cc: Don't do CompositeAndReadback when using DelegatingRenderer.

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 42 matching lines @@
 
 bool SingleThreadProxy::CompositeAndReadback(void* pixels, gfx::Rect rect) {
   TRACE_EVENT0("cc", "SingleThreadProxy::CompositeAndReadback");
   DCHECK(Proxy::IsMainThread());
 
   gfx::Rect device_viewport_damage_rect = rect;
 
   LayerTreeHostImpl::FrameData frame;
   if (!CommitAndComposite(base::TimeTicks::Now(),
                           device_viewport_damage_rect,
+                          true,  // for_readback
                           &frame))
     return false;
 
   {
     DebugScopedSetImplThread impl(this);
     layer_tree_host_impl_->Readback(pixels, rect);
 
     if (layer_tree_host_impl_->IsContextLost())
       return false;
 
@@ skipping 257 matching lines @@
 }
 
 // Called by the legacy scheduling path (e.g. where render_widget does the
 // scheduling)
 void SingleThreadProxy::CompositeImmediately(base::TimeTicks frame_begin_time) {
   gfx::Rect device_viewport_damage_rect;
 
   LayerTreeHostImpl::FrameData frame;
   if (CommitAndComposite(frame_begin_time,
                          device_viewport_damage_rect,
+                         false,  // for_readback
                          &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
@@ skipping 13 matching lines @@
     if (layer_tree_host_impl_->renderer()) {
       DCHECK(!layer_tree_host_->output_surface_lost());
       layer_tree_host_impl_->renderer()->DoNoOp();
     }
   }
 }
 
 bool SingleThreadProxy::CommitAndComposite(
     base::TimeTicks frame_begin_time,
     gfx::Rect device_viewport_damage_rect,
+    bool for_readback,
     LayerTreeHostImpl::FrameData* frame) {
   DCHECK(Proxy::IsMainThread());
 
   if (!layer_tree_host_->InitializeOutputSurfaceIfNeeded())
     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,
                             device_viewport_damage_rect,
+                            for_readback,
                             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,
     gfx::Rect device_viewport_damage_rect,
+    bool for_readback,
     LayerTreeHostImpl::FrameData* frame) {
   DCHECK(!layer_tree_host_->output_surface_lost());
 
   bool lost_output_surface = false;
   {
     DebugScopedSetImplThread impl(this);
     base::AutoReset<bool> mark_inside(&inside_draw_, true);
 
     layer_tree_host_impl_->resource_provider()->
         set_offscreen_context_provider(offscreen_context_provider);
 
+    bool can_do_readback = layer_tree_host_impl_->renderer()->CanReadPixels();
+
     // 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()) {
+    if (!ShouldComposite() || (for_readback && !can_do_readback)) {
       layer_tree_host_impl_->UpdateBackgroundAnimateTicking(true);
       return false;
     }
 
     layer_tree_host_impl_->Animate(
         layer_tree_host_impl_->CurrentFrameTimeTicks(),
         layer_tree_host_impl_->CurrentFrameTime());
     layer_tree_host_impl_->UpdateBackgroundAnimateTicking(false);
 
     layer_tree_host_impl_->PrepareToDraw(frame, device_viewport_damage_rect);
@@ skipping 28 matching lines @@
 
 bool SingleThreadProxy::CommitPendingForTesting() { return false; }
 
 skia::RefPtr<SkPicture> SingleThreadProxy::CapturePicture() {
   // Impl-side painting only.
   NOTREACHED();
   return skia::RefPtr<SkPicture>();
 }
 
 }  // namespace cc