mix-blend-mode implementation for accelerated layers

cc/trees/layer_tree_host_common.cc

 // Copyright 2011 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/trees/layer_tree_host_common.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "cc/base/math_util.h"
@@ skipping 557 matching lines @@
   if (LayerIsInExisting3DRenderingContext(layer) && !layer->preserves_3d() &&
       num_descendants_that_draw_content > 0) {
     TRACE_EVENT_INSTANT0(
         "cc",
         "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface flattening",
         TRACE_EVENT_SCOPE_THREAD);
     DCHECK(!is_root);
     return true;
   }
 
+  // If the layer has blending.
+  // TODO(rosca): this is temporary, until blending is implemented for other
+  // types of quads than RenderPassQuad. Layers having descendants that draw
+  // content will still create a separate rendering surface.
+  if (!layer->uses_default_blend_mode()) {
+      TRACE_EVENT_INSTANT0(
+          "cc",
+          "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface blending",
+          TRACE_EVENT_SCOPE_THREAD);
+      return true;
+  }
+
+  // If the layer has isolation.
+  // TODO(rosca): to be optimized - create separate rendering surface only when
+  // the blending descendants might have access to the content behind this layer
+  // (layer has transparent background or descendants overflow)
+  if (layer->is_root_for_isolated_group()) {
+    TRACE_EVENT_INSTANT0(
+        "cc",
+        "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface isolation",
+        TRACE_EVENT_SCOPE_THREAD);
+    return true;
+  }
+
   // If the layer clips its descendants but it is not axis-aligned with respect
   // to its parent.
   bool layer_clips_external_content =
       LayerClipsSubtree(layer) || layer->HasDelegatedContent();
   if (layer_clips_external_content && !axis_aligned_with_respect_to_parent &&
       !layer->draw_properties().descendants_can_clip_selves) {
     TRACE_EVENT_INSTANT0(
         "cc",
         "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface clipping",
         TRACE_EVENT_SCOPE_THREAD);
@@ skipping 1639 matching lines @@
   // At this point, we think the point does hit the touch event handler region
   // on the layer, but we need to walk up the parents to ensure that the layer
   // was not clipped in such a way that the hit point actually should not hit
   // the layer.
   if (PointIsClippedBySurfaceOrClipRect(screen_space_point, layer_impl))
     return false;
 
   return true;
 }
 }  // namespace cc