用OpenSceneGraph实现的NeHe OpenGL教程 - 第四十六课

• 简介

NeHe教程在这节课向我们介绍了OpenGL的扩展（ARB_MULTISAMPLE）多重采样技术。利用这种技术可以实现全屏反走样。这样可以使图形看起来更美观。

在OSG中多重采样是作为节点的StateSet来开启和关闭的，实现过程十分简单。

• 实现

首先添加四边形到场景中，这一过程前面已经重复很多遍了，代码如下：

	for(int i=-10;i<10;i++)
	{
		for(int j=-10;j<10;j++)
		{
			osg::MatrixTransform *transMT = new osg::MatrixTransform;
			transMT->addUpdateCallback(new TransCallback(i, j));
			osg::MatrixTransform *rotMT = new osg::MatrixTransform;
			rotMT->addUpdateCallback(new RotCallback);
			osg::Geode *geode = new osg::Geode;
			osg::Geometry *geometry = new osg::Geometry;
			osg::Vec3Array *vertexArray = new osg::Vec3Array;
			osg::Vec3Array *colorArray = new osg::Vec3Array;
			colorArray->push_back(osg::Vec3(1, 0, 0));

			vertexArray->push_back(osg::Vec3(i, j, 0.0));
			colorArray->push_back(osg::Vec3(0, 1, 0));
			vertexArray->push_back(osg::Vec3(i + 2.0f,j,0.0f));
			colorArray->push_back(osg::Vec3(0,0,1));
			vertexArray->push_back(osg::Vec3(i + 2.0f,j + 2.0f,0.0f));
			colorArray->push_back(osg::Vec3(1,1,1));
			vertexArray->push_back(osg::Vec3(i,j + 2.0f,0.0f));

			geometry->setVertexArray(vertexArray);
			geometry->setColorArray(colorArray, osg::Array::BIND_PER_VERTEX);
			geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
			geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::QUADS, 0, vertexArray->size()));
			geode->addDrawable(geometry);

			transMT->addChild(rotMT);
			rotMT->addChild(geode);

			root->addChild(transMT);
		}
	}

在创建窗口Traits的时候需要将窗口采样值设置为4，这样才能开启多重采样：

		traits->sampleBuffers = ds->getMultiSamples();
		traits->samples = 4/*ds->getNumMultiSamples()*/;

之后为了让这些四边形旋转和移动，在节点中添加若干的回调：

class TransCallback : public osg::NodeCallback
{
public:
	TransCallback(float i, float j) : _i(i), _j(j){}

	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if(!mt)
			return;
		mt->setMatrix(osg::Matrix::translate(_i*2.0f,_j*2.0f,-5.0f));
		traverse(node, nv);
	}
	float _i;
	float _j;
};

对节点启用多重采样：

	osg::Multisample *ms = new osg::Multisample;
	ms->setHint(osg::Multisample::NICEST);
	root->getOrCreateStateSet()->setAttributeAndModes(ms, osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE);

与键盘交互中切换多重采样的开启和关闭模式：

				if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Space)
				{
					if(!g_Root)
						return false;
					static bool flag = true;
					if (flag){
						g_Root->getOrCreateStateSet()->setMode(GL_MULTISAMPLE_ARB, false);
					}else{
						g_Root->getOrCreateStateSet()->setMode(GL_MULTISAMPLE_ARB, true);
					}
					flag = !flag;
				}

编译运行程序，可以看到在按下空格的时候四边形的边缘锯齿感有明显的变化：

附：本课源码(源码中可能存在错误和不足之处，仅供参考)

#include "../osgNeHe.h"

#include <QtCore/QTimer>
#include <QtGui/QApplication>
#include <QtGui/QVBoxLayout>

#include <osgViewer/Viewer>
#include <osgDB/ReadFile>
#include <osgQt/GraphicsWindowQt>

#include <osg/MatrixTransform>
#include <osg/Multisample>

osg::Group	*g_Root = NULL;

class ManipulatorSceneHandler : public osgGA::GUIEventHandler
{
public:
	ManipulatorSceneHandler()
	{
	}

public:
	virtual bool handle(const osgGA::GUIEventAdapter& ea, osgGA::GUIActionAdapter& aa)
	{
		osgViewer::Viewer *viewer = dynamic_cast<osgViewer::Viewer*>(&aa);
		if (!viewer)
			return false;
		if (!viewer->getSceneData())
			return false;
		if (ea.getHandled()) 
			return false;

		osg::Group *root = viewer->getSceneData()->asGroup();

		switch(ea.getEventType())
		{

		case(osgGA::GUIEventAdapter::KEYDOWN):
			{
				if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Space)
				{
					if(!g_Root)
						return false;
					static bool flag = true;
					if (flag){
						g_Root->getOrCreateStateSet()->setMode(GL_MULTISAMPLE_ARB, false);
					}else{
						g_Root->getOrCreateStateSet()->setMode(GL_MULTISAMPLE_ARB, true);
					}
					flag = !flag;
				}
			}
			break;

		default: break;
		}
		return false;
	}
};

class ViewerWidget : public QWidget, public osgViewer::Viewer
{
public:
	ViewerWidget(osg::Node *scene = NULL)
	{
		QWidget* renderWidget = getRenderWidget( createGraphicsWindow(0,0,100,100), scene);

		QVBoxLayout* layout = new QVBoxLayout;
		layout->addWidget(renderWidget);
		layout->setContentsMargins(0, 0, 0, 1);
		setLayout( layout );

		connect( &_timer, SIGNAL(timeout()), this, SLOT(update()) );
		_timer.start( 10 );
	}

	QWidget* getRenderWidget( osgQt::GraphicsWindowQt* gw, osg::Node* scene )
	{
		osg::Camera* camera = this->getCamera();
		camera->setGraphicsContext( gw );

		const osg::GraphicsContext::Traits* traits = gw->getTraits();

		camera->setClearColor( osg::Vec4(0.0, 0.0, 0.0, 1.0) );
		camera->setViewport( new osg::Viewport(0, 0, traits->width, traits->height) );
		camera->setProjectionMatrixAsPerspective(45.0f, static_cast<double>(traits->width)/static_cast<double>(traits->height), 0.1f, 100.0f );
		camera->setViewMatrixAsLookAt(osg::Vec3d(0, 0, 1), osg::Vec3d(0, 0, 0), osg::Vec3d(0, 1, 0));

		this->setSceneData( scene );
		this->addEventHandler(new ManipulatorSceneHandler);
		return gw->getGLWidget();
	}

	osgQt::GraphicsWindowQt* createGraphicsWindow( int x, int y, int w, int h, const std::string& name="", bool windowDecoration=false )
	{
		osg::DisplaySettings* ds = osg::DisplaySettings::instance().get();
		osg::ref_ptr<osg::GraphicsContext::Traits> traits = new osg::GraphicsContext::Traits;
		traits->windowName = name;
		traits->windowDecoration = windowDecoration;
		traits->x = x;
		traits->y = y;
		traits->width = w;
		traits->height = h;
		traits->doubleBuffer = true;
		traits->alpha = ds->getMinimumNumAlphaBits();
		traits->stencil = ds->getMinimumNumStencilBits();
		traits->sampleBuffers = ds->getMultiSamples();
		traits->samples = 4/*ds->getNumMultiSamples()*/;

		return new osgQt::GraphicsWindowQt(traits.get());
	}

	virtual void paintEvent( QPaintEvent* event )
	{ 
		frame(); 
	}

protected:

	QTimer _timer;
};


class TransCallback : public osg::NodeCallback
{
public:
	TransCallback(float i, float j) : _i(i), _j(j){}

	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if(!mt)
			return;
		mt->setMatrix(osg::Matrix::translate(_i*2.0f,_j*2.0f,-5.0f));
		traverse(node, nv);
	}
	float _i;
	float _j;
};


class RotCallback : public osg::NodeCallback
{
public:
	
	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		static float angle = 0.0;

		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if(!mt)
			return;

		mt->setMatrix(osg::Matrix::rotate(angle, osg::Z_AXIS));
		angle += osg::DegreesToRadians(0.001f);

		traverse(node, nv);
	}


};



osg::Node*	buildScene()
{
	osg::Group *root = new osg::Group;
	g_Root = root;
	osg::Multisample *ms = new osg::Multisample;
	ms->setHint(osg::Multisample::NICEST);
	root->getOrCreateStateSet()->setAttributeAndModes(ms, osg::StateAttribute::ON | osg::StateAttribute::OVERRIDE);

	for(int i=-10;i<10;i++)
	{
		for(int j=-10;j<10;j++)
		{
			osg::MatrixTransform *transMT = new osg::MatrixTransform;
			transMT->addUpdateCallback(new TransCallback(i, j));
			osg::MatrixTransform *rotMT = new osg::MatrixTransform;
			rotMT->addUpdateCallback(new RotCallback);
			osg::Geode *geode = new osg::Geode;
			osg::Geometry *geometry = new osg::Geometry;
			osg::Vec3Array *vertexArray = new osg::Vec3Array;
			osg::Vec3Array *colorArray = new osg::Vec3Array;
			colorArray->push_back(osg::Vec3(1, 0, 0));

			vertexArray->push_back(osg::Vec3(i, j, 0.0));
			colorArray->push_back(osg::Vec3(0, 1, 0));
			vertexArray->push_back(osg::Vec3(i + 2.0f,j,0.0f));
			colorArray->push_back(osg::Vec3(0,0,1));
			vertexArray->push_back(osg::Vec3(i + 2.0f,j + 2.0f,0.0f));
			colorArray->push_back(osg::Vec3(1,1,1));
			vertexArray->push_back(osg::Vec3(i,j + 2.0f,0.0f));

			geometry->setVertexArray(vertexArray);
			geometry->setColorArray(colorArray, osg::Array::BIND_PER_VERTEX);
			geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
			geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::QUADS, 0, vertexArray->size()));
			geode->addDrawable(geometry);

			transMT->addChild(rotMT);
			rotMT->addChild(geode);

			root->addChild(transMT);
		}
	}

	return root;
}



int main( int argc, char** argv )
{
	QApplication app(argc, argv);
	ViewerWidget* viewWidget = new ViewerWidget(buildScene());
	viewWidget->setGeometry( 100, 100, 640, 480 );
	viewWidget->show();
	return app.exec();
}