Define step timing function for the cc animation framework.

Source/core/animation/CompositorAnimations.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 127 matching lines @@
     const KeyframeEffectModelBase& keyframeEffect = toKeyframeEffectModelBase(effect);
 
     PropertySet properties = keyframeEffect.properties();
 
     if (properties.isEmpty())
         return false;
 
     for (const auto& property : properties) {
         const PropertySpecificKeyframeVector& keyframes = keyframeEffect.getPropertySpecificKeyframes(property);
         ASSERT(keyframes.size() >= 2);
-        auto* lastKeyframe = keyframes.last().get();
         for (const auto& keyframe : keyframes) {
             // FIXME: Determine candidacy based on the CSSValue instead of a snapshot AnimatableValue.
             if (keyframe->composite() != AnimationEffect::CompositeReplace || !keyframe->getAnimatableValue())
                 return false;
 
             switch (property) {
             case CSSPropertyOpacity:
                 break;
             case CSSPropertyTransform:
                 if (toAnimatableTransform(keyframe->getAnimatableValue().get())->transformOperations().dependsOnBoxSize())
                     return false;
                 break;
             case CSSPropertyWebkitFilter: {
                 const FilterOperations& operations = toAnimatableFilterOperations(keyframe->getAnimatableValue().get())->operations();
                 if (operations.hasFilterThatMovesPixels())
                     return false;
                 break;
             }
             default:
                 return false;
             }
-
-            // FIXME: Remove this check when crbug.com/229405 is resolved
-            if (keyframe != lastKeyframe && keyframe->easing().type() == TimingFunction::StepsFunction)
-                return false;
         }
     }
 
     CompositorAnimationsImpl::CompositorTiming out;
     if (!CompositorAnimationsImpl::convertTimingForCompositor(timing, 0, out, playerPlaybackRate))
         return false;
 
     if (timing.timingFunction->type() != TimingFunction::LinearFunction) {
         // Checks the of size of KeyframeVector instead of PropertySpecificKeyframeVector.
         const KeyframeVector& keyframes = keyframeEffect.getFrames();
-        if (keyframes.size() == 2 && keyframes.first()->easing().type() == TimingFunction::LinearFunction && timing.timingFunction->type() != TimingFunction::StepsFunction)
+        if (keyframes.size() == 2 && keyframes.first()->easing().type() == TimingFunction::LinearFunction)
             return true;
 
         // FIXME: Support non-linear timing functions in the compositor for
-        // more than two keyframes and step timing functions in the compositor.
+        // more than two keyframes.
         return false;
     }
 
     return true;
 }
 
 bool CompositorAnimations::canStartAnimationOnCompositor(const Element& element)
 {
     return element.renderer() && element.renderer()->compositingState() == PaintsIntoOwnBacking;
 }
@@ skipping 124 matching lines @@
                 ASSERT_NOT_REACHED();
                 return;
             }
 
             curve.add(keyframe, easeType);
         }
         return;
     }
 
     case TimingFunction::StepsFunction:
-    default:
-        ASSERT_NOT_REACHED();
+        const StepsTimingFunction* steps = toStepsTimingFunction(timingFunction);
+
+        float stepsStartOffset;
+        switch (steps->stepAtPosition()) {
+        case StepsTimingFunction::Start:
+            stepsStartOffset = 1;
+            break;
+        case StepsTimingFunction::Middle:
+            stepsStartOffset = 0.5;
+            break;
+        case StepsTimingFunction::End:
+            stepsStartOffset = 0;
+            break;
+        default:
+            ASSERT_NOT_REACHED();
+            return;
+        }
+        curve.add(keyframe, steps->numberOfSteps(), stepsStartOffset);
         return;
     }
 }
 
 } // namespace anoymous
 
 void CompositorAnimationsImpl::addKeyframesToCurve(WebCompositorAnimationCurve& curve, const PropertySpecificKeyframeVector& keyframes, const Timing& timing)
 {
     auto* lastKeyframe = keyframes.last().get();
     for (const auto& keyframe : keyframes) {
@@ skipping 127 matching lines @@
             break;
         default:
             ASSERT_NOT_REACHED();
         }
         animations.append(animation.release());
     }
     ASSERT(!animations.isEmpty());
 }
 
 } // namespace blink