Fix nested border radius with composited child.

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

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index bea0b2b92a1e6ba000bf830e3065c3c771a8d571..035d4e26ce2b23f559475a69c7decd1696842c3d 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -550,26 +550,6 @@ void CompositedLayerMapping::UpdateCompositingReasons() {
       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,
@@ -620,10 +600,20 @@ void CompositedLayerMapping::
   // 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() {