前言

osgearth_tracks示例，演示了所有图标沿着路径进行移动(路径是不可见的)。

执行效果

执行命令：osgearth_tracksd.exe earth_image\world.earth

右下角的控制面板功能：

【注】最后两个值，有时候观察也不是太明显。

代码分析

此示例中，涉及到一些新的类和方法。下面简单进行分析。

1、控制面板功能的重要类

osgEarth::ScreenSpaceLayoutOptions 通过选项控制annotation清除的引擎类。比如上面表格中说的：scale、alpha、activate、deactivate等内容的控制。

osgEarth::ScreenSpaceLayout::setOptions ( ScreenSpaceLayout::getOptions() ) 控制activate、 deactivate、 enable(是否开启)等内容。

以上两个类是同时使用的。

2、坐标系

在此显示状态时，坐标系并非是我们熟知的经纬度，而是 osgEarth::Util::s_format(MGRSFormatter::PRECISION_10000M)

3、轨迹模拟器

通过osg的方式，实现的。struct TrackSim : public osg::Referenced，重写 update() 方法。struct TrackSimUpdate : public osg::Operation，重写 operator() 方法。

4、绘制标签和图标的方式

typedef std::map TrackNodeFieldSchema schema;

schema[FIELD_NAME] = TrackNodeField(TextSymbol* nameSymbol, false);// 通过键值对构造

osgEarth::Annotation::TrackNode * track = new TrackNode(pos, image.get(), schema);

osgEarth::Annotation::TrackNodeField 

5、控制面板的ui界面，本节仅有的新内容，是通过仅设置一个方法，就能为多个滑块添加事件。

6、

    // attach the simulator to the viewer. 将仿真器和视景器关联起来
    viewer.addUpdateOperation( new TrackSimUpdate(trackSims) );
    viewer.setRunFrameScheme( viewer.CONTINUOUS );

完整代码

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include #include 
#include 
#include using namespace osgEarth;
using namespace osgEarth::Util;
using namespace osgEarth::Util::Controls;
using namespace osgEarth::Annotation;
using namespace osgEarth::Symbology;#define LC "[osgearth_tracks] "/*** Demonstrates use of the TrackNode to display entity track symbols.*/// field names for the track labelsL
#define FIELD_NAME     "name"
#define FIELD_POSITION "position"
#define FIELD_NUMBER   "number"// icon to use, and size in pixels
#define ICON_URL       "m2525_air.png"
#define ICON_SIZE      40// format coordinates as MGRS 坐标系格式MGRS
static MGRSFormatter s_format(MGRSFormatter::PRECISION_10000M);// globals for this demo
bool                g_showCoords        = true;
optional     g_duration          = 60.0;
unsigned            g_numTracks         = 500;
// 用于控制 清除引擎(图标和其他内容变小消失) 的选项。
ScreenSpaceLayoutOptions g_dcOptions;/** Prints an error message */
int
usage( const std::string& message )
{OE_WARN << LC << message << std::endl;return -1;
}/** A little track simulator that goes a simple great circle interpolation */
// 一个小小的轨迹模拟器，可以进行简单的大圆插值。
struct TrackSim : public osg::Referenced
{TrackNode* _track;GeoPoint _start, _end;void update( double t ){osg::Vec3d pos;GeoPoint geo = _start.interpolate(_end, t);geo.alt() = 10000.0; // 高度默认// update the position label._track->setPosition(geo);if ( g_showCoords )// 此参数通过checkbox控制是否需要显示{_track->setFieldValue( FIELD_POSITION, s_format(geo) );// s_format 转化坐标格式}else_track->setFieldValue( FIELD_POSITION, "" );}
};
typedef std::list< osg::ref_ptr > TrackSims;/** Update operation that runs the simulators. */
// 运行的模拟器的更新操作
struct TrackSimUpdate : public osg::Operation
{TrackSimUpdate(TrackSims& sims) : osg::Operation( "tasksim", true ), _sims(sims) { }void operator()( osg::Object* obj ) {osg::View* view = dynamic_cast(obj);double t = fmod(view->getFrameStamp()->getSimulationTime(), (double)g_duration.get()) / (double)g_duration.get();for( TrackSims::iterator i = _sims.begin(); i != _sims.end(); ++i )i->get()->update( t );// 更新每一个TrackSim}TrackSims& _sims;
};/*** Creates a field schema that we'll later use as a labeling template for* TrackNode instances.*/
// 创建一个字段模式，稍后将用作TrackNode实例的标签模板。
// typedef std::map TrackNodeFieldSchema;
// TrackNodeField：定义与TrackNode关联的标签字段。TrackNode可以有零个或多个“字段”，每个字段都是与节点图标一起呈现的文本标签。
void
createFieldSchema( TrackNodeFieldSchema& schema )
{const float R = 2.0f;// 三个字段，分别显示名称、坐标、当前编号，分别位于图标的上、下、左侧。// 关于位置的设定，->pixelOffset()与->alignment() 的属性设置，需要放在一起看，才能更明白。// draw the track name above the icon:TextSymbol* nameSymbol = new TextSymbol();nameSymbol->pixelOffset()->set( 0, R+ICON_SIZE/2 );// 文本偏移nameSymbol->alignment() = TextSymbol::ALIGN_CENTER_BOTTOM;// 文本位置nameSymbol->halo()->color() = Color::Black;nameSymbol->size() = nameSymbol->size()->eval() + 2.0f;schema[FIELD_NAME] = TrackNodeField(nameSymbol, false); // false => static label (won't change after set)// draw the track coordinates below the icon:TextSymbol* posSymbol = new TextSymbol();posSymbol->pixelOffset()->set( 0, -R-ICON_SIZE/2 );posSymbol->alignment() = TextSymbol::ALIGN_CENTER_TOP;posSymbol->fill()->color() = Color::Yellow;posSymbol->size() = posSymbol->size()->eval() - 2.0f;schema[FIELD_POSITION] = TrackNodeField(posSymbol, true); // true => may change at runtime，位置改变// draw some other field to the left:TextSymbol* numberSymbol = new TextSymbol();numberSymbol->pixelOffset()->set( -R-ICON_SIZE/2, 0 );numberSymbol->alignment() = TextSymbol::ALIGN_RIGHT_CENTER;schema[FIELD_NUMBER] = TrackNodeField(numberSymbol, false);
}/** Builds a bunch of tracks. */
// 创建一堆轨道
void
createTrackNodes(const SpatialReference* mapSRS, osg::Group* parent, const TrackNodeFieldSchema& schema, TrackSims& sims )
{// load an icon to use:osg::ref_ptr srcImage = osgDB::readRefImageFile( ICON_URL );osg::ref_ptr image;// 输入文件，格式化后，变为输出文件imageImageUtils::resizeImage( srcImage.get(), ICON_SIZE, ICON_SIZE, image );// make some tracks, choosing a random simulation for each.Random prng;// 随机数// 获取地理坐标系const SpatialReference* geoSRS = mapSRS->getGeographicSRS();// g_numTracks = 500for( unsigned i=0; isetFieldValue( FIELD_NAME,     Stringify() << "Track:" << i );track->setFieldValue( FIELD_POSITION, Stringify() << s_format(pos) );// 转化坐标格式track->setFieldValue( FIELD_NUMBER,   Stringify() << (1 + prng.next(9)) );// add a prioritytrack->setPriority( float(i) );parent->addChild( track );// add a simulator for this guydouble lon1 = -180.0 + prng.next() * 360.0;double lat1 = -80.0 + prng.next() * 160.0;TrackSim* sim = new TrackSim();// 创建轨道模拟器sim->_track = track;  sim->_start.set(mapSRS, lon0, lat0, 0.0, ALTMODE_ABSOLUTE);sim->_end.set(mapSRS, lon1, lat1, 0.0, ALTMODE_ABSOLUTE);sims.push_back( sim );}
}/** creates some UI controls for adjusting the decluttering parameters. */
// 创建ui面板
Container*
createControls( osgViewer::View* view )
{//ControlCanvas* canvas = ControlCanvas::getOrCreate(view);// title bar 垂直boxVBox* vbox = new VBox(Control::ALIGN_NONE, Control::ALIGN_BOTTOM, 2, 1 );vbox->setBackColor( Color(Color::Black, 0.5) );// 添加一个label控件vbox->addControl( new LabelControl("osgEarth Tracks Demo", Color::Yellow) );// checkbox that toggles decluttering of tracks// 通过复选框，切换 是否开启 清理功能(也就是当两个图标移动靠近时，会有一个逐渐变小以至于隐藏，避免图标覆盖遮挡)struct ToggleDecluttering : public ControlEventHandler {void onValueChanged( Control* c, bool on ) {ScreenSpaceLayout::setDeclutteringEnabled( on );}};HBox* dcToggle = vbox->addControl( new HBox() );dcToggle->addControl( new CheckBoxControl(true, new ToggleDecluttering()) );dcToggle->addControl( new LabelControl("Declutter") );// checkbox that toggles the coordinate display// 切换是否显示图标下方的坐标信息struct ToggleCoords : public ControlEventHandler {void onValueChanged( Control* c, bool on ) {g_showCoords = on;// 是否显示坐标系}};HBox* coordsToggle = vbox->addControl( new HBox() );coordsToggle->addControl( new CheckBoxControl(true, new ToggleCoords()) );coordsToggle->addControl( new LabelControl("Show locations") );// grid for the slider controls so they look nice// 添加网格，然后在网格中绘制滑块，看起来更美观Grid* grid = vbox->addControl( new Grid() );grid->setHorizFill( true );grid->setChildHorizAlign( Control::ALIGN_LEFT );grid->setChildSpacing( 6 );// 子控件的间距unsigned r=0;// event handler for changing decluttering optionsstruct ChangeFloatOption : public ControlEventHandler {optional& _param;LabelControl* _label;ChangeFloatOption( optional& param, LabelControl* label ) : _param(param), _label(label) { }void onValueChanged( Control* c, float value ) {_param = value;_label->setText( Stringify() << std::fixed << std::setprecision(1) << value );// 修改滑块值，此值会显示在label上ScreenSpaceLayout::setOptions( g_dcOptions );// 通过 g_dcOptions 参数设置引擎}};// 设置循环一圈的时间，时间越小，速度越快grid->setControl( 0, r, new LabelControl("Sim loop duration:") );LabelControl* speedLabel = grid->setControl( 2, r, new LabelControl(Stringify() << std::fixed << std::setprecision(1) << *g_duration) );HSliderControl* speedSlider = grid->setControl( 1, r, new HSliderControl( 600.0, 30.0, *g_duration, new ChangeFloatOption(g_duration, speedLabel) ) );// 控制 g_durationspeedSlider->setHorizFill( true, 200 );// 控制最小值，即两个标签靠近时，有一个标签逐渐变小，以至于变到最小的值grid->setControl( 0, ++r, new LabelControl("Min scale:") );LabelControl* minAnimationScaleLabel = grid->setControl( 2, r, new LabelControl(Stringify() << std::fixed << std::setprecision(1) << *g_dcOptions.minAnimationScale()) );grid->setControl( 1, r, new HSliderControl( 0.0, 1.0, *g_dcOptions.minAnimationScale(), new ChangeFloatOption(g_dcOptions.minAnimationScale(), minAnimationScaleLabel) ) );// 更改透明度grid->setControl( 0, ++r, new LabelControl("Min alpha:") );LabelControl* alphaLabel = grid->setControl( 2, r, new LabelControl(Stringify() << std::fixed << std::setprecision(1) << *g_dcOptions.minAnimationAlpha()) );grid->setControl( 1, r, new HSliderControl( 0.0, 1.0, *g_dcOptions.minAnimationAlpha(), new ChangeFloatOption(g_dcOptions.minAnimationAlpha(), alphaLabel) ) );// 激活时间grid->setControl( 0, ++r, new LabelControl("Activate time (s):") );LabelControl* actLabel = grid->setControl( 2, r, new LabelControl(Stringify() << std::fixed << std::setprecision(1) << *g_dcOptions.inAnimationTime()) );grid->setControl( 1, r, new HSliderControl( 0.0, 2.0, *g_dcOptions.inAnimationTime(), new ChangeFloatOption(g_dcOptions.inAnimationTime(), actLabel) ) );// 停止时间grid->setControl( 0, ++r, new LabelControl("Deactivate time (s):") );LabelControl* deactLabel = grid->setControl( 2, r, new LabelControl(Stringify() << std::fixed << std::setprecision(1) << *g_dcOptions.outAnimationTime()) );grid->setControl( 1, r, new HSliderControl( 0.0, 2.0, *g_dcOptions.outAnimationTime(), new ChangeFloatOption(g_dcOptions.outAnimationTime(), deactLabel) ) );return vbox;
}/*** Main application.* Creates some simulated track data and runs the simulation.*/
int
main(int argc, char** argv)
{osg::ArgumentParser arguments(&argc,argv);// initialize a viewer.osgViewer::Viewer viewer( arguments );viewer.setCameraManipulator( new EarthManipulator );// load a map from an earth file.读取earth文件，并且创建界面控制面板osg::Node* earth = MapNodeHelper().load(arguments, &viewer, createControls(&viewer));MapNode* mapNode = MapNode::findMapNode(earth);if ( !mapNode )return usage("Missing required .earth file" );// count on the cmd line? 从控制台输入个数，默认500个arguments.read("--count", g_numTracks);viewer.setSceneData( earth );// build a track field schema.// 创建一个map列表 ，typedef std::map TrackNodeFieldSchema;TrackNodeFieldSchema schema;// 初始化 schema 对象createFieldSchema( schema );// create some track nodes.创建一些跟踪节点TrackSims trackSims;osg::Group* tracks = new osg::Group();createTrackNodes( mapNode->getMapSRS(), tracks, schema, trackSims );mapNode->addChild( tracks );// Set up the automatic decluttering. setEnabled() activates decluttering for// all drawables under that state set. We are also activating priority-based// sorting, which looks at the AnnotationData::priority field for each drawable.// (By default, objects are sorted by disatnce-to-camera.) Finally, we customize // a couple of the decluttering options to get the animation effects we want.g_dcOptions = ScreenSpaceLayout::getOptions();g_dcOptions.inAnimationTime()  = 1.0f;g_dcOptions.outAnimationTime() = 1.0f;g_dcOptions.sortByPriority()   = true;ScreenSpaceLayout::setOptions( g_dcOptions );// attach the simulator to the viewer. 将仿真器和视景器关联起来viewer.addUpdateOperation( new TrackSimUpdate(trackSims) );viewer.setRunFrameScheme( viewer.CONTINUOUS );viewer.getCamera()->setSmallFeatureCullingPixelSize(-1.0f);viewer.run();
}