CSS Motion Path: Place offset-anchor on the path

third_party/WebKit/Source/core/style/ComputedStyle.cpp

Index: third_party/WebKit/Source/core/style/ComputedStyle.cpp
diff --git a/third_party/WebKit/Source/core/style/ComputedStyle.cpp b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
index 935bc431515c0bc859e42937d60581a679ff7a8a..e8ab70766da7183d3ff9104b0821bb5cec3e8710 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.cpp
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
@@ -1344,7 +1344,7 @@ void ComputedStyle::applyTransform(
   }
 
   if (applyMotionPath == ComputedStyle::IncludeMotionPath)
-    applyMotionPathTransform(originX, originY, result);
+    applyMotionPathTransform(originX, originY, boundingBox, result);
 
   const Vector<RefPtr<TransformOperation>>& transformOperations =
       transform().operations();
@@ -1360,11 +1360,11 @@ void ComputedStyle::applyTransform(
 void ComputedStyle::applyMotionPathTransform(
     float originX,
     float originY,
+    const FloatRect& boundingBox,
     TransformationMatrix& transform) const {
   const StyleMotionData& motionData =
       m_rareNonInheritedData->m_transform->m_motion;
-  // TODO(ericwilligers): crbug.com/638055 Apply offset-position and
-  // offset-anchor.
+  // TODO(ericwilligers): crbug.com/638055 Apply offset-position.
   if (!motionData.m_path) {
     return;
   }
@@ -1387,8 +1387,25 @@ void ComputedStyle::applyMotionPathTransform(
   if (motionData.m_rotation.type == OffsetRotationFixed)
     angle = 0;
 
-  transform.translate(point.x() - originX, point.y() - originY);
+  float originShiftX = 0;
+  float originShiftY = 0;
+  if (RuntimeEnabledFeatures::cssOffsetPositionAnchorEnabled()) {
+    // TODO(ericwilligers): crbug.com/638055 Support offset-anchor: auto.
+    const LengthPoint& anchor = offsetAnchor();
+    originShiftX = floatValueForLength(anchor.x(), boundingBox.width()) -
+                   floatValueForLength(transformOriginX(), boundingBox.width());
+    originShiftY =
+        floatValueForLength(anchor.y(), boundingBox.height()) -
+        floatValueForLength(transformOriginY(), boundingBox.height());
+  }
+
+  transform.translate(point.x() - originX + originShiftX,
+                      point.y() - originY + originShiftY);
   transform.rotate(angle + motionData.m_rotation.angle);
+
+  if (RuntimeEnabledFeatures::cssOffsetPositionAnchorEnabled()) {
+    transform.translate(-originShiftX, -originShiftY);
+  }
 }
 
 void ComputedStyle::setTextShadow(PassRefPtr<ShadowList> s) {