Fix position of composited, paginated inlines.

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 787 matching lines @@
   return layerConfigChanged;
 }
 
 static IntRect clipBox(LayoutBox& layoutObject) {
   // TODO(chrishtr): pixel snapping is most likely incorrect here.
   return pixelSnappedIntRect(layoutObject.clippingRect());
 }
 
 static LayoutPoint computeOffsetFromCompositedAncestor(
     const PaintLayer* layer,
-    const PaintLayer* compositedAncestor) {
-  LayoutPoint offset = layer->visualOffsetFromAncestor(compositedAncestor);
+    const PaintLayer* compositedAncestor,
+    const LayoutPoint offsetFromPaintLayer) {

[trchen, 2017/03/09 23:41:16]

const LayoutPoint localRepresentativePointForFragmentation) {

[chrishtr, 2017/03/10 01:50:04]

Done.

+  // Add in the offset of the composited bounds from the coordinate space of
+  // the PaintLayer, since visualOffsetFromAncestor() requires the pre-offset
+  // input to be in the space of the PaintLayer. We also need to add in this
+  // offset before computation of visualOffsetFromAncestor(), because it affects
+  // fragmentation offset if compositedAncestor crosses a pagination boundary.

[trchen, 2017/03/09 23:41:16]

// Currently visual fragmentation for composited layers is not implemented,
// For fragmented contents, we paint in logical coordinate of the flow thread,
// then split the result by fragment boundary and paste each part into each
// fragment's physical position.
// Since composited layers don't support visual fragmentation, we have to
// choose a "representative" fragment to position the painted contents. This
// is where localRepresentativePointForFragmentation comes into play.
// The fragment that the representative point resides in will be chosen as
// the representative fragment for layer position purpose.
// For layers that are not fragmented, the point doesn't affect behavior as
// there is one and only one fragment.

[chrishtr, 2017/03/10 01:50:04]

Done.

+  LayoutPoint offset =
+      layer->visualOffsetFromAncestor(compositedAncestor, offsetFromPaintLayer);
   if (compositedAncestor)
     offset.move(compositedAncestor->compositedLayerMapping()
                     ->owningLayer()
                     .subpixelAccumulation());
+  offset.moveBy(-offsetFromPaintLayer);
   return offset;
 }
 
 void CompositedLayerMapping::computeBoundsOfOwningLayer(
     const PaintLayer* compositedAncestor,
     IntRect& localBounds,
     IntRect& compositingBoundsRelativeToCompositedAncestor,
     LayoutPoint& offsetFromCompositedAncestor,
     IntPoint& snappedOffsetFromCompositedAncestor) {
   LayoutRect localRawCompositingBounds = compositedBounds();
-  offsetFromCompositedAncestor =
-      computeOffsetFromCompositedAncestor(&m_owningLayer, compositedAncestor);
+  offsetFromCompositedAncestor = computeOffsetFromCompositedAncestor(
+      &m_owningLayer, compositedAncestor, localRawCompositingBounds.location());
   snappedOffsetFromCompositedAncestor =
       IntPoint(offsetFromCompositedAncestor.x().round(),
                offsetFromCompositedAncestor.y().round());
 
   LayoutSize subpixelAccumulation =
       offsetFromCompositedAncestor - snappedOffsetFromCompositedAncestor;
   m_owningLayer.setSubpixelAccumulation(subpixelAccumulation);
 
   // Move the bounds by the subpixel accumulation so that it pixel-snaps
   // relative to absolute pixels instead of local coordinates.
@@ skipping 2652 matching lines @@
   } else if (graphicsLayer == m_decorationOutlineLayer.get()) {
     name = "Decoration Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink