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

third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.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/OffscreenCanvasFrameDispatcherImpl.h"
 
 #include "cc/output/compositor_frame.h"
 #include "cc/quads/texture_draw_quad.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "platform/CrossThreadFunctional.h"
 #include "platform/Histogram.h"
 #include "platform/WebTaskRunner.h"
 #include "platform/graphics/OffscreenCanvasPlaceholder.h"
 #include "platform/graphics/gpu/SharedGpuContext.h"
 #include "public/platform/InterfaceProvider.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebGraphicsContext3DProvider.h"
 #include "public/platform/modules/offscreencanvas/offscreen_canvas_surface.mojom-blink.h"
 #include "third_party/khronos/GLES2/gl2.h"
 #include "third_party/khronos/GLES2/gl2ext.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkImage.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/transform.h"
 #include "wtf/typed_arrays/ArrayBuffer.h"
 #include "wtf/typed_arrays/Uint8Array.h"
 
 namespace blink {
 
-// This constant specifies the maximum number of pixel buffer that are allowed
-// to co-exist at a given time. The minimum number is 2 (double buffered).
-// larger numbers can help maintain a steadier frame rates, but they increase
-// latency.
-const int kMaximumOffscreenCanvasBufferCount = 3;
-
 OffscreenCanvasFrameDispatcherImpl::OffscreenCanvasFrameDispatcherImpl(
     OffscreenCanvasFrameDispatcherClient* client,
     uint32_t clientId,
     uint32_t sinkId,
     int canvasId,
     int width,
     int height)
     : OffscreenCanvasFrameDispatcher(client),
       m_frameSinkId(cc::FrameSinkId(clientId, sinkId)),
       m_width(width),
       m_height(height),
       m_changeSizeForNextCommit(false),
+      m_needsBeginFrame(false),
       m_nextResourceId(1u),
       m_binding(this),
       m_placeholderCanvasId(canvasId) {
   m_currentLocalFrameId = m_surfaceIdAllocator.GenerateId();
   DCHECK(!m_sink.is_bound());
   mojom::blink::OffscreenCanvasCompositorFrameSinkProviderPtr provider;
   Platform::current()->interfaceProvider()->getInterface(
       mojo::MakeRequest(&provider));
   provider->CreateCompositorFrameSink(m_frameSinkId,
                                       m_binding.CreateInterfacePtrAndBind(),
                                       mojo::MakeRequest(&m_sink));
 }
 
 OffscreenCanvasFrameDispatcherImpl::~OffscreenCanvasFrameDispatcherImpl() {
-  m_syntheticBeginFrameTask.cancel();
 }
 
 void OffscreenCanvasFrameDispatcherImpl::setTransferableResourceToSharedBitmap(
     cc::TransferableResource& resource,
     RefPtr<StaticBitmapImage> image) {
   std::unique_ptr<cc::SharedBitmap> bitmap =
       Platform::current()->allocateSharedBitmap(IntSize(m_width, m_height));
   if (!bitmap)
     return;
   unsigned char* pixels = bitmap->pixels();
@@ skipping 291 matching lines @@
       }
       break;
     case OffscreenCanvasCommitTypeCount:
       NOTREACHED();
   }
 
   if (m_changeSizeForNextCommit) {
     m_currentLocalFrameId = m_surfaceIdAllocator.GenerateId();
     m_changeSizeForNextCommit = false;
   }
+
   m_sink->SubmitCompositorFrame(m_currentLocalFrameId, std::move(frame));
-
-  // TODO(crbug.com/674744): Get BeginFrame to fire on its own.
-  scheduleSyntheticBeginFrame();
-}
-
-void OffscreenCanvasFrameDispatcherImpl::scheduleSyntheticBeginFrame() {
-  m_syntheticBeginFrameTask =
-      Platform::current()
-          ->currentThread()
-          ->getWebTaskRunner()
-          ->postDelayedCancellableTask(
-              BLINK_FROM_HERE,
-              WTF::bind(&OffscreenCanvasFrameDispatcherImpl::OnBeginFrame,
-                        WTF::unretained(this), cc::BeginFrameArgs()),
-              16);
 }
 
 void OffscreenCanvasFrameDispatcherImpl::DidReceiveCompositorFrameAck() {
   // TODO(fsamuel): Implement this.
 }
 
-void OffscreenCanvasFrameDispatcherImpl::OnBeginFrame(
-    const cc::BeginFrameArgs& beginFrameArgs) {
-  if (!client())
-    return;
-  unsigned framesInFlight = m_cachedImages.size() + m_sharedBitmaps.size() +
-                            m_cachedTextureIds.size();
-
-  // Limit the rate of compositor commits.
-  if (framesInFlight < kMaximumOffscreenCanvasBufferCount) {
-    client()->beginFrame();
-  } else {
-    // TODO(crbug.com/674744): Get BeginFrame to fire on its own.
-    // The following call is to reschedule the frame in cases where we encounter
-    // a backlog.
-    scheduleSyntheticBeginFrame();
+void OffscreenCanvasFrameDispatcherImpl::setNeedsBeginFrame(
+    bool needsBeginFrame) {
+  if (needsBeginFrame != m_needsBeginFrame) {
+    m_needsBeginFrame = needsBeginFrame;
+    m_sink->SetNeedsBeginFrame(needsBeginFrame);
   }
 }
 
+void OffscreenCanvasFrameDispatcherImpl::OnBeginFrame(
+    const cc::BeginFrameArgs& beginFrameArgs) {
+  if (client())

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

Can client() actually be null? It seems like it can't from how it's constructed.

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

It cannot be null. I'm changing this to a DCHECK.

+    client()->beginFrame();
+}
+
 void OffscreenCanvasFrameDispatcherImpl::ReclaimResources(
     const cc::ReturnedResourceArray& resources) {
   for (const auto& resource : resources) {
     RefPtr<StaticBitmapImage> image = m_cachedImages.get(resource.id);
     if (image)
       image->updateSyncToken(resource.sync_token);
     reclaimResource(resource.id);
   }
 }
 
@@ skipping 26 matching lines @@
 
 void OffscreenCanvasFrameDispatcherImpl::reshape(int width, int height) {
   if (m_width != width || m_height != height) {
     m_width = width;
     m_height = height;
     m_changeSizeForNextCommit = true;
   }
 }
 
 }  // namespace blink