Enable map/unmap optimizations for subsurfaces

* subcompositor.c (ViewMap, ViewUnmap): Union view inferior
bounds whenever possible, instead of garbaging the
subcompositor.
* tests/subsurface_test.c (enum test_kind): New test
`SUBSURFACE_STACKING_1_KIND'.
(test_names): Add new name.
(LAST_TEST): Set to SUBSURFACE_STACKING_1_KIND.
(test_single_step): Implement SUBSURFACE_STACKING_1_KIND.

subcompositor.c

@@ -1793,19 +1793,29 @@ ViewMap (View *view)
   if (view->subcompositor
       && (view->link != view->inferior || view->buffer))
     {
-      /* Garbage the subcompositor and recompute bounds, if something
+      /* Recompute bounds, if something is attached to the view or it
-	 is attached to the view or it is not empty.  */
+	 is not empty.  */
-      SetGarbaged (view->subcompositor);
       SubcompositorUpdateBounds (view->subcompositor, DoAll);
+
+      /* Now, if the subcompositor is still not garbaged, damage each
+	 inferior of the view.  */
+      if (!IsGarbaged (view->subcompositor))
+	DamageIncludingInferiors (view);
     }
 }
 
 void
 ViewUnmap (View *view)
 {
+  pixman_region32_t damage;
+
   if (IsViewUnmapped (view))
     return;
 
+  /* Init the damage region.  */
+  pixman_region32_init (&damage);
+  ViewUnionInferiorBounds (view, &damage);
+
   /* Mark the view as unmapped.  */
   SetUnmapped (view);
 
@@ -1824,10 +1834,18 @@ ViewUnmap (View *view)
 	  SubcompositorUpdateBounds (view->subcompositor,
 				     DoAll);
 
-	  /* Garbage the view's subcompositor.  */
+	  /* If the subcompositor is still not garbaged, then apply
-	  SetGarbaged (view->subcompositor);
+	     the bounds of view and all its inferiors as extra
+	     damage.  */
+	  if (!IsGarbaged (view->subcompositor))
+	    pixman_region32_union (&view->subcompositor->additional_damage,
+				   &view->subcompositor->additional_damage,
+				   &damage);
 	}
     }
+
+  /* Finalize the damage region.  */
+  pixman_region32_fini (&damage);
 }
 
 void

tests/subsurface_test.c

@@ -31,6 +31,7 @@ enum test_kind
     SUBSURFACE_STACKING_KIND,
     SUBSURFACE_TREE_KIND,
     SUBSURFACE_GROW_SHRINK_KIND,
+    SUBSURFACE_STACKING_1_KIND,
   };
 
 static const char *test_names[] =
@@ -42,6 +43,7 @@ static const char *test_names[] =
     "subsurface_stacking",
     "subsurface_tree",
     "subsurface_grow_shrink",
+    "subsurface_stacking_1",
   };
 
 struct test_subsurface
@@ -53,7 +55,7 @@ struct test_subsurface
   struct wl_surface *surface;
 };
 
-#define LAST_TEST       SUBSURFACE_GROW_SHRINK_KIND
+#define LAST_TEST       SUBSURFACE_STACKING_1_KIND
 
 /* The display.  */
 static struct test_display *display;
@@ -427,7 +429,6 @@ test_single_step (enum test_kind kind)
 	 disappear!  */
       wl_surface_attach (subsurfaces[1]->surface, NULL, 0, 0);
       wl_surface_commit (subsurfaces[1]->surface);
-      wl_surface_commit (subsurfaces[1]->surface);
       wait_frame_callback (wayland_surface);
       sleep_or_verify ();
 
@@ -504,6 +505,53 @@ test_single_step (enum test_kind kind)
       wl_surface_commit (subsurfaces[1]->surface);
       wait_frame_callback (wayland_surface);
       sleep_or_verify ();
+
+      test_single_step (SUBSURFACE_STACKING_1_KIND);
+      break;
+
+    case SUBSURFACE_STACKING_1_KIND:
+      /* Move the second subsurface above the first.  Then, move the
+	 third subsurface above the fourth, and the fourth below the
+	 second.  */
+      wl_subsurface_place_above (subsurfaces[1]->subsurface,
+				 subsurfaces[0]->surface);
+      wl_subsurface_place_above (subsurfaces[2]->subsurface,
+				 subsurfaces[3]->surface);
+      wl_subsurface_place_below (subsurfaces[3]->subsurface,
+				 subsurfaces[1]->surface);
+
+      /* Next, attach some buffers to the third and fourth
+	 surface.  */
+      wl_surface_attach (subsurfaces[2]->surface, gradient_png, 0, 0);
+      wl_surface_attach (subsurfaces[3]->surface, cow_transparent_png,
+			 0, 0);
+      submit_surface_opaque_region (subsurfaces[2]->surface, 0, 0,
+				    100, 300);
+      wl_surface_commit (subsurfaces[2]->surface);
+      wl_surface_commit (subsurfaces[3]->surface);
+
+      /* Commit the first subsurface.  */
+      wl_surface_commit (subsurfaces[1]->surface);
+      wait_frame_callback (wayland_surface);
+
+      /* The result of the test should be as follows.  Above the first
+	 subsurface lies the fourth subsurface (cow_transparent.png),
+	 above which is the second subsurface (small.png), above which
+	 is the third subsurface (gradient.png).  */
+      sleep_or_verify ();
+
+      /* Next, test moving the third subsurface immediately below the
+	 fourth.  */
+      wl_subsurface_place_below (subsurfaces[2]->subsurface,
+				 subsurfaces[3]->surface);
+      wl_surface_commit (subsurfaces[1]->surface);
+      wait_frame_callback (wayland_surface);
+
+      /* The result of the test should be as follows.  Above the first
+	 subsurface lies the third subsurface (gradient.png), above
+	 which lies the fourth subsurface (cow_transparent.png), and
+	 finally the third (small.png).  */
+      sleep_or_verify ();
       break;
     }