Define accelerated steps time function.

cc/animation/timing_function.h

 // 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.
 
 #ifndef CC_ANIMATION_TIMING_FUNCTION_H_
 #define CC_ANIMATION_TIMING_FUNCTION_H_
 
 #include "cc/animation/animation_curve.h"
 #include "cc/base/cc_export.h"
-#include "ui/gfx/geometry/cubic_bezier.h"
+#include "ui/gfx/animation/cubic_bezier.h"
+#include "ui/gfx/animation/steps.h"
 
 namespace cc {
 
 // See http://www.w3.org/TR/css3-transitions/.
 class CC_EXPORT TimingFunction : public FloatAnimationCurve {
  public:
   virtual ~TimingFunction();
 
   // Partial implementation of FloatAnimationCurve.
   virtual double Duration() const OVERRIDE;
@@ skipping 25 matching lines @@
 
  protected:
   CubicBezierTimingFunction(double x1, double y1, double x2, double y2);
 
   gfx::CubicBezier bezier_;
 
  private:
   DISALLOW_ASSIGN(CubicBezierTimingFunction);
 };
 
+class CC_EXPORT StepsTimingFunction : public TimingFunction {
+ public:
+  static scoped_ptr<StepsTimingFunction> Create(int steps, bool steps_at_start);
+  virtual ~StepsTimingFunction();
+
+  virtual float GetValue(double time) const OVERRIDE;
+  virtual scoped_ptr<AnimationCurve> Clone() const OVERRIDE;
+  virtual void Range(float* min, float* max) const OVERRIDE;
+  // XXX: Should Velocity be a CubicBezierTimingFunction only? It seems to be
+  // used only for ScrollOffsetAnimationCurve. Do ScrollOffsetAnimationCurve
+  // with non bezier curves make sense?

[ajuma, 2014/09/16 14:50:15]

ScrollOffsetAnimationCurves with non-bezier curves make sense (though we don't
have any current use cases).

Defining Velocity to be 0 for a StepsTimingFunction (as you've done) seems
reasonable.

+  virtual float Velocity(double time) const OVERRIDE;
+
+ protected:
+  StepsTimingFunction(int steps, bool steps_at_start);
+
+  gfx::Steps steps_;
+
+ private:
+  DISALLOW_ASSIGN(StepsTimingFunction);
+};
+
 class CC_EXPORT EaseTimingFunction {
  public:
   static scoped_ptr<TimingFunction> Create();
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(EaseTimingFunction);
 };
 
 class CC_EXPORT EaseInTimingFunction {
  public:
@@ skipping 15 matching lines @@
  public:
   static scoped_ptr<TimingFunction> Create();
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(EaseInOutTimingFunction);
 };
 
 }  // namespace cc
 
 #endif  // CC_ANIMATION_TIMING_FUNCTION_H_