CSS Motion Path: animate offset-anchor and offset-position

third_party/WebKit/Source/core/animation/animatable/AnimatableLengthPoint.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 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "core/animation/animatable/AnimatableLengthPoint.h"
 
 namespace blink {
 
+bool AnimatableLengthPoint::usesDefaultInterpolationWith(const AnimatableValue* value) const
+{
+    const AnimatableLengthPoint* other = toAnimatableLengthPoint(value);
+    return this->x()->isUnknown() || other->x()->isUnknown();
+}
+
 PassRefPtr<AnimatableValue> AnimatableLengthPoint::interpolateTo(const AnimatableValue* value, double fraction) const
 {
     const AnimatableLengthPoint* lengthPoint = toAnimatableLengthPoint(value);
     return AnimatableLengthPoint::create(
         AnimatableValue::interpolate(this->x(), lengthPoint->x(), fraction),
         AnimatableValue::interpolate(this->y(), lengthPoint->y(), fraction));
 }
 
 bool AnimatableLengthPoint::equalTo(const AnimatableValue* value) const
 {
     const AnimatableLengthPoint* lengthPoint = toAnimatableLengthPoint(value);
     return x()->equals(lengthPoint->x()) && y()->equals(lengthPoint->y());
 }
 
 } // namespace blink