Split picture layer quads to allow removing more occluded area.

cc/trees/occlusion.cc

Index: cc/trees/occlusion.cc
diff --git a/cc/trees/occlusion.cc b/cc/trees/occlusion.cc
index e86a1a05e32cffd9d5946dffe5c1a8ddcaa11a30..05a428075ab04b84fc0e4f528e805d04c1fb7639 100644
--- a/cc/trees/occlusion.cc
+++ b/cc/trees/occlusion.cc
@@ -5,6 +5,7 @@
 #include "cc/trees/occlusion.h"
 
 #include "cc/base/math_util.h"
+#include "cc/base/region.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace cc {
@@ -16,9 +17,9 @@ Occlusion::Occlusion(const gfx::Transform& draw_transform,
                      const SimpleEnclosedRegion& occlusion_from_outside_target,
                      const SimpleEnclosedRegion& occlusion_from_inside_target)
     : draw_transform_(draw_transform),
+      inverse_draw_transform_(gfx::Transform::kSkipInitialization),
       occlusion_from_outside_target_(occlusion_from_outside_target),
-      occlusion_from_inside_target_(occlusion_from_inside_target) {
-}
+      occlusion_from_inside_target_(occlusion_from_inside_target) {}
 
 Occlusion Occlusion::GetOcclusionWithGivenDrawTransform(
     const gfx::Transform& transform) const {
@@ -56,15 +57,17 @@ gfx::Rect Occlusion::GetUnoccludedContentRect(
   if (unoccluded_rect_in_target_surface.IsEmpty())
     return gfx::Rect();
 
-  gfx::Transform inverse_draw_transform(gfx::Transform::kSkipInitialization);
-  bool ok = draw_transform_.GetInverse(&inverse_draw_transform);
-  // TODO(ajuma): Skip drawing layers with uninvertible draw transforms, and
-  // change this to a DCHECK. crbug.com/517170
-  if (!ok)
-    return content_rect;
+  if (!inverse_transform_initialized_) {
+    bool ok = draw_transform_.GetInverse(&inverse_draw_transform_);
+    // TODO(ajuma): Skip drawing layers with uninvertible draw transforms, and
+    // change this to a DCHECK. crbug.com/517170
+    if (!ok)
+      return content_rect;
+    inverse_transform_initialized_ = true;
+  }
 
   gfx::Rect unoccluded_rect = MathUtil::ProjectEnclosingClippedRect(
-      inverse_draw_transform, unoccluded_rect_in_target_surface);
+      inverse_draw_transform_, unoccluded_rect_in_target_surface);
   unoccluded_rect.Intersect(content_rect);
 
   return unoccluded_rect;
@@ -88,6 +91,27 @@ gfx::Rect Occlusion::GetUnoccludedRectInTargetSurface(
   return unoccluded_rect_in_target_surface;
 }
 
+void Occlusion::OccludeContentRegion(Region* region) const {
+  if (!draw_transform_.IsScaleOrTranslation())
+    return;
+
+  if (!inverse_transform_initialized_) {
+    bool ok = draw_transform_.GetInverse(&inverse_draw_transform_);
+    if (!ok)
+      return;
+    inverse_transform_initialized_ = true;
+  }
+
+  if (!occlusion_from_inside_target_.IsEmpty()) {
+    region->Subtract(MathUtil::MapEnclosedRectWith2dAxisAlignedTransform(
+        inverse_draw_transform_, occlusion_from_inside_target_.bounds()));
+  }
+  if (!occlusion_from_outside_target_.IsEmpty()) {
+    region->Subtract(MathUtil::MapEnclosedRectWith2dAxisAlignedTransform(
+        inverse_draw_transform_, occlusion_from_outside_target_.bounds()));
+  }
+}
+
 bool Occlusion::IsEqual(const Occlusion& other) const {
   return draw_transform_ == other.draw_transform_ &&
          occlusion_from_inside_target_ == other.occlusion_from_inside_target_ &&