[mutter] laters: Use 'before-update' signal from stage

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 110ed7ff8a8f8bcf17224844759926ea4be13ef6
Author: Jonas Ådahl <jadahl gmail com>
Date:   Fri May 29 23:33:46 2020 +0200

    laters: Use 'before-update' signal from stage
    
    Instead of the 'pre-paint' signal on MetaCompositor, rely directly on
    the 'before-update' signal on the stage. A reason for this is that the
    callback should not only invoked in connection to painting, but updating
    in general. Currently the 'pre-paint' signal is emitted no matter
    whether there were any painting or not, but that's both misleading and
    will go away.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1285

 src/compositor/compositor.c | 13 +++++++++++--
 src/compositor/meta-later.c | 23 +++++++++++------------
 2 files changed, 22 insertions(+), 14 deletions(-)
---
diff --git a/src/compositor/compositor.c b/src/compositor/compositor.c
index 5918c90474..ff6a6aa73e 100644
--- a/src/compositor/compositor.c
+++ b/src/compositor/compositor.c
@@ -1246,10 +1246,16 @@ meta_compositor_get_property (GObject    *object,
 static void
 meta_compositor_init (MetaCompositor *compositor)
 {
+}
+
+static void
+meta_compositor_constructed (GObject *object)
+{
+  MetaCompositor *compositor = META_COMPOSITOR (object);
   MetaCompositorPrivate *priv =
     meta_compositor_get_instance_private (compositor);
-  MetaBackend *backend = meta_get_backend ();
-  ClutterBackend *clutter_backend = meta_backend_get_clutter_backend (backend);
+  ClutterBackend *clutter_backend =
+    meta_backend_get_clutter_backend (priv->backend);
 
   priv->context = clutter_backend->cogl_context;
 
@@ -1265,6 +1271,8 @@ meta_compositor_init (MetaCompositor *compositor)
                                            NULL);
 
   priv->laters = meta_laters_new (compositor);
+
+  G_OBJECT_CLASS (meta_compositor_parent_class)->constructed (object);
 }
 
 static void
@@ -1303,6 +1311,7 @@ meta_compositor_class_init (MetaCompositorClass *klass)
 
   object_class->set_property = meta_compositor_set_property;
   object_class->get_property = meta_compositor_get_property;
+  object_class->constructed = meta_compositor_constructed;
   object_class->dispose = meta_compositor_dispose;
 
   klass->remove_window = meta_compositor_real_remove_window;
diff --git a/src/compositor/meta-later.c b/src/compositor/meta-later.c
index 67e229d38a..9265f2e44a 100644
--- a/src/compositor/meta-later.c
+++ b/src/compositor/meta-later.c
@@ -50,7 +50,7 @@ struct _MetaLaters
 
   GSList *laters[META_LATER_N_TYPES];
 
-  gulong pre_paint_handler_id;
+  gulong before_update_handler_id;
 };
 
 static MetaLater *
@@ -165,8 +165,8 @@ run_repaint_laters (GSList **laters_list)
 }
 
 static void
-on_pre_paint (MetaCompositor *compositor,
-              MetaLaters     *laters)
+on_before_update (ClutterStage *stage,
+                  MetaLaters   *laters)
 {
   unsigned int i;
   GSList *l;
@@ -187,11 +187,7 @@ on_pre_paint (MetaCompositor *compositor,
     }
 
   if (needs_schedule_update)
-    {
-      ClutterStage *stage = meta_compositor_get_stage (compositor);
-
-      clutter_stage_schedule_update (stage);
-    }
+    clutter_stage_schedule_update (stage);
 }
 
 static gboolean
@@ -320,14 +316,16 @@ meta_later_remove (unsigned int later_id)
 MetaLaters *
 meta_laters_new (MetaCompositor *compositor)
 {
+  ClutterStage *stage = meta_compositor_get_stage (compositor);
   MetaLaters *laters;
 
   laters = g_new0 (MetaLaters, 1);
   laters->compositor = compositor;
 
-  laters->pre_paint_handler_id = g_signal_connect (compositor, "pre-paint",
-                                                   G_CALLBACK (on_pre_paint),
-                                                   laters);
+  laters->before_update_handler_id =
+    g_signal_connect (stage, "before-update",
+                      G_CALLBACK (on_before_update),
+                      laters);
 
   return laters;
 }
@@ -335,11 +333,12 @@ meta_laters_new (MetaCompositor *compositor)
 void
 meta_laters_free (MetaLaters *laters)
 {
+  ClutterStage *stage = meta_compositor_get_stage (laters->compositor);
   unsigned int i;
 
   for (i = 0; i < G_N_ELEMENTS (laters->laters); i++)
     g_slist_free_full (laters->laters[i], (GDestroyNotify) meta_later_unref);
 
-  g_clear_signal_handler (&laters->pre_paint_handler_id, laters->compositor);
+  g_clear_signal_handler (&laters->before_update_handler_id, stage);
   g_free (laters);
 }