用OpenSceneGraph实现的NeHe OpenGL教程 - 第九课

• 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;};////////////////////////////////////////////////////////////////////////////ColorCallbackclass 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();} }};////////////////////////////////////////////////////////////////////////////RotateCallbackclass 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};////////////////////////////////////////////////////////////////////////////AntiTIltCallbackclass 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();}