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

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

Index: third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.cpp b/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.cpp
index 984731ad183bfb040af56267ed74a04d6043a560..3305cadd14dffd73dc904d8f8b87e580da9defed 100644
--- a/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.cpp
+++ b/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.cpp
@@ -27,12 +27,6 @@
 
 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,
@@ -45,6 +39,7 @@ OffscreenCanvasFrameDispatcherImpl::OffscreenCanvasFrameDispatcherImpl(
       m_width(width),
       m_height(height),
       m_changeSizeForNextCommit(false),
+      m_needsBeginFrame(false),
       m_nextResourceId(1u),
       m_binding(this),
       m_placeholderCanvasId(canvasId) {
@@ -59,7 +54,6 @@ OffscreenCanvasFrameDispatcherImpl::OffscreenCanvasFrameDispatcherImpl(
 }
 
 OffscreenCanvasFrameDispatcherImpl::~OffscreenCanvasFrameDispatcherImpl() {
-  m_syntheticBeginFrameTask.cancel();
 }
 
 void OffscreenCanvasFrameDispatcherImpl::setTransferableResourceToSharedBitmap(
@@ -371,44 +365,26 @@ void OffscreenCanvasFrameDispatcherImpl::dispatchFrame(
     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);
+  m_sink->SubmitCompositorFrame(m_currentLocalFrameId, std::move(frame));
 }
 
 void OffscreenCanvasFrameDispatcherImpl::DidReceiveCompositorFrameAck() {
   // TODO(fsamuel): Implement this.
 }
 
+void OffscreenCanvasFrameDispatcherImpl::setNeedsBeginFrame(
+    bool doesNeedBeginFrame) {

[Justin Novosad, 2017/01/19 18:06:49]

This name doesNeedBeginFrame is a bit awkward. Just "needsBeginFrame" should not
have any conflicts

[xlai (Olivia), 2017/01/19 19:14:34]

Done.

+  if (doesNeedBeginFrame != m_needsBeginFrame) {
+    m_needsBeginFrame = doesNeedBeginFrame;
+    m_sink->SetNeedsBeginFrame(doesNeedBeginFrame);
+  }
+}
+
 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) {
+  if (client())
     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::ReclaimResources(