osg::ref_ptr<osgViewer::Viewer> viewer = new osgViewer::Viewer();
osg::ref_ptr<osg::Group> root = new osg::Group();
osg::ref_ptr<osg::Node> node = osgDB::readNodeFile("skydome.osg");
osg::ref_ptr<osg::ClearNode> clearNode = new osg::ClearNode;
clearNode->setRequiresClear(false); // we've got base and sky to do it.
clearNode->addChild(node.get());
root->addChild(clearNode.get());