Set up scroll and clip parents

Source/core/rendering/RenderLayerBacking.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 153 matching lines @@
         if (page && page->mainFrame() == &frame) {
             m_isMainFrameRenderViewLayer = true;
         }
     }
 
     createPrimaryGraphicsLayer();
 }
 
 RenderLayerBacking::~RenderLayerBacking()
 {
-    updateClippingLayers(false, false);
+    updateClippingLayers(false, false, false);
     updateOverflowControlsLayers(false, false, false);
     updateForegroundLayer(false);
     updateBackgroundLayer(false);
     updateMaskLayer(false);
     updateScrollingLayers(false);
     destroyGraphicsLayers();
 }
 
 PassOwnPtr<GraphicsLayer> RenderLayerBacking::createGraphicsLayer(CompositingReasons reasons)
 {
@@ skipping 226 matching lines @@
 
     if (updateForegroundLayer(compositor->needsContentsCompositingLayer(m_owningLayer)))
         layerConfigChanged = true;
 
     bool needsDescendentsClippingLayer = compositor->clipsCompositingDescendants(m_owningLayer);
 
     // Our scrolling layer will clip.
     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()))
         layerConfigChanged = true;
 
     if (updateScrollingLayers(m_owningLayer->needsCompositedScrolling()))
         layerConfigChanged = true;
 
+    updateScrollParent(scrollParent);
+    updateClipParent(m_owningLayer->clipParent());
+
     if (layerConfigChanged)
         updateInternalHierarchy();
 
     if (updateMaskLayer(renderer->hasMask()))
         m_graphicsLayer->setMaskLayer(m_maskLayer.get());
 
     if (m_owningLayer->hasReflection()) {
         if (m_owningLayer->reflectionLayer()->backing()) {
             GraphicsLayer* reflectionLayer = m_owningLayer->reflectionLayer()->backing()->graphicsLayer();
             m_graphicsLayer->setReplicatedByLayer(reflectionLayer);
@@ skipping 96 matching lines @@
     else
         graphicsLayerParentLocation = renderer()->view()->documentRect().location();
 
     if (compAncestor && compAncestor->needsCompositedScrolling()) {
         RenderBox* renderBox = toRenderBox(compAncestor->renderer());
         IntSize scrollOffset = compAncestor->scrolledContentOffset();
         IntPoint scrollOrigin(renderBox->borderLeft(), renderBox->borderTop());
         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
         // for a compositing layer, rootLayer is the layer itself.
         RenderLayer::ClipRectsContext clipRectsContext(compAncestor, 0, TemporaryClipRects, IgnoreOverlayScrollbarSize, IgnoreOverflowClip);
         IntRect parentClipRect = pixelSnappedIntRect(m_owningLayer->backgroundClipRect(clipRectsContext).rect()); // FIXME: Incorrect for CSS regions.
         ASSERT(parentClipRect != PaintInfo::infiniteRect());
         m_ancestorClippingLayer->setPosition(FloatPoint(parentClipRect.location() - graphicsLayerParentLocation));
         m_ancestorClippingLayer->setSize(parentClipRect.size());
 
@@ skipping 186 matching lines @@
 
     // Page scale is applied as a transform on the root render view layer. Because the scroll
     // layer is further up in the hierarchy, we need to avoid marking the root render view
     // layer as a container.
     bool isContainer = m_owningLayer->hasTransform() && !m_owningLayer->isRootLayer();
     scrollingCoordinator->setLayerIsContainerForFixedPositionLayers(childForSuperlayers(), isContainer);
 }
 
 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)
         m_ancestorClippingLayer->removeAllChildren();
 
     m_graphicsLayer->removeFromParent();
 
     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());
     }
 
     if (m_scrollingLayer) {
         GraphicsLayer* superlayer = m_childContainmentLayer ? m_childContainmentLayer.get() : m_graphicsLayer.get();
         m_scrollingLayer->removeFromParent();
         superlayer->addChild(m_scrollingLayer.get());
     }
@@ skipping 58 matching lines @@
     // FIXME: we could refine this to only allocate backing for one of these layers if possible.
     m_graphicsLayer->setDrawsContent(hasPaintedContent);
     if (m_foregroundLayer)
         m_foregroundLayer->setDrawsContent(hasPaintedContent);
 
     if (m_backgroundLayer)
         m_backgroundLayer->setDrawsContent(hasPaintedContent);
 }
 
 // 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;
 
     if (needsAncestorClip) {
         if (!m_ancestorClippingLayer) {
             m_ancestorClippingLayer = createGraphicsLayer(CompositingReasonLayerForClip);
             m_ancestorClippingLayer->setMasksToBounds(true);
             layersChanged = true;
         }
     } else if (m_ancestorClippingLayer) {
         m_ancestorClippingLayer->removeFromParent();
         m_ancestorClippingLayer = nullptr;
         layersChanged = true;
     }
 
     if (needsDescendantClip) {
         // We don't need a child containment layer if we're the main frame render view
         // layer. It's redundant as the frame clip above us will handle this clipping.
         if (!m_childContainmentLayer && !m_isMainFrameRenderViewLayer) {
             m_childContainmentLayer = createGraphicsLayer(CompositingReasonLayerForClip);
             m_childContainmentLayer->setMasksToBounds(true);
             layersChanged = true;
         }
     } else if (hasClippingLayer()) {
         m_childContainmentLayer->removeFromParent();
         m_childContainmentLayer = nullptr;
         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;
 }
 
 void RenderLayerBacking::setBackgroundLayerPaintsFixedRootBackground(bool backgroundLayerPaintsFixedRootBackground)
 {
     m_backgroundLayerPaintsFixedRootBackground = backgroundLayerPaintsFixedRootBackground;
 }
 
 bool RenderLayerBacking::updateOverflowControlsLayers(bool needsHorizontalScrollbarLayer, bool needsVerticalScrollbarLayer, bool needsScrollCornerLayer)
 {
@@ skipping 202 matching lines @@
         updateInternalHierarchy();
         m_graphicsLayer->setPaintingPhase(paintingPhaseForPrimaryLayer());
         m_graphicsLayer->setNeedsDisplay();
         if (renderer()->view())
             compositor()->scrollingLayerDidChange(m_owningLayer);
     }
 
     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;
     if (!m_backgroundLayer)
         phase |= GraphicsLayerPaintBackground;
     if (!m_foregroundLayer)
         phase |= GraphicsLayerPaintForeground;
     if (!m_maskLayer)
         phase |= GraphicsLayerPaintMask;
 
     if (m_scrollingContentsLayer) {
         phase &= ~GraphicsLayerPaintForeground;
         phase |= GraphicsLayerPaintCompositedScroll;
     }
 
+    if (m_owningLayer->compositingReasons() & CompositingReasonOverflowScrollingParent)
+        phase |= GraphicsLayerPaintCompositedScroll;
+
     return static_cast<GraphicsLayerPaintingPhase>(phase);
 }
 
 float RenderLayerBacking::compositingOpacity(float rendererOpacity) const
 {
     float finalOpacity = rendererOpacity;
 
     for (RenderLayer* curr = m_owningLayer->parent(); curr; curr = curr->parent()) {
         // We only care about parents that are stacking contexts.
         // Recall that opacity creates stacking context.
@@ skipping 317 matching lines @@
 GraphicsLayer* RenderLayerBacking::parentForSublayers() const
 {
     if (m_scrollingContentsLayer)
         return m_scrollingContentsLayer.get();
 
     return m_childContainmentLayer ? m_childContainmentLayer.get() : m_graphicsLayer.get();
 }
 
 GraphicsLayer* RenderLayerBacking::childForSuperlayers() const
 {
+    if (m_ancestorScrollClippingLayer)
+        return m_ancestorScrollClippingLayer.get();
+
     if (m_ancestorClippingLayer)
         return m_ancestorClippingLayer.get();
 
     return m_graphicsLayer.get();
 }
 
 void RenderLayerBacking::setRequiresOwnBackingStore(bool requiresOwnBacking)
 {
     if (requiresOwnBacking == m_requiresOwnBackingStore)
         return;
@@ skipping 446 matching lines @@
         backingMemory += m_layerForScrollCorner->backingStoreMemoryEstimate();
 
     return backingMemory;
 }
 
 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()) {
         name = m_owningLayer->debugName() + " (foreground) Layer";
     } else if (graphicsLayer == m_backgroundLayer.get()) {
         name = m_owningLayer->debugName() + " (background) Layer";
     } else if (graphicsLayer == m_childContainmentLayer.get()) {
         name = "Child Containment Layer";
     } else if (graphicsLayer == m_maskLayer.get()) {
         name = "Mask Layer";
     } else if (graphicsLayer == m_layerForHorizontalScrollbar.get()) {
         name = "Horizontal Scrollbar Layer";
     } else if (graphicsLayer == m_layerForVerticalScrollbar.get()) {
         name = "Vertical Scrollbar Layer";
     } else if (graphicsLayer == m_layerForScrollCorner.get()) {
         name = "Scroll Corner Layer";
     } else if (graphicsLayer == m_scrollingLayer.get()) {
         name = "Scrolling Layer";
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore