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;
+  bool force_rebuild = opacity == 1.f || opacity_ == 1.f;

[ajuma, 2016/05/16 22:05:20]

Please add a comment explaining why we need to unconditionally rebuild in this
case.

[jaydasika, 2016/05/17 01:40:00]

Done.

   opacity_ = opacity;
   SetSubtreePropertyChanged();

[ajuma, 2016/05/16 22:05:20]

I think this is only needed if we rebuild (Layer::SetTransform also calls this
even when not rebuilding, and that seems unnecessary too). Please move this call
and update the test to check for this.

[jaydasika, 2016/05/17 01:40:00]

I think we will need to mark both on the layer and property trees because if we
rebuild property trees for some other reason, we should not loose the damage
tracking info.

+  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