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

cc/trees/single_thread_proxy.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/single_thread_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/debug/trace_event.h"
 #include "cc/base/thread.h"
 #include "cc/output/context_provider.h"
@@ skipping 36 matching lines @@
   TRACE_EVENT0("cc", "SingleThreadProxy::~SingleThreadProxy");
   DCHECK(Proxy::IsMainThread());
   DCHECK(!layer_tree_host_impl_.get() &&
          !layer_tree_host_);  // make sure Stop() got called.
 }
 
 bool SingleThreadProxy::CompositeAndReadback(void* pixels, gfx::Rect rect) {
   TRACE_EVENT0("cc", "SingleThreadProxy::CompositeAndReadback");
   DCHECK(Proxy::IsMainThread());
 
-  if (!CommitAndComposite(base::TimeTicks::Now()))
+  gfx::Rect device_viewport_damage_rect = rect;
+
+  LayerTreeHostImpl::FrameData frame;
+  if (!CommitAndComposite(base::TimeTicks::Now(),
+                          device_viewport_damage_rect,
+                          &frame))
     return false;
 
   {
     DebugScopedSetImplThread impl(this);
     layer_tree_host_impl_->Readback(pixels, rect);
 
     if (layer_tree_host_impl_->IsContextLost())
       return false;
 
-    layer_tree_host_impl_->SwapBuffers();
+    layer_tree_host_impl_->SwapBuffers(frame);
   }
   DidSwapFrame();
 
   return true;
 }
 
 void SingleThreadProxy::FinishAllRendering() {
   DCHECK(Proxy::IsMainThread());
   {
     DebugScopedSetImplThread impl(this);
@@ skipping 245 matching lines @@
 bool SingleThreadProxy::IsInsideDraw() { return inside_draw_; }
 
 void SingleThreadProxy::DidLoseOutputSurfaceOnImplThread() {
   // Cause a commit so we can notice the lost context.
   SetNeedsCommitOnImplThread();
 }
 
 // Called by the legacy scheduling path (e.g. where render_widget does the
 // scheduling)
 void SingleThreadProxy::CompositeImmediately(base::TimeTicks frame_begin_time) {
-  if (CommitAndComposite(frame_begin_time)) {
-    layer_tree_host_impl_->SwapBuffers();
+  gfx::Rect device_viewport_damage_rect;
+
+  LayerTreeHostImpl::FrameData frame;
+  if (CommitAndComposite(frame_begin_time,
+                         device_viewport_damage_rect,
+                         &frame)) {
+    layer_tree_host_impl_->SwapBuffers(frame);
     DidSwapFrame();
   }
 }
 
 scoped_ptr<base::Value> SingleThreadProxy::AsValue() const {
   scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
   {
     // The following line casts away const modifiers because it is just
     // setting debug state. We still want the AsValue() function and its
     // call chain to be const throughout.
     DebugScopedSetImplThread impl(const_cast<SingleThreadProxy*>(this));
 
     state->Set("layer_tree_host_impl",
                layer_tree_host_impl_->AsValue().release());
   }
   return state.PassAs<base::Value>();
 }
 
 void SingleThreadProxy::ForceSerializeOnSwapBuffers() {
   {
     DebugScopedSetImplThread impl(this);
     if (renderer_initialized_)
       layer_tree_host_impl_->renderer()->DoNoOp();
   }
 }
 
 void SingleThreadProxy::OnSwapBuffersCompleteOnImplThread() { NOTREACHED(); }
 
-bool SingleThreadProxy::CommitAndComposite(base::TimeTicks frame_begin_time) {
+bool SingleThreadProxy::CommitAndComposite(
+    base::TimeTicks frame_begin_time,
+    gfx::Rect device_viewport_damage_rect,
+    LayerTreeHostImpl::FrameData* frame) {
   DCHECK(Proxy::IsMainThread());
 
   if (!layer_tree_host_->InitializeRendererIfNeeded())
     return false;
 
   scoped_refptr<cc::ContextProvider> offscreen_context_provider;
   if (renderer_capabilities_for_main_thread_.using_offscreen_context3d &&
       layer_tree_host_->needs_offscreen_context()) {
     offscreen_context_provider =
         layer_tree_host_->client()->OffscreenContextProviderForMainThread();
     if (offscreen_context_provider)
       created_offscreen_context_provider_ = true;
   }
 
   layer_tree_host_->contents_texture_manager()->UnlinkAndClearEvictedBackings();
 
   scoped_ptr<ResourceUpdateQueue> queue =
       make_scoped_ptr(new ResourceUpdateQueue);
   layer_tree_host_->UpdateLayers(
       queue.get(), layer_tree_host_impl_->memory_allocation_limit_bytes());
 
   layer_tree_host_->WillCommit();
   DoCommit(queue.Pass());
-  bool result = DoComposite(offscreen_context_provider, frame_begin_time);
+  bool result = DoComposite(offscreen_context_provider,
+                            frame_begin_time,
+                            device_viewport_damage_rect,
+                            frame);
   layer_tree_host_->DidBeginFrame();
   return result;
 }
 
 bool SingleThreadProxy::ShouldComposite() const {
   DCHECK(Proxy::IsImplThread());
   return layer_tree_host_impl_->visible() &&
          layer_tree_host_impl_->CanDraw();
 }
 
 bool SingleThreadProxy::DoComposite(
     scoped_refptr<cc::ContextProvider> offscreen_context_provider,
-    base::TimeTicks frame_begin_time) {
+    base::TimeTicks frame_begin_time,
+    gfx::Rect device_viewport_damage_rect,
+    LayerTreeHostImpl::FrameData* frame) {
   DCHECK(!output_surface_lost_);
   {
     DebugScopedSetImplThread impl(this);
     base::AutoReset<bool> mark_inside(&inside_draw_, true);
 
     layer_tree_host_impl_->resource_provider()->
         set_offscreen_context_provider(offscreen_context_provider);
 
     // We guard PrepareToDraw() with CanDraw() because it always returns a valid
     // frame, so can only be used when such a frame is possible. Since
     // DrawLayers() depends on the result of PrepareToDraw(), it is guarded on
     // CanDraw() as well.
     if (!ShouldComposite()) {
       layer_tree_host_impl_->UpdateBackgroundAnimateTicking(true);
       return false;
     }
 
     layer_tree_host_impl_->Animate(base::TimeTicks::Now(), base::Time::Now());
     layer_tree_host_impl_->UpdateBackgroundAnimateTicking(false);
 
-    LayerTreeHostImpl::FrameData frame;
-    layer_tree_host_impl_->PrepareToDraw(&frame);
-    layer_tree_host_impl_->DrawLayers(&frame, frame_begin_time);
-    layer_tree_host_impl_->DidDrawAllLayers(frame);
+    layer_tree_host_impl_->PrepareToDraw(frame, device_viewport_damage_rect);
+    layer_tree_host_impl_->DrawLayers(frame, frame_begin_time);
+    layer_tree_host_impl_->DidDrawAllLayers(*frame);
     output_surface_lost_ = layer_tree_host_impl_->IsContextLost();
 
     bool start_ready_animations = true;
     layer_tree_host_impl_->UpdateAnimationState(start_ready_animations);
 
     layer_tree_host_impl_->BeginNextFrame();
   }
 
   if (output_surface_lost_) {
     cc::ContextProvider* offscreen_contexts = layer_tree_host_impl_->
@@ skipping 16 matching lines @@
 
 bool SingleThreadProxy::CommitPendingForTesting() { return false; }
 
 skia::RefPtr<SkPicture> SingleThreadProxy::CapturePicture() {
   // Impl-side painting only.
   NOTREACHED();
   return skia::RefPtr<SkPicture>();
 }
 
 }  // namespace cc