Fix nested border radius with composited child.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 532 matching lines @@
 }
 
 void CompositedLayerMapping::UpdateCompositingReasons() {
   // All other layers owned by this mapping will have the same compositing
   // reason for their lifetime, so they are initialized only when created.
   graphics_layer_->SetCompositingReasons(owning_layer_.GetCompositingReasons());
   graphics_layer_->SetSquashingDisallowedReasons(
       owning_layer_.GetSquashingDisallowedReasons());
 }
 
-bool CompositedLayerMapping::AncestorRoundedCornersWontClip(
-    const LayoutBoxModelObject& child,
-    const LayoutBoxModelObject& clipping_ancestor) {
-  LayoutRect local_visual_rect = composited_bounds_;
-  child.MapToVisualRectInAncestorSpace(&clipping_ancestor, local_visual_rect);
-  FloatRoundedRect rounded_clip_rect =
-      clipping_ancestor.Style()->GetRoundedInnerBorderFor(
-          clipping_ancestor.LocalVisualRect());
-  FloatRect inner_clip_rect = rounded_clip_rect.RadiusCenterRect();
-  // The first condition catches cases where the child is certainly inside
-  // the rounded corner portion of the border, and cannot be clipped by
-  // the rounded portion. The second catches cases where the child is
-  // entirely outside the rectangular border (ignoring rounded corners) so
-  // is also unaffected by the rounded corners. In both cases the existing
-  // rectangular clip is adequate and the mask is unnecessary.
-  return inner_clip_rect.Contains(FloatRect(local_visual_rect)) ||
-         !local_visual_rect.Intersects(
-             EnclosingLayoutRect(rounded_clip_rect.Rect()));
-}
-
 void CompositedLayerMapping::
     OwningLayerClippedOrMaskedByLayerNotAboveCompositedAncestor(
         const PaintLayer* scroll_parent,
         bool& owning_layer_is_clipped,
         bool& owning_layer_is_masked) {
   owning_layer_is_clipped = false;
   owning_layer_is_masked = false;
 
   if (!owning_layer_.Parent())
     return;
@@ skipping 21 matching lines @@
   // setting up m_ancestorClippingLayer otherwise
   // updateAncestorClippingLayerGeometry will fail as the clip rect will be
   // infinite.
   // FIXME: this should use cached clip rects, but this sometimes give
   // inaccurate results (and trips the ASSERTS in PaintLayerClipper).
   ClipRectsContext clip_rects_context(compositing_ancestor, kUncachedClipRects,
                                       kIgnorePlatformOverlayScrollbarSize);
   clip_rects_context.SetIgnoreOverflowClip();
 
   ClipRect clip_rect;
   owning_layer_.Clipper(PaintLayer::kDoNotUseGeometryMapper)

[chrishtr, 2017/06/09 17:29:30]

1. clip_rect will be in the space of compositing_ancestor. That's because you
(correctly) set compositing_ancestor as the root for the ClipRectsContext.

[Stephen Chennney, 2017/06/09 20:52:37]

Acknowledged.

       .CalculateBackgroundClipRect(clip_rects_context, clip_rect);
   IntRect parent_clip_rect = PixelSnappedIntRect(clip_rect.Rect());
   owning_layer_is_clipped = parent_clip_rect != LayoutRect::InfiniteIntRect();
 
   // TODO(schenney): CSS clips are not applied to composited children, and
   // should be via mask or by compositing the parent too.
   // https://bugs.chromium.org/p/chromium/issues/detail?id=615870
   DCHECK(clipping_container->Style());
-  owning_layer_is_masked =
-      owning_layer_is_clipped &&
-      clipping_container->Style()->HasBorderRadius() &&
-      !AncestorRoundedCornersWontClip(GetLayoutObject(), *clipping_container);
+  bool clip_rect_has_radius = clip_rect.HasRadius();
+  LayoutRect local_visual_rect = composited_bounds_;

[chrishtr, 2017/06/09 17:29:30]

2. local_visual_rect is in the space of owning_layer_'s PaintLayer, which is
the same as it's LayoutObject's border box space.

[Stephen Chennney, 2017/06/09 20:52:37]

Acknowledged.

+  GetLayoutObject().MapToVisualRectInAncestorSpace(clipping_container,

[chrishtr, 2017/06/09 17:29:30]

(1) and (2) lead me to conclude that you should use compositing_ancestor as
the first parameter to MapToVisualRectInAncestorSpace. I think that should
be the only fix needed to this code.

[Stephen Chennney, 2017/06/09 20:52:37]

Acknowledged.

+                                                   local_visual_rect);
+  clip_rect.Intersect(local_visual_rect);
+  owning_layer_is_masked = owning_layer_is_clipped && clip_rect_has_radius &&
+                           !clip_rect.IsEmpty() &&
+                           clip_rect.Rect() != local_visual_rect;
+
+#ifndef NDEBUG
+  LOG(INFO) << "clipped? " << owning_layer_is_clipped << " masked? "
+            << owning_layer_is_masked << "clip_rect: " << clip_rect.ToString()
+            << " local rect " << local_visual_rect.ToString();
+#endif
 }
 
 const PaintLayer* CompositedLayerMapping::ScrollParent() {
   const PaintLayer* scroll_parent = owning_layer_.ScrollParent();
   if (scroll_parent && !scroll_parent->NeedsCompositedScrolling())
     return nullptr;
   return scroll_parent;
 }
 
 bool CompositedLayerMapping::UpdateGraphicsLayerConfiguration() {
@@ skipping 3026 matching lines @@
   } else if (graphics_layer == decoration_outline_layer_.get()) {
     name = "Decoration Layer";
   } else {
     NOTREACHED();
   }
 
   return name;
 }
 
 }  // namespace blink