osgEarth示例分析——osgearth_tracks

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 
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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<float>     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image
    ImageUtils::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 = 500
    for( unsigned i=0; i
    {
		// prng.next()：a double in the range [0..1]
        double lon0 = -180.0 + prng.next() * 360.0;
        double lat0 = -80.0 + prng.next() * 160.0;
 
        GeoPoint pos(geoSRS, lon0, lat0);
 
        TrackNode* track = new TrackNode(pos, image.get(), schema);
 
        track->setFieldValue( 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 priority
        track->setPriority( float(i) );
 
        parent->addChild( track );
 
        // add a simulator for this guy
        double 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box
    VBox* 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 options
    struct ChangeFloatOption : public ControlEventHandler {
        optional<float>& _param;
        LabelControl* _label;
        ChangeFloatOption( optional<float>& 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_duration
    speedSlider->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();
}