Web Animations - responsive interpolation

Source/core/css/resolver/StyleResolver.cpp

Index: Source/core/css/resolver/StyleResolver.cpp
diff --git a/Source/core/css/resolver/StyleResolver.cpp b/Source/core/css/resolver/StyleResolver.cpp
index 67a7eb1662c837d93419ca41b0a44c690b868be1..664efcd06d2a58afb340a18760aa79b3a11c0394 100644
--- a/Source/core/css/resolver/StyleResolver.cpp
+++ b/Source/core/css/resolver/StyleResolver.cpp
@@ -752,14 +752,19 @@ PassRefPtr<RenderStyle> StyleResolver::styleForKeyframe(Element* element, const
 
 // This function is used by the WebAnimations JavaScript API method animate().
 // FIXME: Remove this when animate() switches away from resolution-dependent parsing.
-PassRefPtrWillBeRawPtr<AnimatableValue> StyleResolver::createAnimatableValueSnapshot(Element& element, CSSPropertyID property, CSSValue* value)
+PassRefPtrWillBeRawPtr<AnimatableValue> StyleResolver::applyAndSnapshotAnimatableValue(Element& element, CSSPropertyID property, CSSValue& value, RenderStyle* mutableStyle)
 {
-    // We use a fresh RenderStyle here because certain values (eg. background-position) won't always completely replace the previously applied property.
-    RefPtr<RenderStyle> style = element.renderStyle() ? RenderStyle::clone(element.renderStyle()) : RenderStyle::create();
+    RefPtr<RenderStyle> style;
+    if (mutableStyle)
+        style = mutableStyle;
+    else if (element.renderStyle())
+        style = RenderStyle::clone(element.renderStyle());
+    else
+        style = RenderStyle::create();

[shans, 2014/05/26 03:31:01]

This looks like a recipe for introducing bugs in the future. Please provide
separate code paths!!

[alancutter (OOO until 2018), 2014/05/26 05:22:41]

Perhaps the style parameter should be non-optional (a reference) and the check
should be reworked into the callsites.

     StyleResolverState state(element.document(), &element);
     state.setStyle(style.get());
     state.fontBuilder().initForStyleResolve(state.document(), state.style(), state.useSVGZoomRules());
-    StyleBuilder::applyProperty(property, state, value);
+    StyleBuilder::applyProperty(property, state, &value);
     return CSSAnimatableValueFactory::create(property, *style);
 }