Implement closed shadow adjustment for Element.offsetParent

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 740 matching lines @@
     FloatRect constrainingRect = computeStickyConstrainingRect();
     PaintLayerScrollableArea* scrollableArea = ancestorOverflowLayer->getScrollableArea();
 
     // The sticky offset is physical, so we can just return the delta computed in absolute coords (though it may be wrong with transforms).
     // TODO: Force compositing input update if we ask for offset with stale compositing inputs.
     if (!scrollableArea->stickyConstraintsMap().contains(layer()))
         return LayoutSize();
     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.
     if (isBody() || !parent())
         return LayoutPoint();
 
     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;
 
     if (const LayoutBoxModelObject* offsetParent = element->layoutBoxModelObject()) {
         if (offsetParent->isBox() && !offsetParent->isBody())
             referencePoint.move(-toLayoutBox(offsetParent)->borderLeft(), -toLayoutBox(offsetParent)->borderTop());
         if (!isOutOfFlowPositioned() || flowThreadContainingBlock()) {
             if (isInFlowPositioned())
                 referencePoint.move(offsetForInFlowPosition());
 
@@ skipping 23 matching lines @@
     if (isStickyPositioned())
         return stickyPositionOffset();
 
     return LayoutSize();
 }
 
 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
 {
     return snapSizeToPixel(offsetWidth(), offsetLeft());
 }
 
 int LayoutBoxModelObject::pixelSnappedOffsetHeight() const
 {
     return snapSizeToPixel(offsetHeight(), offsetTop());
@@ skipping 290 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink