Take CSS Clip and contain: paint into account when computing visual rects.

third_party/WebKit/Source/core/layout/LayoutBox.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, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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 993 matching lines @@
     ASSERT(hasOverflowClip());
     ASSERT(hasLayer());
     // FIXME: Return DoubleSize here. crbug.com/414283.
     PaintLayerScrollableArea* scrollableArea = getScrollableArea();
     IntSize result = flooredIntSize(scrollableArea->scrollOffset()) + originAdjustmentForScrollbars();
     if (isHorizontalWritingMode() && shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
         result.expand(-verticalScrollbarWidth(), 0);
     return result;
 }
 
+
+LayoutRect LayoutBox::clippingRect() const
+{
+    LayoutRect result = LayoutRect(LayoutRect::infiniteIntRect());
+    if (hasOverflowClip() || style()->containsPaint())
+        result = overflowClipRect(LayoutPoint());
+
+    if (hasClip())
+        result.intersect(clipRect(LayoutPoint()));
+
+    return result;
+}
+
 bool LayoutBox::mapScrollingContentsRectToBoxSpace(LayoutRect& rect, ApplyOverflowClipFlag applyOverflowClip, VisualRectFlags visualRectFlags) const
 {
-    if (!hasOverflowClip())
+    if (!hasClipRelatedProperty())
         return true;
 
-    if (applyOverflowClip == ApplyNonScrollOverflowClip && scrollsOverflow()) {
+    if (applyOverflowClip == ApplyNonScrollOverflowClip && scrollsOverflow())
         return true;
+
+    if (hasOverflowClip()) {
+        LayoutSize offset = LayoutSize(-scrolledContentOffset());
+        rect.move(offset);
     }
 
-    LayoutSize offset = LayoutSize(-scrolledContentOffset());
-    rect.move(offset);
-
-    LayoutRect clipRect = overflowClipRect(LayoutPoint());
+    // This won't work fully correctly for fixed-position elements, who should receive CSS clip but for whom the current object
+    // is not in the containing block chain.
+    LayoutRect clipRect = clippingRect();
 
     bool doesIntersect;
     if (visualRectFlags & EdgeInclusive) {
         doesIntersect = rect.inclusiveIntersect(clipRect);
     } else {
         rect.intersect(clipRect);
         doesIntersect = !rect.isEmpty();
     }
+
     return doesIntersect;
 }
 
 void LayoutBox::computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidth, LayoutUnit& maxLogicalWidth) const
 {
     minLogicalWidth = minPreferredLogicalWidth() - borderAndPaddingLogicalWidth();
     maxLogicalWidth = maxPreferredLogicalWidth() - borderAndPaddingLogicalWidth();
 }
 
 LayoutUnit LayoutBox::minPreferredLogicalWidth() const
@@ skipping 3723 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink