Disable frame sync for GtkPlug

Plug windows weren't redrawing properly because the embedded
window was expecting to get messages for each frame from the
compositor, but the compositor doesn't know about embedded
windows. Simply disable frame sync for GtkPlug's GdkWindow -
extending XEMBED to handle frame sync isn't interesting
at this point.

A new API gdk_x11_window_set_frame_sync_enabled() is added
to allow this to be done.

https://bugzilla.gnome.org/show_bug.cgi?id=701613

gdk/x11/gdkwindow-x11.c

@@ -157,6 +157,7 @@ gdk_window_impl_x11_init (GdkWindowImplX11 *impl)
   impl->device_cursor = g_hash_table_new_full (NULL, NULL,
                                                NULL, g_object_unref);
   impl->window_scale = 1;
+  impl->frame_sync_enabled = TRUE;
 }
 
 GdkToplevelX11 *
@@ -403,7 +404,8 @@ gdk_x11_window_end_frame (GdkWindow *window)
 		       impl->toplevel->extended_update_counter,
 		       impl->toplevel->current_counter_value);
 
-      if (gdk_x11_screen_supports_net_wm_hint (gdk_window_get_screen (window),
+      if (impl->frame_sync_enabled &&
+          gdk_x11_screen_supports_net_wm_hint (gdk_window_get_screen (window),
 					       gdk_atom_intern_static_string ("_NET_WM_FRAME_DRAWN")))
         {
           impl->toplevel->frame_pending = TRUE;
@@ -5443,6 +5445,37 @@ gdk_x11_window_get_scale_factor (GdkWindow *window)
   return impl->window_scale;
 }
 
+/**
+ * gdk_x11_window_set_frame_sync_enabled:
+ * @window: (type GdkX11Window): a native #GdkWindow
+ * @frame_sync_enabled: whether frame-synchronization should be enabled
+ *
+ * This function can be used to disable frame synchronization for a window.
+ * Normally frame synchronziation will be enabled or disabled based on whether
+ * the system has a compositor that supports frame synchronization, but if
+ * the window is not directly managed by the window manager, then frame
+ * synchronziation may need to be disabled. This is the case for a window
+ * embedded via the XEMBED protocol.
+ *
+ * Since: 3.8
+ */
+void
+gdk_x11_window_set_frame_sync_enabled (GdkWindow *window,
+                                       gboolean   frame_sync_enabled)
+{
+  /* Try to ensure the window has a native window */
+  if (!_gdk_window_has_impl (window))
+    gdk_window_ensure_native (window);
+
+  if (!GDK_WINDOW_IS_X11 (window))
+    {
+      g_warning (G_STRLOC " drawable is not a native X11 window");
+      return;
+    }
+
+  GDK_WINDOW_IMPL_X11 (window->impl)->frame_sync_enabled = FALSE;
+}
+
 static void
 gdk_window_impl_x11_class_init (GdkWindowImplX11Class *klass)
 {

gdk/x11/gdkwindow-x11.h

@@ -74,6 +74,7 @@ struct _GdkWindowImplX11
                            * unset during resizing and scaling */
   guint override_redirect : 1;
   guint frame_clock_connected : 1;
+  guint frame_sync_enabled : 1;
 
   cairo_surface_t *cairo_surface;
 
@@ -176,6 +177,8 @@ GType gdk_window_impl_x11_get_type (void);
 
 void            gdk_x11_window_set_user_time        (GdkWindow *window,
 						     guint32    timestamp);
+void            gdk_x11_window_set_frame_sync_enabled (GdkWindow *window,
+                                                       gboolean   frame_sync_enabled);
 
 GdkToplevelX11 *_gdk_x11_window_get_toplevel        (GdkWindow *window);
 void            _gdk_x11_window_tmp_unset_bg        (GdkWindow *window,

gdk/x11/gdkx11window.h

@@ -71,6 +71,10 @@ void     gdk_x11_window_set_hide_titlebar_when_maximized (GdkWindow *window,
 GDK_AVAILABLE_IN_ALL
 void     gdk_x11_window_move_to_current_desktop (GdkWindow   *window);
 
+GDK_AVAILABLE_IN_3_8
+void     gdk_x11_window_set_frame_sync_enabled (GdkWindow *window,
+                                                gboolean   frame_sync_enabled);
+
 /**
  * GDK_WINDOW_XDISPLAY:
  * @win: a #GdkWindow.

gtk/gtkplug.c

@@ -1053,6 +1053,13 @@ gtk_plug_realize (GtkWidget *widget)
       else /* If it's a passive plug, we use the root window */
         gdk_window = gdk_window_new (gtk_widget_get_root_window (widget),
                                      &attributes, attributes_mask);
+      /* Because the window isn't known to the window manager,
+       * frame sync won't work. In theory, XEMBED could be extended
+       * so that embedder did frame sync like a window manager, but
+       * it's just not worth the effort considering the current
+       * minimal use of XEMBED.
+       */
+      gdk_x11_window_set_frame_sync_enabled (gdk_window, FALSE);
       gtk_widget_set_window (widget, gdk_window);
 
       gdk_display_sync (gtk_widget_get_display (widget));