clutter/actor: Remove the paint signal and keep the paint vfunc

The "paint" signal of ClutterActor has been a pain for everyone involved
long enough now, turns out we actually use it nowhere except tests
anymore (which has been handled in the last commits), so get rid of it
for good before anyone starts using it again.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1522

clutter/clutter/clutter-actor.c

@@ -167,16 +167,11 @@
  *   clutter_paint_node_unref (node);
  * }
  *
- * The #ClutterActorClass.paint() virtual function is invoked when the
- * #ClutterActor::paint signal is emitted, and after the other signal
- * handlers have been invoked. Overriding the paint virtual function
- * gives total control to the paint sequence of the actor itself,
- * including the children of the actor, if any.
- *
- * It is strongly discouraged to override the #ClutterActorClass.paint()
- * virtual function, as well as connecting to the #ClutterActor::paint
- * signal. These hooks into the paint sequence are considered legacy, and
- * will be removed when the Clutter API changes.
+ * The #ClutterActorClass.paint() virtual function function gives total
+ * control to the paint sequence of the actor itself, including the
+ * children of the actor, if any. It is strongly discouraged to override
+ * the #ClutterActorClass.paint() virtual function and it will be removed
+ * when the Clutter API changes.
  *
  * ## Handling events on an actor ## {#clutter-actor-event-handling}
  *
@@ -372,13 +367,6 @@
  * sub-class of #ClutterActor only for actors that should be used as leaf
  * nodes of a scene graph.
  *
- * If your actor should be painted in a custom way, you should
- * override the #ClutterActor::paint signal class handler. You can either
- * opt to chain up to the parent class implementation or decide to fully
- * override the default paint implementation; Clutter will set up the
- * transformations and clip regions prior to emitting the #ClutterActor::paint
- * signal.
- *
  * By overriding the #ClutterActorClass.get_preferred_width() and
  * #ClutterActorClass.get_preferred_height() virtual functions it is
  * possible to change or provide the preferred size of an actor; similarly,
@@ -3731,8 +3719,8 @@ clutter_actor_paint_node (ClutterActor        *actor,
  * This function is context-aware, and will either cause a
  * regular paint or a pick paint.
  *
- * This function will emit the #ClutterActor::paint signal or
- * the #ClutterActor::pick signal, depending on the context.
+ * This function will call the #ClutterActorClass.paint() virtual
+ * function.
  *
  * This function does not paint the actor if the actor is set to 0,
  * unless it is performing a pick paint.
@@ -3978,17 +3966,12 @@ clutter_actor_continue_paint (ClutterActor        *self,
       clutter_paint_node_set_static_name (dummy, "Root");
 
       /* XXX - for 1.12, we use the return value of paint_node() to
-       * decide whether we should emit the ::paint signal.
+       * decide whether we should call the paint() vfunc.
        */
       clutter_actor_paint_node (self, dummy, paint_context);
       clutter_paint_node_unref (dummy);
 
-      /* XXX:2.0 - Call the paint() virtual directly */
-      if (g_signal_has_handler_pending (self, actor_signals[PAINT],
-                                        0, TRUE))
-        g_signal_emit (self, actor_signals[PAINT], 0, paint_context);
-      else
-        CLUTTER_ACTOR_GET_CLASS (self)->paint (self, paint_context);
+      CLUTTER_ACTOR_GET_CLASS (self)->paint (self, paint_context);
     }
   else
     {
@@ -7828,39 +7811,6 @@ clutter_actor_class_init (ClutterActorClass *klass)
                               G_TYPE_FROM_CLASS (object_class),
                               _clutter_marshal_BOOLEAN__BOXEDv);
 
-  /**
-   * ClutterActor::paint:
-   * @actor: the #ClutterActor that received the signal
-   * @paint_context: a #ClutterPaintContext
-   *
-   * The ::paint signal is emitted each time an actor is being painted.
-   *
-   * Subclasses of #ClutterActor should override the #ClutterActorClass.paint
-   * virtual function paint themselves in that function.
-   *
-   * It is strongly discouraged to connect a signal handler to
-   * the #ClutterActor::paint signal; if you want to change the paint
-   * sequence of an existing #ClutterActor instance, either create a new
-   * #ClutterActor class and override the #ClutterActorClass.paint virtual
-   * function, or use a #ClutterEffect. The #ClutterActor::paint signal
-   * will be removed in a future version of Clutter.
-   *
-   * Since: 0.8
-   *
-   * Deprecated: 1.12: Override the #ClutterActorClass.paint virtual
-   *   function, use a #ClutterContent implementation, or a #ClutterEffect
-   *   instead of connecting to this signal.
-   */
-  actor_signals[PAINT] =
-    g_signal_new (I_("paint"),
-                  G_TYPE_FROM_CLASS (object_class),
-                  G_SIGNAL_RUN_LAST |
-                  G_SIGNAL_NO_HOOKS |
-                  G_SIGNAL_DEPRECATED,
-                  G_STRUCT_OFFSET (ClutterActorClass, paint),
-                  NULL, NULL, NULL,
-                  G_TYPE_NONE, 1,
-                  CLUTTER_TYPE_PAINT_CONTEXT);
   /**
    * ClutterActor::realize:
    * @actor: the #ClutterActor that received the signal
@@ -14821,9 +14771,8 @@ _clutter_actor_set_in_clone_paint (ClutterActor *self,
  *
  * Checks whether @self is being currently painted by a #ClutterClone
  *
- * This function is useful only inside the ::paint virtual function
- * implementations or within handlers for the #ClutterActor::paint
- * signal
+ * This function is useful only inside implementations of the
+ * #ClutterActorClass.paint() virtual function.
  *
  * This function should not be used by applications
  *
@@ -15738,46 +15687,6 @@ _clutter_actor_get_paint_volume_real (ClutterActor *self,
       return FALSE;
     }
 
-  /* Check if there are any handlers connected to the paint
-   * signal. If there are then all bets are off for what the paint
-   * volume for this actor might possibly be!
-   *
-   * XXX: It's expected that this is going to end up being quite a
-   * costly check to have to do here, but we haven't come up with
-   * another solution that can reliably catch paint signal handlers at
-   * the right time to either avoid artefacts due to invalid stage
-   * clipping or due to incorrect culling.
-   *
-   * Previously we checked in clutter_actor_paint(), but at that time
-   * we may already be using a stage clip that could be derived from
-   * an invalid paint-volume. We used to try and handle that by
-   * queuing a follow up, unclipped, redraw but still the previous
-   * checking wasn't enough to catch invalid volumes involved in
-   * culling (considering that containers may derive their volume from
-   * children that haven't yet been painted)
-   *
-   * Longer term, improved solutions could be:
-   * - Disallow painting in the paint signal, only allow using it
-   *   for tracking when paints happen. We can add another API that
-   *   allows monkey patching the paint of arbitrary actors but in a
-   *   more controlled way and that also supports modifying the
-   *   paint-volume.
-   * - If we could be notified somehow when signal handlers are
-   *   connected we wouldn't have to poll for handlers like this.
-   *
-   * XXX:2.0 - Remove when we remove the paint signal
-   */
-  if (g_signal_has_handler_pending (self,
-                                    actor_signals[PAINT],
-                                    0,
-                                    TRUE))
-    {
-      CLUTTER_NOTE (CLIPPING, "Bail from get_paint_volume (%s): "
-                    "Actor has \"paint\" signal handlers",
-                    _clutter_actor_get_debug_name (self));
-      return FALSE;
-    }
-
   _clutter_paint_volume_init_static (pv, self);
 
   if (!CLUTTER_ACTOR_GET_CLASS (self)->get_paint_volume (self, pv))