用OpenSceneGraph实现的NeHe OpenGL教程 - 第九课

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本课程实现了一种在场景中绘制旋转星星的方法，通过设置纹理图片颜色、操作物体实现简单动画，结合更新回调实现星星颜色变化、旋转和平移。详细介绍了如何创建星星节点、设置纹理、颜色变换及旋转动画，最终生成动态旋转的星星场景。

简介

本课实现在场景中绘制旋转的星星，主要的内容包括使用Blend方式设置纹理图片的颜色，在场景中操作物体实现简单的动画效果。

本课中描述的内容在前面的课程中已经有比较详细的介绍，本课综合运用了前面课程所学内容。

实现

首先同NeHe教程中设置的一样，我们先创建50颗星星，代码如下

	osg::Group *starGroup = new osg::Group;

	for (unsigned i = 0; i < StarNumber; ++i)
	{
		float dist=(float(i)/StarNumber)*5.0f;
		float angle= float(i)/(StarNumber * 30);

		osg::Group *star = new osg::Group;
		
                //设置变换节点抵消对整个场景的倾斜
		osg::MatrixTransform *antiTileMT = new osg::MatrixTransform;
		antiTileMT->setUpdateCallback(new AntiTiltCallback);

		//设置变换节点抵消每颗星星的旋转
                osg::MatrixTransform *antiDirectMT = new osg::MatrixTransform;
		antiDirectMT->setUpdateCallback(new RotateCallback(osg::Z_AXIS, -angle));

		osg::MatrixTransform *directionMT = new osg::MatrixTransform;
		directionMT->setUpdateCallback(new RotateCallback(osg::Z_AXIS, angle));
		
		osg::MatrixTransform *moveMT = new osg::MatrixTransform;
		moveMT->setMatrix(osg::Matrix::translate(dist, 0, 0));
		moveMT->setUpdateCallback(new TranslateCallback);
		
		osg::MatrixTransform *spinMT = new osg::MatrixTransform;
		spinMT->setUpdateCallback(new RotateCallback(osg::Z_AXIS, 0.02));

		star->addChild(directionMT);
		directionMT->addChild(moveMT);

		//星星叶节点
		osg::Geode *starQuad = new osg::Geode;
		osg::Geometry *starGeometry = new osg::Geometry;

		osg::Texture2D *texture = new osg::Texture2D;
		texture->setImage(osgDB::readImageFile("Data/Star.bmp"));
		texture->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);
		texture->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);
		
		osg::Vec3Array *coords = new osg::Vec3Array;
		coords->push_back(osg::Vec3(-1.0f,-1.0f, 0.0f));
		coords->push_back(osg::Vec3(1.0f,-1.0f, 0.0f));
		coords->push_back(osg::Vec3(1.0f,1.0f, 0.0f));
		coords->push_back(osg::Vec3(-1.0f,1.0f, 0.0f));
		starGeometry->setVertexArray(coords);

		osg::Vec4Array *colors = new osg::Vec4Array;
		colors->push_back(osg::Vec4(rand() % 256 / 255.0f, rand() % 256 / 255.0f, rand() % 256 / 255.0f, 1.0));
		starGeometry->setColorArray(colors);
		starGeometry->setColorBinding(osg::Geometry::BIND_OVERALL);
		starGeometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::QUADS, 0, 4));

		osg::Vec2Array *textureArray = new osg::Vec2Array;
		textureArray->push_back(osg::Vec2(0.0f, 0.0f));
		textureArray->push_back(osg::Vec2(1.0f, 0.0f));
		textureArray->push_back(osg::Vec2(1.0f, 1.0f));
		textureArray->push_back(osg::Vec2(0.0f, 1.0f));
		starGeometry->setTexCoordArray(0, textureArray);

		starGeometry->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture);
		starGeometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
		starGeometry->getOrCreateStateSet()->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);
		osg::BlendFunc *blendFunc = new osg::BlendFunc(GL_SRC_ALPHA, GL_ONE, 0.5, 0.5);
		starGeometry->getOrCreateStateSet()->setAttributeAndModes(blendFunc,osg::StateAttribute::ON);
		starGeometry->setUseVertexBufferObjects(true);
		starGeometry->setUseDisplayList(false);
		starGeometry->setUpdateCallback(new ColorCallback);
		starQuad->addDrawable(starGeometry);

		moveMT->addChild(antiDirectMT);
		antiDirectMT->addChild(antiTileMT);
		antiTileMT->addChild(spinMT);
		spinMT->addChild(starQuad);

		starGroup->addChild(star);

我们将每一颗星星设置为一个osg::Group的节点，和NeHe教程中一样对每颗星星设置了旋转和平移，并将所有的星星添加到starGroup这个组节点下面。

为了实现每一帧对场景进行更新实现动画效果，我们定义了一系列的更新回调

实现星星颜色的变化，我们定义了ColorCallback(继承于osg::Drawable::UpdateCallback)

class ColorCallback : public osg::Drawable::UpdateCallback
{
	 virtual void update(osg::NodeVisitor* nv, osg::Drawable* drawable)
	 {
		 osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
		 if (!geometry)
		 {
			 return;
		 }

		 osg::Vec4Array *colorArray = dynamic_cast<osg::Vec4Array*>(geometry->getColorArray());
		if (colorArray)
		{
			osg::Vec4 color;
			color.set(rand() % 256 / 255.0f, rand() % 256 / 255.0f, rand() % 256 / 255.0f, 1.0);
			colorArray->clear();
			colorArray->push_back(color);
			colorArray->dirty();
		}
	 }
};

为了实现星星的旋转我们定义了旋转更新回调(与前面课程中一样)

class RotateCallback : public osg::NodeCallback
{

public:
	RotateCallback(osg::Vec3d rotateAxis, double rotateSpeed) : 
	  osg::NodeCallback(),
		  _rotateAxis(rotateAxis), 
		  _rotateSpeed(rotateSpeed),
		  _rotateAngle(0.0)
	  {
		  //Nop
	  }

	  void setRotateSpeed(double speed)
	  {
		  _rotateSpeed = speed;
	  }

	  double getRotateSpeed() const
	  {
		  return _rotateSpeed;
	  }

	  virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	  {
		  osg::MatrixTransform *currentMT = dynamic_cast<osg::MatrixTransform*>(node);
		  if (currentMT)
		  {
			  //获取当前的平移位置
			  osg::Vec3d currentTranslate = currentMT->getMatrix().getTrans();
			  osg::Matrix newMatrix = osg::Matrix::rotate(_rotateAngle, _rotateAxis) * osg::Matrix::translate(currentTranslate);
			  currentMT->setMatrix(newMatrix);
			  _rotateAngle += _rotateSpeed;
		  }

		  traverse(node, nv);
	  }


private:
	osg::Vec3d _rotateAxis;			//旋转轴
	double        _rotateSpeed;		//旋转速度
	double        _rotateAngle;		//当前旋转的角度
};

同样实现平移操作也定义了更新回调

class TranslateCallback : public osg::NodeCallback
{
public:

	  virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	  {
		  osg::MatrixTransform *currentMT = dynamic_cast<osg::MatrixTransform*>(node);
		  if (currentMT)
		  {
			  osg::Vec3d dist = currentMT->getMatrix().getTrans();
			  double x = dist.x();
			  x -= 0.01;
			  if(x < 0.0f)
				  x += 5.0;
			  osg::Vec3d newDist = osg::Vec3d(x, 0, 0);

			  currentMT->setMatrix(osg::Matrix::translate(newDist));
		  }

		  traverse(node, nv);
	  }
};

响应键盘操作定义在MainpulatorSceneHandler

class ManipulatorSceneHandler : public osgGA::GUIEventHandler

该类在第八课中已有介绍

最后将创建的星星节点添加到根节点下

osg::Node*	buildScene()
{
	createStars();

	osg::Group *root = new osg::Group;

	osg::MatrixTransform *zoomMT = new osg::MatrixTransform;
	zoomMT->setName("zoomMT");
	zoomMT->setMatrix(osg::Matrix::translate(0, 0, -15.0f));
	root->addChild(zoomMT);

	osg::MatrixTransform *tiltMT = new osg::MatrixTransform;
	tiltMT->setName("tiltMT");
	tiltMT->setMatrix(osg::Matrix::rotate(0, osg::X_AXIS));
	zoomMT->addChild(tiltMT);

	tiltMT->addChild(createStars());

	return root;
}

需要注意的是在星星叶节点创建的时候开启Blend，同时关闭深度测试和光照(OSG中默认开启这点和OpenGL中不一致)

编译运行程序，一个漂亮的场景就出现了。

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

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

#include <osg/MatrixTransform>
#include <osg/Texture2D>

#include <osgGA/GUIEventAdapter>
#include <osg/BlendFunc>

#include <osg/Drawable>

const int StarNumber = 50;
double tilt = 0.0;


//////////////////////////////////////////////////////////////////////////
//FindFirstNamedNodeVisitor用来遍历寻找与指定名称相同的节点

class FindFirstNamedNodeVisitor : public osg::NodeVisitor
{
public:
	FindFirstNamedNodeVisitor(const std::string& name):
	  osg::NodeVisitor(osg::NodeVisitor::TRAVERSE_ALL_CHILDREN),
		  _name(name), _foundNode(NULL) {}

	  virtual void apply(osg::Node& node)
	  {
		  if (node.getName()==_name)
		  {
			  _foundNode = &node;
			  return;
		  }
		  traverse(node);
	  }

	  std::string _name;
	  osg::Node *_foundNode;
};


//////////////////////////////////////////////////////////////////////////
//ColorCallback

class ColorCallback : public osg::Drawable::UpdateCallback
{
	 virtual void update(osg::NodeVisitor* nv, osg::Drawable* drawable)
	 {
		 osg::Geometry *geometry = dynamic_cast<osg::Geometry*>(drawable);
		 if (!geometry)
		 {
			 return;
		 }

		 osg::Vec4Array *colorArray = dynamic_cast<osg::Vec4Array*>(geometry->getColorArray());
		if (colorArray)
		{
			osg::Vec4 color;
			color.set(rand() % 256 / 255.0f, rand() % 256 / 255.0f, rand() % 256 / 255.0f, 1.0);
			colorArray->clear();
			colorArray->push_back(color);
			colorArray->dirty();
		}
	 }
};


//////////////////////////////////////////////////////////////////////////
//RotateCallback

class RotateCallback : public osg::NodeCallback
{

public:
	RotateCallback(osg::Vec3d rotateAxis, double rotateSpeed) : 
	  osg::NodeCallback(),
		  _rotateAxis(rotateAxis), 
		  _rotateSpeed(rotateSpeed),
		  _rotateAngle(0.0)
	  {
		  //Nop
	  }

	  void setRotateSpeed(double speed)
	  {
		  _rotateSpeed = speed;
	  }

	  double getRotateSpeed() const
	  {
		  return _rotateSpeed;
	  }

	  virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	  {
		  osg::MatrixTransform *currentMT = dynamic_cast<osg::MatrixTransform*>(node);
		  if (currentMT)
		  {
			  //获取当前的平移位置
			  osg::Vec3d currentTranslate = currentMT->getMatrix().getTrans();
			  osg::Matrix newMatrix = osg::Matrix::rotate(_rotateAngle, _rotateAxis) * osg::Matrix::translate(currentTranslate);
			  currentMT->setMatrix(newMatrix);
			  _rotateAngle += _rotateSpeed;
		  }

		  traverse(node, nv);
	  }


private:
	osg::Vec3d _rotateAxis;			//旋转轴
	double        _rotateSpeed;		//旋转速度
	double        _rotateAngle;		//当前旋转的角度
};


//////////////////////////////////////////////////////////////////////////
//AntiTIltCallback

class AntiTiltCallback : public osg::NodeCallback
{
public:

	virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	{
		osg::MatrixTransform *currentMT = dynamic_cast<osg::MatrixTransform*>(node);
		if (currentMT)
		{
			currentMT->setMatrix(osg::Matrix::rotate(-tilt, osg::X_AXIS));
		}

		traverse(node, nv);
	}
};


//////////////////////////////////////////////////////////////////////////
//TranslateCallback 


class TranslateCallback : public osg::NodeCallback
{
public:

	  virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
	  {
		  osg::MatrixTransform *currentMT = dynamic_cast<osg::MatrixTransform*>(node);
		  if (currentMT)
		  {
			  osg::Vec3d dist = currentMT->getMatrix().getTrans();
			  double x = dist.x();
			  x -= 0.01;
			  if(x < 0.0f)
				  x += 5.0;
			  osg::Vec3d newDist = osg::Vec3d(x, 0, 0);

			  currentMT->setMatrix(osg::Matrix::translate(newDist));
		  }

		  traverse(node, nv);
	  }
};




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

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

	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_Page_Up)
				{
					FindFirstNamedNodeVisitor fnv("tiltMT");
					root->accept(fnv);

					osg::Node *mtNode = fnv._foundNode;
					osg::MatrixTransform *tiltMT = dynamic_cast<osg::MatrixTransform*>(mtNode);
					if (!tiltMT)
						return false;

					osg::Matrix tiltMatrix = tiltMT->getMatrix();
					osg::Quat original = tiltMatrix.getRotate();		
					double angle;
					osg::Vec3 vec;
					original.getRotate(angle, vec);
					angle += 0.03;
					tiltMT->setMatrix(osg::Matrix::rotate(angle, osg::X_AXIS));
					tilt = angle;
				}

				if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Page_Down)
				{
					FindFirstNamedNodeVisitor fnv("tiltMT");
					root->accept(fnv);

					osg::Node *mtNode = fnv._foundNode;
					osg::MatrixTransform *tiltMT = dynamic_cast<osg::MatrixTransform*>(mtNode);
					if (!tiltMT)
						return false;

					osg::Matrix tiltMatrix = tiltMT->getMatrix();
					osg::Quat original = tiltMatrix.getRotate();
					double angle;
					osg::Vec3 vec;
					original.getRotate(angle, vec);
					angle -= 0.03;
					tiltMT->setMatrix(osg::Matrix::rotate(angle, osg::X_AXIS));
					tilt = angle;
				}

				if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Up)
				{
					FindFirstNamedNodeVisitor fnv("zoomMT");
					root->accept(fnv);

					osg::Node *mtNode = fnv._foundNode;
					osg::MatrixTransform *zoomMT = dynamic_cast<osg::MatrixTransform*>(mtNode);
					if (!zoomMT)
						return false;
					zoomMT->setMatrix(osg::Matrix::translate(zoomMT->getMatrix().getTrans() + osg::Vec3(0, 0, 0.5)));
				}

				if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Down)
				{
					FindFirstNamedNodeVisitor fnv("zoomMT");
					root->accept(fnv);

					osg::Node *mtNode = fnv._foundNode;
					osg::MatrixTransform *zoomMT = dynamic_cast<osg::MatrixTransform*>(mtNode);
					if (!zoomMT)
						return false;
					zoomMT->setMatrix(osg::Matrix::translate(zoomMT->getMatrix().getTrans() + osg::Vec3(0, 0, -0.5)));					
				}
			}
		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, 0.5) );
		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 = ds->getNumMultiSamples();

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

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

protected:

	QTimer _timer;
};


osg::Group* createStars()
{
	osg::Group *starGroup = new osg::Group;

	for (unsigned i = 0; i < StarNumber; ++i)
	{
		float dist=(float(i)/StarNumber)*5.0f;
		float angle= float(i)/(StarNumber * 30);

		osg::Group *star = new osg::Group;
		
		osg::MatrixTransform *antiTileMT = new osg::MatrixTransform;
		antiTileMT->setUpdateCallback(new AntiTiltCallback);

		osg::MatrixTransform *antiDirectMT = new osg::MatrixTransform;
		antiDirectMT->setUpdateCallback(new RotateCallback(osg::Z_AXIS, -angle));

		osg::MatrixTransform *directionMT = new osg::MatrixTransform;
		directionMT->setUpdateCallback(new RotateCallback(osg::Z_AXIS, angle));
		
		osg::MatrixTransform *moveMT = new osg::MatrixTransform;
		moveMT->setMatrix(osg::Matrix::translate(dist, 0, 0));
		moveMT->setUpdateCallback(new TranslateCallback);
		
		osg::MatrixTransform *spinMT = new osg::MatrixTransform;
		spinMT->setUpdateCallback(new RotateCallback(osg::Z_AXIS, 0.02));

		star->addChild(directionMT);
		directionMT->addChild(moveMT);

		//星星叶节点
		osg::Geode *starQuad = new osg::Geode;
		osg::Geometry *starGeometry = new osg::Geometry;

		osg::Texture2D *texture = new osg::Texture2D;
		texture->setImage(osgDB::readImageFile("Data/Star.bmp"));
		texture->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);
		texture->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);
		
		osg::Vec3Array *coords = new osg::Vec3Array;
		coords->push_back(osg::Vec3(-1.0f,-1.0f, 0.0f));
		coords->push_back(osg::Vec3(1.0f,-1.0f, 0.0f));
		coords->push_back(osg::Vec3(1.0f,1.0f, 0.0f));
		coords->push_back(osg::Vec3(-1.0f,1.0f, 0.0f));
		starGeometry->setVertexArray(coords);

		osg::Vec4Array *colors = new osg::Vec4Array;
		colors->push_back(osg::Vec4(rand() % 256 / 255.0f, rand() % 256 / 255.0f, rand() % 256 / 255.0f, 1.0));
		starGeometry->setColorArray(colors);
		starGeometry->setColorBinding(osg::Geometry::BIND_OVERALL);
		starGeometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::QUADS, 0, 4));

		osg::Vec2Array *textureArray = new osg::Vec2Array;
		textureArray->push_back(osg::Vec2(0.0f, 0.0f));
		textureArray->push_back(osg::Vec2(1.0f, 0.0f));
		textureArray->push_back(osg::Vec2(1.0f, 1.0f));
		textureArray->push_back(osg::Vec2(0.0f, 1.0f));
		starGeometry->setTexCoordArray(0, textureArray);

		starGeometry->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture);
		starGeometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
		starGeometry->getOrCreateStateSet()->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);
		osg::BlendFunc *blendFunc = new osg::BlendFunc(GL_SRC_ALPHA, GL_ONE, 0.5, 0.5);
		starGeometry->getOrCreateStateSet()->setAttributeAndModes(blendFunc,osg::StateAttribute::ON);
		starGeometry->setUseVertexBufferObjects(true);
		starGeometry->setUseDisplayList(false);
		starGeometry->setUpdateCallback(new ColorCallback);
		starQuad->addDrawable(starGeometry);

		moveMT->addChild(antiDirectMT);
		antiDirectMT->addChild(antiTileMT);
		antiTileMT->addChild(spinMT);
		spinMT->addChild(starQuad);

		starGroup->addChild(star);
	}

	return starGroup;
}



osg::Node*	buildScene()
{
	createStars();

	osg::Group *root = new osg::Group;

	osg::MatrixTransform *zoomMT = new osg::MatrixTransform;
	zoomMT->setName("zoomMT");
	zoomMT->setMatrix(osg::Matrix::translate(0, 0, -15.0f));
	root->addChild(zoomMT);

	osg::MatrixTransform *tiltMT = new osg::MatrixTransform;
	tiltMT->setName("tiltMT");
	tiltMT->setMatrix(osg::Matrix::rotate(0, osg::X_AXIS));
	zoomMT->addChild(tiltMT);

	tiltMT->addChild(createStars());

	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();
}