osg渲染到纹理的代码,把读入的节点当成纹理渲染到一个正方形上

 osg::Group* group =  new osg::Group;
 osg::Node* node = osgDB::readNodeFile("D:\\cow.osg");

 osg::Camera* camera = new osg::Camera;
 camera->setViewport(0, 0, 256, 256);

 osg::Image* img = new osg::Image;
 img->allocateImage(256, 256, 1, GL_RGBA, GL_FLOAT);
 
 osg::Texture2D* texture2D = new osg::Texture2D;

 texture2D->setTextureSize(256, 256);
 texture2D->setInternalFormat(GL_RGBA);

 //camera->attach(Camera::COLOR_BUFFER, texture2D, 0, 0);
 camera->attach(Camera::COLOR_BUFFER, img, 0, 0);
 texture2D->setImage(0, img);

 const osg::BoundingSphere& bs = node->getBound();//osg::Group = new osg::Group

 float znear = 1.0f*bs.radius();
 float zfar  = 3.0f*bs.radius();

 float proj_top   = 0.25f*znear;
 float proj_right = 0.5f*znear;

 znear *= 0.9f;
 zfar *= 1.1f;

 // set up projection.
 camera->setProjectionMatrixAsFrustum(-proj_right,proj_right,-proj_top,proj_top,znear,zfar);

 // set view //set up projection
 camera->setReferenceFrame(osg::Transform::ABSOLUTE_RF);
 camera->setViewMatrixAsLookAt(bs.center()-osg::Vec3(0.0f,2.0f,0.0f)*bs.radius(),bs.center(),osg::Vec3(0.0f,0.0f,1.0f));

 camera->setRenderOrder(osg::Camera::PRE_RENDER);
 camera->setRenderTargetImplementation(Camera::FRAME_BUFFER_OBJECT);

 camera->addChild(node);

 group->addChild(camera);

 osg::Geometry* geometry = new osg::Geometry;
 osg::Vec3Array* vertex = new osg::Vec3Array;
 osg::Vec2Array* coord = new osg::Vec2Array;

 vertex->push_back(osg::Vec3(0.0, 0.0, 0.0));
 vertex->push_back(osg::Vec3(10.0, 0.0, 0.0));
 vertex->push_back(osg::Vec3(10.0, 10.0, 0.0));
 vertex->push_back(osg::Vec3(0.0, 10.0, 0.0));

 coord->push_back(osg::Vec2(0.0, 0.0));
 coord->push_back(osg::Vec2(1.0, 0.0));
 coord->push_back(osg::Vec2(1.0, 1.0));
 coord->push_back(osg::Vec2(0.0, 1.0));

 geometry->setTexCoordArray(0,coord);

 geometry->setVertexArray(vertex);
 geometry->addPrimitiveSet(new osg::DrawArrays(osg::DrawArrays::QUADS, 0, vertex->size() ));
  

 osg::Geode* geode = new osg::Geode;
    geode->addDrawable(geometry);

 osg::StateSet* statsset = new osg::StateSet;
 statsset->setTextureAttributeAndModes(0, texture2D,osg::StateAttribute::ON);

    geometry->setStateSet(statsset);

 group->addChild(geode);

 osgViewer::Viewer viewer;
 viewer.setSceneData(group);
 return viewer.run();