Make OffscreenCanvas animation in sync with its placeholder canvas's parent frame rate

third_party/WebKit/Source/platform/graphics/CanvasSurfaceLayerBridge.cpp

 // Copyright 2016 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 "platform/graphics/CanvasSurfaceLayerBridge.h"
 
 #include "cc/layers/layer.h"
 #include "cc/layers/solid_color_layer.h"
 #include "cc/layers/surface_layer.h"
 #include "cc/surfaces/sequence_surface_reference_factory.h"
 #include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surface_info.h"
 #include "cc/surfaces/surface_sequence.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/mojo/MojoHelper.h"
 #include "public/platform/InterfaceProvider.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCompositorSupport.h"
 #include "public/platform/WebLayer.h"
+#include "public/platform/WebLayerTreeView.h"
 #include "public/platform/modules/offscreencanvas/offscreen_canvas_surface.mojom-blink.h"
 #include "ui/gfx/geometry/size.h"
 #include "wtf/Functional.h"
 
 namespace blink {
 
 namespace {
 
 class OffscreenCanvasSurfaceReferenceFactory
     : public cc::SequenceSurfaceReferenceFactory {
@@ skipping 18 matching lines @@
   }
 
   base::WeakPtr<CanvasSurfaceLayerBridge> m_bridge;
 
   DISALLOW_COPY_AND_ASSIGN(OffscreenCanvasSurfaceReferenceFactory);
 };
 
 }  // namespace
 
 CanvasSurfaceLayerBridge::CanvasSurfaceLayerBridge(
-    CanvasSurfaceLayerBridgeObserver* observer)
+    CanvasSurfaceLayerBridgeObserver* observer,
+    WebLayerTreeView* layerTreeView)
     : m_weakFactory(this),
       m_observer(observer),
       m_binding(this),
       m_frameSinkId(Platform::current()->generateFrameSinkId()) {
   m_refFactory =
       new OffscreenCanvasSurfaceReferenceFactory(m_weakFactory.GetWeakPtr());
 
   DCHECK(!m_service.is_bound());
   mojom::blink::OffscreenCanvasSurfaceFactoryPtr serviceFactory;
   Platform::current()->interfaceProvider()->getInterface(
       mojo::MakeRequest(&serviceFactory));
+  if (layerTreeView) {

[Fady Samuel, 2017/01/19 04:05:43]

Is there any reason why this might be null?

[xlai (Olivia), 2017/01/19 16:43:56]

This variable is passed from HTMLCanvasElement. I've check the reference chain
and found that it can be null only when the parent frame is detached.

[dcheng, 2017/01/20 08:44:12]

Out of curiosity, how do we create this object if the parent frame is detached?

[xlai (Olivia), 2017/01/20 16:36:21]

Just double check with junov@. This variable can be null in the case when the
HTMLCanvasElement
does not have a parent frame (i.e. it is under a Document without a Frame). This
is a weird edge case
when the Document should not be seen and therefore no OnBeginFrame signals (and
so doesn't matter the empty parent frame sink id here, browser will simply
ignore it and not register it to frame sink hierarchy). 

But if the canvas is reparented with a new visible Document then we should turn
on OnBeginFrame signals then. I added TODO comment with the new issue
crbug.com/683172 to remind myself to 
follow up with another CL that handles this edge case.

+    m_parentFrameSinkId = layerTreeView->getFrameSinkId();
+  }
   serviceFactory->CreateOffscreenCanvasSurface(
-      m_frameSinkId, m_binding.CreateInterfacePtrAndBind(),
+      m_parentFrameSinkId, m_frameSinkId, m_binding.CreateInterfacePtrAndBind(),
       mojo::MakeRequest(&m_service));
 }
 
 CanvasSurfaceLayerBridge::~CanvasSurfaceLayerBridge() {
   m_observer = nullptr;
 }
 
 void CanvasSurfaceLayerBridge::createSolidColorLayer() {
   m_CCLayer = cc::SolidColorLayer::Create();
   m_CCLayer->SetBackgroundColor(SK_ColorTRANSPARENT);
@@ skipping 38 matching lines @@
   m_service->Satisfy(sequence);
 }
 
 void CanvasSurfaceLayerBridge::requireCallback(
     const cc::SurfaceId& surfaceId,
     const cc::SurfaceSequence& sequence) {
   m_service->Require(surfaceId, sequence);
 }
 
 }  // namespace blink