Fix nested border radius with composited child.

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintLayerPainter.h"
 
 #include "core/frame/LocalFrameView.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/ClipPathClipper.h"
 #include "core/paint/FilterPainter.h"
@@ skipping 407 matching lines @@
 
   PaintLayerFragments layer_fragments;
   if (should_paint_content || should_paint_self_outline ||
       is_painting_overlay_scrollbars) {
     // Collect the fragments. This will compute the clip rectangles and paint
     // offsets for each layer fragment.
     ClipRectsCacheSlot cache_slot = (paint_flags & kPaintLayerUncachedClipRects)
                                         ? kUncachedClipRects
                                         : kPaintingClipRects;
     LayoutPoint offset_to_clipper;
-    PaintLayer* paint_layer_for_fragments = &paint_layer_;
+    const PaintLayer* paint_layer_for_fragments = &paint_layer_;
     if (paint_flags & kPaintLayerPaintingAncestorClippingMaskPhase) {
-      // Compute fragments and their clips with respect to the clipping
-      // container. The paint rect is in this layer's space, so convert it
-      // to the clipper's layer's space. The rootLayer is also changed to
-      // the clipper's layer to simplify coordinate system adjustments.
-      // The change to rootLayer must persist to correctly record the clips.
+      // Compute fragments and their clips with respect to the outermost
+      // clipping container. This handles nested border radius by including
+      // all of them in the mask.
+      //
+      // The paint rect is in this layer's space, so convert it to the clipper's
+      // layer's space. The rootLayer is also changed to the clipper's layer to
+      // simplify coordinate system adjustments. The change to rootLayer must
+      // persist to correctly record the clips.
       paint_layer_for_fragments =
           paint_layer_.ClippingContainer()->EnclosingLayer();
+      while (const PaintLayer* new_clip_root =

[chrishtr, 2017/06/09 22:45:28]

You can stop at the PaintLayer indicated by CompositingContainer().

[Stephen Chennney, 2017/06/12 14:43:29]

Will do.

+                 paint_layer_for_fragments->ClippingContainer()
+                     ->EnclosingLayer()) {
+        paint_layer_for_fragments = new_clip_root;
+      }
       local_painting_info.root_layer = paint_layer_for_fragments;
       paint_layer_.ConvertToLayerCoords(local_painting_info.root_layer,
                                         offset_to_clipper);
       local_painting_info.paint_dirty_rect.MoveBy(offset_to_clipper);
     }
 
     PaintLayer::GeometryMapperOption geometry_mapper_option =
         PaintLayer::kDoNotUseGeometryMapper;
     if (RuntimeEnabledFeatures::SlimmingPaintInvalidationEnabled())
       geometry_mapper_option = PaintLayer::kUseGeometryMapper;
@@ skipping 551 matching lines @@
           // The ancestor is the thing that needs to clip, so do not include
           // this layer's clips.
           clipping_rule = LayerClipRecorder::kDoNotIncludeSelfForBorderRadius;
           break;
         }
       default:
         clipping_rule = LayerClipRecorder::kIncludeSelfForBorderRadius;
         break;
     }
 
-    // TODO(schenney): Nested border-radius clips are not applied to composited
-    // children, probably due to an incorrect clipRoot.
-    // https://bugs.chromium.org/p/chromium/issues/detail?id=672561
     clip_recorder.emplace(context, paint_layer_.GetLayoutObject(), clip_type,
                           clip_rect, painting_info.root_layer,
                           fragment.pagination_offset, paint_flags,
                           clipping_rule);
   }
 
   // If we are painting a mask for any reason and we have already processed the
   // clips, there is no need to go through the remaining painting pipeline.
   // We know that the mask just needs the area bounded by the clip rects to be
   // filled with black.
@@ skipping 233 matching lines @@
           context, layout_object, kPaintPhaseClippingMask))
     return;
 
   IntRect snapped_clip_rect = PixelSnappedIntRect(clip_rect.Rect());
   LayoutObjectDrawingRecorder drawing_recorder(
       context, layout_object, kPaintPhaseClippingMask, snapped_clip_rect);
   context.FillRect(snapped_clip_rect, Color::kBlack);
 }
 
 }  // namespace blink