用OpenSceneGraph实现的NeHe OpenGL教程 - 第十九课
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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。
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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 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();
}