Add a simple scheduler for animation frames

This CL adds a simple scheduler for animation frames that holds a given interval
in a given phase.  The scheduler can be told the estimated duration of the
BeginFrame callback and can adjust the callback to hit a given vsync interval.

This CL also makes ganesh_app use this scheduler to animate.

R=jamesr@chromium.org, ernstm@chromium.org

Review URL: https://codereview.chromium.org/731893002

engine/src/flutter/scheduler/BUILD.gn

@@ -0,0 +1,18 @@
+# Copyright 2014 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.
+
+static_library("scheduler") {
+  sources = [
+    "scheduler.cc",
+    "scheduler.h",
+    "time_interval.cc",
+    "time_interval.h",
+    "timer.cc",
+    "timer.h",
+  ]
+
+  deps = [
+    "//base",
+  ]
+}

engine/src/flutter/scheduler/scheduler.cc

@@ -0,0 +1,45 @@
+// Copyright 2014 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 "sky/scheduler/scheduler.h"
+
+namespace sky {
+
+Scheduler::Client::~Client() {
+}
+
+Scheduler::Scheduler(Client* client,
+                     scoped_refptr<base::SingleThreadTaskRunner> task_runner)
+    : client_(client), timer_(this, task_runner) {
+}
+
+Scheduler::~Scheduler() {
+}
+
+void Scheduler::SetNeedsFrame() {
+  timer_.SetEnabled(true);
+}
+
+void Scheduler::UpdateFrameDuration(base::TimeDelta estimate) {
+  frame_duration_ = estimate;
+  UpdateTimerInterval();
+}
+
+void Scheduler::UpdateVSync(const TimeInterval& vsync) {
+  vsync_ = vsync;
+  UpdateTimerInterval();
+}
+
+void Scheduler::UpdateTimerInterval() {
+  TimeInterval interval = vsync_;
+  interval.base -= frame_duration_;
+  timer_.SetInterval(interval);
+}
+
+void Scheduler::OnTimerTick(base::TimeTicks now) {
+  timer_.SetEnabled(false);
+  client_->BeginFrame(now, vsync_.NextAfter(now));
+  // We might be deleted here.
+}
+}

engine/src/flutter/scheduler/scheduler.h

@@ -0,0 +1,45 @@
+// Copyright 2014 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.
+
+#ifndef SKY_SCHEDULER_SCHEDULER_H_
+#define SKY_SCHEDULER_SCHEDULER_H_
+
+#include "base/single_thread_task_runner.h"
+#include "base/time/time.h"
+#include "sky/scheduler/timer.h"
+
+namespace sky {
+
+class Scheduler : public Timer::Client {
+ public:
+  class Client {
+   public:
+    virtual void BeginFrame(base::TimeTicks frame_time,
+                            base::TimeTicks deadline) = 0;
+
+   protected:
+    virtual ~Client();
+  };
+
+  Scheduler(Client* client,
+            scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+  ~Scheduler();
+
+  void UpdateFrameDuration(base::TimeDelta estimate);
+  void UpdateVSync(const TimeInterval& vsync);
+
+  void SetNeedsFrame();
+
+ private:
+  void UpdateTimerInterval();
+  void OnTimerTick(base::TimeTicks now) override;
+
+  Client* client_;
+  Timer timer_;
+  TimeInterval vsync_;
+  base::TimeDelta frame_duration_;
+};
+}
+
+#endif  // SKY_SCHEDULER_SCHEDULER_H_

engine/src/flutter/scheduler/time_interval.cc

@@ -0,0 +1,17 @@
+// Copyright 2014 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 "sky/scheduler/time_interval.h"
+
+#include <cstdlib>
+
+namespace sky {
+
+base::TimeTicks TimeInterval::NextAfter(base::TimeTicks when) {
+  int64 offset = std::abs((when - base).ToInternalValue());
+  base::TimeDelta excess =
+      base::TimeDelta::FromInternalValue(offset % duration.ToInternalValue());
+  return when + duration - excess;
+}
+}

engine/src/flutter/scheduler/time_interval.h

@@ -0,0 +1,24 @@
+// Copyright 2014 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.
+
+#ifndef SKY_SCHEDULER_TIME_INTERVAL_H_
+#define SKY_SCHEDULER_TIME_INTERVAL_H_
+
+#include "base/time/time.h"
+
+namespace sky {
+
+struct TimeInterval {
+  TimeInterval() {}
+  TimeInterval(base::TimeTicks base, base::TimeDelta duration)
+      : base(base), duration(duration) {}
+
+  base::TimeTicks NextAfter(base::TimeTicks when);
+
+  base::TimeTicks base;
+  base::TimeDelta duration;
+};
+}
+
+#endif  // SKY_SCHEDULER_TIME_INTERVAL_H_

engine/src/flutter/scheduler/timer.cc

@@ -0,0 +1,94 @@
+// Copyright 2014 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 "sky/scheduler/timer.h"
+
+#include <cstdlib>
+
+#include "base/bind.h"
+#include "base/tracked_objects.h"
+
+namespace sky {
+
+// We're willing to slop around 1/4 of a tick duration to avoid trashing our
+// client with irregular ticks.
+static const int64 kTickSlop = 4;
+
+Timer::Client::~Client() {
+}
+
+Timer::Timer(Client* client,
+             scoped_refptr<base::SingleThreadTaskRunner> task_runner)
+    : client_(client),
+      task_runner_(task_runner),
+      enabled_(false),
+      weak_factory_(this) {
+  DCHECK(client_);
+}
+
+Timer::~Timer() {
+}
+
+void Timer::SetEnabled(bool enabled) {
+  enabled_ = enabled;
+
+  if (enabled_ && current_target_.is_null())
+    ScheduleNextTick(base::TimeTicks::Now());
+}
+
+void Timer::SetInterval(const TimeInterval& interval) {
+  interval_ = interval;
+
+  // We don't have a tick scheduled, so there's no need to reschedule it.
+  if (current_target_.is_null())
+    return;
+
+  base::TimeTicks now = base::TimeTicks::Now();
+
+  base::TimeTicks new_target = NextTickTarget(now);
+  base::TimeDelta delta = base::TimeDelta::FromInternalValue(
+      std::abs((new_target - current_target_).ToInternalValue()));
+
+  if (delta * kTickSlop < interval_.duration)
+    return;
+
+  current_target_ = base::TimeTicks();
+  weak_factory_.InvalidateWeakPtrs();
+  PostTickTask(now, new_target);
+}
+
+base::TimeTicks Timer::NextTickTarget(base::TimeTicks now) {
+  base::TimeTicks target = interval_.NextAfter(now);
+
+  // If we're targeting a time that's too soon since the last tick, we push out
+  // the target to the next tick.
+  if ((target - last_tick_) * kTickSlop < interval_.duration)
+    target += interval_.duration;
+
+  return target;
+}
+
+void Timer::ScheduleNextTick(base::TimeTicks now) {
+  PostTickTask(now, NextTickTarget(now));
+}
+
+void Timer::PostTickTask(base::TimeTicks now, base::TimeTicks target) {
+  DCHECK(current_target_.is_null());
+  current_target_ = target;
+  task_runner_->PostDelayedTask(
+      FROM_HERE, base::Bind(&Timer::OnTimerFired, weak_factory_.GetWeakPtr()),
+      current_target_ - now);
+}
+
+void Timer::OnTimerFired() {
+  current_target_ = base::TimeTicks();
+  if (!enabled_)
+    return;
+  base::TimeTicks now = base::TimeTicks::Now();
+  ScheduleNextTick(now);
+  last_tick_ = now;
+  client_->OnTimerTick(now);
+  // We might be deleted here.
+}
+}

engine/src/flutter/scheduler/timer.h

@@ -0,0 +1,52 @@
+// Copyright 2014 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.
+
+#ifndef SKY_SCHEDULER_TIMER_H_
+#define SKY_SCHEDULER_TIMER_H_
+
+#include "base/memory/weak_ptr.h"
+#include "base/single_thread_task_runner.h"
+#include "base/time/time.h"
+#include "sky/scheduler/time_interval.h"
+
+namespace sky {
+
+class Timer {
+ public:
+  class Client {
+   public:
+    virtual void OnTimerTick(base::TimeTicks now) = 0;
+
+   protected:
+    virtual ~Client();
+  };
+
+  Timer(Client* client,
+        scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+  ~Timer();
+
+  void SetInterval(const TimeInterval& parameters);
+  void SetEnabled(bool enabled);
+
+ private:
+  base::TimeTicks NextTickTarget(base::TimeTicks now);
+  void ScheduleNextTick(base::TimeTicks now);
+  void PostTickTask(base::TimeTicks now, base::TimeTicks target);
+  void OnTimerFired();
+
+  Client* client_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  TimeInterval interval_;
+  base::TimeTicks last_tick_;
+  base::TimeTicks current_target_;
+
+  bool enabled_;
+
+  base::WeakPtrFactory<Timer> weak_factory_;
+};
+
+}
+
+#endif  // SKY_SCHEDULER_TIMER_H_