OpenSceneGraph实现的NeHe OpenGL教程 - 第四十一课

最新推荐文章于 2020-08-31 11:45:25 发布

allenjiao

最新推荐文章于 2020-08-31 11:45:25 发布

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本文介绍如何在OSG中利用雾坐标实现雾效，并提供了一段示例代码。通过设置不同的雾参数，可以达到渐变的视觉效果。

简介

这节课也是在场景中添加雾效的效果，与之类似的是第十六课，所不同的是这节课使用了雾坐标来计算雾效。为了能运行这一课，你的显卡必须支持GL_EXT_fot_coord扩展。

实现

这节课的实现过程比较简单，在OSG中为几何体的顶点封装好了顶点的各项属性，包括顶点坐标、顶点纹理坐标、顶点颜色，当然也包括本课中的雾坐标。

首先我们还是添加顶点的各项数据：

[cpp]view plaincopy 
   
     osg::Geode *geode = new osg::Geode;  
     osg::Geometry *geometry = new osg::Geometry;  
     osg::Vec3Array *vertexArray = new osg::Vec3Array;  
     osg::FloatArray *fogArray = new osg::FloatArray;  
     osg::Vec2Array *textureArray = new osg::Vec2Array;  
         vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,-15.0f));  
         vertexArray->push_back(osg::Vec3(2.5f,-2.5f,-15.0f));  
         vertexArray->push_back(osg::Vec3(2.5f,2.5f,-15.0f));  
         vertexArray->push_back(osg::Vec3(-2.5f,2.5f,-15.0f));  
         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));  
         fogArray->push_back(1.0f);  
         fogArray->push_back(1.0f);  
         fogArray->push_back(1.0f);  
         fogArray->push_back(1.0f);  
         ......  

接着读取纹理：

[cpp]view plaincopy 
   
 osg::Texture2D *texture2D = new osg::Texture2D;  
 texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);  
 texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);  
 texture2D->setImage(osgDB::readImageFile("Data/Wall.bmp"));  
 geometry->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);  

启用雾效特效：

[cpp]view plaincopy 
   
 osg::Fog *fog = new osg::Fog;  
 fog->setMode(osg::Fog::LINEAR);  
 fog->setColor(osg::Vec4(fogColor[0], fogColor[1],fogColor[2],fogColor[3]));  
 fog->setStart(0.0f);  
 fog->setEnd(1.0f);  
 fog->setFogCoordinateSource(osg::Fog::FOG_COORDINATE);  

编译运行程序：

附：本课源码（源码中可能存在错误和不足，仅供参考）

[cpp]view plaincopy 
   
 #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/Fog>  
   
   
 GLfloat fogColor[4] = {0.6f, 0.3f, 0.0f, 1.0f};  
   
 osg::MatrixTransform *g_Trans = NULL;  
   
 class ManipulatorSceneHandler : public osgGA::GUIEventHandler  
 {  
 public:  
     ManipulatorSceneHandler()  
     {  
     }  
   
 public:  
     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;  
   
         switch (ea.getEventType())  
         {  
         case(osgGA::GUIEventAdapter::KEYDOWN):  
             {  
                 if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Up)  
                 {  
                     if (!g_Trans)  
                         return false;  
   
                     osg::Vec3 trans = g_Trans->getMatrix().getTrans();  
                     if(trans.z() < 14.0f)  
                         trans += osg::Vec3(0,0,1);  
   
                     g_Trans->setMatrix(osg::Matrix::translate(trans));  
                 }  
   
                 if (ea.getKey() == osgGA::GUIEventAdapter::KEY_Down)  
                 {  
                     if (!g_Trans)  
                         return false;  
   
                     osg::Vec3 trans = g_Trans->getMatrix().getTrans();  
                     if(trans.z() >-19.0f)  
                         trans -= osg::Vec3(0,0,1);  
   
                     g_Trans->setMatrix(osg::Matrix::translate(trans));  
                 }  
             }  
             break;  
   
         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, 0), osg::Vec3d(0, 0, -1), 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::Node*  buildScene()  
 {  
     osg::Group *root = new osg::Group;  
   
     osg::MatrixTransform *zoomMT = new osg::MatrixTransform;  
     zoomMT->setMatrix(osg::Matrix::translate(0,0,-19.0));  
     g_Trans = zoomMT;  
   
     osg::Geode *geode = new osg::Geode;  
     osg::Geometry *geometry = new osg::Geometry;  
     osg::Vec3Array *vertexArray = new osg::Vec3Array;  
     osg::FloatArray *fogArray = new osg::FloatArray;  
     osg::Vec2Array *textureArray = new osg::Vec2Array;  
   
     vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,-2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(-2.5f,2.5f,-15.0f));  
     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));  
     fogArray->push_back(1.0f);  
     fogArray->push_back(1.0f);  
     fogArray->push_back(1.0f);  
     fogArray->push_back(1.0f);  
   
     vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,-2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,-2.5f,15.0f));  
     vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,15.0f));  
     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));  
     fogArray->push_back(1.0f);  
     fogArray->push_back(1.0f);  
     fogArray->push_back(0.0f);  
     fogArray->push_back(0.0f);  
   
     vertexArray->push_back(osg::Vec3(-2.5f,2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,2.5f,15.0f));  
     vertexArray->push_back(osg::Vec3(-2.5f,2.5f,15.0f));  
     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));  
     fogArray->push_back(1.0f);  
     fogArray->push_back(1.0f);  
     fogArray->push_back(0.0f);  
     fogArray->push_back(0.0f);  
   
     vertexArray->push_back(osg::Vec3(2.5f,-2.5f,15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,2.5f,15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(2.5f,-2.5f,-15.0f));  
     textureArray->push_back(osg::Vec2(0.0f, 0.0f));  
     textureArray->push_back(osg::Vec2(0.0f, 1.0f));  
     textureArray->push_back(osg::Vec2(1.0f, 1.0f));  
     textureArray->push_back(osg::Vec2(1.0f, 0.0f));  
     fogArray->push_back(0.0f);  
     fogArray->push_back(0.0f);  
     fogArray->push_back(1.0f);  
     fogArray->push_back(1.0f);  
   
     vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,15.0f));  
     vertexArray->push_back(osg::Vec3(-2.5f,2.5f,15.0f));  
     vertexArray->push_back(osg::Vec3(-2.5f,2.5f,-15.0f));  
     vertexArray->push_back(osg::Vec3(-2.5f,-2.5f,-15.0f));  
     textureArray->push_back(osg::Vec2(0.0f, 0.0f));  
     textureArray->push_back(osg::Vec2(0.0f, 1.0f));  
     textureArray->push_back(osg::Vec2(1.0f, 1.0f));  
     textureArray->push_back(osg::Vec2(1.0f, 0.0f));  
     fogArray->push_back(0.0f);  
     fogArray->push_back(0.0f);  
     fogArray->push_back(1.0f);  
     fogArray->push_back(1.0f);  
   
     geometry->setVertexArray(vertexArray);  
     geometry->setTexCoordArray(0, textureArray);  
     geometry->setFogCoordArray(fogArray, osg::Array::BIND_PER_VERTEX);  
     geometry->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);  
       
     osg::Texture2D *texture2D = new osg::Texture2D;  
     texture2D->setFilter(osg::Texture::MAG_FILTER, osg::Texture::LINEAR);  
     texture2D->setFilter(osg::Texture::MIN_FILTER, osg::Texture::LINEAR);  
     texture2D->setImage(osgDB::readImageFile("Data/Wall.bmp"));  
     geometry->getOrCreateStateSet()->setTextureAttributeAndModes(0, texture2D);  
   
     osg::Fog *fog = new osg::Fog;  
     fog->setMode(osg::Fog::LINEAR);  
     fog->setColor(osg::Vec4(fogColor[0], fogColor[1],fogColor[2],fogColor[3]));  
     fog->setStart(0.0f);  
     fog->setEnd(1.0f);  
     fog->setFogCoordinateSource(osg::Fog::FOG_COORDINATE);  
       
     geometry->getOrCreateStateSet()->setAttributeAndModes(fog);  
   
     geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::QUADS, 0, vertexArray->size()));  
     geode->addDrawable(geometry);  
   
     zoomMT->addChild(geode);  
     root->addChild(zoomMT);  
   
     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();  
 }  