osgearth-osgEarthUtil-MeasureTool handle代码解析

bool MeasureToolHandler::handle( const osgGA::GUIEventAdapter&
ea, osgGA::GUIActionAdapter& aa )

{   
    if (
ea.getHandled() )
    {
        returnfalse;
    }
 
 
    osgViewer::View* view = static_cast<osgViewer::View*>(aa.asView());
 
    //左键一直按下，_mouseDown区分开鼠标左键是否长按
    if (ea.getEventType()
== osgGA::GUIEventAdapter::PUSH && ea.getButton() == _mouseButton)
    {       
        _mouseDown = true;
        _mouseDownX = ea.getX();
        _mouseDownY = ea.getY();
    }
    //左键释放
    elseif (ea.getEventType()
== osgGA::GUIEventAdapter::RELEASE && ea.getButton() == _mouseButton)
    {       
        float eps
= 1.0f;
        _mouseDown = false;
        //判定鼠标左键按下并释放时，屏幕位置是否相同
        if (osg::equivalent(ea.getX(),
_mouseDownX) && osg::equivalent(ea.getY(), _mouseDownY))
        {
            //相同——单击情况如下
            //获取鼠标点击位置的经纬度
            double lon,
lat;
            if (getLocationAt(view,
ea.getX(), ea.getY(), lon, lat))
            {
                if (!_gotFirstLocation)//获取第一个点击点
                {
                    _finished = false;//取点结束状态为假
                    clear(); //清除所画路径                  
                    _gotFirstLocation = true;//表示已经获得第一个点
                    _feature->getGeometry()->push_back( osg::Vec3d(
lon, lat, 0 ) );//压入矢量点
                }
                else//第一个点已经获取完毕
                {
                    if (_lastPointTemporary)//如果是暂存的最后一个点
                    {
                        //将此点压入矢量点
                        _feature->getGeometry()->back() =
osg::Vec3d( lon, lat, 0 );
                        //暂存的最后一个点状态为false
                        _lastPointTemporary = false;
                    }
                    else//如果是不是暂存的最后一个点
                    {                    
                        _feature->getGeometry()->push_back(
osg::Vec3d( lon, lat, 0 ) );
                    }
                    //初始化featureNode
                    _featureNode->init();
 
                    //_gotFirstLocation
= false;
                    //_finished
= true;
                    //如果绘制结束或者画的是不是多条线段
                    if (_finished
|| !_isPath) {
                        _gotFirstLocation = false;//获取第一点为假
                    }
 
#ifdef SHOW_EXTENT
                    const GeoExtent
ex( _feature->getSRS(), _feature->getGeometry()->getBounds() );
                    //OE_INFO
<< "extent = " << ex.toString() << std::endl;
                    Geometry* eg = _extentFeature->getGeometry();
                    osg::Vec3d fc = ex.getCentroid();
                    eg->clear();
                    eg->push_back( ex.west(), ex.south()
);
                    if (
ex.width() >= 180.0 )
                        eg->push_back( fc.x(), ex.south()
);
                    eg->push_back( ex.east(), ex.south()
);
                    eg->push_back( ex.east(), ex.north()
);
                    if (
ex.width() >= 180.0 )
                        eg->push_back( fc.x(), ex.north()
);
                    eg->push_back( ex.west(), ex.north()
);
                    _extentFeatureNode->init();
#endif
 
                    fireDistanceChanged();
                    //触发重绘事件
                    aa.requestRedraw();
                }
            }
        }
    } 
    elseif (ea.getEventType()
== osgGA::GUIEventAdapter::DOUBLECLICK) {       
        if (_gotFirstLocation)//如果得到第一个点为真
        {
            //_gotFirstLocation
= false;
            _finished = true;    //结束绘制
            aa.requestRedraw(); //重绘
            returntrue;
        }
    }
    elseif (ea.getEventType()
== osgGA::GUIEventAdapter::MOVE)
    {
        if (_gotFirstLocation)//如果得到第一个点为真
        {
            double lon,
lat;
            if (getLocationAt(view,
ea.getX(), ea.getY(), lon, lat))
            {
                //如果最后一点暂存点为假
                if (!_lastPointTemporary)
                {
                    _feature->getGeometry()->push_back( osg::Vec3d(
lon, lat, 0 ) );                 
                    _lastPointTemporary = true;
                }                       
                else
                {
                    _feature->getGeometry()->back() = osg::Vec3d(
lon, lat, 0 );
                }
                _featureNode->init();
                fireDistanceChanged();
                aa.requestRedraw();
            }
        }
    }   
    returnfalse;
}
//获取屏幕所在点的世界坐标系坐标
bool MeasureToolHandler::getLocationAt(osgViewer::View*
view, double x, double y, double &lon, double &lat)
{
    osgUtil::LineSegmentIntersector::Intersections results;           
    if (
getMapNode() &&  view->computeIntersections( x, y, results, _intersectionMask ) )
    {
        //
find the first hit under the mouse:
        osgUtil::LineSegmentIntersector::Intersection first
= *(results.begin());
        osg::Vec3d point = first.getWorldIntersectPoint();
 
        double lat_rad,
lon_rad, height;      
        getMapNode()->getMap()->getProfile()->getSRS()->getEllipsoid()->convertXYZToLatLongHeight(
            point.x(), point.y(), point.z(), lat_rad, lon_rad,
height );
 
        lat = osg::RadiansToDegrees( lat_rad );
        lon = osg::RadiansToDegrees( lon_rad );
        returntrue;
    }
    returnfalse;
}