OSG 裁剪回调

struct DrawableCullCallback : public osg::Drawable::CullCallback//自定义裁剪回调节点
{
	/** do customized cull code.*/
	virtual bool cull(osg::NodeVisitor*, osg::Drawable* drawable, osg::State* /*state*/) const
	{
		std::cout<<"Drawable cull callback "<<drawable<<std::endl;
		return false;
	}
};
geode.getDrawable(i)->setCullCallback(new DrawableCullCallback());//为节点设置裁剪回调

void ViewerBase::frame(double simulationTime)
{
	renderingTraversals();//从渲染回调更新开始
}
 void ViewerBase::renderingTraversals()
{
	for(Cameras::iterator camItr = cameras.begin();
		camItr != cameras.end();
		++camItr)
	{
		osg::Camera* camera = *camItr;
		Renderer* renderer = dynamic_cast<Renderer*>(camera->getRenderer());
		if (renderer)
		{
			if (!renderer->getGraphicsThreadDoesCull() && !(camera->getCameraThread()))
			{
				renderer->cull();
			}
		}
	}
} void Renderer::cull()
{
	sceneView->cull();// osgUtil::SceneView* sceneView 
} void SceneView::cull()
{
	bool computeNearFar = cullStage(
		getProjectionMatrix(),
		getViewMatrix(),
		_cullVisitor.get(),
		_stateGraph.get(),
		_renderStage.get(),
		getViewport());
}
 bool SceneView::cullStage(const osg::Matrixd& projection,const osg::Matrixd& modelview,
			   osgUtil::CullVisitor* cullVisitor, osgUtil::StateGraph* rendergraph,
			   osgUtil::RenderStage* renderStage, osg::Viewport *viewport)
{
	// traverse the scene graph to generate the rendergraph.    
	// If the camera has a cullCallback execute the callback which has the  
	// requirement that it must traverse the camera's children.
	{
		osg::NodeCallback* callback = _camera->getCullCallback();
		if (callback) (*callback)(_camera.get(), cullVisitor);
		else cullVisitor->traverse(*_camera);
	}
} inline void NodeVistor:: traverse(Node& node)//裁剪回调的Vistor
{
	if (_traversalMode==TRAVERSE_PARENTS) node.ascend(*this);
	else if (_traversalMode!=TRAVERSE_NONE) node.traverse(*this);
}

 inline void CullVisitor:: handle_cull_callbacks_and_traverse(osg::Node& node)
{
	osg::NodeCallback* callback = node.getCullCallback();
//调用的Node的Callback，再经过一系列的过程，调用Node下Drawable的callback，如下
	if (callback) (*callback)(&node,this);
	else traverse(node);
} void CullVisitor::apply(Geode& node)
{
	for(unsigned int i=0;i<node.getNumDrawables();++i)
	{
		Drawable* drawable = node.getDrawable(i);
		const BoundingBox &bb =drawable->getBound();

		if( drawable->getCullCallback() )
		{
			if( drawable->getCullCallback()->cull( this, drawable, &_renderInfo ) == true )
				continue;
		}
	}  
}


virtual bool Drawable::cull(osg::NodeVisitor* nv, osg::Drawable* drawable, osg::RenderInfo* renderInfo) const
{ return cull(nv, drawable, renderInfo? renderInfo->getState():0); }