WindowManager: Only show notifications after their window was shown

Author: lenemter

src/InternalUtils.vala

@@ -355,5 +355,17 @@ namespace Gala {
                 return Source.REMOVE;
             });
         }
+
+        public static void wait_for_window_actor_to_show (Meta.Window window, owned WindowActorReadyCallback callback) {
+            unowned var window_actor = (Meta.WindowActor) window.get_compositor_private ();
+            if (window_actor.visible) {
+                callback (window_actor);
+                return;
+            }
+
+            InternalUtils.wait_for_window_actor (window, (actor) => {
+                actor.show.connect (() => callback (actor));
+            }); 
+        }
     }
 }

src/WindowManager.vala

@@ -2120,9 +2120,10 @@ namespace Gala {
             // TODO: currently only notifications are handled here, other windows should be too
             switch_workspace_window_created_id = window_created.connect ((window) => {
                 if (NotificationStack.is_notification (window)) {
-                    unowned var actor = (Meta.WindowActor) window.get_compositor_private ();
-                    clutter_actor_reparent (actor, notification_group);
-                    notification_stack.show_notification (actor);
+                    InternalUtils.wait_for_window_actor_to_show (window, (actor) => {
+                        clutter_actor_reparent (actor, notification_group);
+                        notification_stack.show_notification (actor);
+                    });
                 }
             });