compositor-x11: Use check function to make sure we handle all events

If somebody else did an X11 round trip, that could leave events in the
XCB buffer that we wouldn't see until the next X event came in.  The new
event source check function lets us check the XCB queue after dispatching
and this way we'll see events we need to deal with right away.

compositor/compositor-x11.c

@@ -48,6 +48,7 @@ struct x11_compositor {
 	xcb_connection_t	*conn;
 	xcb_screen_t		*screen;
 	xcb_cursor_t		 null_cursor;
+	xcb_generic_event_t     *next_event;
 	struct wl_array		 keys;
 	struct wl_event_source	*xcb_source;
 	struct {
@@ -376,6 +377,20 @@ x11_compositor_find_output(struct x11_compositor *c, xcb_window_t window)
 	return NULL;
 }
 
+static int
+x11_compositor_next_event(struct x11_compositor *c,
+			  xcb_generic_event_t **event)
+{
+	if (c->next_event) {
+		*event = c->next_event;
+		c->next_event = NULL;
+	} else {
+		*event = xcb_poll_for_event (c->conn);
+	}
+
+	return *event != NULL;
+}
+
 static void
 x11_compositor_handle_event(int fd, uint32_t mask, void *data)
 {
@@ -394,7 +409,7 @@ x11_compositor_handle_event(int fd, uint32_t mask, void *data)
 	int i, set;
 
 	prev = NULL;
-	while (event = xcb_poll_for_event (c->conn), event != NULL) {
+	while (x11_compositor_next_event(c, &event)) {
 		switch (prev ? prev->response_type & ~0x80 : 0x80) {
 		case XCB_KEY_RELEASE:
 			key_release = (xcb_key_press_event_t *) prev;
@@ -420,15 +435,6 @@ x11_compositor_handle_event(int fd, uint32_t mask, void *data)
 			}
 
 		case XCB_FOCUS_IN:
-			/* FIXME: There's a bug somewhere in xcb (I
-			 * think) where we don't get all the events in
-			 * the input buffer when calling
-			 * xcb_poll_for_event().  What happens is we
-			 * alt-tab to the compositor window, and get
-			 * the focus_in(mode=while_grabbed), but not
-			 * the following focus_in(mode=ungrab) which
-			 * is the one we care about. */
-
 			/* assert event is keymap_notify */
 			focus_in = (xcb_focus_in_event_t *) prev;
 			keymap_notify = (xcb_keymap_notify_event_t *) event;
@@ -457,7 +463,6 @@ x11_compositor_handle_event(int fd, uint32_t mask, void *data)
 		}
 
 		switch (event->response_type & ~0x80) {
-
 		case XCB_KEY_PRESS:
 			key_press = (xcb_key_press_event_t *) event;
 			notify_key(c->base.input_device,
@@ -561,6 +566,18 @@ x11_compositor_handle_event(int fd, uint32_t mask, void *data)
 	}
 }
 
+static int
+x11_compositor_check_source(struct wl_event_source *source, void *data)
+{
+	struct x11_compositor *c = data;
+
+	/* Really? xcb doesn't have a "get queue length" function that
+	 * doesn't pop an event? */
+	c->next_event = xcb_poll_for_queued_event(c->conn);
+
+	return c->next_event != NULL;
+}
+
 #define F(field) offsetof(struct x11_compositor, field)
 
 static void
@@ -630,15 +647,14 @@ x11_compositor_create(struct wl_display *display, int width, int height)
 	memset(c, 0, sizeof *c);
 
 	c->dpy = XOpenDisplay(NULL);
-
 	if (c->dpy == NULL)
 		return NULL;
 
 	c->conn = XGetXCBConnection(c->dpy);
-
 	if (xcb_connection_has_error(c->conn))
 		return NULL;
 
+	c->next_event = NULL;	
 	s = xcb_setup_roots_iterator(xcb_get_setup(c->conn));
 	c->screen = s.data;
 	wl_array_init(&c->keys);
@@ -667,6 +683,7 @@ x11_compositor_create(struct wl_display *display, int width, int height)
 		wl_event_loop_add_fd(loop, xcb_get_file_descriptor(c->conn),
 				     WL_EVENT_READABLE,
 				     x11_compositor_handle_event, c);
+	wl_event_source_check(c->xcb_source, x11_compositor_check_source);
 
 	return &c->base;
 }