gdk: Allow disabling event retrieval

Just like the other backends can disable the internal event handling,
and use clutter_<backend>_handle_event() to do the native → Clutter
event translation.

clutter/gdk/clutter-backend-gdk.c

@@ -65,6 +65,8 @@ G_DEFINE_TYPE (ClutterBackendGdk, clutter_backend_gdk, CLUTTER_TYPE_BACKEND_COGL
 /* global for pre init setup calls */
 static GdkDisplay  *_foreign_dpy = NULL;
 
+static gboolean disable_event_retrieval = FALSE;
+
 static void
 clutter_backend_gdk_init_settings (ClutterBackendGdk *backend_gdk)
 {
@@ -186,7 +188,8 @@ clutter_backend_gdk_init_events (ClutterBackend *backend)
 {
   CLUTTER_NOTE (EVENT, "initialising the event loop");
 
-  _clutter_backend_gdk_events_init (backend);
+  if (!disable_event_retrieval)
+    _clutter_backend_gdk_events_init (backend);
 }
 
 static void
@@ -452,3 +455,16 @@ clutter_gdk_set_display (GdkDisplay *display)
 
   _foreign_dpy = g_object_ref (display);
 }
+
+void
+clutter_gdk_disable_event_retrieval (void)
+{
+  if (_clutter_context_is_initialized ())
+    {
+      g_warning ("%s() can only be used before calling clutter_init()",
+                 G_STRFUNC);
+      return;
+    }
+
+  disable_event_retrieval = TRUE;
+}

clutter/gdk/clutter-gdk.h

@@ -51,6 +51,8 @@ GdkFilterReturn clutter_gdk_handle_event                (GdkEvent     *event);
 
 ClutterStage *  clutter_gdk_get_stage_from_window       (GdkWindow    *window);
 
+void            clutter_gdk_disable_event_retrieval     (void);
+
 G_END_DECLS
 
 #endif /* __CLUTTER_GDK_H__ */