Define accelerated steps time function.

cc/animation/timing_function.cc

 // Copyright 2012 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 <algorithm>
 #include <cmath>
 
 #include "base/logging.h"
 #include "cc/animation/timing_function.h"
 
@@ skipping 144 matching lines @@
 scoped_ptr<TimingFunction> EaseOutTimingFunction::Create() {
   return CubicBezierTimingFunction::Create(
       0.0, 0.0, 0.58, 1.0).PassAs<TimingFunction>();
 }
 
 scoped_ptr<TimingFunction> EaseInOutTimingFunction::Create() {
   return CubicBezierTimingFunction::Create(
       0.42, 0.0, 0.58, 1).PassAs<TimingFunction>();
 }
 
+scoped_ptr<StepsTimingFunction> StepsTimingFunction::Create(
+    int steps, bool stepsAtStart) {
+  return make_scoped_ptr(new StepsTimingFunction(steps, stepsAtStart));
+}
+
+StepsTimingFunction::StepsTimingFunction(int steps,
+                                         bool stepsAtStart)
+    : steps_(steps), stepsAtStart_(stepsAtStart) {}
+
+StepsTimingFunction::~StepsTimingFunction() {}
+
+float StepsTimingFunction::GetValue(double x) const {
+    return std::min(1.0, (floor(steps_ * x) + stepsAtStart_) / steps_);
+}
+
+scoped_ptr<AnimationCurve> StepsTimingFunction::Clone() const {
+  return make_scoped_ptr(
+      new StepsTimingFunction(*this)).PassAs<AnimationCurve>();
+}
+
+void StepsTimingFunction::Range(float* min, float* max) const {
+  *min = static_cast<float>(stepsAtStart_) / static_cast<float>(steps_);
+  *max = 1.0;
+}
+
 }  // namespace cc