Support edge-inclusive intersections in mapToVisibleRectInAncestorSpace

third_party/WebKit/Source/core/layout/LayoutInline.cpp

Index: third_party/WebKit/Source/core/layout/LayoutInline.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutInline.cpp b/third_party/WebKit/Source/core/layout/LayoutInline.cpp
index 7ba75d8a781b2e2d97b46ee7965b49dc76bbe752..986a4c262c605924cdc84bfc6b19cc41ae68d782 100644
--- a/third_party/WebKit/Source/core/layout/LayoutInline.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutInline.cpp
@@ -1059,7 +1059,7 @@ LayoutRect LayoutInline::clippedOverflowRect(const LayoutBoxModelObject* paintIn
     if (overflowRect.isEmpty())
         return overflowRect;
 
-    mapToVisibleRectInAncestorSpace(paintInvalidationContainer, overflowRect, paintInvalidationState);
+    mapToVisibleRectInAncestorSpace(paintInvalidationContainer, overflowRect, paintInvalidationState, false);
     return overflowRect;
 }
 
@@ -1081,20 +1081,18 @@ LayoutRect LayoutInline::visualOverflowRect() const
     return overflowRect;
 }
 
-void LayoutInline::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect& rect, const PaintInvalidationState* paintInvalidationState) const
+bool LayoutInline::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect& rect, const PaintInvalidationState* paintInvalidationState, bool edgeInclusive) const

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

It's unclear to me why these method would need to be made aware of
edge-inclusion. They're supposed to map the x/y coordinates of the supplied rect
which shouldn't be the same regardless of whether the edge is included or not.
Perhaps I'm missing something here?

Having it return a value is also a bit odd.

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

mapToVisibleRectInAncestorSpace is used by IntersectionObservation to compute
the intersection between to LayoutObject's, and that intersection needs to be
edge-inclusive (required by the spec).  This is the least intrusive way I could
think of for this method to report "the rects intersect, but the intersection is
zero area," as distinct from "the rects do not intersect."

 {
-    if (paintInvalidationState && paintInvalidationState->canMapToAncestor(ancestor)) {
-        paintInvalidationState->mapObjectRectToAncestor(*this, ancestor, rect);
-        return;
-    }
+    if (paintInvalidationState && paintInvalidationState->canMapToAncestor(ancestor))
+        return paintInvalidationState->mapObjectRectToAncestor(*this, ancestor, rect, edgeInclusive);
 
     if (ancestor == this)
-        return;
+        return true;
 
     bool ancestorSkipped;
     LayoutObject* container = this->container(ancestor, &ancestorSkipped);
     if (!container)
-        return;
+        return true;
 
     LayoutPoint topLeft = rect.location();
 
@@ -1112,20 +1110,18 @@ void LayoutInline::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* a
     if (container->hasOverflowClip()) {
         LayoutBox* containerBox = toLayoutBox(container);
         containerBox->mapScrollingContentsRectToBoxSpace(rect);
-        if (container != ancestor)
-            containerBox->applyOverflowClip(rect);
-        if (rect.isEmpty())
-            return;
+        if (container != ancestor && !containerBox->applyOverflowClip(rect, edgeInclusive))
+            return false;
     }
 
     if (ancestorSkipped) {
         // If the paintInvalidationContainer is below o, then we need to map the rect into paintInvalidationContainer's coordinates.
         LayoutSize containerOffset = ancestor->offsetFromAncestorContainer(container);
         rect.move(-containerOffset);
-        return;
+        return true;
     }
 
-    container->mapToVisibleRectInAncestorSpace(ancestor, rect, paintInvalidationState);
+    return container->mapToVisibleRectInAncestorSpace(ancestor, rect, paintInvalidationState, edgeInclusive);
 }
 
 LayoutSize LayoutInline::offsetFromContainer(const LayoutObject* container) const