clutter-actor: Cull actors that don't intersect the redraw clip

Previously we only culled actors that didn't intersect the bounding box
of the redraw clip. Now we also cull those whose paint volume bounds don't
intersect the arbitrary shape of the redraw clip.

This was inspired by the activities overview where idle windows and
workspace previews were being needlessly repainted. In that particular
case this yields more than 10% reduction in render time. But it probably
helps in other situations too.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1359

1 files changed, 37 insertions, 0 deletions

diff --git a/clutter/clutter/clutter-actor.c b/clutter/clutter/clutter-actor.c
index 05148e907..8805b35b1 100644
--- a/clutter/clutter/clutter-actor.c
+++ b/clutter/clutter/clutter-actor.c
@@ -3458,6 +3458,43 @@ cull_actor (ClutterActor        *self,
   *result_out =
     _clutter_paint_volume_cull (&priv->last_paint_volume, stage_clip);
 
+  if (*result_out != CLUTTER_CULL_RESULT_OUT)
+    {
+      const cairo_region_t *redraw_clip;
+
+      redraw_clip = clutter_paint_context_get_redraw_clip (paint_context);
+      if (redraw_clip)
+        {
+          ClutterActorBox paint_box;
+          cairo_rectangle_int_t paint_box_bounds;
+          cairo_region_overlap_t overlap;
+
+          _clutter_paint_volume_get_stage_paint_box (&priv->last_paint_volume,
+                                                     stage,
+                                                     &paint_box);
+
+          paint_box_bounds.x = floorf (paint_box.x1);
+          paint_box_bounds.y = floorf (paint_box.y1);
+          paint_box_bounds.width = ceilf (paint_box.x2 - paint_box_bounds.x);
+          paint_box_bounds.height = ceilf (paint_box.y2 - paint_box_bounds.y);
+
+          overlap = cairo_region_contains_rectangle (redraw_clip,
+                                                     &paint_box_bounds);
+          switch (overlap)
+            {
+            case CAIRO_REGION_OVERLAP_IN:
+              *result_out = CLUTTER_CULL_RESULT_IN;
+              break;
+            case CAIRO_REGION_OVERLAP_PART:
+              *result_out = CLUTTER_CULL_RESULT_PARTIAL;
+              break;
+            case CAIRO_REGION_OVERLAP_OUT:
+              *result_out = CLUTTER_CULL_RESULT_OUT;
+              break;
+            }
+        }
+    }
+
   return TRUE;
 }