Web Animations API: Implement step-middle and steps(x, middle) timing functions.

Source/platform/animation/TimingFunction.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 159 matching lines @@
     double m_y2;
     SubType m_subType;
     mutable OwnPtr<UnitBezier> m_bezier;
 };
 
 class StepsTimingFunction FINAL : public TimingFunction {
 public:
     enum SubType {
         Start,
         End,
+        Middle,
         Custom
     };
 
-    static PassRefPtr<StepsTimingFunction> create(int steps, bool stepAtStart)
+    enum StepAtPosition {
+        StepAtStart,
+        StepAtMiddle,
+        StepAtEnd
+    };
+
+    static PassRefPtr<StepsTimingFunction> create(int steps, StepAtPosition stepAtPosition)
     {
-        return adoptRef(new StepsTimingFunction(Custom, steps, stepAtStart));
+        return adoptRef(new StepsTimingFunction(Custom, steps, stepAtPosition));
     }
 
     static StepsTimingFunction* preset(SubType subType)
     {
         switch (subType) {
         case Start:
             {
-                DEFINE_STATIC_REF(StepsTimingFunction, start, (adoptRef(new StepsTimingFunction(Start, 1, true))));
+                DEFINE_STATIC_REF(StepsTimingFunction, start, (adoptRef(new StepsTimingFunction(Start, 1, StepAtStart))));
                 return start;
             }
+        case Middle:
+            {
+                DEFINE_STATIC_REF(StepsTimingFunction, middle, (adoptRef(new StepsTimingFunction(Middle, 1, StepAtMiddle))));
+                return middle;
+            }
         case End:
             {
-                DEFINE_STATIC_REF(StepsTimingFunction, end, (adoptRef(new StepsTimingFunction(End, 1, false))));
+                DEFINE_STATIC_REF(StepsTimingFunction, end, (adoptRef(new StepsTimingFunction(End, 1, StepAtEnd))));
                 return end;
             }
         default:
             ASSERT_NOT_REACHED();
             return 0;
         }
     }
 
 
     virtual ~StepsTimingFunction() { }
 
     virtual double evaluate(double fraction, double) const OVERRIDE
     {
         ASSERT(RuntimeEnabledFeatures::webAnimationsCSSEnabled() || (fraction >= 0 && fraction <= 1));
         ASSERT_WITH_MESSAGE(!RuntimeEnabledFeatures::webAnimationsCSSEnabled() || (fraction >= 0 && fraction <= 1), "Web Animations not yet implemented: Timing function behavior outside the range [0, 1] is not yet specified");
-        return std::min(1.0, (floor(m_steps * fraction) + m_stepAtStart) / m_steps);
+        double startOffset = 0;
+        switch (m_stepAtPosition) {
+        case StepAtStart:
+            {
+                startOffset = 1;
+                break;
+            }
+        case StepAtMiddle:
+            {
+                startOffset = 0.5;
+                break;
+            }
+        case StepAtEnd:
+            {
+                startOffset = 0;
+                break;
+            }
+        default:
+            {
+                ASSERT_NOT_REACHED();
+                break;
+            }
+        }
+        return std::min(1.0, floor((m_steps * fraction) + startOffset) / m_steps);
     }
 
     int numberOfSteps() const { return m_steps; }
-    bool stepAtStart() const { return m_stepAtStart; }
+    StepAtPosition stepAtPosition() const { return m_stepAtPosition; }
 
     SubType subType() const { return m_subType; }
 
 private:
-    StepsTimingFunction(SubType subType, int steps, bool stepAtStart)
+    StepsTimingFunction(SubType subType, int steps, StepAtPosition stepAtPosition)
         : TimingFunction(StepsFunction)
         , m_steps(steps)
-        , m_stepAtStart(stepAtStart)
+        , m_stepAtPosition(stepAtPosition)
         , m_subType(subType)
     {
     }
 
     int m_steps;
-    bool m_stepAtStart;
+    StepAtPosition m_stepAtPosition;
     SubType m_subType;
 };
 
 class ChainedTimingFunction FINAL : public TimingFunction {
 public:
     static PassRefPtr<ChainedTimingFunction> create()
     {
         return adoptRef(new ChainedTimingFunction);
     }
 
@@ skipping 78 matching lines @@
         value.type() == TimingFunction::typeName##Function)
 
 DEFINE_TIMING_FUNCTION_TYPE_CASTS(Linear);
 DEFINE_TIMING_FUNCTION_TYPE_CASTS(CubicBezier);
 DEFINE_TIMING_FUNCTION_TYPE_CASTS(Steps);
 DEFINE_TIMING_FUNCTION_TYPE_CASTS(Chained);
 
 } // namespace WebCore
 
 #endif // TimingFunction_h