x11: Add XSETTINGS watcher

If we want to be able to get live notification of system settings
changes, we need watch the window that the XSETTINGS client conjures
up for us.

clutter/x11/clutter-backend-x11.c

@@ -101,6 +101,51 @@ static gboolean clutter_synchronise = FALSE;
 static int TrappedErrorCode = 0;
 static int (* old_error_handler) (Display *, XErrorEvent *);
 
+static ClutterX11FilterReturn
+xsettings_filter (XEvent       *xevent,
+                  ClutterEvent *event,
+                  gpointer      data)
+{
+  ClutterBackendX11 *backend_x11 = data;
+
+  if (_clutter_xsettings_client_process_event (backend_x11->xsettings, xevent))
+    return CLUTTER_X11_FILTER_REMOVE;
+  else
+    return CLUTTER_X11_FILTER_CONTINUE;
+}
+
+static Bool
+clutter_backend_x11_xsettings_watch (Window  window,
+                                     Bool    is_start,
+                                     long    mask,
+                                     void   *cb_data)
+{
+  ClutterBackendX11 *backend_x11 = cb_data;
+
+  if (is_start)
+    {
+      backend_x11->xsettings_xwin = window;
+      if (!backend_x11->xsettings_xwin)
+        return False;
+
+      clutter_x11_add_filter (xsettings_filter, backend_x11);
+
+      CLUTTER_NOTE (BACKEND, "Added filter on XSettings manager window 0x%x",
+                    (unsigned int) backend_x11->xsettings_xwin);
+    }
+  else
+    {
+      CLUTTER_NOTE (BACKEND, "Removed filter on XSettings manager window 0x%x",
+                    (unsigned int) backend_x11->xsettings_xwin);
+
+      clutter_x11_remove_filter (xsettings_filter, backend_x11);
+
+      backend_x11->xsettings_xwin = None;
+    }
+
+  return True;
+}
+
 static void
 clutter_backend_x11_xsettings_notify (const char       *name,
                                       XSettingsAction   action,
@@ -276,7 +321,7 @@ clutter_backend_x11_post_parse (ClutterBackend  *backend,
         _clutter_xsettings_client_new (backend_x11->xdpy,
                                        backend_x11->xscreen_num,
                                        clutter_backend_x11_xsettings_notify,
-                                       NULL,
+                                       clutter_backend_x11_xsettings_watch,
                                        backend_x11);
 
       if (clutter_synchronise)
@@ -431,8 +476,6 @@ gboolean
 clutter_backend_x11_handle_event (ClutterBackendX11 *backend_x11,
                                   XEvent *xevent)
 {
-  _clutter_xsettings_client_process_event (backend_x11->xsettings, xevent);
-
   return FALSE;
 }
 

clutter/x11/clutter-backend-x11.h

@@ -87,6 +87,7 @@ struct _ClutterBackendX11
   ClutterDeviceManager *device_manager;
 
   XSettingsClient *xsettings;
+  Window xsettings_xwin;
 };
 
 struct _ClutterBackendX11Class