cc : Rebuild property trees when opacity changes only if its required.

cc/layers/layer.cc

 // Copyright 2010 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/layer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 449 matching lines @@
   if (background_filters_ == filters)
     return;
   background_filters_ = filters;
   SetNeedsCommit();
 }
 
 void Layer::SetOpacity(float opacity) {
   DCHECK(IsPropertyChangeAllowed());
   if (opacity_ == opacity)
     return;
+  // We need to force a property tree rebuild when opacity changes from 1 to a
+  // non-1 value or vice-versa as render surfaces can change.
+  bool force_rebuild = opacity == 1.f || opacity_ == 1.f;
   opacity_ = opacity;
   SetSubtreePropertyChanged();
+  if (layer_tree_host_ && !force_rebuild) {
+    PropertyTrees* property_trees = layer_tree_host_->property_trees();
+    auto effect_id_to_index = property_trees->effect_id_to_index_map.find(id());
+    if (effect_id_to_index != property_trees->effect_id_to_index_map.end()) {
+      EffectNode* node =
+          property_trees->effect_tree.Node(effect_id_to_index->second);
+      node->data.opacity = opacity;
+      node->data.effect_changed = true;
+      property_trees->effect_tree.set_needs_update(true);
+      SetNeedsCommitNoRebuild();
+      return;
+    }
+  }
   SetNeedsCommit();
 }
 
 float Layer::EffectiveOpacity() const {
   return hide_layer_and_subtree_ ? 0.f : opacity_;
 }
 
 bool Layer::OpacityIsAnimating() const {
   DCHECK(layer_tree_host_);
   return layer_tree_host_->IsAnimatingOpacityProperty(this);
@@ skipping 1288 matching lines @@
       ->data.num_copy_requests_in_subtree;
 }
 
 gfx::Transform Layer::screen_space_transform() const {
   DCHECK_NE(transform_tree_index_, -1);
   return draw_property_utils::ScreenSpaceTransform(
       this, layer_tree_host_->property_trees()->transform_tree);
 }
 
 }  // namespace cc