Support edge-inclusive intersections in mapToVisibleRectInAncestorSpace

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

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index fed747b5e5655ad90f9eaebdeff489d04402e052..7771d9408941f0b390f5dcd8fdfa347c6daf0e01 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -973,7 +973,7 @@ void LayoutBox::mapScrollingContentsRectToBoxSpace(LayoutRect& rect) const
     rect.move(offset);
 }
 
-void LayoutBox::applyOverflowClip(LayoutRect& rect) const
+bool LayoutBox::applyOverflowClip(LayoutRect& rect, bool edgeInclusive) const
 {
     ASSERT(hasLayer());
     ASSERT(hasOverflowClip());
@@ -984,8 +984,16 @@ void LayoutBox::applyOverflowClip(LayoutRect& rect) const
     // layer's size instead. Even if the layer's size is wrong, the layer itself will issue paint invalidations
     // anyway if its size does change.
     LayoutRect clipRect(LayoutPoint(), LayoutSize(layer()->size()));
-    rect = intersection(rect, clipRect);
-    flipForWritingMode(rect);
+    bool doesIntersect;
+    if (edgeInclusive) {
+        doesIntersect = rect.inclusiveIntersect(clipRect);
+    } else {
+        rect.intersect(clipRect);
+        doesIntersect = !rect.isEmpty();

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

LayoutRect::intersects will only ever return true for an empty rect if the other
rect is also empty.

Is an intersection between two empty rects really a use-case we need to care
about? I understand supporting zero sized rects to track things like scroll
position but when would the other rect ever be zero sized?

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

That's not true:

bool LayoutRect::intersects(const LayoutRect& other) const                      
                                                           
{                                                                               
                                                           
    // Checking emptiness handles negative widths as well as zero.              
                                                           
    return !isEmpty() && !other.isEmpty()                                       
                                                           
        && x() < other.maxX() && other.x() < maxX()                             
                                                           
        && y() < other.maxY() && other.y() < maxY();                            
                                                           
} 

If either rect is empty, then intersects() returns false.

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

Oh, my bad. You're right. Never mind!

+    }
+    if (doesIntersect)
+        flipForWritingMode(rect);
+    return doesIntersect;
 }
 
 void LayoutBox::computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidth, LayoutUnit& maxLogicalWidth) const
@@ -1474,7 +1482,7 @@ bool LayoutBox::intersectsVisibleViewport()
     LayoutView* layoutView = view();
     while (layoutView->frame()->ownerLayoutObject())
         layoutView = layoutView->frame()->ownerLayoutObject()->view();
-    mapToVisibleRectInAncestorSpace(layoutView, rect, nullptr);
+    mapToVisibleRectInAncestorSpace(layoutView, rect, nullptr, false);
     return rect.intersects(LayoutRect(layoutView->frameView()->getScrollableArea()->visibleContentRectDouble()));
 }
 
@@ -1925,11 +1933,11 @@ LayoutRect LayoutBox::clippedOverflowRectForPaintInvalidation(const LayoutBoxMod
     }
 
     LayoutRect r = visualOverflowRect();
-    mapToVisibleRectInAncestorSpace(paintInvalidationContainer, r, paintInvalidationState);
+    mapToVisibleRectInAncestorSpace(paintInvalidationContainer, r, paintInvalidationState, false);
     return r;
 }
 
-void LayoutBox::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect& rect, const PaintInvalidationState* paintInvalidationState) const
+bool LayoutBox::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect& rect, const PaintInvalidationState* paintInvalidationState, bool edgeInclusive) const
 {
     // The rect we compute at each step is shifted by our x/y offset in the parent container's coordinate space.
     // Only when we cross a writing mode boundary will we have to possibly flipForWritingMode (to convert into a more appropriate
@@ -1949,20 +1957,19 @@ void LayoutBox::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ance
     inflatePaintInvalidationRectForReflectionAndFilter(rect);
 
     if (paintInvalidationState && paintInvalidationState->canMapToAncestor(ancestor) && position != FixedPosition) {
-        paintInvalidationState->mapObjectRectToAncestor(*this, ancestor, rect);
-        return;
+        return paintInvalidationState->mapObjectRectToAncestor(*this, ancestor, rect, edgeInclusive);
     }
 
     if (ancestor == this) {
         if (ancestor->style()->isFlippedBlocksWritingMode())
             flipForWritingMode(rect);
-        return;
+        return true;
     }
 
     bool containerSkipped;
     LayoutObject* container = this->container(ancestor, &containerSkipped);
     if (!container)
-        return;
+        return true;
 
     if (isWritingModeRoot())
         flipForWritingMode(rect);
@@ -1994,10 +2001,8 @@ void LayoutBox::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ance
     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 (containerSkipped) {
@@ -2007,13 +2012,13 @@ void LayoutBox::mapToVisibleRectInAncestorSpace(const LayoutBoxModelObject* ance
         // If the paintInvalidationContainer is fixed, then the rect is already in its coordinates so doesn't need viewport-adjusting.
         if (ancestor->style()->position() != FixedPosition && container->isLayoutView())
             toLayoutView(container)->adjustViewportConstrainedOffset(rect, LayoutView::toViewportConstrainedPosition(position));
-        return;
+        return true;
     }
 
     if (container->isLayoutView())
-        toLayoutView(container)->mapToVisibleRectInAncestorSpace(ancestor, rect, LayoutView::toViewportConstrainedPosition(position), paintInvalidationState);
+        return toLayoutView(container)->mapToVisibleRectInAncestorSpace(ancestor, rect, LayoutView::toViewportConstrainedPosition(position), paintInvalidationState, edgeInclusive);
     else
-        container->mapToVisibleRectInAncestorSpace(ancestor, rect, paintInvalidationState);
+        return container->mapToVisibleRectInAncestorSpace(ancestor, rect, paintInvalidationState, edgeInclusive);
 }
 
 void LayoutBox::inflatePaintInvalidationRectForReflectionAndFilter(LayoutRect& paintInvalidationRect) const