[mutter] clutter/actor: Handle clips correctly when building paint volume

[Marge Bot <marge-bot src gnome org>]

commit b5a7fe4b233ca80c998cb1f0a27fed495e1d13d1
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Sat Nov 21 11:26:42 2020 +0100

    clutter/actor: Handle clips correctly when building paint volume
    
    clutter_actor_paint() implements a clear preference for custom clips
    over clip_to_allocation: If a custom clip is set, clip_to_allocation is
    ignored.
    
    Since the paint volume reflects what Clutter is going to paint, we
    should handle it the same when putting together our paint volume: So
    first handle custom clips, and if one is set, use that. Then handle
    clip_to_allocation, and if that's set, use that. And finally, if both
    aren't set, union our allocation with the children paint volumes to get
    the building volume.
    
    clutter_actor_paint() also doesn't check whether the custom clip is
    empty: If that's the case, it will simply not paint anything. Given that
    that's allowed by clutter_actor_paint(), the paint volume should also
    follow here and return an empty paint volume in case the custom clip is
    empty.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1592>

 clutter/clutter/clutter-actor.c | 32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)
---
diff --git a/clutter/clutter/clutter-actor.c b/clutter/clutter/clutter-actor.c
index 9ba0050a87..cabd95f8f3 100644
--- a/clutter/clutter/clutter-actor.c
+++ b/clutter/clutter/clutter-actor.c
@@ -5701,6 +5701,21 @@ clutter_actor_update_default_paint_volume (ClutterActor       *self,
   if (priv->needs_allocation)
     return FALSE;
 
+  if (priv->has_clip)
+    {
+      graphene_point3d_t origin;
+
+      origin.x = priv->clip.origin.x;
+      origin.y = priv->clip.origin.y;
+      origin.z = 0;
+
+      clutter_paint_volume_set_origin (volume, &origin);
+      clutter_paint_volume_set_width (volume, priv->clip.size.width);
+      clutter_paint_volume_set_height (volume, priv->clip.size.height);
+
+      return TRUE;
+    }
+
   /* we start from the allocation */
   clutter_paint_volume_set_width (volume,
                                   priv->allocation.x2 - priv->allocation.x1);
@@ -5722,23 +5737,6 @@ clutter_actor_update_default_paint_volume (ClutterActor       *self,
     {
       ClutterActor *child;
 
-      if (priv->has_clip &&
-          priv->clip.size.width >= 0 &&
-          priv->clip.size.height >= 0)
-        {
-          graphene_point3d_t origin;
-
-          origin.x = priv->clip.origin.x;
-          origin.y = priv->clip.origin.y;
-          origin.z = 0;
-
-          clutter_paint_volume_set_origin (volume, &origin);
-          clutter_paint_volume_set_width (volume, priv->clip.size.width);
-          clutter_paint_volume_set_height (volume, priv->clip.size.height);
-
-          return TRUE;
-        }
-
       /* if we don't have children we just bail out here... */
       if (priv->n_children == 0)
         return res;