cc: Derive draw opacity from property trees

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 <algorithm>
 
 #include "base/atomic_sequence_num.h"
 #include "base/location.h"
@@ skipping 1300 matching lines @@
                     offset_to_transform_parent().y());
   } else {
     // Surfaces need to apply their sublayer scale.
     xform.Scale(target_node->data.sublayer_scale.x(),
                 target_node->data.sublayer_scale.y());
   }
   xform.Scale(1.0 / contents_scale_x(), 1.0 / contents_scale_y());
   return xform;
 }
 
+float Layer::DrawOpacityFromPropertyTrees(const OpacityTree& tree) const {
+  if (!render_target())
+    return 0.f;
+
+  const OpacityNode* target_node =
+      tree.Node(render_target()->opacity_tree_index());
+  const OpacityNode* node = tree.Node(opacity_tree_index());
+  if (node == target_node)
+    return 1.f;
+
+  float draw_opacity = 1.f;
+  while (node != target_node) {
+    draw_opacity *= node->data;
+    node = tree.parent(node);
+  }
+  return draw_opacity;
+}
+
 void Layer::SetFrameTimingRequests(
     const std::vector<FrameTimingRequest>& requests) {
   frame_timing_requests_ = requests;
   frame_timing_requests_dirty_ = true;
   SetNeedsCommit();
 }
 
 }  // namespace cc