Set up scroll and clip parents

Source/core/rendering/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 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 421 matching lines @@
         m_secondaryBackingStoreBytes = 0;
 
         Frame& frame = m_renderView->frameView()->frame();
         LOG(Compositing, "\nUpdate %d of %s.\n", m_rootLayerUpdateCount, isMainFrame() ? "main frame" : frame.tree()->uniqueName().string().utf8().data());
     }
 #endif
 
     if (needHierarchyUpdate) {
         // Update the hierarchy of the compositing layers.
         Vector<GraphicsLayer*> childList;
+        HashSet<RenderLayer*> visited;
         {
             TRACE_EVENT0("blink_rendering", "RenderLayerCompositor::rebuildCompositingLayerTree");
-            rebuildCompositingLayerTree(updateRoot, childList, 0);
+            rebuildCompositingLayerTree(updateRoot, childList, visited, 0);
         }
 
         // Host the document layer in the RenderView's root layer.
         if (isFullUpdate) {
             // Even when childList is empty, don't drop out of compositing mode if there are
             // composited layers that we didn't hit in our traversal (e.g. because of visibility:hidden).
             if (childList.isEmpty() && !hasAnyAdditionalCompositedLayers(updateRoot))
                 destroyRootLayer();
             else
                 m_rootContentLayer->setChildren(childList);
         }
     } else if (needGeometryUpdate) {
         // We just need to do a geometry update. This is only used for position:fixed scrolling;
         // most of the time, geometry is updated via RenderLayer::styleChanged().
-        updateLayerTreeGeometry(updateRoot, 0);
+        HashSet<RenderLayer*> visited;
+        updateLayerTreeGeometry(updateRoot, visited, 0);
     }
 
 #if !LOG_DISABLED
     if (compositingLogEnabled() && isFullUpdate && (needHierarchyUpdate || needGeometryUpdate)) {
         double endTime = currentTime();
         LOG(Compositing, "Total layers   primary   secondary   obligatory backing (KB)   secondary backing(KB)   total backing (KB)  update time (ms)\n");
 
         LOG(Compositing, "%8d %11d %9d %20.2f %22.2f %22.2f %18.2f\n",
             m_obligateCompositedLayerCount + m_secondaryCompositedLayerCount, m_obligateCompositedLayerCount,
             m_secondaryCompositedLayerCount, m_obligatoryBackingStoreBytes / 1024, m_secondaryBackingStoreBytes / 1024, (m_obligatoryBackingStoreBytes + m_secondaryBackingStoreBytes) / 1024, 1000.0 * (endTime - startTime));
@@ skipping 568 matching lines @@
 }
 
 bool RenderLayerCompositor::canAccelerateVideoRendering(RenderVideo* o) const
 {
     if (!m_hasAcceleratedCompositing)
         return false;
 
     return o->supportsAcceleratedRendering();
 }
 
-void RenderLayerCompositor::rebuildCompositingLayerTree(RenderLayer* layer, Vector<GraphicsLayer*>& childLayersOfEnclosingLayer, int depth)
+// The purpose of this function is to ensure that we call rebuildCompostingLayerTree on curLayer's
+// scroll parent (if it has one) before we call it on curLayer. This is necessary because rebuilding the
+// compositing layer tree for curLayer will use values we computed for the scroll parent. Unfortunately,

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

I understand why you need HashSet visited for updateLayerTreeGeometry, because
of the conditional about m_ancestorScrollClippingLayer
RenderLayerBacking::updateGraphicsLayerConfiguration.  However, I don't
understand the connection to rebuildCompositingLayerTree here and why you have
to do that for the scroll parent first.  What am I missing?

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

There are two recursive functions in the RLC which are in change of calling
RLB::updateGraphicsLayerConfiguration, updateLayerTreeGeometry --as you
mentioned -- and rebuildCompositingLayerTree. So I think that in both cases we
must ensure that we recur on the scroll parent before the scroll children.

[enne (OOO), 2013/09/11 23:18:30]

Sad times.  I missed that they both call updateGraphicsLayerConfiguration.

+// the childList needs to be populated as if we'd visited all the layers in paint order. To work around
+// this, when we visit a scroll parent out of order, we'll set its additions to childList aside (in
+// scrollParentChildLists), and add them to the real childList when we visit the scroll parent in paint
+// order.
+void RenderLayerCompositor::rebuildCompositingLayerTreeForLayerAndScrollParents(RenderLayer* curLayer, Vector<GraphicsLayer*>& childList, HashSet<RenderLayer*>& visited, HashMap<RenderLayer*, Vector<GraphicsLayer*> >& scrollParentChildLists, int depth)
+{
+    ASSERT(curLayer->zIndex() >= 0 || !visited.contains(curLayer));
+    if (visited.contains(curLayer)) {
+        // We've already processed this layer, but since we processed it out of order, its
+        // contribution to childList was not added. We must do that now.
+        HashMap<RenderLayer*, Vector<GraphicsLayer*> >::iterator it = scrollParentChildLists.find(curLayer);
+        ASSERT(it != scrollParentChildLists.end());
+        childList.append(it->value);
+        scrollParentChildLists.remove(it);
+        return;
+    }
+
+    if (requiresCompositingForOverflowScrollingParent(curLayer)) {
+        RenderLayer* scrollParent = curLayer->ancestorScrollingLayer();
+        if (!visited.contains(scrollParent)) {
+            ASSERT(!scrollParentChildLists.contains(scrollParent));
+            // We will populate scrollParentChildList rather than childList, since we're visiting it
+            // out of order.
+            Vector<GraphicsLayer*> scrollParentChildList;
+            rebuildCompositingLayerTreeForLayerAndScrollParents(scrollParent, scrollParentChildList, visited, scrollParentChildLists, depth);
+            // We will set aside the scrollParentChildList in scrollParentChildLists so that we can
+            // add it to childList when we visit the scrollParent normally.
+            scrollParentChildLists.add(scrollParent, scrollParentChildList);
+        }
+    }
+
+    rebuildCompositingLayerTree(curLayer, childList, visited, depth);
+}
+
+void RenderLayerCompositor::rebuildCompositingLayerTree(RenderLayer* layer, Vector<GraphicsLayer*>& childLayersOfEnclosingLayer, HashSet<RenderLayer*>& visited, int depth)
 {
     // Make the layer compositing if necessary, and set up clipping and content layers.
     // Note that we can only do work here that is independent of whether the descendant layers
     // have been processed. computeCompositingRequirements() will already have done the repaint if necessary.
 
     // Used for gathering UMA data about the effect on memory usage of promoting all layers
     // that have a webkit-transition on opacity or transform and intersect the viewport.
     static double pixelsWithoutPromotingAllTransitions = 0.0;
     static double pixelsAddedByPromotingAllTransitions = 0.0;
 
     if (!depth) {
         pixelsWithoutPromotingAllTransitions = 0.0;
         pixelsAddedByPromotingAllTransitions = 0.0;
     }
 
+    visited.add(layer);
+
     RenderLayerBacking* layerBacking = layer->backing();
     if (layerBacking) {
         // The compositing state of all our children has been updated already, so now
         // we can compute and cache the composited bounds for this layer.
         layerBacking->updateCompositedBounds();
 
         if (RenderLayer* reflection = layer->reflectionLayer()) {
             if (reflection->backing())
                 reflection->backing()->updateCompositedBounds();
         }
@@ skipping 22 matching lines @@
 
     // If this layer has backing, then we are collecting its children, otherwise appending
     // to the compositing child list of an enclosing layer.
     Vector<GraphicsLayer*> layerChildren;
     Vector<GraphicsLayer*>& childList = layerBacking ? layerChildren : childLayersOfEnclosingLayer;
 
 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(layer);
 #endif
 
+    // Visit the normal flow descendants first. We do this for the sake of scroll
+    // parents. A scroll parent is not a stacking context, so it will either appear
+    // in the normal flow tree, or in the positive z-order list (if it had a positioned
+    // ancestor). Visiting the scroll parent ahead of time if it appears in one
+    // of these lists is a simple matter since we have the lists in hand at this
+    // level of the recursion, but it's tricker for layers in the normal flow tree,
+    // so it will be easier to just process this ahead of time.
+    Vector<GraphicsLayer*> normalFlowChildList;
+
+    if (Vector<RenderLayer*>* normalFlowList = layer->normalFlowList()) {
+        size_t listSize = normalFlowList->size();
+        for (size_t i = 0; i < listSize; ++i) {
+            RenderLayer* curLayer = normalFlowList->at(i);
+            rebuildCompositingLayerTree(curLayer, normalFlowChildList, visited, depth + 1);
+        }
+    }
+
+    HashMap<RenderLayer*, Vector<GraphicsLayer*> > scrollParentChildLists;
     if (layer->isStackingContainer()) {
         if (Vector<RenderLayer*>* negZOrderList = layer->negZOrderList()) {
             size_t listSize = negZOrderList->size();
             for (size_t i = 0; i < listSize; ++i) {
                 RenderLayer* curLayer = negZOrderList->at(i);
-                rebuildCompositingLayerTree(curLayer, childList, depth + 1);
+                rebuildCompositingLayerTreeForLayerAndScrollParents(curLayer, childList, visited, scrollParentChildLists, depth + 1);
             }
         }
 
         // If a negative z-order child is compositing, we get a foreground layer which needs to get parented.
         if (layerBacking && layerBacking->foregroundLayer())
             childList.append(layerBacking->foregroundLayer());
     }
 
-    if (Vector<RenderLayer*>* normalFlowList = layer->normalFlowList()) {
-        size_t listSize = normalFlowList->size();
-        for (size_t i = 0; i < listSize; ++i) {
-            RenderLayer* curLayer = normalFlowList->at(i);
-            rebuildCompositingLayerTree(curLayer, childList, depth + 1);
-        }
-    }
+    childList.append(normalFlowChildList);
 
     if (layer->isStackingContainer()) {
         if (Vector<RenderLayer*>* posZOrderList = layer->posZOrderList()) {
             size_t listSize = posZOrderList->size();
             for (size_t i = 0; i < listSize; ++i) {
                 RenderLayer* curLayer = posZOrderList->at(i);
-                rebuildCompositingLayerTree(curLayer, childList, depth + 1);
+                rebuildCompositingLayerTreeForLayerAndScrollParents(curLayer, childList, visited, scrollParentChildLists, depth + 1);
             }
         }
     }
 
     if (layerBacking) {
         bool parented = false;
         if (layer->renderer()->isRenderPart())
             parented = parentFrameContentLayers(toRenderPart(layer->renderer()));
 
         if (!parented)
@@ skipping 160 matching lines @@
     RenderLayerBacking* backing = layer->backing();
     GraphicsLayer* hostingLayer = backing->parentForSublayers();
     GraphicsLayer* rootLayer = innerCompositor->rootGraphicsLayer();
     if (hostingLayer->children().size() != 1 || hostingLayer->children()[0] != rootLayer) {
         hostingLayer->removeAllChildren();
         hostingLayer->addChild(rootLayer);
     }
     return true;
 }
 
+// The purpose of this function is to ensure that we call updateLayerTreeGeometry on layer's
+// scroll parent (if it has one) before we call it on layer. This is necessary because updating
+// layer tree geometry for layer will use values we computed for its scroll parent.
+void RenderLayerCompositor::updateLayerTreeGeometryForLayerAndScrollParents(RenderLayer* layer, HashSet<RenderLayer*>& visited, int depth)
+{
+    ASSERT(layer->zIndex() >= 0 || !visited.contains(layer));
+    if (visited.contains(layer))
+        return;
+
+    if (requiresCompositingForOverflowScrollingParent(layer)) {
+        RenderLayer* scrollParent = layer->ancestorScrollingLayer();
+        if (!visited.contains(scrollParent))
+            updateLayerTreeGeometryForLayerAndScrollParents(scrollParent, visited, depth);
+    }
+
+    updateLayerTreeGeometry(layer, visited, depth);
+}
 // This just updates layer geometry without changing the hierarchy.
-void RenderLayerCompositor::updateLayerTreeGeometry(RenderLayer* layer, int depth)
+void RenderLayerCompositor::updateLayerTreeGeometry(RenderLayer* layer, HashSet<RenderLayer*>& visited, int depth)
 {
+    visited.add(layer);
+
     if (RenderLayerBacking* layerBacking = layer->backing()) {
         // The compositing state of all our children has been updated already, so now
         // we can compute and cache the composited bounds for this layer.
         layerBacking->updateCompositedBounds();
 
         if (RenderLayer* reflection = layer->reflectionLayer()) {
             if (reflection->backing())
                 reflection->backing()->updateCompositedBounds();
         }
 
         layerBacking->updateGraphicsLayerConfiguration();
         layerBacking->updateGraphicsLayerGeometry();
 
         if (!layer->parent())
             updateRootLayerPosition();
 
 #if !LOG_DISABLED
         logLayerInfo(layer, depth);
 #else
         UNUSED_PARAM(depth);
 #endif
     }
 
 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(layer);
 #endif
 
+    if (Vector<RenderLayer*>* normalFlowList = layer->normalFlowList()) {
+        size_t listSize = normalFlowList->size();
+        for (size_t i = 0; i < listSize; ++i)
+            updateLayerTreeGeometry(normalFlowList->at(i), visited, depth + 1);
+    }
+
     if (layer->isStackingContainer()) {
         if (Vector<RenderLayer*>* negZOrderList = layer->negZOrderList()) {
             size_t listSize = negZOrderList->size();
             for (size_t i = 0; i < listSize; ++i)
-                updateLayerTreeGeometry(negZOrderList->at(i), depth + 1);
+                updateLayerTreeGeometryForLayerAndScrollParents(negZOrderList->at(i), visited, depth + 1);
         }
     }
 
-    if (Vector<RenderLayer*>* normalFlowList = layer->normalFlowList()) {
-        size_t listSize = normalFlowList->size();
-        for (size_t i = 0; i < listSize; ++i)
-            updateLayerTreeGeometry(normalFlowList->at(i), depth + 1);
-    }
-
     if (layer->isStackingContainer()) {
         if (Vector<RenderLayer*>* posZOrderList = layer->posZOrderList()) {
             size_t listSize = posZOrderList->size();
             for (size_t i = 0; i < listSize; ++i)
-                updateLayerTreeGeometry(posZOrderList->at(i), depth + 1);
+                updateLayerTreeGeometryForLayerAndScrollParents(posZOrderList->at(i), visited, depth + 1);
         }
     }
 }
 
 // Recurs down the RenderLayer tree until its finds the compositing descendants of compositingAncestor and updates their geometry.
 void RenderLayerCompositor::updateCompositingDescendantGeometry(RenderLayer* compositingAncestor, RenderLayer* layer, bool compositedChildrenOnly)
 {
     if (layer != compositingAncestor) {
         if (RenderLayerBacking* layerBacking = layer->backing()) {
             layerBacking->updateCompositedBounds();
@@ skipping 370 matching lines @@
 
     return "";
 }
 #endif
 
 // Return true if the given layer has some ancestor in the RenderLayer hierarchy that clips,
 // up to the enclosing compositing ancestor. This is required because compositing layers are parented
 // according to the z-order hierarchy, yet clipping goes down the renderer hierarchy.
 // Thus, a RenderLayer can be clipped by a RenderLayer that is an ancestor in the renderer hierarchy,
 // but a sibling in the z-order hierarchy.
-bool RenderLayerCompositor::clippedByAncestor(RenderLayer* layer) const
+bool RenderLayerCompositor::clippedByAncestor(const RenderLayer* layer) const
 {
     if (!layer->isComposited() || !layer->parent())
         return false;
 
-    RenderLayer* compositingAncestor = layer->ancestorCompositingLayer();
+    // Scroll children use their scrolling ancestor as their clip root.
+    RenderLayer* compositingAncestor = requiresCompositingForOverflowScrollingParent(layer)
+        ? layer->ancestorScrollingLayer()
+        : layer->ancestorCompositingLayer();
+
     if (!compositingAncestor)
         return false;
 
     // If the compositingAncestor clips, that will be taken care of by clipsCompositingDescendants(),
     // so we only care about clipping between its first child that is our ancestor (the computeClipRoot),
     // and layer.
-    RenderLayer* computeClipRoot = 0;
-    RenderLayer* curr = layer;
+    const RenderLayer* computeClipRoot = 0;
+    const RenderLayer* curr = layer;
     while (curr) {
-        RenderLayer* next = curr->parent();
+        const RenderLayer* next = curr->parent();
         if (next == compositingAncestor) {
             computeClipRoot = curr;
             break;
         }
         curr = next;
     }
 
     if (!computeClipRoot || computeClipRoot == layer)
         return false;
 
@@ skipping 191 matching lines @@
     return renderer->hasFilter();
 }
 
 bool RenderLayerCompositor::requiresCompositingForBlending(RenderObject* renderer) const
 {
     return renderer->hasBlendMode();
 }
 
 bool RenderLayerCompositor::requiresCompositingForOverflowScrollingParent(const RenderLayer* layer) const
 {
-    if (!layer->compositorDrivenAcceleratedScrollingEnabled())
-        return false;
-
-    // A layer scrolls with its containing block. So to find the overflow scrolling layer
-    // that we scroll with respect to, we must ascend the layer tree until we reach the
-    // first overflow scrolling div at or above our containing block. I will refer to this
-    // layer as our 'scrolling ancestor'.
-    //
-    // Now, if we reside in a normal flow list, then we will naturally scroll with our scrolling
-    // ancestor, and we need not be composited. If, on the other hand, we reside in a z-order
-    // list, and on our walk upwards to our scrolling ancestor we find no layer that is a stacking
-    // context, then we know that in the stacking tree, we will not be in the subtree rooted at
-    // our scrolling ancestor, and we will therefore not scroll with it. In this case, we must
-    // be a composited layer since the compositor will need to take special measures to ensure
-    // that we scroll with our scrolling ancestor and it cannot do this if we do not promote.
-    RenderLayer* scrollParent = layer->ancestorScrollingLayer();
-
-    if (!scrollParent || scrollParent->isStackingContext())
-        return false;
-
-    // If we hit a stacking context on our way up to the ancestor scrolling layer, it will already
-    // be composited due to an overflow scrolling parent, so we don't need to.
-    for (RenderLayer* ancestor = layer->parent(); ancestor && ancestor != scrollParent; ancestor = ancestor->parent()) {
-        if (ancestor->isStackingContext())
-            return false;
-    }
-
-    return true;
+    return !!layer->scrollParent();
 }
 
 bool RenderLayerCompositor::requiresCompositingForOutOfFlowClipping(const RenderLayer* layer) const
 {
     return layer->compositorDrivenAcceleratedScrollingEnabled() && layer->isUnclippedDescendant();
 }
 
 bool RenderLayerCompositor::requiresCompositingForPosition(RenderObject* renderer, const RenderLayer* layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason) const
 {
     // position:fixed elements that create their own stacking context (e.g. have an explicit z-index,
@@ skipping 716 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "Frame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore