clutter/actor: Add API to invalidate cached paint volumes

ClutterActors can override the get_paint_volume() vfunc in case they
draw outside the allocation. That's used by a bunch of actors, for
example ClutterText or StViewport in gnome-shell.

In case of StViewport, the paint volume returned depends on the value of
the StAdjustment, which means when we start to cache paint volumes more
agressively in ClutterActor, we'll need to add API that allows
StViewport to invalidate the paint volume. So introduce
clutter_actor_invalidate_paint_volume() to invalidate the cached paint
volume.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1773>

clutter/clutter/clutter-actor.c

@@ -19533,6 +19533,23 @@ clutter_actor_invalidate_transform (ClutterActor *self)
   transform_changed (self);
 }
 
+/**
+ * clutter_actor_invalidate_paint_volume:
+ * @self: A #ClutterActor
+ *
+ * Invalidates the cached paint volume of @self. This is needed for
+ * implementations overriding the #ClutterActorClass.get_paint_volume()
+ * virtual function and has to be called every time the paint volume
+ * returned by that function would change.
+ */
+void
+clutter_actor_invalidate_paint_volume (ClutterActor *self)
+{
+  g_return_if_fail (CLUTTER_IS_ACTOR (self));
+
+  self->priv->needs_paint_volume_update = TRUE;
+}
+
 gboolean
 clutter_actor_get_redraw_clip (ClutterActor       *self,
                                ClutterPaintVolume *dst_old_pv,

clutter/clutter/clutter-actor.h

@@ -931,6 +931,9 @@ GList * clutter_actor_peek_stage_views (ClutterActor *self);
 CLUTTER_EXPORT
 void clutter_actor_invalidate_transform (ClutterActor *self);
 
+CLUTTER_EXPORT
+void clutter_actor_invalidate_paint_volume (ClutterActor *self);
+
 G_END_DECLS
 
 #endif /* __CLUTTER_ACTOR_H__ */