Add offset of content in composited layer to sticky position offset.

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 217 matching lines @@
 
 void CompositedLayerMapping::createPrimaryGraphicsLayer() {
   m_graphicsLayer =
       createGraphicsLayer(m_owningLayer.getCompositingReasons(),
                           m_owningLayer.getSquashingDisallowedReasons());
 
   updateOpacity(layoutObject()->styleRef());
   updateTransform(layoutObject()->styleRef());
   updateFilters(layoutObject()->styleRef());
   updateBackdropFilters(layoutObject()->styleRef());
-  updateStickyConstraints(layoutObject()->styleRef());
   updateLayerBlendMode(layoutObject()->styleRef());
   updateIsRootForIsolatedGroup();
 }
 
 void CompositedLayerMapping::destroyGraphicsLayers() {
   if (m_graphicsLayer)
     m_graphicsLayer->removeFromParent();
 
   m_ancestorClippingLayer = nullptr;
   m_ancestorClippingMaskLayer = nullptr;
@@ skipping 59 matching lines @@
             &m_owningLayer);
 
     // Find the layout offset of the unshifted sticky box within its enclosing
     // layer.
     LayoutPoint enclosingLayerOffset;
     m_owningLayer.enclosingLayerWithCompositedLayerMapping(ExcludeSelf)
         ->convertToLayerCoords(m_owningLayer.ancestorOverflowLayer(),
                                enclosingLayerOffset);
     FloatPoint stickyBoxOffset =
         constraints.scrollContainerRelativeStickyBoxRect().location();
-    stickyBoxOffset.moveBy(FloatPoint(-enclosingLayerOffset));
+    DCHECK(!m_contentOffsetInCompositingLayerDirty);
+    stickyBoxOffset.moveBy(FloatPoint(-enclosingLayerOffset) -
+                           FloatSize(contentOffsetInCompositingLayer()));

[chrishtr, 2017/01/17 23:07:26]

Is it possible for |layoutObject()| to be both sticky and squashed rather
than directly composited?

[flackr, 2017/01/18 13:28:45]

If it was squashed its position would have to be updated on the main thread.
IIUC this sticky CompositedLayerMapping is not squashed right? If it was it
wouldn't have a CLM as I understand it.

 
     webConstraint.isSticky = true;
     webConstraint.isAnchoredLeft =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeLeft;
     webConstraint.isAnchoredRight =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeRight;
     webConstraint.isAnchoredTop =
         constraints.anchorEdges() &
@@ skipping 607 matching lines @@
   // Set opacity, if it is not animating.
   if (!layoutObject()->style()->isRunningOpacityAnimationOnCompositor())
     updateOpacity(layoutObject()->styleRef());
 
   if (!layoutObject()->style()->isRunningFilterAnimationOnCompositor())
     updateFilters(layoutObject()->styleRef());
 
   if (!layoutObject()->style()->isRunningBackdropFilterAnimationOnCompositor())
     updateBackdropFilters(layoutObject()->styleRef());
 
-  updateStickyConstraints(layoutObject()->styleRef());
-
   // We compute everything relative to the enclosing compositing layer.
   IntRect ancestorCompositingBounds;
   if (compositingContainer) {
     ASSERT(compositingContainer->hasCompositedLayerMapping());
     ancestorCompositingBounds = compositingContainer->compositedLayerMapping()
                                     ->pixelSnappedCompositedBounds();
   }
 
   IntRect localCompositingBounds;
   IntRect relativeCompositingBounds;
@@ skipping 16 matching lines @@
   FloatSize contentsSize(relativeCompositingBounds.size());
 
   updateMainGraphicsLayerGeometry(relativeCompositingBounds,
                                   localCompositingBounds,
                                   graphicsLayerParentLocation);
   updateOverflowControlsHostLayerGeometry(compositingStackingContext,
                                           compositingContainer,
                                           graphicsLayerParentLocation);
   updateContentsOffsetInCompositingLayer(snappedOffsetFromCompositedAncestor,
                                          graphicsLayerParentLocation);
+  updateStickyConstraints(layoutObject()->styleRef());
   updateSquashingLayerGeometry(
       graphicsLayerParentLocation, compositingContainer, m_squashedLayers,
       m_squashingLayer.get(), &m_squashingLayerOffsetFromTransformedAncestor,
       layersNeedingPaintInvalidation);
 
   // If we have a layer that clips children, position it.
   IntRect clippingBox;
   if (m_childContainmentLayer && layoutObject()->isBox())
     clippingBox = clipBox(toLayoutBox(layoutObject()));
 
@@ skipping 2450 matching lines @@
   } else if (graphicsLayer == m_decorationOutlineLayer.get()) {
     name = "Decoration Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink