Handle nested position:sticky elements correctly (compositor)

third_party/WebKit/Source/core/page/scrolling/StickyPositionScrollingConstraints.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef StickyPositionScrollingConstraints_h
 #define StickyPositionScrollingConstraints_h
 
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/FloatSize.h"
 
@@ skipping 30 matching lines @@
         m_scrollContainerRelativeContainingBlockRect(
             other.m_scrollContainerRelativeContainingBlockRect),
         m_scrollContainerRelativeStickyBoxRect(
             other.m_scrollContainerRelativeStickyBoxRect),
         m_nearestStickyBoxShiftingStickyBox(
             other.m_nearestStickyBoxShiftingStickyBox),
         m_nearestStickyBoxShiftingContainingBlock(
             other.m_nearestStickyBoxShiftingContainingBlock),
         m_totalStickyBoxStickyOffset(other.m_totalStickyBoxStickyOffset),
         m_totalContainingBlockStickyOffset(
-            other.m_totalContainingBlockStickyOffset) {}
+            other.m_totalContainingBlockStickyOffset),
+        m_localStickyOffset(other.m_localStickyOffset) {}
 
   FloatSize computeStickyOffset(
       const FloatRect& viewportRect,
       const StickyPositionScrollingConstraints* ancestorStickyBoxConstraints,
       const StickyPositionScrollingConstraints*
           ancestorContainingBlockConstraints);
 
   bool hasAncestorStickyElement() const {
     return m_nearestStickyBoxShiftingStickyBox ||
            m_nearestStickyBoxShiftingContainingBlock;
@@ skipping 44 matching lines @@
     return m_nearestStickyBoxShiftingContainingBlock;
   }
 
   const FloatSize& getTotalStickyBoxStickyOffset() const {
     return m_totalStickyBoxStickyOffset;
   }
   const FloatSize& getTotalContainingBlockStickyOffset() const {
     return m_totalContainingBlockStickyOffset;
   }
 
+  const LayoutBoxModelObject* nearestStickyAncestor() const {
+    return m_nearestStickyBoxShiftingStickyBox
+               ? m_nearestStickyBoxShiftingStickyBox
+               : m_nearestStickyBoxShiftingContainingBlock;
+  }
+
   bool operator==(const StickyPositionScrollingConstraints& other) const {
     return m_leftOffset == other.m_leftOffset &&
            m_rightOffset == other.m_rightOffset &&
            m_topOffset == other.m_topOffset &&
            m_bottomOffset == other.m_bottomOffset &&
            m_scrollContainerRelativeContainingBlockRect ==
                other.m_scrollContainerRelativeContainingBlockRect &&
            m_scrollContainerRelativeStickyBoxRect ==
                other.m_scrollContainerRelativeStickyBoxRect &&
            m_nearestStickyBoxShiftingStickyBox ==
                other.m_nearestStickyBoxShiftingStickyBox &&
            m_nearestStickyBoxShiftingContainingBlock ==
                other.m_nearestStickyBoxShiftingContainingBlock &&
            m_totalStickyBoxStickyOffset == other.m_totalStickyBoxStickyOffset &&
            m_totalContainingBlockStickyOffset ==
-               other.m_totalContainingBlockStickyOffset;
+               other.m_totalContainingBlockStickyOffset &&
+           m_localStickyOffset == other.m_localStickyOffset;
   }
 
   bool operator!=(const StickyPositionScrollingConstraints& other) const {
     return !(*this == other);
   }
 
  private:
   AnchorEdges m_anchorEdges;
   float m_leftOffset;
   float m_rightOffset;
@@ skipping 14 matching lines @@
   // sticky elements to offset their constraint rects. Because we can either
   // affect the sticky box constraint rect or the containing block constraint
   // rect, we need to accumulate both.
   //
   // The case where we can affect both the sticky box constraint rect and the
   // constraining block constriant rect for different sticky descendants is
   // quite complex. See the StickyPositionComplexTableNesting test in
   // LayoutBoxModelObjectTest.cpp.
   FloatSize m_totalStickyBoxStickyOffset;
   FloatSize m_totalContainingBlockStickyOffset;
+
+  FloatSize m_localStickyOffset;

[flackr, 2017/03/17 15:01:56]

This seems unused, remove it?

[smcgruer, 2017/03/17 17:36:52]

Done.

 };
 
 }  // namespace blink
 
 #endif  // StickyPositionScrollingConstraints_h