Initial surface aggregator implementation

cc/quads/shared_quad_state.h

 // 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.
 
 #ifndef CC_QUADS_SHARED_QUAD_STATE_H_
 #define CC_QUADS_SHARED_QUAD_STATE_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
 #include "third_party/skia/include/core/SkXfermode.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/transform.h"
 
 namespace base {
 class Value;
 }
 
 namespace cc {
 
+// SharedQuadState holds a set of properties that are common across multiple
+// DrawQuads. It's purely an optimization - the properties behave in exactly the
+// same way as if they were replicated on each DrawQuad. A given SharedQuadState
+// can only be shared by DrawQuads that are adjacent in their RenderPass'
+// QuadList.
 class CC_EXPORT SharedQuadState {
  public:
   static scoped_ptr<SharedQuadState> Create();
   ~SharedQuadState();
 
   scoped_ptr<SharedQuadState> Copy() const;
 
   void SetAll(const gfx::Transform& content_to_target_transform,
               gfx::Size content_bounds,
               const gfx::Rect& visible_content_rect,
@@ skipping 15 matching lines @@
   float opacity;
   SkXfermode::Mode blend_mode;
 
  private:
   SharedQuadState();
 };
 
 }  // namespace cc
 
 #endif  // CC_QUADS_SHARED_QUAD_STATE_H_