mix-blend-mode implementation for accelerated layers

cc/layers/delegated_renderer_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/delegated_renderer_layer.h"
 
 #include "cc/layers/delegated_renderer_layer_client.h"
 #include "cc/layers/delegated_renderer_layer_impl.h"
 #include "cc/output/delegated_frame_data.h"
 #include "cc/quads/render_pass_draw_quad.h"
@@ skipping 89 matching lines @@
   SetNextCommitWaitsForActivation();
 }
 
 void DelegatedRendererLayer::SetDisplaySize(gfx::Size size) {
   if (display_size_ == size)
     return;
   display_size_ = size;
   SetNeedsCommit();
 }
 
-static bool FrameDataHasFilter(DelegatedFrameData* frame) {
+static bool FrameDataRequiresFilterContext(const DelegatedFrameData* frame) {
   for (size_t i = 0; i < frame->render_pass_list.size(); ++i) {
     const QuadList& quad_list = frame->render_pass_list[i]->quad_list;
     for (size_t j = 0; j < quad_list.size(); ++j) {
+      if (quad_list[j]->shared_quad_state->blend_mode !=
+          SkXfermode::kSrcOver_Mode)
+        return true;
       if (quad_list[j]->material != DrawQuad::RENDER_PASS)
         continue;
       const RenderPassDrawQuad* render_pass_quad =
           RenderPassDrawQuad::MaterialCast(quad_list[j]);
       if (!render_pass_quad->filters.IsEmpty() ||
           !render_pass_quad->background_filters.IsEmpty())
         return true;
     }
   }
   return false;
 }
 
 bool DelegatedRendererLayer::Update(ResourceUpdateQueue* queue,
                                     const OcclusionTracker* occlusion) {
   bool updated = Layer::Update(queue, occlusion);
   if (!should_collect_new_frame_)
     return updated;
 
   frame_data_ =
       frame_provider_->GetFrameDataAndRefResources(this, &frame_damage_);
   should_collect_new_frame_ = false;
 
-  // If any quad has a filter operation, then we need a filter context to draw
-  // this layer's content.
-  if (FrameDataHasFilter(frame_data_) && layer_tree_host())
+  // If any quad has a filter operation or a blend mode other than normal,
+  // then we need an offscreen context to draw this layer's content.
+  if (FrameDataRequiresFilterContext(frame_data_))
     layer_tree_host()->set_needs_filter_context();
 
   return true;
 }
 
 }  // namespace cc