用OpenSceneGraph实现的NeHe OpenGL教程 - 第十九课

• 简介

这节课我们将使用osg实现一个简单的粒子系统。从NeHe的教程中可以看到，制作一个简单的粒子系统并没有想象中的那么困难，不过粒子系统涉及的细节计算还是有些繁琐的。粒子系统主要用来模拟三维场景中的雨雪、爆炸、火焰、喷泉等效果。主要是对大量的可绘制几何体(如简单的三角形、四边形、三角形条带等)进行它们位置、方向、显示时间(生命)的一些设置。

• 实现

首先我们按照NeHe教程中，定义了一个粒子的结构体，代表场景中产生的一个粒子的参数：

struct Particle{bool active;  //是否是激活状态float life;      //存活时间float fade;    //消失的速度float r;        float g;float b;float x;float y;float z;float xi;    float yi;    float zi;float xg;float yg;float zg;};

同样在初始化的时候给所有的粒子(1000个)一些初始值

for (int i=0;  i<MaxParticles; i++){particles[i].active=true;particles[i].life=1.0f;particles[i].fade=float(rand()%100)/1000.0f+0.003f;particles[i].r=colors[int(i*(12.0/MaxParticles))][0];particles[i].g=colors[int(i*(12.0/MaxParticles))][1];particles[i].b=colors[int(i*(12.0/MaxParticles))][2];particles[i].xi=float((rand()%50)-26.0f)*10.0f;particles[i].yi=float((rand()%50)-25.0f)*10.0f;particles[i].zi=float((rand()%50)-25.0f)*10.0f;particles[i].xg=0.0f;particles[i].yg=-0.8f;particles[i].zg=0.0f;}

粒子系统中的每一个粒子实际上就是一个简单的可绘制几何体（Geometry），设置它的各项参数如下：

osg::Geometry *particle = new osg::Geometry();float x=particles[i].x;float y=particles[i].y;float z=particles[i].z+zoom;//设置顶点osg::Vec3Array *vertexArray = new osg::Vec3Array;vertexArray->push_back(osg::Vec3(x+0.5f,y+0.5f,z));vertexArray->push_back(osg::Vec3(x-0.5f,y+0.5f,z));vertexArray->push_back(osg::Vec3(x+0.5f,y-0.5f,z));vertexArray->push_back(osg::Vec3(x-0.5f,y-0.5f,z));//设置纹理坐标osg::Vec2Array *texArray = new osg::Vec2Array;texArray->push_back(osg::Vec2(1,1));texArray->push_back(osg::Vec2(0,1));texArray->push_back(osg::Vec2(1,0));texArray->push_back(osg::Vec2(0,0));//设置颜色osg::Vec4Array *colorArray = new osg::Vec4Array;colorArray->push_back(osg::Vec4(particles[i].r,particles[i].g,particles[i].b,particles[i].life));colorArray->setBinding(osg::Array::BIND_OVERALL);//设置纹理osg::Texture2D *texture = new osg::Texture2D;texture->setImage(osgDB::readImageFile("Data/Particle.bmp"));texture->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);texture->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);particle->setVertexArray(vertexArray);particle->setTexCoordArray(0, texArray);particle->setColorArray(colorArray);particle->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::TRIANGLE_STRIP, 0, 4));particle->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture);osg::BlendFunc *blendFunc = new osg::BlendFunc(GL_SRC_ALPHA, GL_ONE);particle->getOrCreateStateSet()->setAttributeAndModes(blendFunc,osg::StateAttribute::ON);particle->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);particle->getOrCreateStateSet()->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);particle->setUseDisplayList(false);particle->setUpdateCallback(new ParticleDrawableCallback(i));

注意我们需要设置混合的模式和禁用深度测试，这样纹理图片的背景黑色才能被清除掉

在每一帧中需要更新粒子的位置和颜色等参数，我们设置一个Geode的更新回调用来完成对所有粒子参数的更新

class ParticleUpdateCallback : public osg::NodeCallback

另外在绘制粒子的时候需要用到更新的新数据，我们在粒子对象的更新回调中完成它坐标位置、颜色的更新

class ParticleDrawableCallback : public osg::Drawable::UpdateCallback{public:ParticleDrawableCallback(int index) : _index(index){ }

每一个粒子的序号绑定到_index之上

最后在ParticleEventHandler之中完成粒子系统中一些参数的交互，这部分和NeHe教程中是一样的：

class ParticleEventHandler : public osgGA::GUIEventHandler{

代码我只是贴出了一部分，详细的代码参考后面的完整代码部分。

编译运行程序：

附：本课完整代码(代码中可能存在着错误和不足，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 <osg/BlendFunc>#include <osg/PrimitiveSet>//////////////////////////////////////////////////////////////////////////const int MaxParticles = 1000;float slowdown = 2.0f;float xspeed;float yspeed;float zoom = -40.0f;GLuint delay;int col;struct Particle{bool active;  //是否是激活状态float life;      //存活时间float fade;    //消失的速度float r;        float g;float b;float x;float y;float z;float xi;    float yi;    float zi;float xg;float yg;float zg;};Particle particles[MaxParticles];static GLfloat colors[12][3] ={{1.0f,0.5f,0.5f},{1.0f,0.75f,0.5f},{1.0f,1.0f,0.5f},{0.75f,1.0f,0.5f},{0.5f,1.0f,0.5f},{0.5f,1.0f,0.75f},{0.5f,1.0f,1.0f},{0.5f,0.75f,1.0f},{0.5f,0.5f,1.0f},{0.75f,0.5f,1.0f},{1.0f,0.5f,1.0f},{1.0f,0.5f,0.75f}};////////////////////////////////////////////////////////////////////////////Particle Manipulatorclass ParticleEventHandler : public osgGA::GUIEventHandler{public:ParticleEventHandler(){}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_8){for(int i = 0; i < MaxParticles; ++i)if ((particles[i].yg<1.5f)) particles[i].yg+=0.01f;}if (ea.getKey() == osgGA::GUIEventAdapter::KEY_2){for(int i = 0; i < MaxParticles; ++i)if ((particles[i].yg>-1.5f)) particles[i].yg-=0.01f;}if (ea.getKey() == osgGA::GUIEventAdapter::KEY_6){for(int i = 0; i < MaxParticles; ++i)if (particles[i].xg<1.5f) particles[i].xg+=0.01f;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_4){for(int i = 0; i < MaxParticles; ++i)if (particles[i].xg>-1.5f) particles[i].xg-=0.01f;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Tab){for(int i = 0; i < MaxParticles; ++i){particles[i].x=0.0f;particles[i].y=0.0f;particles[i].z=0.0f;particles[i].xi=float((rand()%50)-26.0f)*10.0f;particles[i].yi=float((rand()%50)-25.0f)*10.0f;particles[i].zi=float((rand()%50)-25.0f)*10.0f;}}if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Page_Up){zoom += 0.1;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Page_Down){zoom -= 0.1;}if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Plus){if (slowdown>1.0f) slowdown-=0.01f;}if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Minus){if (slowdown<4.0f) slowdown+=0.01f;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Up){if ((yspeed<200)) yspeed+=1.0f;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Down){if ((yspeed>-200)) yspeed-=1.0f;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Left){if ((xspeed>-200)) xspeed-=1.0f;}if (ea.getKey()== osgGA::GUIEventAdapter::KEY_Right){if ((xspeed<200)) xspeed+=1.0f;}}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, 0.0) );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, 1), osg::Vec3d(0, 0, 0), osg::Vec3d(0, 1, 0));this->setSceneData( scene );addEventHandler(new ParticleEventHandler);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;};////////////////////////////////////////////////////////////////////////////Particle Geode's UpdateCallbackclass ParticleUpdateCallback : public osg::NodeCallback{public:virtual void operator()(osg::Node* node, osg::NodeVisitor* nv){for(int i = 0; i < MaxParticles; ++i){particles[i].x+=particles[i].xi/(slowdown*1000);particles[i].y+=particles[i].yi/(slowdown*1000);particles[i].z+=particles[i].zi/(slowdown*1000);particles[i].xi+=particles[i].xg;particles[i].yi+=particles[i].yg;particles[i].zi+=particles[i].zg;particles[i].life-=particles[i].fade;if (particles[i].life<0.0f){if (col > 11){col = 0;}++col;particles[i].life=1.0f;particles[i].fade=float(rand()%100)/1000.0f+0.003f;particles[i].x=0.0f;particles[i].y=0.0f;particles[i].z=0.0f;particles[i].xi=xspeed+float((rand()%60)-32.0f);particles[i].yi=yspeed+float((rand()%60)-30.0f);particles[i].zi=float((rand()%60)-30.0f);particles[i].r=colors[col][0];particles[i].g=colors[col][1];particles[i].b=colors[col][2];}}}};////////////////////////////////////////////////////////////////////////////ParticleDrawableCallbackclass ParticleDrawableCallback : public osg::Drawable::UpdateCallback{public:ParticleDrawableCallback(int index) : _index(index){ }virtual void update(osg::NodeVisitor*, 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){colorArray->clear();colorArray->push_back(osg::Vec4(particles[_index].r,particles[_index].g,particles[_index].b,particles[_index].life));colorArray->dirty();}osg::Vec3Array *vertexArray = dynamic_cast<osg::Vec3Array*>(geometry->getVertexArray());if (vertexArray){float x=particles[_index].x;float y=particles[_index].y;float z=particles[_index].z+zoom;vertexArray->clear();vertexArray->push_back(osg::Vec3(x+0.5f,y+0.5f,z));vertexArray->push_back(osg::Vec3(x-0.5f,y+0.5f,z));vertexArray->push_back(osg::Vec3(x+0.5f,y-0.5f,z));vertexArray->push_back(osg::Vec3(x-0.5f,y-0.5f,z));vertexArray->dirty();}}int_index;};//////////////////////////////////////////////////////////////////////////////osg::Node*buildScene(){for (int i=0;  i<MaxParticles; i++){particles[i].active=true;particles[i].life=1.0f;particles[i].fade=float(rand()%100)/1000.0f+0.003f;particles[i].r=colors[int(i*(12.0/MaxParticles))][0];particles[i].g=colors[int(i*(12.0/MaxParticles))][1];particles[i].b=colors[int(i*(12.0/MaxParticles))][2];particles[i].xi=float((rand()%50)-26.0f)*10.0f;particles[i].yi=float((rand()%50)-25.0f)*10.0f;particles[i].zi=float((rand()%50)-25.0f)*10.0f;particles[i].xg=0.0f;particles[i].yg=-0.8f;particles[i].zg=0.0f;}osg::Geode *particleGeode = new osg::Geode;for (int i = 0; i < MaxParticles; ++i){osg::Geometry *particle = new osg::Geometry();float x=particles[i].x;float y=particles[i].y;float z=particles[i].z+zoom;//设置顶点osg::Vec3Array *vertexArray = new osg::Vec3Array;vertexArray->push_back(osg::Vec3(x+0.5f,y+0.5f,z));vertexArray->push_back(osg::Vec3(x-0.5f,y+0.5f,z));vertexArray->push_back(osg::Vec3(x+0.5f,y-0.5f,z));vertexArray->push_back(osg::Vec3(x-0.5f,y-0.5f,z));//设置纹理坐标osg::Vec2Array *texArray = new osg::Vec2Array;texArray->push_back(osg::Vec2(1,1));texArray->push_back(osg::Vec2(0,1));texArray->push_back(osg::Vec2(1,0));texArray->push_back(osg::Vec2(0,0));//设置颜色osg::Vec4Array *colorArray = new osg::Vec4Array;colorArray->push_back(osg::Vec4(particles[i].r,particles[i].g,particles[i].b,particles[i].life));colorArray->setBinding(osg::Array::BIND_OVERALL);//设置纹理osg::Texture2D *texture = new osg::Texture2D;texture->setImage(osgDB::readImageFile("Data/Particle.bmp"));texture->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);texture->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);particle->setVertexArray(vertexArray);particle->setTexCoordArray(0, texArray);particle->setColorArray(colorArray);particle->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::TRIANGLE_STRIP, 0, 4));particle->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture);osg::BlendFunc *blendFunc = new osg::BlendFunc(GL_SRC_ALPHA, GL_ONE);particle->getOrCreateStateSet()->setAttributeAndModes(blendFunc,osg::StateAttribute::ON);particle->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);particle->getOrCreateStateSet()->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);particle->setUseDisplayList(false);particle->setUpdateCallback(new ParticleDrawableCallback(i));particleGeode->addDrawable(particle);}particleGeode->addUpdateCallback(new ParticleUpdateCallback);osg::Group *root = new osg::Group;root->addChild(particleGeode);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();}