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/memory/ptr_util.h"
#include "base/profiler/scoped_tracker.h"
#include "base/trace_event/trace_event.h"
#include "cc/animation/animation_events.h"
#include "cc/debug/benchmark_instrumentation.h"
#include "cc/debug/devtools_instrumentation.h"
#include "cc/output/context_provider.h"
#include "cc/output/output_surface.h"
#include "cc/quads/draw_quad.h"
#include "cc/scheduler/commit_earlyout_reason.h"
#include "cc/scheduler/compositor_timing_history.h"
#include "cc/scheduler/scheduler.h"
#include "cc/trees/layer_tree_host.h"
#include "cc/trees/layer_tree_host_common.h"
#include "cc/trees/layer_tree_host_single_thread_client.h"
#include "cc/trees/layer_tree_impl.h"
#include "cc/trees/scoped_abort_remaining_swap_promises.h"

namespace cc {

std::unique_ptr<Proxy> SingleThreadProxy::Create(
    LayerTreeHost* layer_tree_host,
    LayerTreeHostSingleThreadClient* client,
    TaskRunnerProvider* task_runner_provider) {
  return base::WrapUnique(
      new SingleThreadProxy(layer_tree_host, client, task_runner_provider));
}

SingleThreadProxy::SingleThreadProxy(LayerTreeHost* layer_tree_host,
                                     LayerTreeHostSingleThreadClient* client,
                                     TaskRunnerProvider* task_runner_provider)
    : layer_tree_host_(layer_tree_host),
      client_(client),
      task_runner_provider_(task_runner_provider),
      next_frame_is_newly_committed_frame_(false),
#if DCHECK_IS_ON()
      inside_impl_frame_(false),
#endif
      inside_draw_(false),
      defer_commits_(false),
      animate_requested_(false),
      commit_requested_(false),
      inside_synchronous_composite_(false),
      output_surface_creation_requested_(false),
      weak_factory_(this) {
  TRACE_EVENT0("cc", "SingleThreadProxy::SingleThreadProxy");
  DCHECK(task_runner_provider_);
  DCHECK(task_runner_provider_->IsMainThread());
  DCHECK(layer_tree_host);
}

void SingleThreadProxy::Start(
    std::unique_ptr<BeginFrameSource> external_begin_frame_source) {
  DebugScopedSetImplThread impl(task_runner_provider_);
  external_begin_frame_source_ = std::move(external_begin_frame_source);

  if (layer_tree_host_->settings().single_thread_proxy_scheduler &&
      !scheduler_on_impl_thread_) {
    SchedulerSettings scheduler_settings(
        layer_tree_host_->settings().ToSchedulerSettings());
    scheduler_settings.commit_to_active_tree = CommitToActiveTree();

    std::unique_ptr<CompositorTimingHistory> compositor_timing_history(
        new CompositorTimingHistory(
            scheduler_settings.using_synchronous_renderer_compositor,
            CompositorTimingHistory::BROWSER_UMA,
            layer_tree_host_->rendering_stats_instrumentation()));

    BeginFrameSource* frame_source = nullptr;
    if (!layer_tree_host_->settings().use_output_surface_begin_frame_source) {
      frame_source = external_begin_frame_source_.get();
      if (!scheduler_settings.throttle_frame_production) {
        // Unthrottled source takes precedence over external sources.
        unthrottled_begin_frame_source_.reset(new BackToBackBeginFrameSource(
            task_runner_provider_->MainThreadTaskRunner()));
        frame_source = unthrottled_begin_frame_source_.get();
      }
      if (!frame_source) {
        synthetic_begin_frame_source_.reset(new SyntheticBeginFrameSource(
            task_runner_provider_->MainThreadTaskRunner(),
            BeginFrameArgs::DefaultInterval()));
        frame_source = synthetic_begin_frame_source_.get();
      }
    }

    scheduler_on_impl_thread_ =
        Scheduler::Create(this, scheduler_settings, layer_tree_host_->id(),
                          task_runner_provider_->MainThreadTaskRunner(),
                          frame_source, std::move(compositor_timing_history));
  }

  layer_tree_host_impl_ = layer_tree_host_->CreateLayerTreeHostImpl(this);
}

SingleThreadProxy::~SingleThreadProxy() {
  TRACE_EVENT0("cc", "SingleThreadProxy::~SingleThreadProxy");
  DCHECK(task_runner_provider_->IsMainThread());
  // Make sure Stop() got called or never Started.
  DCHECK(!layer_tree_host_impl_);
}

void SingleThreadProxy::FinishAllRendering() {
  TRACE_EVENT0("cc", "SingleThreadProxy::FinishAllRendering");
  DCHECK(task_runner_provider_->IsMainThread());
  {
    DebugScopedSetImplThread impl(task_runner_provider_);
    layer_tree_host_impl_->FinishAllRendering();
  }
}

bool SingleThreadProxy::IsStarted() const {
  DCHECK(task_runner_provider_->IsMainThread());
  return !!layer_tree_host_impl_;
}

bool SingleThreadProxy::CommitToActiveTree() const {
  // With SingleThreadProxy we skip the pending tree and commit directly to the
  // active tree.
  return true;
}

void SingleThreadProxy::SetVisible(bool visible) {
  TRACE_EVENT1("cc", "SingleThreadProxy::SetVisible", "visible", visible);
  DebugScopedSetImplThread impl(task_runner_provider_);

  layer_tree_host_impl_->SetVisible(visible);

  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetVisible(layer_tree_host_impl_->visible());
}

void SingleThreadProxy::RequestNewOutputSurface() {
  DCHECK(task_runner_provider_->IsMainThread());
  DCHECK(layer_tree_host_->output_surface_lost());
  output_surface_creation_callback_.Cancel();
  if (output_surface_creation_requested_)
    return;
  output_surface_creation_requested_ = true;
  layer_tree_host_->RequestNewOutputSurface();
}

void SingleThreadProxy::ReleaseOutputSurface() {
  // |layer_tree_host_| should already be aware of this.
  DCHECK(layer_tree_host_->output_surface_lost());

  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->DidLoseOutputSurface();
  return layer_tree_host_impl_->ReleaseOutputSurface();
}

void SingleThreadProxy::SetOutputSurface(OutputSurface* output_surface) {
  DCHECK(task_runner_provider_->IsMainThread());
  DCHECK(layer_tree_host_->output_surface_lost());
  DCHECK(output_surface_creation_requested_);
  renderer_capabilities_for_main_thread_ = RendererCapabilities();

  bool success;
  {
    DebugScopedSetMainThreadBlocked main_thread_blocked(task_runner_provider_);
    DebugScopedSetImplThread impl(task_runner_provider_);
    success = layer_tree_host_impl_->InitializeRenderer(output_surface);
  }

  if (success) {
    layer_tree_host_->DidInitializeOutputSurface();
    if (scheduler_on_impl_thread_)
      scheduler_on_impl_thread_->DidCreateAndInitializeOutputSurface();
    else if (!inside_synchronous_composite_)
      SetNeedsCommit();
    output_surface_creation_requested_ = false;
  } else {
    // DidFailToInitializeOutputSurface is treated as a RequestNewOutputSurface,
    // and so output_surface_creation_requested remains true.
    layer_tree_host_->DidFailToInitializeOutputSurface();
  }
}

const RendererCapabilities& SingleThreadProxy::GetRendererCapabilities() const {
  DCHECK(task_runner_provider_->IsMainThread());
  DCHECK(!layer_tree_host_->output_surface_lost());
  return renderer_capabilities_for_main_thread_;
}

void SingleThreadProxy::SetNeedsAnimate() {
  TRACE_EVENT0("cc", "SingleThreadProxy::SetNeedsAnimate");
  DCHECK(task_runner_provider_->IsMainThread());
  client_->RequestScheduleAnimation();
  if (animate_requested_)
    return;
  animate_requested_ = true;
  DebugScopedSetImplThread impl(task_runner_provider_);
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetNeedsBeginMainFrame();
}

void SingleThreadProxy::SetNeedsUpdateLayers() {
  TRACE_EVENT0("cc", "SingleThreadProxy::SetNeedsUpdateLayers");
  DCHECK(task_runner_provider_->IsMainThread());
  SetNeedsCommit();
}

void SingleThreadProxy::DoCommit() {
  TRACE_EVENT0("cc", "SingleThreadProxy::DoCommit");
  DCHECK(task_runner_provider_->IsMainThread());

  // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509 is
  // fixed.
  tracked_objects::ScopedTracker tracking_profile1(
      FROM_HERE_WITH_EXPLICIT_FUNCTION("461509 SingleThreadProxy::DoCommit1"));
  layer_tree_host_->WillCommit();
  devtools_instrumentation::ScopedCommitTrace commit_task(
      layer_tree_host_->id());

  layer_tree_host_->ReportFixedRasterScaleUseCounters(
      layer_tree_host_impl_->has_fixed_raster_scale_blurry_content(),
      layer_tree_host_impl_
          ->HasFixedRasterScalePotentialPerformanceRegression());

  // Commit immediately.
  {
    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile2(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoCommit2"));
    DebugScopedSetMainThreadBlocked main_thread_blocked(task_runner_provider_);
    DebugScopedSetImplThread impl(task_runner_provider_);

    // This CapturePostTasks should be destroyed before CommitComplete() is
    // called since that goes out to the embedder, and we want the embedder
    // to receive its callbacks before that.
    commit_blocking_task_runner_.reset(new BlockingTaskRunner::CapturePostTasks(
        task_runner_provider_->blocking_main_thread_task_runner()));

    layer_tree_host_impl_->BeginCommit();

    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile6(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoCommit6"));
    if (layer_tree_host_impl_->EvictedUIResourcesExist())
      layer_tree_host_->RecreateUIResources();

    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile7(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoCommit7"));
    layer_tree_host_->FinishCommitOnImplThread(layer_tree_host_impl_.get());

#if DCHECK_IS_ON()
    // In the single-threaded case, the scale and scroll deltas should never be
    // touched on the impl layer tree.
    std::unique_ptr<ScrollAndScaleSet> scroll_info =
        layer_tree_host_impl_->ProcessScrollDeltas();
    DCHECK(!scroll_info->scrolls.size());
    DCHECK_EQ(1.f, scroll_info->page_scale_delta);
#endif

    if (scheduler_on_impl_thread_)
      scheduler_on_impl_thread_->DidCommit();

    layer_tree_host_impl_->CommitComplete();

    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile8(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoCommit8"));
    // Commit goes directly to the active tree, but we need to synchronously
    // "activate" the tree still during commit to satisfy any potential
    // SetNextCommitWaitsForActivation calls.  Unfortunately, the tree
    // might not be ready to draw, so DidActivateSyncTree must set
    // the flag to force the tree to not draw until textures are ready.
    NotifyReadyToActivate();
  }
}

void SingleThreadProxy::CommitComplete() {
  // Commit complete happens on the main side after activate to satisfy any
  // SetNextCommitWaitsForActivation calls.
  DCHECK(!layer_tree_host_impl_->pending_tree())
      << "Activation is expected to have synchronously occurred by now.";
  DCHECK(commit_blocking_task_runner_);

  DebugScopedSetMainThread main(task_runner_provider_);
  commit_blocking_task_runner_.reset();
  layer_tree_host_->CommitComplete();
  layer_tree_host_->DidBeginMainFrame();

  next_frame_is_newly_committed_frame_ = true;
}

void SingleThreadProxy::SetNeedsCommit() {
  DCHECK(task_runner_provider_->IsMainThread());
  client_->RequestScheduleComposite();
  if (commit_requested_)
    return;
  commit_requested_ = true;
  DebugScopedSetImplThread impl(task_runner_provider_);
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetNeedsBeginMainFrame();
}

void SingleThreadProxy::SetNeedsRedraw(const gfx::Rect& damage_rect) {
  TRACE_EVENT0("cc", "SingleThreadProxy::SetNeedsRedraw");
  DCHECK(task_runner_provider_->IsMainThread());
  DebugScopedSetImplThread impl(task_runner_provider_);
  client_->RequestScheduleComposite();
  SetNeedsRedrawRectOnImplThread(damage_rect);
}

void SingleThreadProxy::SetNextCommitWaitsForActivation() {
  // Activation always forced in commit, so nothing to do.
  DCHECK(task_runner_provider_->IsMainThread());
}

void SingleThreadProxy::SetDeferCommits(bool defer_commits) {
  DCHECK(task_runner_provider_->IsMainThread());
  // Deferring commits only makes sense if there's a scheduler.
  if (!scheduler_on_impl_thread_)
    return;
  if (defer_commits_ == defer_commits)
    return;

  if (defer_commits)
    TRACE_EVENT_ASYNC_BEGIN0("cc", "SingleThreadProxy::SetDeferCommits", this);
  else
    TRACE_EVENT_ASYNC_END0("cc", "SingleThreadProxy::SetDeferCommits", this);

  defer_commits_ = defer_commits;
  scheduler_on_impl_thread_->SetDeferCommits(defer_commits);
}

bool SingleThreadProxy::CommitRequested() const {
  DCHECK(task_runner_provider_->IsMainThread());
  return commit_requested_;
}

bool SingleThreadProxy::BeginMainFrameRequested() const {
  DCHECK(task_runner_provider_->IsMainThread());
  // If there is no scheduler, then there can be no pending begin frame,
  // as all frames are all manually initiated by the embedder of cc.
  if (!scheduler_on_impl_thread_)
    return false;
  return commit_requested_;
}

void SingleThreadProxy::Stop() {
  TRACE_EVENT0("cc", "SingleThreadProxy::stop");
  DCHECK(task_runner_provider_->IsMainThread());
  {
    DebugScopedSetMainThreadBlocked main_thread_blocked(task_runner_provider_);
    DebugScopedSetImplThread impl(task_runner_provider_);

    BlockingTaskRunner::CapturePostTasks blocked(
        task_runner_provider_->blocking_main_thread_task_runner());
    scheduler_on_impl_thread_ = nullptr;
    layer_tree_host_impl_ = nullptr;
  }
  layer_tree_host_ = NULL;
}

void SingleThreadProxy::SetMutator(std::unique_ptr<LayerTreeMutator> mutator) {
  DCHECK(task_runner_provider_->IsMainThread());
  DebugScopedSetImplThread impl(task_runner_provider_);
  layer_tree_host_impl_->SetLayerTreeMutator(std::move(mutator));
}

void SingleThreadProxy::OnCanDrawStateChanged(bool can_draw) {
  TRACE_EVENT1(
      "cc", "SingleThreadProxy::OnCanDrawStateChanged", "can_draw", can_draw);
  DCHECK(task_runner_provider_->IsImplThread());
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetCanDraw(can_draw);
}

void SingleThreadProxy::NotifyReadyToActivate() {
  TRACE_EVENT0("cc", "SingleThreadProxy::NotifyReadyToActivate");
  DebugScopedSetImplThread impl(task_runner_provider_);
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->NotifyReadyToActivate();
}

void SingleThreadProxy::NotifyReadyToDraw() {
  TRACE_EVENT0("cc", "SingleThreadProxy::NotifyReadyToDraw");
  DebugScopedSetImplThread impl(task_runner_provider_);
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->NotifyReadyToDraw();
}

void SingleThreadProxy::SetNeedsRedrawOnImplThread() {
  client_->RequestScheduleComposite();
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetNeedsRedraw();
}

void SingleThreadProxy::SetNeedsOneBeginImplFrameOnImplThread() {
  TRACE_EVENT0("cc",
               "SingleThreadProxy::SetNeedsOneBeginImplFrameOnImplThread");
  client_->RequestScheduleComposite();
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetNeedsOneBeginImplFrame();
}

void SingleThreadProxy::SetNeedsPrepareTilesOnImplThread() {
  TRACE_EVENT0("cc", "SingleThreadProxy::SetNeedsPrepareTilesOnImplThread");
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetNeedsPrepareTiles();
}

void SingleThreadProxy::SetNeedsRedrawRectOnImplThread(
    const gfx::Rect& damage_rect) {
  layer_tree_host_impl_->SetViewportDamage(damage_rect);
  SetNeedsRedrawOnImplThread();
}

void SingleThreadProxy::SetNeedsCommitOnImplThread() {
  client_->RequestScheduleComposite();
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetNeedsBeginMainFrame();
}

void SingleThreadProxy::SetVideoNeedsBeginFrames(bool needs_begin_frames) {
  TRACE_EVENT1("cc", "SingleThreadProxy::SetVideoNeedsBeginFrames",
               "needs_begin_frames", needs_begin_frames);
  // In tests the layer tree is destroyed after the scheduler is.
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetVideoNeedsBeginFrames(needs_begin_frames);
}

void SingleThreadProxy::PostAnimationEventsToMainThreadOnImplThread(
    std::unique_ptr<AnimationEvents> events) {
  TRACE_EVENT0(
      "cc", "SingleThreadProxy::PostAnimationEventsToMainThreadOnImplThread");
  DCHECK(task_runner_provider_->IsImplThread());
  DebugScopedSetMainThread main(task_runner_provider_);
  layer_tree_host_->SetAnimationEvents(std::move(events));
}

bool SingleThreadProxy::IsInsideDraw() { return inside_draw_; }

void SingleThreadProxy::DidActivateSyncTree() {
  // Synchronously call to CommitComplete. Resetting
  // |commit_blocking_task_runner| would make sure all tasks posted during
  // commit/activation before CommitComplete.
  CommitComplete();
}

void SingleThreadProxy::WillPrepareTiles() {
  DCHECK(task_runner_provider_->IsImplThread());
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->WillPrepareTiles();
}

void SingleThreadProxy::DidPrepareTiles() {
  DCHECK(task_runner_provider_->IsImplThread());
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->DidPrepareTiles();
}

void SingleThreadProxy::DidCompletePageScaleAnimationOnImplThread() {
  layer_tree_host_->DidCompletePageScaleAnimation();
}

void SingleThreadProxy::UpdateRendererCapabilitiesOnImplThread() {
  DCHECK(task_runner_provider_->IsImplThread());
  renderer_capabilities_for_main_thread_ =
      layer_tree_host_impl_->GetRendererCapabilities().MainThreadCapabilities();
}

void SingleThreadProxy::DidLoseOutputSurfaceOnImplThread() {
  TRACE_EVENT0("cc", "SingleThreadProxy::DidLoseOutputSurfaceOnImplThread");
  {
    DebugScopedSetMainThread main(task_runner_provider_);
    // This must happen before we notify the scheduler as it may try to recreate
    // the output surface if already in BEGIN_IMPL_FRAME_STATE_IDLE.
    layer_tree_host_->DidLoseOutputSurface();
  }
  client_->DidAbortSwapBuffers();
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->DidLoseOutputSurface();
}

void SingleThreadProxy::CommitVSyncParameters(base::TimeTicks timebase,
                                              base::TimeDelta interval) {
  if (interval.is_zero()) {
    // TODO(brianderson): We should not be receiving 0 intervals.
    interval = BeginFrameArgs::DefaultInterval();
  }

  if (synthetic_begin_frame_source_)
    synthetic_begin_frame_source_->OnUpdateVSyncParameters(timebase, interval);
}

void SingleThreadProxy::SetBeginFrameSource(BeginFrameSource* source) {
  DCHECK(layer_tree_host_->settings().single_thread_proxy_scheduler);
  // TODO(enne): this overrides any preexisting begin frame source.  Those
  // other sources will eventually be removed and this will be the only path.
  if (!layer_tree_host_->settings().use_output_surface_begin_frame_source)
    return;
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetBeginFrameSource(source);
}

void SingleThreadProxy::SetEstimatedParentDrawTime(base::TimeDelta draw_time) {
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->SetEstimatedParentDrawTime(draw_time);
}

void SingleThreadProxy::DidSwapBuffersOnImplThread() {
  TRACE_EVENT0("cc", "SingleThreadProxy::DidSwapBuffersOnImplThread");
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->DidSwapBuffers();
  client_->DidPostSwapBuffers();
}

void SingleThreadProxy::DidSwapBuffersCompleteOnImplThread() {
  TRACE_EVENT0("cc,benchmark",
               "SingleThreadProxy::DidSwapBuffersCompleteOnImplThread");
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->DidSwapBuffersComplete();
  layer_tree_host_->DidCompleteSwapBuffers();
}

void SingleThreadProxy::OnDrawForOutputSurface(
    bool resourceless_software_draw) {
  NOTREACHED() << "Implemented by ThreadProxy for synchronous compositor.";
}

void SingleThreadProxy::CompositeImmediately(base::TimeTicks frame_begin_time) {
  TRACE_EVENT0("cc,benchmark", "SingleThreadProxy::CompositeImmediately");
  DCHECK(task_runner_provider_->IsMainThread());
#if DCHECK_IS_ON()
  DCHECK(!inside_impl_frame_);
#endif
  base::AutoReset<bool> inside_composite(&inside_synchronous_composite_, true);

  if (layer_tree_host_->output_surface_lost()) {
    RequestNewOutputSurface();
    // RequestNewOutputSurface could have synchronously created an output
    // surface, so check again before returning.
    if (layer_tree_host_->output_surface_lost())
      return;
  }

  BeginFrameArgs begin_frame_args(BeginFrameArgs::Create(
      BEGINFRAME_FROM_HERE, frame_begin_time, base::TimeTicks(),
      BeginFrameArgs::DefaultInterval(), BeginFrameArgs::NORMAL));

  // Start the impl frame.
  {
    DebugScopedSetImplThread impl(task_runner_provider_);
    WillBeginImplFrame(begin_frame_args);
  }

  // Run the "main thread" and get it to commit.
  {
#if DCHECK_IS_ON()
    DCHECK(inside_impl_frame_);
#endif
    DoBeginMainFrame(begin_frame_args);
    DoCommit();

    DCHECK_EQ(0u, layer_tree_host_->num_queued_swap_promises())
        << "Commit should always succeed and transfer promises.";
  }

  // Finish the impl frame.
  {
    DebugScopedSetImplThread impl(task_runner_provider_);
    layer_tree_host_impl_->ActivateSyncTree();
    DCHECK(
        !layer_tree_host_impl_->active_tree()->needs_update_draw_properties());
    layer_tree_host_impl_->PrepareTiles();
    layer_tree_host_impl_->SynchronouslyInitializeAllTiles();

    // TODO(danakj): Don't do this last... we prepared the wrong things. D:
    layer_tree_host_impl_->Animate();

    LayerTreeHostImpl::FrameData frame;
    DoComposite(&frame);

    // DoComposite could abort, but because this is a synchronous composite
    // another draw will never be scheduled, so break remaining promises.
    layer_tree_host_impl_->active_tree()->BreakSwapPromises(
        SwapPromise::SWAP_FAILS);

    DidFinishImplFrame();
  }
}

bool SingleThreadProxy::SupportsImplScrolling() const {
  return false;
}

bool SingleThreadProxy::ShouldComposite() const {
  DCHECK(task_runner_provider_->IsImplThread());
  return layer_tree_host_impl_->visible() &&
         layer_tree_host_impl_->CanDraw();
}

void SingleThreadProxy::ScheduleRequestNewOutputSurface() {
  if (output_surface_creation_callback_.IsCancelled() &&
      !output_surface_creation_requested_) {
    output_surface_creation_callback_.Reset(
        base::Bind(&SingleThreadProxy::RequestNewOutputSurface,
                   weak_factory_.GetWeakPtr()));
    task_runner_provider_->MainThreadTaskRunner()->PostTask(
        FROM_HERE, output_surface_creation_callback_.callback());
  }
}

DrawResult SingleThreadProxy::DoComposite(LayerTreeHostImpl::FrameData* frame) {
  TRACE_EVENT0("cc", "SingleThreadProxy::DoComposite");
  DCHECK(!layer_tree_host_->output_surface_lost());

  DrawResult draw_result;
  bool draw_frame;
  {
    DebugScopedSetImplThread impl(task_runner_provider_);
    base::AutoReset<bool> mark_inside(&inside_draw_, true);

    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile1(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoComposite1"));

    // 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()) {
      return DRAW_ABORTED_CANT_DRAW;
    }

    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile2(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoComposite2"));
    draw_result = layer_tree_host_impl_->PrepareToDraw(frame);
    draw_frame = draw_result == DRAW_SUCCESS;
    if (draw_frame) {
      // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
      // is fixed.
      tracked_objects::ScopedTracker tracking_profile3(
          FROM_HERE_WITH_EXPLICIT_FUNCTION(
              "461509 SingleThreadProxy::DoComposite3"));
      layer_tree_host_impl_->DrawLayers(frame);
    }
    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile4(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoComposite4"));
    layer_tree_host_impl_->DidDrawAllLayers(*frame);

    bool start_ready_animations = draw_frame;
    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile5(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoComposite5"));
    layer_tree_host_impl_->UpdateAnimationState(start_ready_animations);

    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile7(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoComposite7"));
  }

  if (draw_frame) {
    DebugScopedSetImplThread impl(task_runner_provider_);

    // This CapturePostTasks should be destroyed before
    // DidCommitAndDrawFrame() is called since that goes out to the
    // embedder,
    // and we want the embedder to receive its callbacks before that.
    // NOTE: This maintains consistent ordering with the ThreadProxy since
    // the DidCommitAndDrawFrame() must be post-tasked from the impl thread
    // there as the main thread is not blocked, so any posted tasks inside
    // the swap buffers will execute first.
    DebugScopedSetMainThreadBlocked main_thread_blocked(task_runner_provider_);

    BlockingTaskRunner::CapturePostTasks blocked(
        task_runner_provider_->blocking_main_thread_task_runner());
    // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
    // is fixed.
    tracked_objects::ScopedTracker tracking_profile8(
        FROM_HERE_WITH_EXPLICIT_FUNCTION(
            "461509 SingleThreadProxy::DoComposite8"));
    layer_tree_host_impl_->SwapBuffers(*frame);
  }
  // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509 is
  // fixed.
  tracked_objects::ScopedTracker tracking_profile9(
      FROM_HERE_WITH_EXPLICIT_FUNCTION(
          "461509 SingleThreadProxy::DoComposite9"));
  DidCommitAndDrawFrame();

  return draw_result;
}

void SingleThreadProxy::DidCommitAndDrawFrame() {
  if (next_frame_is_newly_committed_frame_) {
    DebugScopedSetMainThread main(task_runner_provider_);
    next_frame_is_newly_committed_frame_ = false;
    layer_tree_host_->DidCommitAndDrawFrame();
  }
}

bool SingleThreadProxy::MainFrameWillHappenForTesting() {
  if (layer_tree_host_->output_surface_lost())
    return false;
  if (!scheduler_on_impl_thread_)
    return false;
  return scheduler_on_impl_thread_->MainFrameForTestingWillHappen();
}

void SingleThreadProxy::WillBeginImplFrame(const BeginFrameArgs& args) {
  DebugScopedSetImplThread impl(task_runner_provider_);
#if DCHECK_IS_ON()
  DCHECK(!inside_impl_frame_)
      << "WillBeginImplFrame called while already inside an impl frame!";
  inside_impl_frame_ = true;
#endif
  layer_tree_host_impl_->WillBeginImplFrame(args);
}

void SingleThreadProxy::ScheduledActionSendBeginMainFrame(
    const BeginFrameArgs& begin_frame_args) {
  TRACE_EVENT0("cc", "SingleThreadProxy::ScheduledActionSendBeginMainFrame");
  // Although this proxy is single-threaded, it's problematic to synchronously
  // have BeginMainFrame happen after ScheduledActionSendBeginMainFrame.  This
  // could cause a commit to occur in between a series of SetNeedsCommit calls
  // (i.e. property modifications) causing some to fall on one frame and some to
  // fall on the next.  Doing it asynchronously instead matches the semantics of
  // ThreadProxy::SetNeedsCommit where SetNeedsCommit will not cause a
  // synchronous commit.
#if DCHECK_IS_ON()
  DCHECK(inside_impl_frame_)
      << "BeginMainFrame should only be sent inside a BeginImplFrame";
#endif

  task_runner_provider_->MainThreadTaskRunner()->PostTask(
      FROM_HERE, base::Bind(&SingleThreadProxy::BeginMainFrame,
                            weak_factory_.GetWeakPtr(), begin_frame_args));
}

void SingleThreadProxy::SendBeginMainFrameNotExpectedSoon() {
  layer_tree_host_->BeginMainFrameNotExpectedSoon();
}

void SingleThreadProxy::BeginMainFrame(const BeginFrameArgs& begin_frame_args) {
  if (scheduler_on_impl_thread_) {
    scheduler_on_impl_thread_->NotifyBeginMainFrameStarted(
        base::TimeTicks::Now());
  }

  commit_requested_ = false;
  animate_requested_ = false;

  if (defer_commits_) {
    TRACE_EVENT_INSTANT0("cc", "EarlyOut_DeferCommit",
                         TRACE_EVENT_SCOPE_THREAD);
    BeginMainFrameAbortedOnImplThread(
        CommitEarlyOutReason::ABORTED_DEFERRED_COMMIT);
    return;
  }

  // This checker assumes NotifyReadyToCommit in this stack causes a synchronous
  // commit.
  ScopedAbortRemainingSwapPromises swap_promise_checker(layer_tree_host_);

  if (!layer_tree_host_->visible()) {
    TRACE_EVENT_INSTANT0("cc", "EarlyOut_NotVisible", TRACE_EVENT_SCOPE_THREAD);
    BeginMainFrameAbortedOnImplThread(
        CommitEarlyOutReason::ABORTED_NOT_VISIBLE);
    return;
  }

  if (layer_tree_host_->output_surface_lost()) {
    TRACE_EVENT_INSTANT0(
        "cc", "EarlyOut_OutputSurfaceLost", TRACE_EVENT_SCOPE_THREAD);
    BeginMainFrameAbortedOnImplThread(
        CommitEarlyOutReason::ABORTED_OUTPUT_SURFACE_LOST);
    return;
  }

  // Prevent new commits from being requested inside DoBeginMainFrame.
  // Note: We do not want to prevent SetNeedsAnimate from requesting
  // a commit here.
  commit_requested_ = true;

  DoBeginMainFrame(begin_frame_args);
}

void SingleThreadProxy::DoBeginMainFrame(
    const BeginFrameArgs& begin_frame_args) {
  layer_tree_host_->WillBeginMainFrame();
  layer_tree_host_->BeginMainFrame(begin_frame_args);
  layer_tree_host_->AnimateLayers(begin_frame_args.frame_time);
  layer_tree_host_->RequestMainFrameUpdate();

  // New commits requested inside UpdateLayers should be respected.
  commit_requested_ = false;

  layer_tree_host_->UpdateLayers();

  // TODO(enne): SingleThreadProxy does not support cancelling commits yet,
  // search for CommitEarlyOutReason::FINISHED_NO_UPDATES inside
  // thread_proxy.cc
  if (scheduler_on_impl_thread_)
    scheduler_on_impl_thread_->NotifyReadyToCommit();
}

void SingleThreadProxy::BeginMainFrameAbortedOnImplThread(
    CommitEarlyOutReason reason) {
  DebugScopedSetImplThread impl(task_runner_provider_);
  DCHECK(scheduler_on_impl_thread_->CommitPending());
  DCHECK(!layer_tree_host_impl_->pending_tree());

  layer_tree_host_impl_->BeginMainFrameAborted(reason);
  scheduler_on_impl_thread_->BeginMainFrameAborted(reason);
}

DrawResult SingleThreadProxy::ScheduledActionDrawAndSwapIfPossible() {
  DebugScopedSetImplThread impl(task_runner_provider_);
  LayerTreeHostImpl::FrameData frame;
  return DoComposite(&frame);
}

DrawResult SingleThreadProxy::ScheduledActionDrawAndSwapForced() {
  NOTREACHED();
  return INVALID_RESULT;
}

void SingleThreadProxy::ScheduledActionCommit() {
  DebugScopedSetMainThread main(task_runner_provider_);
  DoCommit();
}

void SingleThreadProxy::ScheduledActionActivateSyncTree() {
  DebugScopedSetImplThread impl(task_runner_provider_);
  layer_tree_host_impl_->ActivateSyncTree();
}

void SingleThreadProxy::ScheduledActionBeginOutputSurfaceCreation() {
  DebugScopedSetMainThread main(task_runner_provider_);
  DCHECK(scheduler_on_impl_thread_);
  // If possible, create the output surface in a post task.  Synchronously
  // creating the output surface makes tests more awkward since this differs
  // from the ThreadProxy behavior.  However, sometimes there is no
  // task runner.
  if (task_runner_provider_->MainThreadTaskRunner()) {
    ScheduleRequestNewOutputSurface();
  } else {
    RequestNewOutputSurface();
  }
}

void SingleThreadProxy::ScheduledActionPrepareTiles() {
  TRACE_EVENT0("cc", "SingleThreadProxy::ScheduledActionPrepareTiles");
  DebugScopedSetImplThread impl(task_runner_provider_);
  layer_tree_host_impl_->PrepareTiles();
}

void SingleThreadProxy::ScheduledActionInvalidateOutputSurface() {
  NOTREACHED();
}

void SingleThreadProxy::UpdateTopControlsState(TopControlsState constraints,
                                               TopControlsState current,
                                               bool animate) {
  NOTREACHED() << "Top Controls are used only in threaded mode";
}

void SingleThreadProxy::DidFinishImplFrame() {
  layer_tree_host_impl_->DidFinishImplFrame();
#if DCHECK_IS_ON()
  DCHECK(inside_impl_frame_)
      << "DidFinishImplFrame called while not inside an impl frame!";
  inside_impl_frame_ = false;
#endif
}

}  // namespace cc