Generate scroll/clip display item hierarchy for SPv2

Source/core/paint/DeprecatedPaintLayer.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. 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>
@@ skipping 124 matching lines @@
     const DeprecatedPaintLayerReflectionInfo* reflectionInfo() const { return m_reflectionInfo.get(); }
 
     const DeprecatedPaintLayer* root() const
     {
         const DeprecatedPaintLayer* curr = this;
         while (curr->parent())
             curr = curr->parent();
         return curr;
     }
 
-    const LayoutPoint& location() const { ASSERT(!m_needsPositionUpdate); return m_location; }
+    enum LocationQueryBehavior {
+        IncludeScroll,
+        ExcludeScroll
+    };
+    LayoutPoint location(LocationQueryBehavior behavior = IncludeScroll) const { ASSERT(!m_needsPositionUpdate); return behavior == IncludeScroll ? m_location : locationExcludeOverflowScroll(); }

[pdr., 2015/09/03 06:16:59]

With SPV2, won't all location(...)/convertToLayerCoords(...)/etc use
ExcludeScroll? If so, can we refactor these functions like so:
LayoutPoint location() const
{
    ...
    if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
        return m_location;

    // Compute and return locationExcludeOverflowScroll here.
}

And if we can do this, can we write unittests for these functions and land these
changes before the big patch?

[trchen, 2015/09/04 06:10:14]

Better, we can exclude scroll offset in the beginning by changing
DPL::updateLayerPosition().

There are many things that still rely on DPL geometry, e.g. hit-testing. IMO the
smoother way to proceed is to gradually migrate to SPv2, then delete the
IncludeScroll version afterwards.

+    // Note: This function is only needed during the transition period to SPv2.
+    // Once we have eliminated layer-based hit testing and clipping,
+    // we can cache the unscrolled location instead.
+    LayoutPoint locationExcludeOverflowScroll() const;
     // FIXME: size() should ASSERT(!m_needsPositionUpdate) as well, but that fails in some tests,
     // for example, fast/repaint/clipped-relative.html.
     const IntSize& size() const { return m_size; }
     void setSizeHackForLayoutTreeAsText(const IntSize& size) { m_size = size; }
 
     LayoutRect rect() const { return LayoutRect(location(), LayoutSize(size())); }
 
     bool isRootLayer() const { return m_isRootLayer; }
 
     DeprecatedPaintLayerCompositor* compositor() const;
@@ skipping 64 matching lines @@
     DeprecatedPaintLayer* enclosingLayerForPaintInvalidationCrossingFrameBoundaries() const;
 
     bool hasAncestorWithFilterOutsets() const;
 
     bool canUseConvertToLayerCoords() const
     {
         // These LayoutObjects have an impact on their layers without the layoutObjects knowing about it.
         return !layoutObject()->hasTransformRelatedProperty() && !layoutObject()->isSVGRoot();
     }
 
-    void convertToLayerCoords(const DeprecatedPaintLayer* ancestorLayer, LayoutPoint&) const;
+    void convertToLayerCoords(const DeprecatedPaintLayer* ancestorLayer, LayoutPoint&, LocationQueryBehavior = IncludeScroll) const;
     void convertToLayerCoords(const DeprecatedPaintLayer* ancestorLayer, LayoutRect&) const;
 
     // Does the same as convertToLayerCoords() when not in multicol. For multicol, however,
     // convertToLayerCoords() calculates the offset in flow-thread coordinates (what the layout
     // engine uses internally), while this method calculates the visual coordinates; i.e. it figures
     // out which column the layer starts in and adds in the offset. See
     // http://www.chromium.org/developers/design-documents/multi-column-layout for more info.
     LayoutPoint visualOffsetFromAncestor(const DeprecatedPaintLayer* ancestorLayer) const;
 
     // The hitTest() method looks for mouse events by walking layers that intersect the point from front to back.
     bool hitTest(HitTestResult&);
 
     // Pass offsetFromRoot if known.
     bool intersectsDamageRect(const LayoutRect& layerBounds, const LayoutRect& damageRect, const DeprecatedPaintLayer* rootLayer, const LayoutPoint* offsetFromRoot = 0) const;
 
     // Bounding box relative to some ancestor layer. Pass offsetFromRoot if known.
     LayoutRect physicalBoundingBox(const DeprecatedPaintLayer* ancestorLayer, const LayoutPoint* offsetFromRoot = 0) const;
-    LayoutRect physicalBoundingBoxIncludingReflectionAndStackingChildren(const DeprecatedPaintLayer* ancestorLayer, const LayoutPoint& offsetFromRoot) const;
+    LayoutRect physicalBoundingBoxIncludingReflectionAndStackingChildren(const LayoutPoint& offsetFromRoot) const;

[pdr., 2015/09/03 06:16:59]

Lets pull the physicalBoundingBoxIncludingReflectionAndStackingChildren change
into a separate patch.

[trchen, 2015/09/04 06:10:14]

Good point! Done.

     LayoutRect fragmentsBoundingBox(const DeprecatedPaintLayer* ancestorLayer) const;
 
     LayoutRect boundingBoxForCompositingOverlapTest() const;
 
     // If true, this layer's children are included in its bounds for overlap testing.
     // We can't rely on the children's positions if this layer has a filter that could have moved the children's pixels around.
     bool overlapBoundsIncludeChildren() const { return hasFilter() && layoutObject()->style()->filter().hasFilterThatMovesPixels(); }
 
     // MaybeIncludeTransformForAncestorLayer means that a transform on |ancestorLayer| may be applied to the bounding box,
     // in particular if paintsWithTransform() is true.
@@ skipping 478 matching lines @@
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const blink::DeprecatedPaintLayer*);
 void showLayerTree(const blink::LayoutObject*);
 #endif
 
 #endif // Layer_h