简介

这节课我们将讨论如何在OSG中使用键盘和灯光。我们将会学习指定三种纹理过滤方式，学习如何使用键盘来移动场景中的立方体。

在osg中通过osgGA库来实现与用户的交互，在用户端，通常使用GUIEventAdapter类作为系统交互事件和OSG交互事件的适配接口。

实现

首先定义一个类用来查找场景中我们需要的节点，这个类会遍历场景子节点，返回第一个查找到与输入名称相同的节点。

[cpp]  view plain  copy   //   //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;   };   为了实现用户设备与场景的交互，我们定义继承自osgGA::GUIEventHandler的类

[cpp]  view plain  copy   class ManipulatorSceneHandler : public osgGA::GUIEventHandler   {   public:       ManipulatorSceneHandler()       {       }          virtual bool handle(const osgGA::GUIEventAdapter& ea, osgGA::GUIActionAdapter& aa);   };   主要需要交互的代码在重载的handle函数中完成

使用PageDown和PageUp可以对场景进行Zoom in 和Zoom out的操作，通过修改平移矩阵来完成

[cpp]  view plain  copy   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));   }   对X轴和Y轴的旋转，同样可以修改旋转矩阵参数完成

[cpp]  view plain  copy   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);   }   osg中默认开启了0号灯光LIGHT0， 同时osg和opengl一样也开启了环境光LightModel，使得场景中存在微弱的环境光（默认为(0.2, 0.2, 0.2, 1.0)）

[cpp]  view plain  copy   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);   }   上述代码设置了环境光为0，同时我们可以设置osg中的默认开启的LIGHT0(在osg::View类中进行设置)，也可以自己声明一个灯光，灯光的设置方式如下：

通过一个LightSource来关联Light，并将LightSource添加到场景之中。

[cpp]  view plain  copy   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);    在点击L键时，关闭和打开光照计算

[cpp]  view plain  copy   if (ea.getKey()== osgGA::GUIEventAdapter::KEY_L)   {       static int i = 0;       if (i % 2 == 0) {           root->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF);       } else {           root->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::ON);       }       ++i;   }   点击F键时，通过修改节点纹理状态参数完成纹理的Filter方式

[cpp]  view plain  copy   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;   }   最后将我们定义的GUIEventHandler添加到Viewer之中，之后就可以实现场景与外设的交互

[cpp]  view plain  copy   this->addEventHandler(new ManipulatorSceneHandler());   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 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/NodeVisitor>   #include <osg/Texture2D>      #include <osgGA/GUIEventAdapter>      #include <osg/Light>   #include <osg/LightModel>   #include <osg/LightSource>      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;   };      //   //RotateCallback      class 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::OFF);                       } else {                           root->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::ON);                       }                       ++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, 1.0) );           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));              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::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/Crate.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();   }