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 100f82d56d3e49ad7e59cf5d006a69f0c719477d..9f7c6f8e557211dd2067507ed55218829bf212a9 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 +549,29 @@ void RenderLayerBacking::updateGraphicsLayerGeometry()
         graphicsLayerParentLocation = scrollOrigin - scrollOffset;
     }
 
+    if (compAncestor && m_ancestorScrollClippingLayer) {

[enne (OOO), 2013/09/10 23:45:01]

Just as a sanity check, the ancestor scroll clipping layer is to essentially
apply the clip for the overflow scroll to scroll child.  Scroll parent / scroll
child are potentially siblings in the RenderLayer (and GraphicsLayer) tree.  So,
you need to both scroll the scroll child (which happens in cc) but also have the
correct clip (which needs to be added here, per scroll child)?  And, the clip
needs to be in the space that the clip for the scroll parent is in, so you're
compensating here?

I still feel like this patch really needs a diagram, even if it's just a comment
in outline form of what scroll parent and scroll child layer tree looks like,
what layers are optional, when they're needed, and what needs to move where and
why.

[Ian Vollick, 2013/09/11 17:57:52]

I've added a detailed description of all layers in the hierarchy in RLB.h. Can
you please let me know if it's the sort of thing you're after?

+        // 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()) {
+            position = position + toFloatSize(scrollAncestor->position());

[enne (OOO), 2013/09/10 23:45:01]

Maybe also ASSERT that there's no transform applied to these layers?

[Ian Vollick, 2013/09/11 17:57:52]

Done.

+            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 +778,9 @@ 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 +791,13 @@ 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 +876,7 @@ 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 +906,18 @@ 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 +1140,18 @@ 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 +1167,9 @@ GraphicsLayerPaintingPhase RenderLayerBacking::paintingPhaseForPrimaryLayer() co
         phase |= GraphicsLayerPaintCompositedScroll;
     }
 
+    if (m_owningLayer->compositingReasons() & CompositingReasonOverflowScrollingParent)
+        phase |= GraphicsLayerPaintCompositedScroll;
+
     return static_cast<GraphicsLayerPaintingPhase>(phase);
 }
 
@@ -1441,6 +1507,9 @@ GraphicsLayer* RenderLayerBacking::parentForSublayers() const
 
 GraphicsLayer* RenderLayerBacking::childForSuperlayers() const
 {
+    if (m_ancestorScrollClippingLayer)
+        return m_ancestorScrollClippingLayer.get();
+
     if (m_ancestorClippingLayer)
         return m_ancestorClippingLayer.get();
 
@@ -1907,6 +1976,8 @@ 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()) {