cc: Introduce BeginFrame sequence numbers and acknowledgements.

cc/surfaces/display_begin_frame_source.cc

+// 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 "cc/surfaces/display_begin_frame_source.h"
+
+#include <algorithm>
+
+namespace cc {
+
+DisplayBeginFrameSource::DisplayBeginFrameSource(
+    std::unique_ptr<BeginFrameSource> wrapped_source)
+    : wrapped_source_(std::move(wrapped_source)),
+      observing_begin_frames_(false),
+      frame_active_(false),
+      current_source_id_(0),
+      oldest_incorporated_frame_(0),
+      client_(nullptr),
+      client_needs_begin_frames_(false) {}
+
+DisplayBeginFrameSource::~DisplayBeginFrameSource() {
+  if (wrapped_source_ && observing_begin_frames_)
+    wrapped_source_->RemoveObserver(this);
+}
+
+void DisplayBeginFrameSource::SetClient(DisplayBeginFrameSourceClient* client) {
+  client_ = client;
+  ObserverStatusChanged();
+}
+
+void DisplayBeginFrameSource::SetClientNeedsBeginFrames(
+    bool needs_begin_frames) {
+  DCHECK(client_);
+
+  if (client_needs_begin_frames_ == needs_begin_frames)
+    return;
+  client_needs_begin_frames_ = needs_begin_frames;
+
+  if (client_needs_begin_frames_ && observing_begin_frames_) {
+    // We were already observing, but the client may have missed the last
+    // BeginFrame.
+    BeginFrameArgs missed_args =
+        GetMissedArgs(client_->LastUsedBeginFrameArgs());
+    if (missed_args.IsValid())
+      client_->OnBeginFrame(missed_args);
+  }
+
+  UpdateObservingBeginFrames();
+}
+
+void DisplayBeginFrameSource::FinishClientFrame(bool had_updates,
+                                                bool has_pending_updates) {
+  DCHECK(frame_active_);
+  frame_active_ = false;
+
+  // Only update the oldest_incorporated_frame if there are no further pending
+  // updates (i.e. the Display didn't have to draw or drew successfully).
+  if (!has_pending_updates)
+    oldest_incorporated_frame_ = ack_tracker_.OldestIncorporatedFrame();
+
+  BeginFrameAck ack(current_begin_frame_args_.source_id,
+                    current_begin_frame_args_.sequence_number,
+                    oldest_incorporated_frame_, 0, had_updates);
+  if (wrapped_source_)
+    wrapped_source_->DidFinishFrame(this, ack);
+}
+
+bool DisplayBeginFrameSource::HasObservers() const {
+  return !observers_.empty();
+}
+
+bool DisplayBeginFrameSource::AllObserversFinishedFrame() const {
+  return ack_tracker_.AllObserversFinishedFrame();
+}
+
+void DisplayBeginFrameSource::SwapWrappedSource(
+    std::unique_ptr<BeginFrameSource>* begin_frame_source) {
+  if (wrapped_source_ && observing_begin_frames_)
+    wrapped_source_->RemoveObserver(this);
+
+  wrapped_source_.swap(*begin_frame_source);
+
+  if (wrapped_source_ && observing_begin_frames_)
+    wrapped_source_->AddObserver(this);
+}
+
+void DisplayBeginFrameSource::DidFinishFrame(BeginFrameObserver* obs,
+                                             const BeginFrameAck& ack) {
+  ack_tracker_.OnObserverFinishedFrame(obs, ack);
+  ObserverStatusChanged();
+}
+
+void DisplayBeginFrameSource::AddObserver(BeginFrameObserver* obs) {
+  observers_.insert(obs);
+  ack_tracker_.OnObserverAdded(obs);
+
+  if (observing_begin_frames_) {
+    // We were already observing, but the observer may have missed the last
+    // BeginFrame.
+    BeginFrameArgs missed_args = GetMissedArgs(obs->LastUsedBeginFrameArgs());
+    if (missed_args.IsValid()) {
+      obs->OnBeginFrame(missed_args);
+      ack_tracker_.OnObserverBeginFrame(obs, missed_args);
+    }
+  }
+
+  UpdateObservingBeginFrames();
+  ObserverStatusChanged();
+}
+
+void DisplayBeginFrameSource::RemoveObserver(BeginFrameObserver* obs) {
+  observers_.erase(obs);
+  ack_tracker_.OnObserverRemoved(obs);
+
+  UpdateObservingBeginFrames();
+  ObserverStatusChanged();
+}
+
+bool DisplayBeginFrameSource::IsThrottled() const {
+  if (wrapped_source_)
+    return wrapped_source_->IsThrottled();
+  return true;
+}
+
+void DisplayBeginFrameSource::OnBeginFrame(const BeginFrameArgs& args) {
+  if (client_ && client_needs_begin_frames_)
+    client_->OnBeginFrame(args);
+
+  // Reset for the new frame.
+  frame_active_ = true;
+  ack_tracker_.OnBeginFrame(args);
+
+  // BeginFrameObserverAckTracker will have updated the oldest incorporated
+  // frame if the wrapped source changes.
+  if (args.source_id != current_source_id_)
+    oldest_incorporated_frame_ = ack_tracker_.OldestIncorporatedFrame();
+
+  current_begin_frame_args_ = args;
+
+  // Observers may remove themselves during OnBeginFrame(), so use a copy.
+  std::set<BeginFrameObserver*> observers = observers_;
+  for (BeginFrameObserver* obs : observers) {
+    obs->OnBeginFrame(args);
+    ack_tracker_.OnObserverBeginFrame(obs, args);
+  }
+
+  ObserverStatusChanged();
+}
+
+const BeginFrameArgs& DisplayBeginFrameSource::LastUsedBeginFrameArgs() const {
+  return current_begin_frame_args_;
+}
+
+void DisplayBeginFrameSource::OnBeginFrameSourcePausedChanged(bool paused) {
+  // BeginFrameSources used as wrapped sources do not make use of this feature.
+  DCHECK(!paused);
+}
+
+void DisplayBeginFrameSource::UpdateObservingBeginFrames() {
+  bool should_observe = client_needs_begin_frames_ || !observers_.empty();
+  if (should_observe == observing_begin_frames_)
+    return;
+
+  observing_begin_frames_ = should_observe;
+
+  if (!wrapped_source_)
+    return;
+
+  if (observing_begin_frames_) {
+    // We need to start observing, a missed BeginFrame will be triggered by
+    // the wrapped source and forwarded to the client or observer.
+    wrapped_source_->AddObserver(this);
+  } else {
+    wrapped_source_->RemoveObserver(this);
+  }
+}
+
+BeginFrameArgs DisplayBeginFrameSource::GetMissedArgs(
+    const BeginFrameArgs& last_args) const {
+  if (!current_begin_frame_args_.IsValid() || !wrapped_source_ ||
+      !frame_active_)
+    return BeginFrameArgs();
+
+  if (last_args.IsValid() &&
+      (last_args.sequence_number >= current_begin_frame_args_.sequence_number))
+    return BeginFrameArgs();
+
+  BeginFrameArgs missed_args = current_begin_frame_args_;
+  missed_args.type = BeginFrameArgs::MISSED;
+  return missed_args;
+}
+
+void DisplayBeginFrameSource::ObserverStatusChanged() {
+  if (client_)
+    client_->BeginFrameObserverStatusChanged();
+}
+
+}  // namespace cc