Support edge-inclusive intersections in mapToVisibleRectInAncestorSpace

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

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index 387058354128dc2e7c11ef76bba0ec84dd51844c..13ea135ad572cc47043dd1c271372a22cbb9e726 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -1148,7 +1148,10 @@ public:
     // 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 flags is EdgeInclusive, the return value can be true even if the
+    // resulting rect is zero-area.

[chrishtr, 2016/03/22 17:25:49]

"intersection" might lead to the wrong conclusions here. Maybe better is: the
return
value indicates whether the visible rect computed is not "empty". If
EdgeInclusive is
false, this is the same as !rect.isEmpty(); if EdgeInclusive is true it can be
true
if the rect has zero area but its bounds intersected all clips. The latter is
still
kind of confusing, an example would be good.

[szager1, 2016/03/22 18:33:35]

I think the best documentation is what I wrote for
LayoutRect::inclusiveIntersect:

"Set this rect to be the intersection of itself and the argument rect
using edge-inclusive geometry.  If the two rectangles overlap but the
overlap region is zero-area (either because one of the two rectangles
is zero-area, or because the rectangles overlap at an edge or a corner),
the result is the zero-area intersection.  The return value indicates
whether the two rectangle actually have an intersection, since checking
the result for isEmpty() is not conclusive."

I can copy-paste that here, or I can just say, "EdgeInclusive means clipping
will be calculated using LayoutRect::inclusiveIntersect; see documentation for
that method."

WDYT?

+    virtual bool mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect&, const PaintInvalidationState*, int flags = 0) const;

[chrishtr, 2016/03/22 17:25:49]

IntersectionFlags instead of int

[eae, 2016/03/22 17:54:16]

Use unsigned (or typedef for unsigned as Chris suggested) for flags.

[szager1, 2016/03/22 19:42:24]

Done.

 
     // 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.