WIP: Implement CSS transitions on top of InterpolationTypes instead of AnimatableValues

third_party/WebKit/Source/core/animation/StackableInterpolation.cpp

+// Copyright 2016 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 "core/animation/StackableInterpolation.h"
+
+#include "core/animation/InterpolationType.h"
+#include "core/animation/TypedInterpolationValue.h"
+#include "core/animation/UnderlyingValueOwner.h"
+
+namespace blink {
+
+void StackableInterpolation::applyStack(const ActiveInterpolations& interpolations, InterpolationEnvironment& environment)
+{
+    DCHECK(!interpolations.isEmpty());
+    size_t startingIndex = 0;
+
+    // Compute the underlying value to composite onto.
+    UnderlyingValueOwner underlyingValueOwner;
+    const StackableInterpolation& firstInterpolation = toStackableInterpolation(*interpolations.at(startingIndex));
+    if (firstInterpolation.dependsOnUnderlyingValue()) {
+        underlyingValueOwner.set(firstInterpolation.maybeConvertUnderlyingValue(environment));
+    } else {
+        const TypedInterpolationValue* firstValue = firstInterpolation.ensureValidInterpolation(environment, underlyingValueOwner);
+        // Fast path for replace interpolations that are the only one to apply.
+        if (interpolations.size() == 1) {
+            if (firstValue) {
+                firstInterpolation.setFlagIfInheritUsed(environment);
+                firstValue->type().apply(firstValue->interpolableValue(), firstValue->getNonInterpolableValue(), environment);
+            }
+            return;
+        }
+        underlyingValueOwner.set(firstValue);
+        startingIndex++;
+    }
+
+    // Composite interpolations onto the underlying value.
+    bool shouldApply = false;
+    for (size_t i = startingIndex; i < interpolations.size(); i++) {
+        const StackableInterpolation& currentInterpolation = toStackableInterpolation(*interpolations.at(i));
+        DCHECK(currentInterpolation.dependsOnUnderlyingValue());
+        const TypedInterpolationValue* currentValue = currentInterpolation.ensureValidInterpolation(environment, underlyingValueOwner);
+        if (!currentValue)
+            continue;
+        shouldApply = true;
+        currentInterpolation.setFlagIfInheritUsed(environment);
+        double underlyingFraction = currentInterpolation.underlyingFraction();
+        if (underlyingFraction == 0 || !underlyingValueOwner || underlyingValueOwner.type() != currentValue->type())
+            underlyingValueOwner.set(currentValue);
+        else
+            currentValue->type().composite(underlyingValueOwner, underlyingFraction, currentValue->value(), currentInterpolation.m_currentFraction);
+    }
+
+    if (shouldApply && underlyingValueOwner)
+        underlyingValueOwner.type().apply(*underlyingValueOwner.value().interpolableValue, underlyingValueOwner.value().nonInterpolableValue.get(), environment);
+}
+
+} // namespace blink