event = xcb_poll_for_event(connection))) {
       switch (event->response_type & ~0x80) {
@@ -121,6 +140,7 @@ found_visual: {}
 
   xcb_destroy_window(connection, wid);
   xcb_disconnect(connection);
+  return EXIT_SUCCESS;
 }
 
 void render(xcb_connection_t *connection, int wid, cairo_t *cr, int win_w, int win_h) {
@@ -150,3 +170,69 @@ void set_window_title(xcb_connection_t *connection, xcb_window_t wid, const char
       strlen(title), title);
   xcb_flush(connection);
 }
+
+bool get_window_geometry(xcb_connection_t *connection, xcb_window_t wid, xcb_rectangle_t *rect) {
+  xcb_get_geometry_cookie_t cookie = xcb_get_geometry(connection, wid);
+  xcb_get_geometry_reply_t *reply = xcb_get_geometry_reply(connection, cookie, 0);
+  if (!reply) return false;
+
+  rect->x = reply->x;
+  rect->y = reply->y;
+  rect->width = reply->width;
+  rect->height = reply->height;
+
+  free(reply);
+  return true;
+}
+
+bool get_window_name(xcb_connection_t *connection, xcb_window_t wid, char *name) {
+  xcb_get_property_cookie_t cookie = xcb_get_property(connection, 0, wid, XCB_ATOM_WM_NAME, XCB_ATOM_STRING, 0, 0);
+  xcb_get_property_reply_t *reply = xcb_get_property_reply(connection, cookie, 0);
+  if (!reply) {
+    name[0] = 1;
+    return false;
+  }
+
+  int len = xcb_get_property_value_length(reply);
+  if (len == 0) {
+    name[0] = 2;
+    free(reply);
+    return false;
+  }
+
+  strcpy(name, xcb_get_property_value(reply));
+
+  free(reply);
+  return true;
+}
+
+bool get_window_attributes(xcb_connection_t *connection, xcb_window_t wid, xcb_get_window_attributes_reply_t *out) {
+  xcb_get_window_attributes_cookie_t cookie = xcb_get_window_attributes(connection, wid);
+  xcb_get_window_attributes_reply_t *reply = xcb_get_window_attributes_reply(connection, cookie, 0);
+  if (!reply) return false;
+  memcpy(out, reply, sizeof(xcb_get_window_attributes_reply_t));
+  free(reply);
+  return true;
+}
+
+xcb_window_t find_subwindow(xcb_connection_t *connection, xcb_window_t win, int w, int h) {
+  xcb_query_tree_reply_t *qt_reply;
+  xcb_query_tree_cookie_t qt_cookie = xcb_query_tree(connection, win);
+
+  if ((qt_reply = xcb_query_tree_reply(connection, qt_cookie, 0))) {
+    xcb_window_t *children = xcb_query_tree_children(qt_reply);
+    xcb_rectangle_t rect;
+    xcb_get_window_attributes_reply_t attrs;
+    for (int i = 0; i < xcb_query_tree_children_length(qt_reply); i++) {
+      if (!get_window_geometry(connection, children[i], &rect)) continue;
+      if (!get_window_attributes(connection, children[i], &attrs)) continue;
+
+      if (attrs.map_state != 0 && rect.width == w && rect.height == h) {
+        free(qt_reply);
+        return children[i];
+      }
+    }
+    free(qt_reply);
+  }
+  return win;
+}