[2/5] Disable transformed rasterization if layer is opaque

cc/layers/picture_layer.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/picture_layer.h"
 
 #include "base/auto_reset.h"
 #include "base/trace_event/trace_event.h"
 #include "cc/layers/content_layer_client.h"
 #include "cc/layers/picture_layer_impl.h"
@@ skipping 230 matching lines @@
     picture_layer_inputs_.recorded_viewport = gfx::Rect();
     picture_layer_inputs_.display_list = nullptr;
     picture_layer_inputs_.painter_reported_memory_usage = 0;
   }
 }
 
 bool PictureLayer::ShouldUseTransformedRasterization() const {
   if (!picture_layer_inputs_.allow_transformed_rasterization)
     return false;
 
+  // Background color overfill is undesirable with transformed rasterization.
+  // However, without background overfill, the tiles will be non-opaque on
+  // external edges, and layer opaque region can't be computed in layer space
+  // due to rounding under extreme scaling. This defeats many opaque layer
+  // optimization. Prefer optimization over quality for this particular case.
+  if (contents_opaque())
+    return false;
+
   const TransformTree& transform_tree =
       layer_tree_host()->property_trees()->transform_tree;
   DCHECK(!transform_tree.needs_update());
   if (transform_tree.Node(transform_tree_index())
           ->to_screen_is_potentially_animated)
     return false;
 
   const gfx::Transform& to_screen =
       transform_tree.ToScreen(transform_tree_index());
   if (!to_screen.IsScaleOrTranslation())
     return false;
 
   float origin_x =
       to_screen.matrix().getFloat(0, 3) + offset_to_transform_parent().x();
   float origin_y =
       to_screen.matrix().getFloat(1, 3) + offset_to_transform_parent().y();
   if (origin_x - floorf(origin_x) == 0.f && origin_y - floorf(origin_y) == 0.f)
     return false;
 
   return true;
 }
 
 const DisplayItemList* PictureLayer::GetDisplayItemList() {
   return picture_layer_inputs_.display_list.get();
 }
 
 }  // namespace cc