用OpenSceneGraph实现的NeHe OpenGL教程 - 第四十八课

• 简介

NeHe教程在这节课向我们介绍了轨迹球技术。轨迹球技术可以让用户使用鼠标直接旋转物体，这是所有交互式3D软件必须提供的最基本的功能。在OSG中已经提供了功能强大的漫游器，包括TrackballManipulator、FirstPersonManipulator、DriveManipulator等等，具体实现的代码可以参看osgGA库中的源码部分。

• 实现

首先创建场景中的两个几何体：

osg::Geode*	createSphereGeode()
osg::Geode*	createTorusGeode(float MinorRadius, float MajorRadius)

将两者添加到场景根节点中

	osg::MatrixTransform *torusMT = new osg::MatrixTransform;
	torusMT->setMatrix(osg::Matrix::translate(-1.5, 0.0, -6.0));	
	torusMT->addChild(createTorusGeode(0.3,1.0));

	osg::MatrixTransform *sphereMT = new osg::MatrixTransform;
	sphereMT->setMatrix(osg::Matrix::translate(1.5, 0.0, -6.0));
	sphereMT->addChild(createSphereGeode());

	root->addChild(torusMT);
	root->addChild(sphereMT);

最后只需要添加一行代码，将漫游器添加到场景之中：

		this->setCameraManipulator(new osgGA::TrackballManipulator);

编译运行程序：

附：本课源码（源码中可能存在着错误和不足之处，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/ShapeDrawable>
#include <osgGA/TrackballManipulator>




osg::Geode*	createSphereGeode()
{
	osg::Geode *sphereGeode = new osg::Geode;

	osg::ShapeDrawable *shapeDrawable = new osg::ShapeDrawable;
	shapeDrawable->setShape(new osg::Sphere(osg::Vec3(), 1.3));
	shapeDrawable->setColor(osg::Vec4(1.0f,0.75f,0.75f, 1.0f));
	sphereGeode->addDrawable(shapeDrawable);

	return sphereGeode;
}


osg::Geode*	createTorusGeode(float MinorRadius, float MajorRadius)
{
	osg::Geode *geode = new osg::Geode;
	osg::Geometry *geometry = new osg::Geometry;
	osg::Vec3Array *vertexArray = new osg::Vec3Array;
	osg::Vec3Array *normalArray = new osg::Vec3Array;
	osg::Vec3Array *colorArray = new osg::Vec3Array;

	colorArray->push_back(osg::Vec3(0.75f,0.75f,1.0f));

	for (int i=0; i<20; i++ )										// Stacks
	{
		for (int j=-1; j<20; j++)									// Slices
		{
			float wrapFrac = (j%20)/(float)20;
			float phi = 2* osg::PI*wrapFrac;
			float sinphi = float(sin(phi));
			float cosphi = float(cos(phi));

			float r = MajorRadius + MinorRadius*cosphi;

			normalArray->push_back(osg::Vec3(float(sin(2* osg::PI*(i%20+wrapFrac)/(float)20))*cosphi, sinphi, float(cos(2* osg::PI*(i%20+wrapFrac)/(float)20))*cosphi));
			vertexArray->push_back(osg::Vec3(float(sin(2* osg::PI*(i%20+wrapFrac)/(float)20))*r,MinorRadius*sinphi,float(cos(2* osg::PI*(i%20+wrapFrac)/(float)20))*r));
			normalArray->push_back(osg::Vec3(float(sin(2* osg::PI*(i+1%20+wrapFrac)/(float)20))*cosphi, sinphi, float(cos(2* osg::PI*(i+1%20+wrapFrac)/(float)20))*cosphi));
			vertexArray->push_back(osg::Vec3(float(sin(2* osg::PI*(i+1%20+wrapFrac)/(float)20))*r,MinorRadius*sinphi,float(cos(2* osg::PI*(i+1%20+wrapFrac)/(float)20))*r));
		}
	}

	geometry->setVertexArray(vertexArray);
	geometry->setNormalArray(normalArray, osg::Array::BIND_PER_VERTEX);
	geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::TRIANGLE_STRIP, 0, vertexArray->size()));
	geode->addDrawable(geometry);

	return geode;
}



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 );

		//添加轨迹球
		this->setCameraManipulator(new osgGA::TrackballManipulator);

		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 = ds->getNumMultiSamples();

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

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

protected:

	QTimer _timer;
};



osg::Node*	buildScene()
{
	osg::Group *root = new osg::Group;

	osg::MatrixTransform *torusMT = new osg::MatrixTransform;
	torusMT->setMatrix(osg::Matrix::translate(-1.5, 0.0, -6.0));	
	torusMT->addChild(createTorusGeode(0.3,1.0));

	osg::MatrixTransform *sphereMT = new osg::MatrixTransform;
	sphereMT->setMatrix(osg::Matrix::translate(1.5, 0.0, -6.0));
	sphereMT->addChild(createSphereGeode());

	root->addChild(torusMT);
	root->addChild(sphereMT);

	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();
}