Implement closed shadow adjustment for Element.offsetParent

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 3161 matching lines @@
     ASSERT(m_node);
 
     // Image change notifications should not be received during paint because
     // the resulting invalidations will be cleared following paint. This can also
     // lead to modifying the tree out from under paint(), see: crbug.com/616700.
     DCHECK(document().lifecycle().state() != DocumentLifecycle::LifecycleState::InPaint);
 
     imageChanged(static_cast<WrappedImagePtr>(image), rect);
 }
 
-Element* LayoutObject::offsetParent() const
+Element* LayoutObject::offsetParent(const Element* unclosedBase) const
 {
     if (isDocumentElement() || isBody())
         return nullptr;
 
-    if (isOutOfFlowPositioned() && style()->position() == FixedPosition)
+    if (isFixedPositioned())
         return nullptr;
 
     float effectiveZoom = style()->effectiveZoom();
     Node* node = nullptr;
     for (LayoutObject* ancestor = parent(); ancestor; ancestor = ancestor->parent()) {
         // Spec: http://www.w3.org/TR/cssom-view/#offset-attributes
 
         node = ancestor->node();
 
         if (!node)
             continue;
 
+        // TODO(kochi): If |unclosedBase| or |node| is nested deep in shadow roots, this loop may
+        // get expensive, as isUnclosedNodeOf() can take up to O(N+M) time (N and M are depths).
+        if (unclosedBase && (!node->isUnclosedNodeOf(*unclosedBase) || (node->isInShadowTree() && node->containingShadowRoot()->type() == ShadowRootType::UserAgent))) {
+            // If 'position: fixed' node is found while traversing up, terminate the loop and
+            // return null.
+            if (ancestor->isFixedPositioned())
+                return nullptr;
+            continue;
+        }
+
         if (ancestor->isPositioned())
             break;
 
         if (isHTMLBodyElement(*node))
             break;
 
         if (!isPositioned() && (isHTMLTableElement(*node) || isHTMLTableCellElement(*node)))
             break;
 
         // Webkit specific extension where offsetParent stops at zoom level changes.
@@ skipping 426 matching lines @@
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     } else {
         fprintf(stderr, "Cannot showLayoutTree. Root is (nil)\n");
     }
 }
 
 #endif