Add an intermediate function to generate 2 paint-order lists.

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 002087445a3e37caf1f18c52c60962f6f4cc14a4..a458d915e953b993de5ed6570b513f072c50f5ea 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -100,6 +100,7 @@
 #include "Settings.h"
 #include "ShadowRoot.h"
 #include "SourceGraphic.h"
+#include "StaticHashSetNodeList.h"
 #include "StylePropertySet.h"
 #include "StyleResolver.h"
 #include "TextStream.h"
@@ -639,6 +640,230 @@ void RenderLayer::updateDescendantsAreContiguousInStackingOrderRecursive(const H
     }
 }
 
+static inline bool isPositionedContainer(const RenderLayer* layer)
+{
+    // FIXME: This is not in sync with containingBlock.
+    // RenderObject::canContainFixedPositionedObject() should probably be used
+    // instead.
+    RenderLayerModelObject* layerRenderer = layer->renderer();
+    return layer->isRootLayer() || layerRenderer->isPositioned() || layer->hasTransform();
+}
+
+enum StackingOrderDirection { FromBackground, FromForeground };
+
+// We'd like to be able to iterate through a single paint order list, but for
+// efficiency's sake, we hang onto two lists instead (namely, the pos and neg
+// z-order lists produced by CollectLayers). This function allows us to index
+// into these two lists as if they were one. It also allows us to index into
+// this virtual list either from the start or from the end (i.e., in either
+// stacking order direction).
+static const RenderLayer* getStackingOrderElementAt(const Vector<RenderLayer*>* posZOrderList, const Vector<RenderLayer*>* negZOrderList, const StackingOrderDirection direction, const size_t index)
+{
+    size_t negZOrderListSize = negZOrderList ? negZOrderList->size() : 0;
+
+    if (direction == FromBackground) {
+        if (index < negZOrderListSize)
+            return negZOrderList->at(index);
+
+        return posZOrderList->at(index - negZOrderListSize);
+    }
+
+    size_t posZOrderListSize = posZOrderList ? posZOrderList->size() : 0;
+
+    if (index < posZOrderListSize)
+        return posZOrderList->at(posZOrderListSize - index - 1);
+
+    return negZOrderList->at(negZOrderListSize - (index - posZOrderListSize) - 1);
+}
+
+// Compute what positive and negative z-order lists would look like before and
+// after promotion, so we can later ensure that proper stacking order is
+// preserved between the two sets of lists.
+//
+// A few examples:
+// c = currentLayer
+// - = negative z-order child of currentLayer
+// + = positive z-order child of currentLayer
+// a = positioned ancestor of currentLayer
+// x = any other RenderLayer in the list
+//
+// (a) xxxxx-----++a+++x
+// (b) xxx-----c++++++xx
+//
+//
+// Normally the current layer would be painted in the normal flow list if it
+// doesn't already appear in the positive z-order list. However, in the case
+// that the layer has a positioned ancestor, it will paint directly after the
+// positioned ancestor. In example (a), the current layer would be painted in
+// the middle of its own positive z-order children, so promoting would cause a
+// change in paint order (since a promoted layer will paint all of its positive
+// z-order children strictly after it paints itself).
+//
+// In example (b), it is ok to promote the current layer only if it does not
+// have a background. If it has a background, the background gets painted before
+// the layer's negative z-order children, so again, a promotion would cause a
+// change in paint order (causing the background to get painted after the
+// negative z-order children instead of before).
+void RenderLayer::collectBeforePromotionZOrderList(RenderLayer* ancestorStackingContext, OwnPtr<Vector<RenderLayer*> >& posZOrderListBeforePromote, OwnPtr<Vector<RenderLayer*> >& negZOrderListBeforePromote, size_t& posZOrderListSizeBeforePromote, size_t& negZOrderListSizeBeforePromote)
+{
+    // We can't use TemporaryChange<> here since m_needsCompositedScrolling and
+    // m_isNormalFlowOnly are both bitfields, so we have to do it the
+    // old-fashioned way.
+    bool oldNeedsCompositedScrolling = m_needsCompositedScrolling;
+    bool oldIsNormalFlowOnly = m_isNormalFlowOnly;
+
+    // Set the flag on the current layer, then rebuild ancestor stacking
+    // context's lists. This way, we can see the exact effects that promoting
+    // this layer would cause.
+    m_needsCompositedScrolling = false;
+    m_isNormalFlowOnly = shouldBeNormalFlowOnly();
+    ancestorStackingContext->rebuildZOrderLists(StopAtStackingContexts, posZOrderListBeforePromote, negZOrderListBeforePromote, 0);
+
+    m_needsCompositedScrolling = oldNeedsCompositedScrolling;
+    m_isNormalFlowOnly = oldIsNormalFlowOnly;
+
+
+    posZOrderListSizeBeforePromote = posZOrderListBeforePromote ? posZOrderListBeforePromote->size() : 0;
+    negZOrderListSizeBeforePromote = negZOrderListBeforePromote ? negZOrderListBeforePromote->size() : 0;
+
+    const RenderLayer* positionedAncestor = parent();
+    while (positionedAncestor && !isPositionedContainer(positionedAncestor) && !positionedAncestor->isStackingContext())
+        positionedAncestor = positionedAncestor->parent();
+    if (positionedAncestor && (!isPositionedContainer(positionedAncestor) || positionedAncestor->isStackingContext()))
+        positionedAncestor = 0;
+
+    bool currentLayerIsInPosZOrderListBeforePromote = false;
+
+    for (size_t index = 0; index < posZOrderListSizeBeforePromote; index++) {
+        if (posZOrderListBeforePromote->at(index) == this) {
+            currentLayerIsInPosZOrderListBeforePromote = true;
+            break;
+        }
+    }
+
+    // Insert this into the posZOrderListBeforePromote directly after the
+    // positioned ancestor, if there is one. Otherwise, add it to the very
+    // beginning.
+    //
+    // The current layer will appear in the z-order lists after promotion, so
+    // for a meaningful comparison, we must insert it in the z-order lists
+    // before promotion if it does not appear there already.
+    if (!currentLayerIsInPosZOrderListBeforePromote) {
+        if (!positionedAncestor) {
+            if (!posZOrderListBeforePromote)
+                posZOrderListBeforePromote = adoptPtr(new Vector<RenderLayer*>());
+
+            posZOrderListBeforePromote->prepend(this);
+            posZOrderListSizeBeforePromote++;
+        } else {
+            for (size_t index = 0; index < posZOrderListSizeBeforePromote; index++) {
+                if (posZOrderListBeforePromote->at(index) == positionedAncestor) {
+                    posZOrderListBeforePromote->insert(index + 1, this);
+                    posZOrderListSizeBeforePromote++;
+                    break;
+                }
+            }
+        }
+    }
+}
+
+void RenderLayer::collectAfterPromotionZOrderList(RenderLayer* ancestorStackingContext, OwnPtr<Vector<RenderLayer*> >& posZOrderListAfterPromote, OwnPtr<Vector<RenderLayer*> >& negZOrderListAfterPromote, size_t& posZOrderListSizeAfterPromote, size_t& negZOrderListSizeAfterPromote)
+{
+    // We can't use TemporaryChange<> here since m_needsCompositedScrolling and
+    // m_isNormalFlowOnly are both bitfields, so we have to do it the
+    // old-fashioned way.
+    bool oldNeedsCompositedScrolling = m_needsCompositedScrolling;
+    bool oldIsNormalFlowOnly = m_isNormalFlowOnly;
+
+    // Set the flag on the current layer, then rebuild ancestor stacking
+    // context's lists. This way, we can see the exact effects that promoting
+    // this layer would cause.
+    m_isNormalFlowOnly = false;
+    m_needsCompositedScrolling = true;
+    ancestorStackingContext->rebuildZOrderLists(StopAtStackingContexts, posZOrderListAfterPromote, negZOrderListAfterPromote, this);
+
+    m_needsCompositedScrolling = oldNeedsCompositedScrolling;
+    m_isNormalFlowOnly = oldIsNormalFlowOnly;
+
+    posZOrderListSizeAfterPromote = posZOrderListAfterPromote ? posZOrderListAfterPromote->size() : 0;
+    negZOrderListSizeAfterPromote = negZOrderListAfterPromote ? negZOrderListAfterPromote->size() : 0;
+}
+
+#ifndef NDEBUG
+String RenderLayer::paintOrderListsAsText()
+{
+    OwnPtr<Vector<RenderLayer*> > posZOrderListBeforePromote;
+    OwnPtr<Vector<RenderLayer*> > negZOrderListBeforePromote;
+    OwnPtr<Vector<RenderLayer*> > posZOrderListAfterPromote;
+    OwnPtr<Vector<RenderLayer*> > negZOrderListAfterPromote;
+    size_t posZOrderListSizeBeforePromote, negZOrderListSizeBeforePromote, posZOrderListSizeAfterPromote, negZOrderListSizeAfterPromote;
+
+    RenderLayer* stackingContext = ancestorStackingContext();
+
+    if (!stackingContext)
+        return String();
+
+    collectBeforePromotionZOrderList(stackingContext, posZOrderListBeforePromote, negZOrderListBeforePromote, posZOrderListSizeBeforePromote, negZOrderListSizeBeforePromote);
+    collectAfterPromotionZOrderList(stackingContext, posZOrderListAfterPromote, negZOrderListAfterPromote, posZOrderListSizeAfterPromote, negZOrderListSizeAfterPromote);
+
+    size_t sizeBeforePromote = posZOrderListSizeBeforePromote + negZOrderListSizeBeforePromote;
+    size_t sizeAfterPromote = posZOrderListSizeAfterPromote + negZOrderListSizeAfterPromote;
+
+    TextStream ts;
+
+    ts << "Layer: " << this << " \"" << debugName() << "\", z-index: " << renderer()->style()->zIndex() << "\n";
+
+    ts << "  stacking context's paint order list BEFORE promote:\n";
+    for (size_t index = 0; index < sizeBeforePromote; index++) {
+        const RenderLayer* layerBeforePromote = getStackingOrderElementAt(posZOrderListBeforePromote.get(), negZOrderListBeforePromote.get(), FromBackground, index);
+        ts << "    " << layerBeforePromote << " \"" << layerBeforePromote->debugName() << "\", z-index: " << layerBeforePromote->renderer()->style()->zIndex() << "\n";
+    }
+
+    ts << "  stacking context's paint order list AFTER promote:\n";
+    for (size_t index = 0; index < sizeAfterPromote; index++) {
+        const RenderLayer* layerAfterPromote = getStackingOrderElementAt(posZOrderListAfterPromote.get(), negZOrderListAfterPromote.get(), FromBackground, index);
+        ts << "    " << layerAfterPromote << " \"" << layerAfterPromote->debugName() << "\", z-index: " << layerAfterPromote->renderer()->style()->zIndex() << "\n";
+    }
+
+    return ts.release();
+}
+#endif
+
+PassRefPtr<NodeList> RenderLayer::paintOrderList(PaintOrderListType type)
+{
+    OwnPtr<Vector<RenderLayer*> > posZOrderList;
+    OwnPtr<Vector<RenderLayer*> > negZOrderList;
+    size_t posZOrderListSize, negZOrderListSize;
+
+    RenderLayer* stackingContext = ancestorStackingContext();
+
+    if (!stackingContext)
+        return 0;
+
+    switch(type) {
+        case BeforePromote:
+            collectBeforePromotionZOrderList(stackingContext, posZOrderList, negZOrderList, posZOrderListSize, negZOrderListSize);
+            break;
+
+        case AfterPromote:
+            collectAfterPromotionZOrderList(stackingContext, posZOrderList, negZOrderList, posZOrderListSize, negZOrderListSize);
+            break;
+
+        default:
+            return 0;
+    }
+
+    size_t size = posZOrderListSize + negZOrderListSize;
+
+    ListHashSet<RefPtr<Node> > list;
+    for (size_t index = 0; index < size; index++) {
+        const RenderLayer* layer = getStackingOrderElementAt(posZOrderList.get(), negZOrderList.get(), FromBackground, index);
+        list.add(layer->renderer()->node());
+    }
+
+    return StaticHashSetNodeList::adopt(list);
+}
+
 void RenderLayer::computeRepaintRects(const RenderLayerModelObject* repaintContainer, const RenderGeometryMap* geometryMap)
 {
     ASSERT(!m_visibleContentStatusDirty);
@@ -1268,12 +1493,6 @@ RenderLayer* RenderLayer::ancestorStackingContext() const
     return ancestor;
 }
 
-static inline bool isPositionedContainer(RenderLayer* layer)
-{
-    RenderLayerModelObject* layerRenderer = layer->renderer();
-    return layer->isRootLayer() || layerRenderer->isPositioned() || layer->hasTransform();
-}
-
 static inline bool isFixedPositionedContainer(RenderLayer* layer)
 {
     return layer->isRootLayer() || layer->hasTransform();
@@ -5540,12 +5759,12 @@ void RenderLayer::rebuildZOrderLists()
     m_zOrderListsDirty = false;
 }
 
-void RenderLayer::rebuildZOrderLists(CollectLayersBehavior behavior, OwnPtr<Vector<RenderLayer*> >& posZOrderList, OwnPtr<Vector<RenderLayer*> >& negZOrderList)
+void RenderLayer::rebuildZOrderLists(CollectLayersBehavior behavior, OwnPtr<Vector<RenderLayer*> >& posZOrderList, OwnPtr<Vector<RenderLayer*> >& negZOrderList, const RenderLayer* layerToForceAsStackingContainer)
 {
     bool includeHiddenLayers = compositor()->inCompositingMode();
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         if (!m_reflection || reflectionLayer() != child)
-            child->collectLayers(includeHiddenLayers, behavior, posZOrderList, negZOrderList);
+            child->collectLayers(includeHiddenLayers, behavior, posZOrderList, negZOrderList, layerToForceAsStackingContainer);
 
     // Sort the two lists.
     if (posZOrderList)
@@ -5590,7 +5809,7 @@ void RenderLayer::updateNormalFlowList()
     m_normalFlowListDirty = false;
 }
 
-void RenderLayer::collectLayers(bool includeHiddenLayers, CollectLayersBehavior behavior, OwnPtr<Vector<RenderLayer*> >& posBuffer, OwnPtr<Vector<RenderLayer*> >& negBuffer)
+void RenderLayer::collectLayers(bool includeHiddenLayers, CollectLayersBehavior behavior, OwnPtr<Vector<RenderLayer*> >& posBuffer, OwnPtr<Vector<RenderLayer*> >& negBuffer, const RenderLayer* layerToForceAsStackingContainer)
 {
 #if ENABLE(DIALOG_ELEMENT)
     if (isInTopLayer())
@@ -5599,7 +5818,18 @@ void RenderLayer::collectLayers(bool includeHiddenLayers, CollectLayersBehavior
 
     updateDescendantDependentFlags();
 
-    bool isStacking = behavior == StopAtStackingContexts ? isStackingContext() : isStackingContainer();
+    bool isStacking = false;
+
+    switch (behavior) {
+        case StopAtStackingContexts:
+            isStacking = (this == layerToForceAsStackingContainer) || isStackingContext();
+            break;
+
+        case StopAtStackingContainers:
+            isStacking = (this == layerToForceAsStackingContainer) || isStackingContainer();
+            break;
+    }
+
     // Overflow layers are just painted by their enclosing layers, so they don't get put in zorder lists.
     bool includeHiddenLayer = includeHiddenLayers || (m_hasVisibleContent || (m_hasVisibleDescendant && isStacking));
     if (includeHiddenLayer && !isNormalFlowOnly() && !isOutOfFlowRenderFlowThread()) {
@@ -5620,7 +5850,7 @@ void RenderLayer::collectLayers(bool includeHiddenLayers, CollectLayersBehavior
         for (RenderLayer* child = firstChild(); child; child = child->nextSibling()) {
             // Ignore reflections.
             if (!m_reflection || reflectionLayer() != child)
-                child->collectLayers(includeHiddenLayers, behavior, posBuffer, negBuffer);
+                child->collectLayers(includeHiddenLayers, behavior, posBuffer, negBuffer, layerToForceAsStackingContainer);
         }
     }
 }