Handle nested position:sticky elements

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/)
@@ skipping 2054 matching lines @@
       if (container->style()->isFlippedBlocksWritingMode()) {
         IntPoint centerPoint = roundedIntPoint(transformState.mappedPoint());
         transformState.move(toLayoutBox(container)->flipForWritingMode(
                                 LayoutPoint(centerPoint)) -
                             centerPoint);
       }
       mode &= ~ApplyContainerFlip;
     }
   }
 
-  LayoutSize containerOffset = offsetFromContainer(container);
+  LayoutSize containerOffset =
+      offsetFromContainer(container, mode & IgnoreSticky);

[flackr, 2017/01/31 00:20:33]

I think this might be cleaner if we add staticOffsetFromContainer which excludes
the in flow positioning (and called from offsetFromContainer) or if you just
directly remove offsetForInFlowPosition here if the element is sticky and
ignoresticky is set. Adding arguments to offsetFromContainer feels a bit hacky.

[smcgruer, 2017/01/31 16:07:06]

I've gone for the direct removal for now. It's not pretty, but when I tried to
do the staticOffsetFromContainer implementation I ran into layout test failures
I didnt understand, so leaving the ugliness in for now :).

   if (isLayoutFlowThread()) {
     // So far the point has been in flow thread coordinates (i.e. as if
     // everything in the fragmentation context lived in one tall single column).
     // Convert it to a visual point now, since we're about to escape the flow
     // thread.
     containerOffset += columnOffset(LayoutPoint(transformState.mappedPoint()));
   }
 
   // Text objects just copy their parent's computed style, so we need to ignore
   // them.
@@ skipping 213 matching lines @@
 
 TransformationMatrix LayoutObject::localToAncestorTransform(
     const LayoutBoxModelObject* ancestor,
     MapCoordinatesFlags mode) const {
   TransformState transformState(TransformState::ApplyTransformDirection);
   mapLocalToAncestor(ancestor, transformState,
                      mode | ApplyContainerFlip | UseTransforms);
   return transformState.accumulatedTransform();
 }
 
-LayoutSize LayoutObject::offsetFromContainer(const LayoutObject* o) const {
+LayoutSize LayoutObject::offsetFromContainer(const LayoutObject* o,
+                                             bool ignoreSticky) const {
   ASSERT(o == container());
   return o->hasOverflowClip()
              ? LayoutSize(-toLayoutBox(o)->scrolledContentOffset())
              : LayoutSize();
 }
 
 LayoutSize LayoutObject::offsetFromAncestorContainer(
     const LayoutObject* ancestorContainer) const {
   if (ancestorContainer == this)
     return LayoutSize();
@@ skipping 1172 matching lines @@
     const blink::LayoutObject* root = object1;
     while (root->parent())
       root = root->parent();
     root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
   } else {
     WTFLogAlways("%s", "Cannot showLayoutTree. Root is (nil)");
   }
 }
 
 #endif