void RenderLayerStackingNode::collectLayers(OwnPtr<Vector<RenderLayerStackingNode*> >& posBuffer, OwnPtr<Vector<RenderLayerStackingNode*> >& negBuffer,
    const RenderLayerStackingNode* nodeToForceAsStackingContainer, CollectLayersBehavior collectLayersBehavior)
{
    if (layer()->isInTopLayer())
        return;

    layer()->updateDescendantDependentFlags();

    bool isStacking = false;
    bool isNormalFlow = false;

    switch (collectLayersBehavior) {
    case ForceLayerToStackingContainer:
        ASSERT(nodeToForceAsStackingContainer);
        if (this == nodeToForceAsStackingContainer) {
            isStacking = true;
            isNormalFlow = false;
        } else {
            isStacking = isStackingContext();
            isNormalFlow = shouldBeNormalFlowOnlyIgnoringCompositedScrolling();
        }
        break;
    case OverflowScrollCanBeStackingContainers:
        ASSERT(!nodeToForceAsStackingContainer);
        isStacking = isStackingContainer();
        isNormalFlow = isNormalFlowOnly();
        break;
    case OnlyStackingContextsCanBeStackingContainers:
        isStacking = isStackingContext();
        isNormalFlow = shouldBeNormalFlowOnlyIgnoringCompositedScrolling();
        break;
    }

    // Overflow layers are just painted by their enclosing layers, so they don't get put in zorder lists.
    if (!isNormalFlow && !layer()->isOutOfFlowRenderFlowThread()) {
        // Determine which buffer the child should be in.
        OwnPtr<Vector<RenderLayerStackingNode*> >& buffer = (zIndex() >= 0) ? posBuffer : negBuffer;

        // Create the buffer if it doesn't exist yet.
        if (!buffer)
            buffer = adoptPtr(new Vector<RenderLayerStackingNode*>);

        // Append ourselves at the end of the appropriate buffer.
        buffer->append(this);
    }

    // Recur into our children to collect more layers, but only if we don't establish
    // a stacking context/container.
    if (!isStacking) {
        for (RenderLayer* child = layer()->firstChild(); child; child = child->nextSibling()) {
            // Ignore reflections.
            if (!layer()->reflectionInfo() || layer()->reflectionInfo()->reflectionLayer() != child)
                child->stackingNode()->collectLayers(posBuffer, negBuffer, nodeToForceAsStackingContainer, collectLayersBehavior);
        }
    }
}
void RenderLayerStackingNode::collectLayers(OwnPtr<Vector<RenderLayerStackingNode*> >& posBuffer, OwnPtr<Vector<RenderLayerStackingNode*> >& negBuffer)
{
    if (layer()->isInTopLayer())
        return;

    layer()->updateDescendantDependentFlags();

    if (!isNormalFlowOnly()) {
        OwnPtr<Vector<RenderLayerStackingNode*> >& buffer = (zIndex() >= 0) ? posBuffer : negBuffer;
        if (!buffer)
            buffer = adoptPtr(new Vector<RenderLayerStackingNode*>);
        buffer->append(this);
    }

    if (!isStackingContext()) {
        for (RenderLayer* child = layer()->firstChild(); child; child = child->nextSibling()) {
            if (!layer()->reflectionInfo() || layer()->reflectionInfo()->reflectionLayer() != child)
                child->stackingNode()->collectLayers(posBuffer, negBuffer);
        }
    }
}