cc: Don't draw and swap if the frame will not change.

cc/trees/layer_tree_host_impl.h

 // 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.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time.h"
@@ skipping 107 matching lines @@
     FrameData();
     ~FrameData();
 
     std::vector<gfx::Rect> occluding_screen_space_rects;
     std::vector<gfx::Rect> non_occluding_screen_space_rects;
     RenderPassList render_passes;
     RenderPassIdHashMap render_passes_by_id;
     const LayerList* render_surface_layer_list;
     LayerList will_draw_layers;
     bool contains_incomplete_tile;
+    bool has_no_damage;

[enne (OOO), 2013/03/26 01:42:07]

Weren't you just saying FrameData had too many members?

[danakj, 2013/03/26 02:00:10]

Yes, this is bad and I feel bad.

I tried to do this differently, but you can't just decide based on the
|render_passes| being empty, or on the damage being empty, because these are
always true once you get to SwapBuffers(). So.. yeh.

 
     // RenderPassSink implementation.
     virtual void AppendRenderPass(scoped_ptr<RenderPass> render_pass) OVERRIDE;
   };
 
   virtual void BeginCommit();
   virtual void CommitComplete();
   virtual void Animate(base::TimeTicks monotonic_time,
                        base::Time wall_clock_time);
 
   void ManageTiles();
   void SetAnticipatedDrawTime(base::TimeTicks time);
 
   // Returns false if problems occured preparing the frame, and we should try
   // to avoid displaying the frame. If PrepareToDraw is called, DidDrawAllLayers
   // must also be called, regardless of whether DrawLayers is called between the
   // two.
-  virtual bool PrepareToDraw(FrameData* frame);
+  virtual bool PrepareToDraw(FrameData* frame,
+                             gfx::Rect device_viewport_damage_rect);
   virtual void DrawLayers(FrameData* frame, base::TimeTicks frame_begin_time);
   // Must be called if and only if PrepareToDraw was called.
   void DidDrawAllLayers(const FrameData& frame);
 
   const LayerTreeSettings& settings() const { return settings_; }
 
   // Returns the currently visible viewport size in DIP. This value excludes
   // the URL bar and non-overlay scrollbars.
   gfx::SizeF VisibleViewportSize() const;
 
@@ skipping 35 matching lines @@
 
   void FinishAllRendering();
   int SourceAnimationFrameNumber() const;
 
   virtual bool InitializeRenderer(scoped_ptr<OutputSurface> output_surface);
   bool IsContextLost();
   TileManager* tile_manager() { return tile_manager_.get(); }
   Renderer* renderer() { return renderer_.get(); }
   const RendererCapabilities& GetRendererCapabilities() const;
 
-  virtual bool SwapBuffers();
+  virtual bool SwapBuffers(const FrameData& frame);
 
   void Readback(void* pixels, gfx::Rect rect_in_device_viewport);
 
   LayerTreeImpl* active_tree() { return active_tree_.get(); }
   const LayerTreeImpl* active_tree() const { return active_tree_.get(); }
   LayerTreeImpl* pending_tree() { return pending_tree_.get(); }
   const LayerTreeImpl* pending_tree() const { return pending_tree_.get(); }
   const LayerTreeImpl* recycle_tree() const { return recycle_tree_.get(); }
   void CreatePendingTree();
   void CheckForCompletedTileUploads();
@@ skipping 228 matching lines @@
 
   scoped_ptr<FrameRateCounter> fps_counter_;
   scoped_ptr<PaintTimeCounter> paint_time_counter_;
   scoped_ptr<MemoryHistory> memory_history_;
   scoped_ptr<DebugRectHistory> debug_rect_history_;
 
   int64 num_impl_thread_scrolls_;
   int64 num_main_thread_scrolls_;
 
   int64 cumulative_num_layers_drawn_;
-
   int64 cumulative_num_missing_tiles_;
 
   size_t last_sent_memory_visible_bytes_;
   size_t last_sent_memory_visible_and_nearby_bytes_;
   size_t last_sent_memory_use_bytes_;
 
+  bool next_frame_damages_full_device_viewport_;
+
   base::TimeTicks current_frame_time_;
 
   scoped_ptr<AnimationRegistrar> animation_registrar_;
 
   RenderingStatsInstrumentation* rendering_stats_instrumentation_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_