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。
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：
[cpp] view plain copy 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
[cpp] view plain copy 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：
[cpp] view plain copy 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
[cpp] view plain copy 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
[cpp] view plain copy 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：
[cpp] view plain copy 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)
[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 <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 Manipulator class 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 UpdateCallback class 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]; } } } }; // //ParticleDrawableCallback class 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(); }
