Implemented additive animations for length

Source/core/animation/Interpolation.cpp

 // 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 "config.h"
 #include "core/animation/Interpolation.h"
 
+#include "platform/animation/AnimationUtilities.h"
+
 namespace blink {
 
 namespace {
 
 bool typesMatch(const InterpolableValue* start, const InterpolableValue* end)
 {
     if (start->isNumber())
         return end->isNumber();
     if (start->isBool())
         return end->isBool();
@@ skipping 10 matching lines @@
             return false;
     }
     return true;
 }
 
 }
 
 Interpolation::Interpolation(PassOwnPtrWillBeRawPtr<InterpolableValue> start, PassOwnPtrWillBeRawPtr<InterpolableValue> end)
     : m_start(start)
     , m_end(end)
+    , m_compositeStart(AnimationEffect::CompositeReplace)
+    , m_compositeEnd(AnimationEffect::CompositeReplace)
     , m_cachedFraction(0)
     , m_cachedIteration(0)
     , m_cachedValue(m_start->clone())
+    , m_cachedUnderlyingFraction(0)
 {
     RELEASE_ASSERT(typesMatch(m_start.get(), m_end.get()));
 }
 
 Interpolation::~Interpolation()
 {
 }
 
+Interpolation::Interpolation(PassOwnPtrWillBeRawPtr<InterpolableValue> start, PassOwnPtrWillBeRawPtr<InterpolableValue> end,
+    AnimationEffect::CompositeOperation compositeStart, AnimationEffect::CompositeOperation compositeEnd)
+    : m_start(start)
+    , m_end(end)
+    , m_compositeStart(compositeStart)
+    , m_compositeEnd(compositeEnd)
+    , m_cachedFraction(0)
+    , m_cachedIteration(0)
+    , m_cachedValue(m_start->clone())
+    , m_cachedUnderlyingFraction(0)
+{
+    RELEASE_ASSERT(typesMatch(m_start.get(), m_end.get()));
+
+    if (m_compositeStart == m_compositeEnd) {
+        if (m_compositeStart == AnimationEffect::CompositeReplace)
+            m_cachedUnderlyingFraction = 0;
+        else if (m_compositeStart == AnimationEffect::CompositeAdd)
+            m_cachedUnderlyingFraction = 1;
+    }

[alancutter (OOO until 2018), 2015/02/12 05:55:45]

Shouldn't this just be "if start == add: UF = 1"?

+}
+
 void Interpolation::interpolate(int iteration, double fraction) const
 {
     if (m_cachedFraction != fraction || m_cachedIteration != iteration) {
         m_start->interpolate(*m_end, fraction, *m_cachedValue);
         m_cachedIteration = iteration;
         m_cachedFraction = fraction;
+
+        if (m_compositeStart == AnimationEffect::CompositeReplace && m_compositeEnd == AnimationEffect::CompositeReplace)
+            m_cachedUnderlyingFraction = 0;
+        else if (m_compositeStart == AnimationEffect::CompositeAdd && m_compositeEnd == AnimationEffect::CompositeAdd)
+            m_cachedUnderlyingFraction = 1;
+        else if (m_compositeStart == AnimationEffect::CompositeAdd && m_compositeEnd == AnimationEffect::CompositeReplace)
+            m_cachedUnderlyingFraction = blend(1.0, 0.0, fraction);

[alancutter (OOO until 2018), 2015/02/12 05:55:45]

Just use 1 - fraction.

+        else if (m_compositeStart == AnimationEffect::CompositeReplace && m_compositeEnd == AnimationEffect::CompositeAdd)
+            m_cachedUnderlyingFraction = blend(0.0, 1.0, fraction);

[alancutter (OOO until 2018), 2015/02/12 05:55:45]

Just use fraction.

     }
 }
 
 void Interpolation::trace(Visitor* visitor)
 {
     visitor->trace(m_start);
     visitor->trace(m_end);
     visitor->trace(m_cachedValue);
 }
 
 }