clutter: Propagate events only inside the grab

The grab actor becomes the "root" of the events being handled, events
inside propagate normally, but become silenced when falling outside
the grab area.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2068>

clutter/clutter/clutter-main.c

@@ -683,7 +683,9 @@ emit_event_chain (ClutterEvent *event)
       return;
     }
 
-  _clutter_actor_handle_event (event->any.source, NULL, event);
+  _clutter_actor_handle_event (event->any.source,
+                               clutter_stage_get_grab_actor (event->any.stage),
+                               event);
 }
 
 /*

clutter/clutter/clutter-stage.c

@@ -3846,3 +3846,15 @@ clutter_grab_dismiss (ClutterGrab *grab)
 
   g_free (grab);
 }
+
+ClutterActor *
+clutter_stage_get_grab_actor (ClutterStage *stage)
+{
+  ClutterStagePrivate *priv = stage->priv;
+
+  if (!priv->topmost_grab)
+    return NULL;
+
+  /* Return active grab */
+  return priv->topmost_grab->actor;
+}

clutter/clutter/clutter-stage.h

@@ -274,6 +274,9 @@ CLUTTER_EXPORT
 ClutterGrab * clutter_stage_grab (ClutterStage *stage,
                                   ClutterActor *actor);
 
+CLUTTER_EXPORT
+ClutterActor * clutter_stage_get_grab_actor (ClutterStage *stage);
+
 G_END_DECLS
 
 #endif /* __CLUTTER_STAGE_H__ */