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

third_party/WebKit/Source/core/layout/LayoutBox.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 785 matching lines @@
     };
     PaginationBreakability getPaginationBreakability() const;
 
     LayoutRect localCaretRect(InlineBox*, int caretOffset, LayoutUnit* extraWidthToEndOfLine = nullptr) override;
 
     virtual LayoutRect overflowClipRect(const LayoutPoint& location, OverlayScrollbarClipBehavior = IgnoreOverlayScrollbarSize) const;
     LayoutRect clipRect(const LayoutPoint& location) const;
     virtual bool hasControlClip() const { return false; }
     virtual LayoutRect controlClipRect(const LayoutPoint&) const { return LayoutRect(); }
 
+    // Returns the combination of overflow clip, contain: paint clip and CSS clip for this object, in local space.

[Xianzhu, 2016/08/12 17:07:57]

What about control clip?

[chrishtr, 2016/08/12 17:56:24]

Control clip on only affects LayoutButton, LayoutMenuList and
LayoutTextControlSingleLine. I tried to modify
PaintPropertyTreeBuilderTest.ControlClip to check visual rects for hidden layout
children of the button, but the LayoutBlockFlow which contains the LayoutText of
the button already has a size that is smaller than the control clip, and the
LayoutText doesn't
have an ObjectPaintProperties object at present (optimized out), which makes it
more boilerplate to test.

I don't think it's worth it to add this. WDYT?

[Xianzhu, 2016/08/12 18:45:46]

SGTM.

+    LayoutRect clippingRect() const;
+
     virtual void paintBoxDecorationBackground(const PaintInfo&, const LayoutPoint&) const;
     virtual void paintMask(const PaintInfo&, const LayoutPoint&) const;
     void imageChanged(WrappedImagePtr, const IntRect* = nullptr) override;
     ResourcePriority computeResourcePriority() const final;
 
     void logicalExtentAfterUpdatingLogicalWidth(const LayoutUnit& logicalTop, LogicalExtentComputedValues&);
 
     PositionWithAffinity positionForPoint(const LayoutPoint&) override;
 
     void removeFloatingOrPositionedChildFromBlockLists();
@@ skipping 417 matching lines @@
         || breakValue == BreakLeft
         || breakValue == BreakPage
         || breakValue == BreakRecto
         || breakValue == BreakRight
         || breakValue == BreakVerso;
 }
 
 } // namespace blink
 
 #endif // LayoutBox_h