Set up scroll and clip parents

Source/core/rendering/RenderLayerBacking.cpp

Index: Source/core/rendering/RenderLayerBacking.cpp
diff --git a/Source/core/rendering/RenderLayerBacking.cpp b/Source/core/rendering/RenderLayerBacking.cpp
index a83a536ff496025e5d4b1f3fc6170ab2cc0e746c..97b89babe01dd485409cf883b68acb114f300dd6 100644
--- a/Source/core/rendering/RenderLayerBacking.cpp
+++ b/Source/core/rendering/RenderLayerBacking.cpp
@@ -171,7 +171,7 @@ RenderLayerBacking::RenderLayerBacking(RenderLayer* layer)
 
 RenderLayerBacking::~RenderLayerBacking()
 {
-    updateClippingLayers(false, false);
+    updateClippingLayers(false, false, false);
     updateOverflowControlsLayers(false, false, false);
     updateForegroundLayer(false);
     updateBackgroundLayer(false);
@@ -418,7 +418,10 @@ bool RenderLayerBacking::updateGraphicsLayerConfiguration()
     if (m_owningLayer->needsCompositedScrolling())
         needsDescendentsClippingLayer = false;
 
-    if (updateClippingLayers(compositor->clippedByAncestor(m_owningLayer), needsDescendentsClippingLayer))
+    RenderLayer* scrollParent = m_owningLayer->scrollParent();
+    bool needsAncestorClip = compositor->clippedByAncestor(m_owningLayer);
+    bool needsScrollClip = !!scrollParent;
+    if (updateClippingLayers(needsAncestorClip, needsDescendentsClippingLayer, needsScrollClip))
         layerConfigChanged = true;
 
     if (updateOverflowControlsLayers(requiresHorizontalScrollbarLayer(), requiresVerticalScrollbarLayer(), requiresScrollCornerLayer()))
@@ -427,6 +430,9 @@ bool RenderLayerBacking::updateGraphicsLayerConfiguration()
     if (updateScrollingLayers(m_owningLayer->needsCompositedScrolling()))
         layerConfigChanged = true;
 
+    updateScrollParent(scrollParent);
+    updateClipParent(m_owningLayer->clipParent());
+
     if (layerConfigChanged)
         updateInternalHierarchy();
 
@@ -543,6 +549,30 @@ void RenderLayerBacking::updateGraphicsLayerGeometry()
         graphicsLayerParentLocation = scrollOrigin - scrollOffset;
     }
 
+    if (compAncestor && m_ancestorScrollClippingLayer) {
+        // Our scroll parent must have been processed before us. The code in RenderLayerCompositor
+        // that coordinates updating graphics layer geometry has been set up to guarantee that this is the case.
+        RenderLayer* scrollParent = m_owningLayer->ancestorScrollingLayer();
+        GraphicsLayer* scrollParentClippingLayer = scrollParent->backing()->scrollingLayer();
+
+        // Not relative to our parent graphics layer.
+        FloatPoint position;
+        GraphicsLayer* scrollParentChildForSuperlayers = scrollParent->backing()->childForSuperlayers();
+
+        for (GraphicsLayer* scrollAncestor = scrollParentClippingLayer; scrollAncestor; scrollAncestor = scrollAncestor->parent()) {
+            ASSERT(scrollAncestor->transform().isIdentity());
+            position = position + toFloatSize(scrollAncestor->position());
+            if (scrollAncestor == scrollParentChildForSuperlayers)
+                break;
+        }
+
+        m_ancestorScrollClippingLayer->setPosition(position);
+        m_ancestorScrollClippingLayer->setSize(scrollParentClippingLayer->size());
+        m_ancestorScrollClippingLayer->setOffsetFromRenderer(toIntSize(roundedIntPoint(-position)));
+
+        graphicsLayerParentLocation = roundedIntPoint(position);
+    }
+
     if (compAncestor && m_ancestorClippingLayer) {
         // Call calculateRects to get the backgroundRect which is what is used to clip the contents of this
         // layer. Note that we call it with temporaryClipRects = true because normally when computing clip rects
@@ -749,6 +779,9 @@ void RenderLayerBacking::registerScrollingLayers()
 
 void RenderLayerBacking::updateInternalHierarchy()
 {
+    if (m_ancestorScrollClippingLayer)
+        m_ancestorScrollClippingLayer->removeAllChildren();
+
     // m_foregroundLayer has to be inserted in the correct order with child layers,
     // so it's not inserted here.
     if (m_ancestorClippingLayer)
@@ -759,6 +792,13 @@ void RenderLayerBacking::updateInternalHierarchy()
     if (m_ancestorClippingLayer)
         m_ancestorClippingLayer->addChild(m_graphicsLayer.get());
 
+    if (m_ancestorScrollClippingLayer) {
+        if (m_ancestorClippingLayer)
+            m_ancestorScrollClippingLayer->addChild(m_ancestorClippingLayer.get());
+        else
+            m_ancestorScrollClippingLayer->addChild(m_graphicsLayer.get());
+    }
+
     if (m_childContainmentLayer) {
         m_childContainmentLayer->removeFromParent();
         m_graphicsLayer->addChild(m_childContainmentLayer.get());
@@ -837,7 +877,7 @@ void RenderLayerBacking::updateDrawsContent(bool isSimpleContainer)
 }
 
 // Return true if the layers changed.
-bool RenderLayerBacking::updateClippingLayers(bool needsAncestorClip, bool needsDescendantClip)
+bool RenderLayerBacking::updateClippingLayers(bool needsAncestorClip, bool needsDescendantClip, bool needsScrollClip)
 {
     bool layersChanged = false;
 
@@ -867,6 +907,18 @@ bool RenderLayerBacking::updateClippingLayers(bool needsAncestorClip, bool needs
         layersChanged = true;
     }
 
+    if (needsScrollClip) {
+        if (!m_ancestorScrollClippingLayer) {
+            m_ancestorScrollClippingLayer = createGraphicsLayer(CompositingReasonLayerForClip);
+            m_ancestorScrollClippingLayer->setMasksToBounds(true);
+            layersChanged = true;
+        }
+    } else if (m_ancestorScrollClippingLayer) {
+        m_ancestorScrollClippingLayer->removeFromParent();
+        m_ancestorScrollClippingLayer = nullptr;
+        layersChanged = true;
+    }
+
     return layersChanged;
 }
 
@@ -1089,6 +1141,18 @@ bool RenderLayerBacking::updateScrollingLayers(bool needsScrollingLayers)
     return layerChanged;
 }
 
+void RenderLayerBacking::updateScrollParent(RenderLayer* scrollParent)
+{
+    if (ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer))
+        scrollingCoordinator->updateScrollParentForLayer(m_owningLayer, scrollParent);
+}
+
+void RenderLayerBacking::updateClipParent(RenderLayer* clipParent)
+{
+    if (ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer))
+        scrollingCoordinator->updateClipParentForLayer(m_owningLayer, clipParent);
+}
+
 GraphicsLayerPaintingPhase RenderLayerBacking::paintingPhaseForPrimaryLayer() const
 {
     unsigned phase = 0;
@@ -1104,6 +1168,9 @@ GraphicsLayerPaintingPhase RenderLayerBacking::paintingPhaseForPrimaryLayer() co
         phase |= GraphicsLayerPaintCompositedScroll;
     }
 
+    if (m_owningLayer->compositingReasons() & CompositingReasonOverflowScrollingParent)
+        phase |= GraphicsLayerPaintCompositedScroll;
+
     return static_cast<GraphicsLayerPaintingPhase>(phase);
 }
 
@@ -1441,6 +1508,9 @@ GraphicsLayer* RenderLayerBacking::parentForSublayers() const
 
 GraphicsLayer* RenderLayerBacking::childForSuperlayers() const
 {
+    if (m_ancestorScrollClippingLayer)
+        return m_ancestorScrollClippingLayer.get();
+
     if (m_ancestorClippingLayer)
         return m_ancestorClippingLayer.get();
 
@@ -1907,6 +1977,8 @@ String RenderLayerBacking::debugName(const GraphicsLayer* graphicsLayer)
     String name;
     if (graphicsLayer == m_graphicsLayer.get()) {
         name = m_owningLayer->debugName();
+    } else if (graphicsLayer == m_ancestorScrollClippingLayer.get()) {
+        name = "Ancestor Scroll Clipping Layer";
     } else if (graphicsLayer == m_ancestorClippingLayer.get()) {
         name = "Ancestor Clipping Layer";
     } else if (graphicsLayer == m_foregroundLayer.get()) {