osgGA::UFOManipulator

osgGA::UFOManipulator是OpenSceneGraph中的一个相机操作器，可以通过鼠标和键盘控制相机的移动、缩放和旋转。其中，UFO代表Unidentified Flying Object，意为不明飞行物，因为这个操作器可以让相机在场景中自由飞行，并且可以观察到任意视角。

UFOManipulator的使用方法如下：

1. 创建UFOManipulator对象并设置到Viewer中：

osg::ref_ptr<osgGA::UFOManipulator> ufoManipulator = new osgGA::UFOManipulator();
viewer->setCameraManipulator(ufoManipulator.get());

2. 设置UFOManipulator的参数，例如相机的初始位置、旋转速度、缩放速度等：

ufoManipulator->setHomePosition(osg::Vec3(0, 0, 100), osg::Vec3(), osg::Vec3(0, 1, 0));
ufoManipulator->setRotationMode(osgGA::UFOManipulator::TRACKBALL);
ufoManipulator->setWheelZoomFactor(0.1f);

3. 监听鼠标和键盘事件，根据事件类型调用UFOManipulator的对应方法：

// 监听鼠标事件
viewer->addEventHandler(new osgGA::StateSetManipulator(viewer->getCamera()->getOrCreateStateSet()));
viewer->addEventHandler(new osgViewer::StatsHandler);
viewer->addEventHandler(new osgViewer::WindowSizeHandler);
viewer->addEventHandler(new osgViewer::ThreadingHandler);
viewer->addEventHandler(new osgViewer::RecordCameraPathHandler);
viewer->addEventHandler(new osgViewer::LODScaleHandler);
viewer->addEventHandler(ufoManipulator.get());

// 监听键盘事件
osg::ref_ptr<osgGA::KeySwitchMatrixManipulator> keyswitchManipulator = new osgGA::KeySwitchMatrixManipulator;
keyswitchManipulator->addMatrixManipulator('1', "Trackball", new osgGA::TrackballManipulator());
keyswitchManipulator->addMatrixManipulator('2', "Flight", new osgGA::FlightManipulator());
keyswitchManipulator->addMatrixManipulator('3', "Drive", new osgGA::DriveManipulator());
keyswitchManipulator->addMatrixManipulator('4', "Terrain", new osgGA::TerrainManipulator());
keyswitchManipulator->addMatrixManipulator('5', "UFO", ufoManipulator.get());
viewer->setCameraManipulator(keyswitchManipulator.get());

UFOManipulator可以让用户自由控制相机的移动，可以应用于场景漫游、模型浏览等应用场景。