Implement closed shadow adjustment for Element.offsetParent

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
index cb416dca18088a6b66608b98352cce926530b206..1cc2e651513a393665d805641e59883a71410d91 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
@@ -758,7 +758,7 @@ LayoutSize LayoutBoxModelObject::stickyPositionOffset() const
     return LayoutSize(scrollableArea->stickyConstraintsMap().get(layer()).computeStickyOffset(constrainingRect));
 }
 
-LayoutPoint LayoutBoxModelObject::adjustedPositionRelativeToOffsetParent(const LayoutPoint& startPoint) const
+LayoutPoint LayoutBoxModelObject::adjustedPositionRelativeToUnclosedOffsetParent(const LayoutPoint& startPoint) const
 {
     // If the element is the HTML body element or doesn't have a parent
     // return 0 and stop this algorithm.
@@ -768,10 +768,12 @@ LayoutPoint LayoutBoxModelObject::adjustedPositionRelativeToOffsetParent(const L
     LayoutPoint referencePoint = startPoint;
     referencePoint.move(parent()->columnOffset(referencePoint));
 
-    // If the offsetParent of the element is null, or is the HTML body element,
+    // Calling unclosedOffsetParent() here to skip through non-unclosed (i.e.
+    // inaccessible in a closed shadow or UA shadow) nodes to get offset parent.
+    // If the unclosedOffsetParent of the element is null,
     // return the distance between the canvas origin and the left border edge
     // of the element and stop this algorithm.
-    Element* element = offsetParent();
+    Element* element = unclosedOffsetParent();

[hayato, 2016/06/10 01:41:51]

Why did you change the behavior of
LayoutBoxModelObject::adjustedPositionRelativeToOffsetParent?
I do not see a reason from the comment. It looks wrong to me.

[kochi, 2016/06/10 02:07:49]

adjustedPositionRelativeToOffsetParent() is called from other Layout*
classes (LayoutBox, LayoutInline, LayoutBoxModel) for calculating
offsetTop/offsetLeft which are used for Element.offsetTop/offsetLeft.

Unless they use the relative value to unclosedOffsetParent, it can return
wrong value (not relative to unclosed offset parent, relative to offset parent).

     if (!element)
         return referencePoint;
 
@@ -815,14 +817,14 @@ LayoutUnit LayoutBoxModelObject::offsetLeft() const
 {
     // Note that LayoutInline and LayoutBox override this to pass a different
     // startPoint to adjustedPositionRelativeToOffsetParent.
-    return adjustedPositionRelativeToOffsetParent(LayoutPoint()).x();
+    return adjustedPositionRelativeToUnclosedOffsetParent(LayoutPoint()).x();
 }
 
 LayoutUnit LayoutBoxModelObject::offsetTop() const
 {
     // Note that LayoutInline and LayoutBox override this to pass a different
     // startPoint to adjustedPositionRelativeToOffsetParent.
-    return adjustedPositionRelativeToOffsetParent(LayoutPoint()).y();
+    return adjustedPositionRelativeToUnclosedOffsetParent(LayoutPoint()).y();
 }
 
 int LayoutBoxModelObject::pixelSnappedOffsetWidth() const