osg 雾效果

osg具有雾效果，也是非常简单可以实现的。先看一下效果：

设置回调函数：

#pragma once
#include <osg/StateSet>

class FogCallBack :	public osg::StateSet::Callback {
public:
	FogCallBack();
	~FogCallBack();

	virtual void operator() (osg::StateSet* ss, osg::NodeVisitor*nv)override;
};  

#include "FogCallBack.h"
#include <osg/Fog>
#include <osg/StateAttribute>

FogCallBack::FogCallBack() {
}


FogCallBack::~FogCallBack() {
}

void FogCallBack::operator() (osg::StateSet* ss, osg::NodeVisitor*nv) {
	osg::Fog* fog = dynamic_cast<osg::Fog*>(ss->getAttribute(osg::StateAttribute::FOG));
	if (fog){
		float start = fog->getStart();
		if (start<fog->getEnd()){
			fog->setStart(start + 2.0);
		}
	}
}

void createFog() {
	osg::ref_ptr<osg::Group> root = new osg::Group;

	osg::ref_ptr<osg::Node> cowNode = osgDB::readNodeFile("lz.osgt");
	
	root->addChild(cowNode);

	osg::ref_ptr<osg::Fog> fog = new osg::Fog;
	fog->setColor(osg::Vec4(1.0, 1.0, 1.0, 0.5));//设置颜色
	fog->setStart(1.0);//设置雾效的近距离
	fog->setEnd(2000.0);//设置雾效的远距离
	fog->setDensity(10.0);//设置雾效的密度
	fog->setMode(osg::Fog::LINEAR);//设置雾效的类型-线型

	root->getOrCreateStateSet()->setUpdateCallback(new FogCallBack);

	root->getOrCreateStateSet()->setAttributeAndModes(fog.get(), osg::StateAttribute::ON| osg::StateAttribute::OVERRIDE);

	osg::ref_ptr<osgViewer::Viewer> viewer = new osgViewer::Viewer();
	viewer->addEventHandler(new osgViewer::WindowSizeHandler());
	viewer->addEventHandler(new osgViewer::StatsHandler());
	viewer->setSceneData(root.get());

	viewer->realize();
	viewer->run();
}

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