Adjust OffscreenCanvas throttling to allow two frames of backlog

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 "platform/wtf/typed_arrays/ArrayBuffer.h"
 #include "platform/wtf/typed_arrays/Uint8Array.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"
 
 namespace blink {
 
+enum {
+  kMaxCompositorPendingFrames = 2,

[Eric Seckler, 2017/04/28 08:19:10]

same here?

+};
+
 OffscreenCanvasFrameDispatcherImpl::OffscreenCanvasFrameDispatcherImpl(
     OffscreenCanvasFrameDispatcherClient* client,
     uint32_t client_id,
     uint32_t sink_id,
     int canvas_id,
     int width,
     int height)
     : OffscreenCanvasFrameDispatcher(client),
       frame_sink_id_(cc::FrameSinkId(client_id, sink_id)),
       width_(width),
@@ skipping 352 matching lines @@
       break;
     case kOffscreenCanvasCommitTypeCount:
       NOTREACHED();
   }
 
   if (change_size_for_next_commit_) {
     current_local_surface_id_ = local_surface_id_allocator_.GenerateId();
     change_size_for_next_commit_ = false;
   }
 
-  compositor_has_pending_frame_ = true;
+  compositor_pending_frames_++;
   sink_->SubmitCompositorFrame(current_local_surface_id_, std::move(frame));
 }
 
 void OffscreenCanvasFrameDispatcherImpl::DidReceiveCompositorFrameAck(
     const cc::ReturnedResourceArray& resources) {
   ReclaimResources(resources);
-  compositor_has_pending_frame_ = false;
+  compositor_pending_frames_--;
+  DCHECK_GE(compositor_pending_frames_, 0);
 }
 
 void OffscreenCanvasFrameDispatcherImpl::SetNeedsBeginFrame(
     bool needs_begin_frame) {
   if (sink_ && needs_begin_frame != needs_begin_frame_) {
     needs_begin_frame_ = needs_begin_frame;
     sink_->SetNeedsBeginFrame(needs_begin_frame);
   }
 }
 
 void OffscreenCanvasFrameDispatcherImpl::OnBeginFrame(
     const cc::BeginFrameArgs& begin_frame_args) {
   DCHECK(Client());
 
   // TODO(eseckler): Set correct |latest_confirmed_sequence_number|.
   current_begin_frame_ack_ = cc::BeginFrameAck(
       begin_frame_args.source_id, begin_frame_args.sequence_number,
       begin_frame_args.sequence_number, false);
 
-  if (compositor_has_pending_frame_ ||
+  if (compositor_pending_frames_ >= kMaxCompositorPendingFrames ||
       (begin_frame_args.type == cc::BeginFrameArgs::MISSED &&
        base::TimeTicks::Now() > begin_frame_args.deadline)) {
     sink_->BeginFrameDidNotSwap(current_begin_frame_ack_);
     return;
   }
 
   Client()->BeginFrame();
   // TODO(eseckler): Tell |m_sink| if we did not draw during the BeginFrame.
   current_begin_frame_ack_.sequence_number =
       cc::BeginFrameArgs::kInvalidFrameNumber;
@@ skipping 47 matching lines @@
 
 void OffscreenCanvasFrameDispatcherImpl::Reshape(int width, int height) {
   if (width_ != width || height_ != height) {
     width_ = width;
     height_ = height;
     change_size_for_next_commit_ = true;
   }
 }
 
 }  // namespace blink