Fix border radius on composited children.

third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 171 matching lines @@
         return clipRect;
 
     LayoutPoint clippingRootOffset;
     m_layer.convertToLayerCoords(clippingRootLayer, clippingRootOffset);
     clipRect.moveBy(-clippingRootOffset);
 
     return clipRect;
 }
 
 void PaintLayerClipper::calculateRects(const ClipRectsContext& context, const LayoutRect& paintDirtyRect, LayoutRect& layerBounds,
-    ClipRect& backgroundRect, ClipRect& foregroundRect, const LayoutPoint* offsetFromRoot) const
+    ClipRect& backgroundRect, ClipRect& foregroundRect, const LayoutPoint* offsetFromRoot, const bool addAncestorClips) const
 {
     bool isClippingRoot = &m_layer == context.rootLayer;
     LayoutBoxModelObject& layoutObject = *m_layer.layoutObject();
 
     if (!isClippingRoot && m_layer.parent()) {
         backgroundRect = backgroundClipRect(context);
         backgroundRect.move(context.subPixelAccumulation);
         backgroundRect.intersect(paintDirtyRect);
     } else {
         backgroundRect = paintDirtyRect;
     }
 
     foregroundRect = backgroundRect;
 
     LayoutPoint offset;
     if (offsetFromRoot)
         offset = *offsetFromRoot;
     else
         m_layer.convertToLayerCoords(context.rootLayer, offset);
     layerBounds = LayoutRect(offset, LayoutSize(m_layer.size()));
 
     // Update the clip rects that will be passed to child layers.
-    if ((layoutObject.hasOverflowClip() || layoutObject.styleRef().containsPaint()) && shouldRespectOverflowClip(context)) {
+    if (addAncestorClips || ((layoutObject.hasOverflowClip() || layoutObject.styleRef().containsPaint()) && shouldRespectOverflowClip(context))) {
         foregroundRect.intersect(toLayoutBox(layoutObject).overflowClipRect(offset, context.overlayScrollbarClipBehavior));
-        if (layoutObject.styleRef().hasBorderRadius())
+        if (layoutObject.styleRef().hasBorderRadius() || addAncestorClips)

[chrishtr, 2016/10/21 23:16:20]

What does this one achieve? It seems to force setting radius to true, which
can't be true for all masks?

[Stephen Chennney, 2016/10/24 20:15:27]

This is the hackish part of the whole thing. It's relying on the fact that the
only way addAncestorClips can be true is if, sometime back in
CompositedLayerMapping, we discovered a border radius clip and added a layer and
added a paint phase etc etc.

It's one of the things I want to improve.

             foregroundRect.setHasRadius(true);
 
         // FIXME: Does not do the right thing with columns yet, since we don't yet factor in the
         // individual column boxes as overflow.
 
         // The LayoutView is special since its overflow clipping rect may be larger than its box rect (crbug.com/492871).
         LayoutRect layerBoundsWithVisualOverflow = layoutObject.isLayoutView() ? toLayoutView(layoutObject).viewRect() : toLayoutBox(layoutObject).visualOverflowRect();
         toLayoutBox(layoutObject).flipForWritingMode(layerBoundsWithVisualOverflow); // PaintLayer are in physical coordinates, so the overflow has to be flipped.
         layerBoundsWithVisualOverflow.moveBy(offset);
         backgroundRect.intersect(layerBoundsWithVisualOverflow);
@@ skipping 97 matching lines @@
 
 ClipRects& PaintLayerClipper::paintingClipRects(const PaintLayer* rootLayer, ShouldRespectOverflowClipType respectOverflowClip, const LayoutSize& subpixelAccumulation) const
 {
     ClipRectsContext context(rootLayer, PaintingClipRects, IgnoreOverlayScrollbarSize, subpixelAccumulation);
     if (respectOverflowClip == IgnoreOverflowClip)
         context.setIgnoreOverflowClip();
     return getClipRects(context);
 }
 
 } // namespace blink