[mutter/wip/carlosg/clip-me-harder: 5/5] compositor: Clip obscured background areas

[Carlos Garnacho <carlosg src gnome org>]

commit 7944d7057fc5b1e2b1cf412fa3d76d9c1b7ad994
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sun Jan 27 15:49:41 2019 +0100

    compositor: Clip obscured background areas
    
    The MetaBackgroundActor was ignoring the unobscured area altogether,
    and just painted according to the clip area. Check the unobscured
    area too, as it might well be covered by client windows.

 src/compositor/meta-background-actor.c | 64 +++++++++++++++++++++++++---------
 1 file changed, 48 insertions(+), 16 deletions(-)
---
diff --git a/src/compositor/meta-background-actor.c b/src/compositor/meta-background-actor.c
index 267f762cc..7820de2cf 100644
--- a/src/compositor/meta-background-actor.c
+++ b/src/compositor/meta-background-actor.c
@@ -177,6 +177,7 @@ struct _MetaBackgroundActor
   gboolean force_bilinear;
 
   cairo_region_t *clip_region;
+  cairo_region_t *unobscured_region;
 };
 
 static void cullable_iface_init (MetaCullableInterface *iface);
@@ -193,12 +194,22 @@ set_clip_region (MetaBackgroundActor *self,
     self->clip_region = cairo_region_copy (clip_region);
 }
 
+static void
+set_unobscured_region (MetaBackgroundActor *self,
+                       cairo_region_t      *unobscured_region)
+{
+  g_clear_pointer (&self->unobscured_region, cairo_region_destroy);
+  if (unobscured_region)
+    self->unobscured_region = cairo_region_copy (unobscured_region);
+}
+
 static void
 meta_background_actor_dispose (GObject *object)
 {
   MetaBackgroundActor *self = META_BACKGROUND_ACTOR (object);
 
   set_clip_region (self, NULL);
+  set_unobscured_region (self, NULL);
   meta_background_actor_set_background (self, NULL);
   if (self->pipeline)
     {
@@ -500,7 +511,8 @@ meta_background_actor_paint (ClutterActor *actor)
   ClutterActorBox actor_box;
   cairo_rectangle_int_t actor_pixel_rect;
   CoglFramebuffer *fb;
-  int i;
+  cairo_region_t *region;
+  int i, n_rects;
 
   if ((self->clip_region && cairo_region_is_empty (self->clip_region)))
     return;
@@ -522,27 +534,43 @@ meta_background_actor_paint (ClutterActor *actor)
 
   /* Now figure out what to actually paint.
    */
-  if (self->clip_region != NULL)
+  if (self->clip_region)
     {
-      int n_rects = cairo_region_num_rectangles (self->clip_region);
-      if (n_rects <= MAX_RECTS)
-        {
-           for (i = 0; i < n_rects; i++)
-             {
-               cairo_rectangle_int_t rect;
-               cairo_region_get_rectangle (self->clip_region, i, &rect);
+      region = cairo_region_copy (self->clip_region);
+      cairo_region_intersect_rectangle (region, &actor_pixel_rect);
+    }
+  else
+    {
+      region = cairo_region_create_rectangle (&actor_pixel_rect);
+    }
 
-               if (!gdk_rectangle_intersect (&actor_pixel_rect, &rect, &rect))
-                 continue;
+  if (self->unobscured_region)
+    cairo_region_intersect (region, self->unobscured_region);
 
-               paint_clipped_rectangle (fb, self->pipeline, &rect, &self->texture_area);
-             }
+  if (cairo_region_is_empty (region))
+    {
+      cairo_region_destroy (region);
+      return;
+    }
 
-           return;
+  n_rects = cairo_region_num_rectangles (region);
+  if (n_rects <= MAX_RECTS)
+    {
+      for (i = 0; i < n_rects; i++)
+        {
+          cairo_rectangle_int_t rect;
+          cairo_region_get_rectangle (region, i, &rect);
+          paint_clipped_rectangle (fb, self->pipeline, &rect,
+                                   &self->texture_area);
         }
     }
-
-  paint_clipped_rectangle (fb, self->pipeline, &actor_pixel_rect, &self->texture_area);
+  else
+    {
+      cairo_rectangle_int_t rect;
+      cairo_region_get_extents (region, &rect);
+      paint_clipped_rectangle (fb, self->pipeline, &rect,
+                               &self->texture_area);
+    }
 }
 
 static void
@@ -796,6 +824,8 @@ meta_background_actor_cull_out (MetaCullable   *cullable,
                                 cairo_region_t *clip_region)
 {
   MetaBackgroundActor *self = META_BACKGROUND_ACTOR (cullable);
+
+  set_unobscured_region (self, unobscured_region);
   set_clip_region (self, clip_region);
 }
 
@@ -803,6 +833,8 @@ static void
 meta_background_actor_reset_culling (MetaCullable *cullable)
 {
   MetaBackgroundActor *self = META_BACKGROUND_ACTOR (cullable);
+
+  set_unobscured_region (self, NULL);
   set_clip_region (self, NULL);
 }