void View::setCameraManipulator(osgGA::CameraManipulator* manipulator, bool resetPosition)
{_cameraManipulator = manipulator;if (_cameraManipulator.valid()){_cameraManipulator->setCoordinateFrameCallback(new ViewerCoordinateFrameCallback(this));if (getSceneData()) _cameraManipulator->setNode(getSceneData());if (resetPosition){osg::ref_ptr<osgGA::GUIEventAdapter> dummyEvent = _eventQueue->createEvent();_cameraManipulator->home(*dummyEvent, *this);}}
}

可以看到这个函数同时设置了home位置，也就是说如果我们自己的漫游器想有一个初始的位置，那么可以重新实现home这个虚函数来达到这样的目的。

void ViewerBase::frame(double simulationTime)
{if (_done) return;// OSG_NOTICE<<std::endl<<"CompositeViewer::frame()"<<std::endl<<std::endl;if (_firstFrame){viewerInit();if (!isRealized()){realize();}_firstFrame = false;}advance(simulationTime);eventTraversal();updateTraversal();renderingTraversals();
}

很显然漫游器的对事件的处理应该是在eventTraversal函数中，漫游器更新的代码应该在updateTraversal中，事实上确实如此：

    for(osgGA::EventQueue::Events::iterator itr = events.begin();itr != events.end();++itr){osgGA::Event* event = itr->get();if (event && _cameraManipulator.valid()){_cameraManipulator->handle( event, 0, _eventVisitor.get());}}

同样在更新完场景中节点的更新回调与遍历之后，在函数的最后处理漫游器的更新：

    if (_cameraManipulator.valid()){setFusionDistance( getCameraManipulator()->getFusionDistanceMode(),getCameraManipulator()->getFusionDistanceValue() );_cameraManipulator->updateCamera(*_camera);}

updateCamera函数的调用如下（默认实现方式 ）

virtual void updateCamera(osg::Camera& camera) { camera.setViewMatrix(getInverseMatrix()); }

直接调用相机的观察矩阵，矩阵从漫游器的getInverseMatrix函数中获取，这是我们编写自己漫游器的关键函数，这个函数在所有漫游器基类CameraManipulator中是一个纯虚函数，需要我们实现，它被调用的位置就是在此处。

• 如何实现自己的漫游器

#include <osgGA/CameraManipulator>//定义操作器
class ZoomManipulator : public osgGA::CameraManipulator
{
public://构造函数传入节点计算包围盒ZoomManipulator(osg::Node *node);~ZoomManipulator();//所有漫游器都必须实现的4个纯虚函数virtual void setByMatrix(const osg::Matrixd& matrix){}virtual void setByInverseMatrix(const osg::Matrixd& matrix){}virtual osg::Matrixd getMatrix() const{return osg::Matrix();}virtual osg::Matrixd getInverseMatrix() const;//获取传入节点，用于使用CameraManipulator中的computeHomePositionvirtual const osg::Node* getNode() const { return _root; }virtual osg::Node* getNode() { return _root;  }virtual bool handle(const osgGA::GUIEventAdapter& ea,osgGA::GUIActionAdapter& us);osg::Vec3   _eye;               //视点位置osg::Vec3   _direction;         //视点方向osg::Vec3   _up;                //向上方向osg::Node*    _root;
};

在实现代码中通过计算鼠标点处的世界坐标，使视点沿着与鼠标点世界坐标的连线移动

#include <osgViewer/Viewer>ZoomManipulator::ZoomManipulator(osg::Node *node)
{_root = node;computeHomePosition();_eye = _homeEye;_direction = _homeCenter - _homeEye;_up = _homeUp;
}ZoomManipulator::~ZoomManipulator()
{}osg::Matrixd ZoomManipulator::getInverseMatrix() const
{osg::Matrix mat;mat.makeLookAt(_eye, _eye + _direction, _up);return mat;
}bool ZoomManipulator::handle(const osgGA::GUIEventAdapter& ea,osgGA::GUIActionAdapter& us)
{switch(ea.getEventType()){case (osgGA::GUIEventAdapter::SCROLL):{osgViewer::Viewer *viewer = dynamic_cast<osgViewer::Viewer*>(&us);osg::Camera *camera = viewer->getCamera();osg::Matrix MVPW = camera->getViewMatrix() * camera->getProjectionMatrix() * camera->getViewport()->computeWindowMatrix();osg::Matrix inverseMVPW = osg::Matrix::inverse(MVPW);osg::Vec3 mouseWorld = osg::Vec3(ea.getX(), ea.getY(), 0) * inverseMVPW;osg::Vec3 direction = mouseWorld - _eye;direction.normalize();          if (ea.getScrollingMotion() == osgGA::GUIEventAdapter::SCROLL_UP){_eye += direction * 20.0;}else if (ea.getScrollingMotion() == osgGA::GUIEventAdapter::SCROLL_DOWN){_eye -= direction * 20.0;}}default:return false;}
}