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

[cpp]  view plain  copy   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)

[cpp]  view plain  copy   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)

[cpp]  view plain  copy   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

[cpp]  view plain  copy   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

[cpp]  view plain  copy   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

[cpp]  view plain  copy   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)

[cpp]  view plain  copy   #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();   }