Support edge-inclusive intersections in mapToVisibleRectInAncestorSpace

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

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google 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
@@ skipping 1130 matching lines @@
     void setShouldDoFullPaintInvalidationIncludingNonCompositingDescendants();
 
     // Returns the rect that should have paint invalidated whenever this object changes. The rect is in the view's
     // coordinate space. This method deals with outlines and overflow.
     virtual LayoutRect absoluteClippedOverflowRect() const;
     virtual LayoutRect clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject* paintInvalidationContainer, const PaintInvalidationState* = nullptr) const;
 
     // Given a rect in the object's coordinate space, compute a rect in the coordinate space of |ancestor|.  If
     // intermediate containers have clipping or scrolling of any kind, it is applied; but overflow clipping is *not*
     // applied for |ancestor| itself. The output rect is suitable for purposes such as paint invalidation.
-    virtual void mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect&, const PaintInvalidationState*) const;
+    // The return value indicates whether the output rect actually has a visible intersection
+    // with the ancestor.  If edgeInclusive is true, the return value can be true even if the
+    // resulting rect is zero-area.
+    virtual bool mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect&, const PaintInvalidationState*, bool edgeInclusive) const;

[eae, 2016/03/22 00:13:50]

Adding a second capability (intersection detection) to a translation method
seems really odd to me and I don't understand why that is needed. Shouldn't the
intersection check be done on the resulting rects _after_ translation?

[szager1, 2016/03/22 00:55:48]

One of the core features of this method is that it applies clipping up the
hierarchy, but prior to this patch the clipping was not edge-aware, as required
by IntersectionObserver.  Adding a flag and a bool return value was the least
intrusive way I could think of to add that capability.

[eae, 2016/03/22 17:54:15]

Oh, I see. Didn't realize it did clipping until I start digging into the code
this morning. We might want to rename mapToVisibleRectInAncestorSpace to include
the word clipping (in a subsequent patch, not as a part of this one).

 
     // Return the offset to the column in which the specified point (in flow-thread coordinates)
     // lives. This is used to convert a flow-thread point to a visual point.
     virtual LayoutSize columnOffset(const LayoutPoint&) const { return LayoutSize(); }
 
     virtual unsigned length() const { return 1; }
 
     bool isFloatingOrOutOfFlowPositioned() const { return (isFloating() || isOutOfFlowPositioned()); }
 
     bool isTransparent() const { return style()->hasOpacity(); }
@@ skipping 1006 matching lines @@
 void showTree(const blink::LayoutObject*);
 void showLineTree(const blink::LayoutObject*);
 void showLayoutTree(const blink::LayoutObject* object1);
 // We don't make object2 an optional parameter so that showLayoutTree
 // can be called from gdb easily.
 void showLayoutTree(const blink::LayoutObject* object1, const blink::LayoutObject* object2);
 
 #endif
 
 #endif // LayoutObject_h