add: if(scene == NullFC) return 1;
context: int main(int argc, char **argv){    osgInit(argc,argv);            int winid = setupGLUT(&argc, argv);    GLUTWindowPtr gwin= GLUTWindow::create();    gwin->setId(winid);    gwin->init();    scene =createScenegraph();    mgr = new SimpleSceneManager;    mgr->setWindow(gwin );    mgr->setRoot  (scene);    mgr->showAll();        glutMainLoop();    return 0;}