Scheduler: Switch from high to low latency mode if possible.

cc/scheduler/scheduler.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/scheduler/scheduler.h"
 
 #include <algorithm>
 #include "base/auto_reset.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 166 matching lines @@
 }
 
 void Scheduler::BeginImplFrame(const BeginFrameArgs& args) {
   TRACE_EVENT0("cc", "Scheduler::BeginImplFrame");
   DCHECK(state_machine_.begin_impl_frame_state() ==
          SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_IDLE);
   DCHECK(state_machine_.HasInitializedOutputSurface());
   last_begin_impl_frame_args_ = args;
   last_begin_impl_frame_args_.deadline -= client_->DrawDurationEstimate();
   state_machine_.OnBeginImplFrame(last_begin_impl_frame_args_);
+
+  if (settings_.switch_to_low_latency_if_possible) {
+    state_machine_.SetSkipBeginMainFrameToReduceLatency(
+        state_machine_.InHighLatencyMode() && CanOperateInLowLatencyMode());
+  }
+
   ProcessScheduledActions();
 
   if (!state_machine_.HasInitializedOutputSurface())
     return;
 
   state_machine_.OnBeginImplFrameDeadlinePending();
 
   if (settings_.using_synchronous_renderer_compositor) {
     // The synchronous renderer compositor has to make its GL calls
     // within this call to BeginImplFrame.
@@ skipping 140 matching lines @@
   client_->DidAnticipatedDrawTimeChange(AnticipatedDrawTime());
 
   if (state_machine_.ShouldTriggerBeginImplFrameDeadlineEarly())
     PostBeginImplFrameDeadline(base::TimeTicks());
 }
 
 bool Scheduler::WillDrawIfNeeded() const {
   return !state_machine_.PendingDrawsShouldBeAborted();
 }
 
+bool Scheduler::CanOperateInLowLatencyMode() const {
+  // If the main thread computation and commit can be finished before the
+  // deadline we can operate in low latency mode.
+  base::TimeTicks estimated_draw_time =
+      last_begin_impl_frame_args_.frame_time +
+      client_->BeginMainFrameToCommitDurationEstimate() +
+      client_->CommitToActivateDurationEstimate();
+
+  return estimated_draw_time < last_begin_impl_frame_args_.deadline;
+}
+
 }  // namespace cc