Adapt and reland old position sticky implementation

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 304 matching lines @@
         // in this case, there is no need to dirty our ancestors further.
         if (layer->isSelfPaintingLayer()) {
             ASSERT(!parent() || parent()->m_hasSelfPaintingLayerDescendantDirty || parent()->m_hasSelfPaintingLayerDescendant);
             break;
         }
     }
 }
 
 bool PaintLayer::scrollsWithViewport() const
 {
-    return layoutObject()->style()->position() == FixedPosition && layoutObject()->containerForFixedPosition() == layoutObject()->view();
+    return (layoutObject()->style()->position() == FixedPosition && layoutObject()->containerForFixedPosition() == layoutObject()->view())
+        || (layoutObject()->style()->position() == StickyPosition && !ancestorScrollingLayer());
 }
 
 bool PaintLayer::scrollsWithRespectTo(const PaintLayer* other) const
 {
     if (scrollsWithViewport() != other->scrollsWithViewport())
         return true;
     return ancestorScrollingLayer() != other->ancestorScrollingLayer();
 }
 
 void PaintLayer::updateLayerPositionsAfterOverflowScroll(const DoubleSize& scrollDelta)
@@ skipping 377 matching lines @@
     }
 
     // If we live in a 3d hierarchy, then the layer at the root of that hierarchy needs
     // the m_has3DTransformedDescendant set.
     if (preserves3D())
         return has3DTransform() || m_has3DTransformedDescendant;
 
     return has3DTransform();
 }
 
-bool PaintLayer::updateLayerPosition()
+void PaintLayer::updateLayerPosition()
 {
     LayoutPoint localPoint;
     LayoutPoint inlineBoundingBoxOffset; // We don't put this into the Layer x/y for inlines, so we need to subtract it out when done.
 
     if (layoutObject()->isInline() && layoutObject()->isLayoutInline()) {
         LayoutInline* inlineFlow = toLayoutInline(layoutObject());
         IntRect lineBox = inlineFlow->linesBoundingBox();
         m_size = lineBox.size();
         inlineBoundingBoxOffset = lineBox.location();
         localPoint.moveBy(inlineBoundingBoxOffset);
@@ skipping 30 matching lines @@
 
         if (containingLayer->layoutObject()->isInFlowPositioned() && containingLayer->layoutObject()->isLayoutInline()) {
             LayoutSize offset = toLayoutInline(containingLayer->layoutObject())->offsetForInFlowPositionedInline(*toLayoutBox(layoutObject()));
             localPoint += offset;
         }
     } else if (parent() && parent()->layoutObject()->hasOverflowClip()) {
         IntSize scrollOffset = parent()->layoutBox()->scrolledContentOffset();
         localPoint -= scrollOffset;
     }
 
-    bool positionOrOffsetChanged = false;
     if (layoutObject()->isInFlowPositioned()) {
         LayoutSize newOffset = layoutObject()->offsetForInFlowPosition();
-        positionOrOffsetChanged = newOffset != m_offsetForInFlowPosition;
         m_offsetForInFlowPosition = newOffset;
         localPoint.move(m_offsetForInFlowPosition);
     } else {
         m_offsetForInFlowPosition = LayoutSize();
     }
 
     // FIXME: We'd really like to just get rid of the concept of a layer rectangle and rely on the layoutObjects.
     localPoint.moveBy(-inlineBoundingBoxOffset);
 
     if (m_location != localPoint) {
-        positionOrOffsetChanged = true;
         setNeedsRepaint();
     }
     m_location = localPoint;
 
 #if ENABLE(ASSERT)
     m_needsPositionUpdate = false;
 #endif
-    return positionOrOffsetChanged;
 }
 
 TransformationMatrix PaintLayer::perspectiveTransform() const
 {
     if (!layoutObject()->hasTransformRelatedProperty())
         return TransformationMatrix();
 
     const ComputedStyle& style = layoutObject()->styleRef();
     if (!style.hasPerspective())
         return TransformationMatrix();
@@ skipping 2025 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif