[mutter] background-actor: Do not copy empty clip/unobscured regions

[Carlos Garnacho <carlosg src gnome org>]

commit 39a8c047d18bf0ee88f294892fb64fe82928f5b4
Author: Robert Mader <robert mader posteo de>
Date:   Tue Feb 25 20:10:48 2020 +0100

    background-actor: Do not copy empty clip/unobscured regions
    
    Clip and unobscured regions stricly shrink during culling. If they
    are already empty, simply reference the empty region to reduce allocations.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/1082

 src/compositor/meta-background-actor.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
---
diff --git a/src/compositor/meta-background-actor.c b/src/compositor/meta-background-actor.c
index 466dfc2ab..54a6fa5f4 100644
--- a/src/compositor/meta-background-actor.c
+++ b/src/compositor/meta-background-actor.c
@@ -193,7 +193,12 @@ set_clip_region (MetaBackgroundActor *self,
 {
   g_clear_pointer (&self->clip_region, cairo_region_destroy);
   if (clip_region)
-    self->clip_region = cairo_region_copy (clip_region);
+    {
+      if (cairo_region_is_empty (clip_region))
+        self->clip_region = cairo_region_reference (clip_region);
+      else
+        self->clip_region = cairo_region_copy (clip_region);
+    }
 }
 
 static void
@@ -202,7 +207,12 @@ set_unobscured_region (MetaBackgroundActor *self,
 {
   g_clear_pointer (&self->unobscured_region, cairo_region_destroy);
   if (unobscured_region)
-    self->unobscured_region = cairo_region_copy (unobscured_region);
+    {
+      if (cairo_region_is_empty (unobscured_region))
+        self->unobscured_region = cairo_region_reference (unobscured_region);
+      else
+        self->unobscured_region = cairo_region_copy (unobscured_region);
+    }
 }
 
 static void