产生渲染叶

inline RenderLeaf* CullVisitor::createOrReuseRenderLeaf(osg::Drawable* drawable,osg::RefMatrix* projection,osg::RefMatrix* matrix, float depth)
{
    // Skips any already reused renderleaf.
    while (_currentReuseRenderLeafIndex<_reuseRenderLeafList.size() &&
           _reuseRenderLeafList[_currentReuseRenderLeafIndex]->referenceCount()>1)///循环一次，找到没有被引用的渲染叶指针,通过引用计数判断
    {
        osg::notify(osg::NOTICE)<<"Warning:createOrReuseRenderLeaf() skipping multiply refrenced entry."<< std::endl;
        ++_currentReuseRenderLeafIndex;
    }

    // If still within list, element must be singularly referenced then return it to be reused.
    if (_currentReuseRenderLeafIndex<_reuseRenderLeafList.size())//如果找到，则不需要产生新的
    {
        RenderLeaf* renderleaf = _reuseRenderLeafList[_currentReuseRenderLeafIndex++].get();
        renderleaf->set(drawable,projection,matrix,depth);
        return renderleaf;
    }

    // Otherwise need to create new renderleaf.
    RenderLeaf* renderleaf = new RenderLeaf(drawable,projection,matrix,depth);//否则产生新的渲染叶
    _reuseRenderLeafList.push_back(renderleaf);
    ++_currentReuseRenderLeafIndex;
    return renderleaf;
}