用OpenSceneGraph实现的NeHe OpenGL教程 - 第八课

• 简介

本课是在第七课的基础上实现将立方体变透明的效果，其中用到了OpenGL中的混合(Blend)

• 实现

在OpenGL中如何实现混合以及混合实现的原理和过程在NeHe教程中已经解释的很清楚了，在这里就不在赘述，本课主要探讨在OSG中实现混合的效果，混合同样是作为一种StateSet的方式来进行处理的，OSG中的混合主要涉及到一下几个类BlendFunc、BlendEquation和BlendColor，对应于OpenGL中的glBlendFunc 、glBlendEquation和glBlendColor三个函数，对混合的参数进行一些设置。本课中我们参考NeHe教程中设置混合的计算方式定义如下的BlendFunc

osg::BlendFunc *blendFunc = new osg::BlendFunc(GL_SRC_ALPHA, GL_ONE, 0.5, 0.5);quadGeometry->getOrCreateStateSet()->setAttribute(blendFunc,osg::StateAttribute::ON);

需要注意的是我们需要将初始的清除背景的颜色的alpha值设置为0.5

camera->setClearColor( osg::Vec4(0.0, 0.0, 0.0, 0.5) );

在按下键盘上B键的时候开启和关闭混合模式

if (ea.getKey()== osgGA::GUIEventAdapter::KEY_B){static int i = 0;if (i % 2 == 0) {root->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::ON);} else {root->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::OFF);}++i;}

其他的代码与第七课相同，编译运行程序后点击B键时可以看到透明的效果。

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/NodeVisitor>#include <osg/Texture2D>#include <osgGA/GUIEventAdapter>#include <osg/Light>#include <osg/LightModel>#include <osg/LightSource>#include <osg/BlendFunc>float textureVertices[][2] = {//Front Face{0.0f, 0.0f},{1.0f, 0.0f},{1.0f, 1.0f},{0.0f, 1.0f},// Back Face{1.0f, 0.0f},{1.0f, 1.0f},{0.0f, 1.0f},{0.0f, 0.0f},// Top Face{0.0f, 1.0f},{0.0f, 0.0f},{1.0f, 0.0f},{1.0f, 1.0f},// Bottom Face{1.0f, 1.0f},{0.0f, 1.0f},{0.0f, 0.0f},{1.0f, 0.0f},// Right face{1.0f, 0.0f},{1.0f, 1.0f},{0.0f, 1.0f},{0.0f, 0.0f},// Left Face{0.0f, 0.0f},{1.0f, 0.0f},{1.0f, 1.0f},{0.0f, 1.0f}};float QuadVertices[][3] = {{-1.0f, -1.0f,  1.0f},{ 1.0f, -1.0f,  1.0f},{ 1.0f,  1.0f,  1.0f},{-1.0f,  1.0f,  1.0f},{-1.0f, -1.0f, -1.0f},{-1.0f,  1.0f, -1.0f},{ 1.0f,  1.0f, -1.0f},{ 1.0f, -1.0f, -1.0f},{-1.0f,  1.0f, -1.0f},{-1.0f,  1.0f,  1.0f},{ 1.0f,  1.0f,  1.0f},{ 1.0f,  1.0f, -1.0f},{-1.0f, -1.0f, -1.0f},{ 1.0f, -1.0f, -1.0f},{ 1.0f, -1.0f,  1.0f},{-1.0f, -1.0f,  1.0f},{ 1.0f, -1.0f, -1.0f},{ 1.0f,  1.0f, -1.0f},{ 1.0f,  1.0f,  1.0f},{ 1.0f, -1.0f,  1.0f},{-1.0f, -1.0f, -1.0f},{-1.0f, -1.0f,  1.0f},{-1.0f,  1.0f,  1.0f},{-1.0f,  1.0f, -1.0f}};float normalVertics[][3] = {// Front Face{ 0.0f, 0.0f, 1.0f},// Back Face{ 0.0f, 0.0f,-1.0f},// Top Face{ 0.0f, 1.0f, 0.0f},// Bottom Face{ 0.0f,-1.0f, 0.0f},// Right face{ 1.0f, 0.0f, 0.0f},// Left Face{-1.0f, 0.0f, 0.0f}};////////////////////////////////////////////////////////////////////////////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;};////////////////////////////////////////////////////////////////////////////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};//////////////////////////////////////////////////////////////////////////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_Left){FindFirstNamedNodeVisitor fnv("yRotMT");root->accept(fnv);osg::Node *mtNode = fnv._foundNode;osg::MatrixTransform *yRotMT = dynamic_cast<osg::MatrixTransform*>(mtNode);if (!yRotMT)return false;RotateCallback *rotCallback = dynamic_cast<RotateCallback*>(yRotMT->getUpdateCallback());if (!rotCallback)return false;double speed = rotCallback->getRotateSpeed();speed += 0.02;rotCallback->setRotateSpeed(speed);}if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Right){FindFirstNamedNodeVisitor fnv("yRotMT");root->accept(fnv);osg::Node *mtNode = fnv._foundNode;osg::MatrixTransform *yRotMT = dynamic_cast<osg::MatrixTransform*>(mtNode);if (!yRotMT)return false;RotateCallback *rotCallback = dynamic_cast<RotateCallback*>(yRotMT->getUpdateCallback());if (!rotCallback)return false;double speed = rotCallback->getRotateSpeed();speed -= 0.02;rotCallback->setRotateSpeed(speed);}if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Up){FindFirstNamedNodeVisitor fnv("xRotMT");root->accept(fnv);osg::Node *mtNode = fnv._foundNode;osg::MatrixTransform *xRotMT = dynamic_cast<osg::MatrixTransform*>(mtNode);if (!xRotMT)return false;RotateCallback *rotCallback = dynamic_cast<RotateCallback*>(xRotMT->getUpdateCallback());if (!rotCallback)return false;double speed = rotCallback->getRotateSpeed();speed += 0.02;rotCallback->setRotateSpeed(speed);}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Down){FindFirstNamedNodeVisitor fnv("xRotMT");root->accept(fnv);osg::Node *mtNode = fnv._foundNode;osg::MatrixTransform *xRotMT = dynamic_cast<osg::MatrixTransform*>(mtNode);if (!xRotMT)return false;RotateCallback *rotCallback = dynamic_cast<RotateCallback*>(xRotMT->getUpdateCallback());if (!rotCallback)return false;double speed = rotCallback->getRotateSpeed();speed -= 0.02;rotCallback->setRotateSpeed(speed);}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Page_Up){FindFirstNamedNodeVisitor fnv("zoomMT");root->accept(fnv);osg::Node *mtNode = fnv._foundNode;osg::MatrixTransform *zoomMT = dynamic_cast<osg::MatrixTransform*>(mtNode);if (!zoomMT)return false;osg::Vec3 trans = zoomMT->getMatrix().getTrans();trans.set(trans.x(), trans.y(), trans.z() + 0.2);zoomMT->setMatrix(osg::Matrix::translate(trans));}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Page_Down){FindFirstNamedNodeVisitor fnv("zoomMT");root->accept(fnv);osg::Node *mtNode = fnv._foundNode;osg::MatrixTransform *zoomMT = dynamic_cast<osg::MatrixTransform*>(mtNode);if (!zoomMT)return false;osg::Vec3 trans = zoomMT->getMatrix().getTrans();trans.set(trans.x(), trans.y(), trans.z() - 0.2);zoomMT->setMatrix(osg::Matrix::translate(trans));}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_L){static int i = 0;if (i % 2 == 0) {root->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::ON);} else {root->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);}++i;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_B){static int i = 0;if (i % 2 == 0) {root->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::ON);} else {root->getOrCreateStateSet()->setMode(GL_BLEND, osg::StateAttribute::OFF);}++i;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_F){FindFirstNamedNodeVisitor fnv("quadGeode");root->accept(fnv);osg::Node *mtNode = fnv._foundNode;osg::Geode *quadGeode = dynamic_cast<osg::Geode*>(mtNode);if (!quadGeode)return false;osg::Texture2D *texture2D = dynamic_cast<osg::Texture2D*>(quadGeode->getOrCreateStateSet()->getTextureAttribute(0, osg::StateAttribute::TEXTURE));static int i = 0;if (i % 3 == 0) {texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);} else if (i % 3 == 1) {texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR_MIPMAP_NEAREST);} else {texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::NEAREST);texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::NEAREST);}++i;}}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));osg::StateSet* globalStateset = camera->getStateSet();if (globalStateset){osg::LightModel* lightModel = new osg::LightModel;lightModel->setAmbientIntensity(osg::Vec4(0,0,0,0));globalStateset->setAttributeAndModes(lightModel, osg::StateAttribute::ON);}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::Node*buildScene(){osg::Group *root = new osg::Group;osg::Light* light = new osg::Light();light->setLightNum(0);light->setAmbient(osg::Vec4(0.5f, 0.5f, 0.5f, 1.0f));light->setDiffuse(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f));light->setPosition(osg::Vec4(0.0f, 0.0f, 2.0f, 1.0f));osg::LightSource* lightsource = new osg::LightSource();lightsource->setLight (light);root->addChild (lightsource); osg::MatrixTransform *quadMT = new osg::MatrixTransform;quadMT->setName("zoomMT");quadMT->setMatrix(osg::Matrix::translate(0.0, 0.0, -5.0));osg::MatrixTransform *quadXRotMT = new osg::MatrixTransform;quadXRotMT->setName("xRotMT");RotateCallback *xRotCallback = new RotateCallback(osg::X_AXIS, 0.0);quadXRotMT->setUpdateCallback(xRotCallback);osg::MatrixTransform *quadYRotMT = new osg::MatrixTransform;quadYRotMT->setName("yRotMT");RotateCallback *yRotCallback = new RotateCallback(osg::Y_AXIS, 0.0);quadYRotMT->setUpdateCallback(yRotCallback);osg::Geometry *quadGeometry = new osg::Geometry;osg::Vec3Array *quadVertexArray = new osg::Vec3Array;for (unsigned i = 0; i < sizeof(QuadVertices); ++i){quadVertexArray->push_back(osg::Vec3(QuadVertices[i][0], QuadVertices[i][1], QuadVertices[i][2]));}quadGeometry->setVertexArray(quadVertexArray);osg::Vec4Array *colorArray = new osg::Vec4Array;colorArray->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 0.5));quadGeometry->setColorArray(colorArray, osg::Array::BIND_OVERALL);osg::BlendFunc *blendFunc = new osg::BlendFunc(GL_SRC_ALPHA, GL_ONE, 0.5, 0.5);quadGeometry->getOrCreateStateSet()->setRenderingHint(osg::StateSet::TRANSPARENT_BIN );quadGeometry->getOrCreateStateSet()->setAttribute(blendFunc,osg::StateAttribute::ON);osg::Vec2Array* texcoords = new osg::Vec2Array;for (unsigned i = 0; i < sizeof(textureVertices); ++i){texcoords->push_back(osg::Vec2(textureVertices[i][0], textureVertices[i][1]));}quadGeometry->setTexCoordArray(0,texcoords);osg::Vec3Array *quadNormalArray = new osg::Vec3Array;for (unsigned i = 0; i < sizeof(normalVertics); ++i){quadNormalArray->push_back(osg::Vec3(normalVertics[i][0], normalVertics[i][1], normalVertics[i][2]));}quadGeometry->setNormalArray(quadNormalArray, osg::Array::BIND_PER_PRIMITIVE_SET);int first = 0;for (unsigned i = 0; i < 6; ++i){osg::DrawArrays *vertexIndices = new osg::DrawArrays(osg::PrimitiveSet::QUADS, first, 4);first += 4;quadGeometry->addPrimitiveSet(vertexIndices);}osg::Image *textureImage = osgDB::readImageFile("Data/Glass.bmp");osg::Texture2D *texture2D = new osg::Texture2D;texture2D->setImage(textureImage);texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::NEAREST);texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::NEAREST);osg::Geode *quadGeode = new osg::Geode;quadGeode->setName("quadGeode");quadGeode->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);quadGeode->addDrawable(quadGeometry);quadYRotMT->addChild(quadGeode);quadXRotMT->addChild(quadYRotMT);quadMT->addChild(quadXRotMT);root->addChild(quadMT);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();}