用OpenSceneGraph实现的NeHe OpenGL教程 - 第三十九课

简介

这节课NeHe课程主要向我们展示了将物理运动规律引入到三维场景中，模拟真实物体的位置变化过程。这节课分别模拟了如下几种运动方式：

（1）在重力作用下的抛物线运动；

（2）匀速运动

（3）一种类似于弹簧一样的来回运动

这些运动的方程在Physics.h头文件中描述的很清楚，稍有物理知识应该不难理解。

实现

首先我们在场景中添加各种几何体：

root->addChild(createBackGroundGeode()); //网状背景
	root->addChild(constantVelocityNode());  //匀速模拟
	root->addChild(underGravitationNode());  // 重力模拟
	root->addChild(massConnectedWithSpringNode()); //弹簧来回运动模拟

另外需要添加场景中的说明文字：

osg::Node *timeEllapsedNode = glPrint(-15.0f, 14, 0, osg::Vec4(1,1,1,1), "Time elapsed (seconds): %.2f", timeElapsed);
	timeEllapsedNode->addUpdateCallback(new TimeEllapsedUpdateCallback);
	root->addChild(timeEllapsedNode);

	osg::Node *ratioNode = glPrint(-15.0f, 13, 0, osg::Vec4(1,1,1,1),"Slow motion ratio: %.2f", slowMotionRatio);
	ratioNode->addUpdateCallback(new RatioUpdateCallback);

	root->addChild(ratioNode);
	root->addChild(glPrint(-15.0f, 12, 0, osg::Vec4(1,1,1,1),"Press F2 for normal motion"));
	root->addChild(glPrint(-15.0f, 11, 0, osg::Vec4(1,1,1,1),"Press F3 for slow motion"));

接下来便是一系列的更新回调，按照物理运动的规律更新节点位置：

//Constant Callback

class ConstantPointUpdateCallback : public osg::Drawable::UpdateCallback
{
public:

	virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
	{
		osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
		if (!geometry)
			return;
		
		osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
		if (!vertexArray)
			return;

		vertexArray->clear();
		
		for (int a = 0; a < constantVelocity->numOfMasses; ++a)
		{
			Mass* mass = constantVelocity->getMass(a);
			Vector3D* pos = &mass->pos;
			vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
		}
		geometry->setVertexArray(vertexArray);
		vertexArray->dirty();
	}
};

class ConstantWordUpdateCallback : public osg::NodeCallback
{
public:
	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if (!mt)
			return;

		for (int a = 0; a < constantVelocity->numOfMasses; ++a)
		{
			Mass* mass = constantVelocity->getMass(a);
			Vector3D* pos = &mass->pos;
			mt->setMatrix(osg::Matrix::translate(pos->x, pos->y + 1, pos->z));
		}
		
		traverse(node, nv);
	}
};

为了篇幅限制，这里只给出匀速运动的回调代码，其他部分参看附录中的源码。

我们需要在每帧中计算时间以及在每帧中更新物理运动的参数，这部分在交互的代码FRAME(帧循环事件)中给出：

case (osgGA::GUIEventAdapter::FRAME):
			{
				double dt = 0.0;
				_currentTick = osg::Timer::instance()->tick();
				if (_currentTick != _lastTick)
				{		
					dt = osg::Timer::instance()->delta_s(_lastTick, _currentTick);
					_lastTick = _currentTick;
				}
				dt /= slowMotionRatio;
				timeElapsed += dt;

				float maxPossible_dt = 0.1f;
				int numOfIterations = (int)(dt / maxPossible_dt) + 1;
				if (numOfIterations != 0)
					dt = dt / numOfIterations;	

				for (int a = 0; a < numOfIterations; ++a)
				{
					constantVelocity->operate(dt);
					motionUnderGravitation->operate(dt);
					massConnectedWithSpring->operate(dt);
				}
			}

此外在按下F2和F3时调整运动的速度：

if (ea.getKey() == osgGA::GUIEventAdapter::KEY_F2)
				{
					slowMotionRatio = 1.0f;
				}

				if (ea.getKey() == osgGA::GUIEventAdapter::KEY_F3)
				{
					slowMotionRatio = 10.0f;
				}

编译运行程序：



附：本课源码(源码中可能存在错误和不足，仅供参考)

#include "../osgNeHe.h"

#include "Physics1.h"
#include <QtCore/QTimer>
#include <QtGui/QApplication>
#include <QtGui/QVBoxLayout>

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

#include <osg/MatrixTransform>

#include <osgText/Text>
#include <osg/Point>

#include <osgGA/TrackballManipulator>

//////////////////////////////////////////////////////////////////////////

ConstantVelocity* constantVelocity = new ConstantVelocity();

MotionUnderGravitation* motionUnderGravitation = 
										new MotionUnderGravitation(Vector3D(0.0f, -9.81f, 0.0f));

MassConnectedWithSpring* massConnectedWithSpring = new MassConnectedWithSpring(2.0f);

float slowMotionRatio = 10.0f;
float timeElapsed = 0;	

osg::Node* glPrint(GLfloat x, GLfloat y, GLfloat z, const osg::Vec4& fontColor, const char *string, ...)
{
	char		text[256];	
	va_list		ap;

	if (string == NULL)
		return NULL;

	va_start(ap, string);
	vsprintf(text, string, ap);
	va_end(ap);

	osg::MatrixTransform *posMT = new osg::MatrixTransform;
	posMT->setMatrix(osg::Matrix::translate(x, y, z));

	osgText::Text *textWords = new osgText::Text;
	textWords->setColor(fontColor);
	textWords->setText(text);
	textWords->setFont("Fonts/Arial.ttf");
	textWords->setCharacterSize(1.0f);

	osg::Geode *fontGeode = new osg::Geode;
	fontGeode->addDrawable(textWords);

	posMT->addChild(fontGeode);
	return posMT;
}

//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////

class ManipulatorSceneHandler : public osgGA::GUIEventHandler
{
public:
	ManipulatorSceneHandler()
	{
		_lastTick  =  osg::Timer::instance()->tick();
		_currentTick = _lastTick;
	}

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::FRAME):
			{
				double dt = 0.0;
				_currentTick = osg::Timer::instance()->tick();
				if (_currentTick != _lastTick)
				{		
					dt = osg::Timer::instance()->delta_s(_lastTick, _currentTick);
					_lastTick = _currentTick;
				}
				dt /= slowMotionRatio;
				timeElapsed += dt;

				float maxPossible_dt = 0.1f;
				int numOfIterations = (int)(dt / maxPossible_dt) + 1;
				if (numOfIterations != 0)
					dt = dt / numOfIterations;	

				for (int a = 0; a < numOfIterations; ++a)
				{
					constantVelocity->operate(dt);
					motionUnderGravitation->operate(dt);
					massConnectedWithSpring->operate(dt);
				}
			}
			break;
		case(osgGA::GUIEventAdapter::KEYDOWN):
			{
if (ea.getKey() == osgGA::GUIEventAdapter::KEY_F2)
				{
					slowMotionRatio = 1.0f;
				}

				if (ea.getKey() == osgGA::GUIEventAdapter::KEY_F3)
				{
					slowMotionRatio = 10.0f;
				}
			}
			break;

		default: break;
		}
		return false;
	}

	osg::Timer_t _lastTick;
	osg::Timer_t _currentTick;
};

//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////

//Constant Callback

class ConstantPointUpdateCallback : public osg::Drawable::UpdateCallback
{
public:

	virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
	{
		osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
		if (!geometry)
			return;
		
		osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
		if (!vertexArray)
			return;

		vertexArray->clear();
		
		for (int a = 0; a < constantVelocity->numOfMasses; ++a)
		{
			Mass* mass = constantVelocity->getMass(a);
			Vector3D* pos = &mass->pos;
			vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
		}
		geometry->setVertexArray(vertexArray);
		vertexArray->dirty();
	}
};

class ConstantWordUpdateCallback : public osg::NodeCallback
{
public:
	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if (!mt)
			return;

		for (int a = 0; a < constantVelocity->numOfMasses; ++a)
		{
			Mass* mass = constantVelocity->getMass(a);
			Vector3D* pos = &mass->pos;
			mt->setMatrix(osg::Matrix::translate(pos->x, pos->y + 1, pos->z));
		}
		
		traverse(node, nv);
	}
};

//Gravity Callback
class GravitationPointUpdateCallback : public osg::Drawable::UpdateCallback
{
public:

	virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
	{
		osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
		if (!geometry)
			return;

		osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
		if (!vertexArray)
			return;

		vertexArray->clear();

		for (int a = 0; a < motionUnderGravitation->numOfMasses; ++a)
		{
			Mass* mass = motionUnderGravitation->getMass(a);
			Vector3D* pos = &mass->pos;
			vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
		}
		geometry->setVertexArray(vertexArray);
		vertexArray->dirty();
	}
};

class GravitationWordUpdateCallback : public osg::NodeCallback
{
public:
	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if (!mt)
			return;

		for (int a = 0; a < motionUnderGravitation->numOfMasses; ++a)
		{
			Mass* mass = motionUnderGravitation->getMass(a);
			Vector3D* pos = &mass->pos;
			mt->setMatrix(osg::Matrix::translate(pos->x, pos->y + 1, pos->z));
		}

		traverse(node, nv);
	}
};

//SpringCallback
class SpringPointUpdateCallback : public osg::Drawable::UpdateCallback
{
public:

	virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
	{
		osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
		if (!geometry)
			return;

		osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
		if (!vertexArray)
			return;

		vertexArray->clear();

		for (int a = 0; a < massConnectedWithSpring->numOfMasses; ++a)
		{
			Mass* mass = massConnectedWithSpring->getMass(a);
			Vector3D* pos = &mass->pos;
			vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
		}
		geometry->setVertexArray(vertexArray);
		vertexArray->dirty();
	}
};

class SpringWordUpdateCallback : public osg::NodeCallback
{
public:
	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if (!mt)
			return;

		for (int a = 0; a < massConnectedWithSpring->numOfMasses; ++a)
		{
			Mass* mass = massConnectedWithSpring->getMass(a);
			Vector3D* pos = &mass->pos;
			mt->setMatrix(osg::Matrix::translate(pos->x, pos->y + 1, pos->z));
		}

		traverse(node, nv);
	}
};

class SpringLineUpdateCallback : public osg::Drawable::UpdateCallback
{
public:

	virtual void update(osg::NodeVisitor*, osg::Drawable* drawable)
	{
		osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
		if (!geometry)
			return;

		osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());
		if (!vertexArray)
			return;

		vertexArray->clear();

		for (int a = 0; a < massConnectedWithSpring->numOfMasses; ++a)
		{
			Mass* mass = massConnectedWithSpring->getMass(a);
			Vector3D* pos = &mass->pos;
			vertexArray->push_back(osg::Vec3(pos->x, pos->y, pos->z));
			Vector3D *tmp = &massConnectedWithSpring->connectionPos;
			vertexArray->push_back(osg::Vec3(tmp->x, tmp->y, tmp->z));
		}
		geometry->setVertexArray(vertexArray);
		vertexArray->dirty();
	}
};

class TimeEllapsedUpdateCallback : public osg::NodeCallback
{
public:

	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if (!mt)
			return;

		osg::Geode *geode = dynamic_cast<osg::Geode*>(mt->getChild(0));
		if (!geode)
			return;

		osgText::Text *text = dynamic_cast<osgText::Text*>(geode->getDrawable(0));
		if (!text)
			return;

		std::stringstream os;
		std::string str;
		os.precision(2);
		os << std::fixed << "Time elapsed (seconds): " << timeElapsed;
		str = os.str();
		text->setText(str);

		traverse(node, nv);
	}
};

class RatioUpdateCallback : public osg::NodeCallback
{
public:

	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *mt = dynamic_cast<osg::MatrixTransform*>(node);
		if (!mt)
			return;

		osg::Geode *geode = dynamic_cast<osg::Geode*>(mt->getChild(0));
		if (!geode)
			return;

		osgText::Text *text = dynamic_cast<osgText::Text*>(geode->getDrawable(0));
		if (!text)
			return;

		std::stringstream os;
		std::string str;
		os.precision(2);
		os << std::fixed << "Slow motion ratio: " << slowMotionRatio;
		str = os.str();
		text->setText(str);

		traverse(node, nv);
	}

};

//绘制背景网格
osg::Geode*	createBackGroundGeode()
{
	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(0, 0, 1.0));
	geometry->setColorArray(colorArray, osg::Array::BIND_OVERALL);

	for (float x = -20; x <= 20; x += 1.0f)						
	{
		vertexArray->push_back(osg::Vec3(x, 20, 0));
		vertexArray->push_back(osg::Vec3(x,-20, 0));
	}

	for (float y = -20; y <= 20; y += 1.0f)
	{
		vertexArray->push_back(osg::Vec3(20, y, 0));
		vertexArray->push_back(osg::Vec3(-20, y, 0));
	}

	geometry->setVertexArray(vertexArray);
	geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
	geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::LINES, 0, vertexArray->size()));
	geode->addDrawable(geometry);
	return geode;
}

osg::Geode*	createPoint(const osg::Vec3& pos, const osg::Vec3& color, float size)
{
	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(color);
	geometry->setColorArray(colorArray, osg::Array::BIND_OVERALL);
	vertexArray->push_back(pos);
	geometry->setVertexArray(vertexArray);
	geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::POINTS, 0, vertexArray->size()));
	
	osg::Point *point = new osg::Point;
	point->setSize(size);
	geometry->getOrCreateStateSet()->setAttributeAndModes(point);
	geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
	
	geode->addDrawable(geometry);
	return geode;
}

osg::Geode*	createLine(const osg::Vec3& posBeg, const osg::Vec3& posEnd, const osg::Vec3& color)
{
	osg::Geode *geode = new osg::Geode;
	osg::Geometry *geometry = new osg::Geometry;

	osg::Vec3Array *vertexArray = new osg::Vec3Array;
	osg::Vec3Array *colorArray = new osg::Vec3Array;
	vertexArray->push_back(posBeg);
	vertexArray->push_back(posEnd);
	geometry->setVertexArray(vertexArray);
	colorArray->push_back(color);
	geometry->setColorArray(colorArray, osg::Array::BIND_OVERALL);
	geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::LINES, 0, vertexArray->size()));
	geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);

	geode->addDrawable(geometry);
	return geode;
}

//绘制Constant Velocity

osg::Node*	constantVelocityNode()
{
	osg::Group *constantVelocityGroup = new osg::Group;

	for (int a = 0; a < constantVelocity->numOfMasses; ++a)
	{
		Mass* mass = constantVelocity->getMass(a);
		Vector3D* pos = &mass->pos;

		osg::Node *node = glPrint(pos->x, pos->y + 1, pos->z, osg::Vec4(1,0,0,1), "Mass with constant vel");
		osg::Geode *geode = createPoint(osg::Vec3(pos->x, pos->y, pos->z), osg::Vec3(1,0,0), 4);
		geode->getDrawable(0)->setUpdateCallback(new ConstantPointUpdateCallback);
		node->addUpdateCallback(new ConstantWordUpdateCallback);
		constantVelocityGroup->addChild(node);
		constantVelocityGroup->addChild(geode);
	}

	return constantVelocityGroup;
}

//绘制motionUnderGravitation

osg::Node*	 underGravitationNode()
{
	osg::Group *group = new osg::Group;
	
	for (int a = 0; a < motionUnderGravitation->numOfMasses; ++a)
	{
		Mass* mass = motionUnderGravitation->getMass(a);
		Vector3D* pos = &mass->pos;

		osg::Node *wordNode = glPrint(pos->x, pos->y + 1, pos->z, osg::Vec4(1,1,0,1), "Motion under gravitation");
		osg::Geode *pointNode = createPoint(osg::Vec3(pos->x, pos->y, pos->z), osg::Vec3(1,1,0), 4);

		wordNode->addUpdateCallback(new GravitationWordUpdateCallback);
		pointNode->getDrawable(0)->setUpdateCallback(new GravitationPointUpdateCallback);

		group->addChild(wordNode);
		group->addChild(pointNode);
	}
	
	return group;
}

//绘制massConnectedWithSpring
osg::Node*	 massConnectedWithSpringNode()
{
	osg::Group *group = new osg::Group;

	for (int a = 0; a < massConnectedWithSpring->numOfMasses; ++a)
	{
		Mass* mass = massConnectedWithSpring->getMass(a);
		Vector3D* pos = &mass->pos;

		osg::Node *wordNode = glPrint(pos->x, pos->y + 1, pos->z, osg::Vec4(0,1,0,1), "Mass connected with spring");
		osg::Geode *pointNode = createPoint(osg::Vec3(pos->x, pos->y, pos->z), osg::Vec3(0,1,0), 8);
		group->addChild(wordNode);
		group->addChild(pointNode);

		wordNode->addUpdateCallback(new SpringWordUpdateCallback);
		pointNode->getDrawable(0)->setUpdateCallback(new SpringPointUpdateCallback);
		
		Vector3D *tmp = &massConnectedWithSpring->connectionPos;
		osg::Geode *lineNode = createLine(osg::Vec3(pos->x, pos->y, pos->z), osg::Vec3(tmp->x, tmp->y, tmp->z), osg::Vec3(0,1,0));
		//Force the lineNode Draw Upon Background
		lineNode->getOrCreateStateSet()->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);
		group->addChild(lineNode);
		lineNode->getDrawable(0)->setUpdateCallback(new SpringLineUpdateCallback);
	}

	return group;
}

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, 40), osg::Vec3d(0, 0, 0), osg::Vec3d(0, 1, 0));

		//OSG默认会将点裁剪掉
		camera->setCullingMode(
			camera->getCullingMode() &
			~osg::CullSettings::SMALL_FEATURE_CULLING); 
		addEventHandler(new ManipulatorSceneHandler);
		this->setSceneData( scene );
		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;

	root->addChild(createBackGroundGeode());
	root->addChild(constantVelocityNode());
	root->addChild(underGravitationNode());
	root->addChild(massConnectedWithSpringNode());

osg::Node *timeEllapsedNode = glPrint(-15.0f, 14, 0, osg::Vec4(1,1,1,1), "Time elapsed (seconds): %.2f", timeElapsed);
	timeEllapsedNode->addUpdateCallback(new TimeEllapsedUpdateCallback);
	root->addChild(timeEllapsedNode);

	osg::Node *ratioNode = glPrint(-15.0f, 13, 0, osg::Vec4(1,1,1,1),"Slow motion ratio: %.2f", slowMotionRatio);
	ratioNode->addUpdateCallback(new RatioUpdateCallback);

	root->addChild(ratioNode);
	root->addChild(glPrint(-15.0f, 12, 0, osg::Vec4(1,1,1,1),"Press F2 for normal motion"));
	root->addChild(glPrint(-15.0f, 11, 0, osg::Vec4(1,1,1,1),"Press F3 for slow motion"));

	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();
}