osgEarth示例分析——osgearth_pick

前言

osgearth_pick示例，展示了鼠标移动(或者鼠标单击)时，触及到的矢量特征、绘制的线、遮盖图等内容，会将这些内容的信息打印输出到屏幕上。

执行命令

// 三维地图或者二维地图都可。

// 三维图
osgearth_pickd.exe earth_image\china-simple.earth

// 二维图
osgearth_pickd.exe earth_image\world_projected.earth

效果

鼠标移动到某条线上(线条会变色)，获取到特征边界线的信息，显示在左上角。左下角显示矢量图。

鼠标移动到遮盖图上（或者线条上，线条会变色），获取遮盖图信息，现实在左上角下。左下角显示图元信息。

 

代码分析

本节示例，代码逻辑比前几篇更难理解一些。

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include 

#include 
#include 
#include 

#define LC "[rttpicker] "

using namespace osgEarth;
using namespace osgEarth::Util;
using namespace osgEarth::Features;
using namespace osgEarth::Annotation;

namespace ui = osgEarth::Util::Controls;

//-----------------------------------------------------------------------

//! Application-wide data.
struct App
{
    App(osg::ArgumentParser& args) : viewer(args), mainView(NULL), rttView(NULL), mapNode(NULL), picker(NULL) { }

	// 多视景器，且通过args初始化viewer
    osgViewer::CompositeViewer viewer;
    osgViewer::View* mainView;// 主视景器
    osgViewer::View* rttView; // rtt视景器
    osgEarth::MapNode* mapNode;
    osgEarth::Util::RTTPicker* picker;// rtt拾取类

    ui::LabelControl* fidLabel;
    ui::LabelControl* nameLabel;
    osg::Uniform*     highlightUniform;// 高亮的变量
};


//! Callback that you install on the RTTPicker.
// 安装RTTPicker后，提供RTTPicker的回调方法
struct MyPickCallback : public RTTPicker::Callback
{
    App& _app;
    MyPickCallback(App& app) : _app(app) { }

    void onHit(ObjectID id)
    {
        // First see whether it's a feature:
        FeatureIndex* index = Registry::objectIndex()->get(id).get();
        Feature* feature = index ? index->getFeature( id ) : 0L;

		// 有feature标签，则拾取feature标签
        if ( feature )
        {
            _app.fidLabel->setText( Stringify() << "Feature ID = " << feature->getFID() << " (oid = " << id << ")" );
            _app.nameLabel->setText( Stringify() << "Name = " << feature->getString("name") );
        }

        else // 存在annotation标注，则拾取annotation标注
        {
            // Check whether it's an annotation:
            AnnotationNode* anno = Registry::objectIndex()->get(id).get();
            if ( anno )
            {
                _app.fidLabel->setText( Stringify() << "ObjectID = " << id );
                _app.nameLabel->setName( Stringify() << "Name = " << anno->getName() );
            }

            // None of the above.. clear. 什么也没有获取到
            else
            {
                _app.fidLabel->setText( Stringify() << "unknown oid = " << id );
                _app.nameLabel->setText( " " );
            }
        }

        _app.highlightUniform->set( id );// 将对象id设置给高亮变量
    }

	// 取消拾取时，回复标签显示
    void onMiss()
    {
        _app.fidLabel->setText( "No pick." );
        _app.nameLabel->setText( " " );
        _app.highlightUniform->set( 0u );
    }

    // pick whenever the mouse moves.
	// 当鼠标移动时，获取。也可以改为鼠标点击时获取
    bool accept(const osgGA::GUIEventAdapter& ea, const osgGA::GUIActionAdapter& aa)
    {
        // return ea.getEventType() == ea.MOVE;// 移动时获取，移动到空白区域，则取消选中和高亮。
		return ea.getEventType() == ea.RELEASE;// 点击时获取，再点击其他地方，则取消选中和高亮。
    }
};

//-----------------------------------------------------------------------

// Shaders that will highlight the currently "picked" feature.
// 顶点着色器和片段着色器
const char* highlightVert =
    "#version " GLSL_VERSION_STR "\n"
    "uniform uint objectid_to_highlight; \n"
    "uint oe_index_objectid;      // Stage global containing object id \n"
    "flat out int selected; \n"
    "void checkForHighlight(inout vec4 vertex) \n"
    "{ \n"
    "    selected = (objectid_to_highlight > 1u && objectid_to_highlight == oe_index_objectid) ? 1 : 0; \n"
    "} \n";

const char* highlightFrag =
    "#version " GLSL_VERSION_STR "\n"
    "flat in int selected; \n"
    "void highlightFragment(inout vec4 color) \n"
    "{ \n"
    "    if ( selected == 1 ) \n"
    "        color.rgb = mix(color.rgb, clamp(vec3(0.5,2.0,2.0)*(1.0-color.rgb), 0.0, 1.0), 0.5); \n"
    "} \n";

// 安装高亮器到app
void installHighlighter(App& app)
{
    osg::StateSet* stateSet = app.mapNode->getOrCreateStateSet();
	// 索引geoemtry时要使用的顶点属性绑定位置。
    int attrLocation = Registry::objectIndex()->getObjectIDAttribLocation();

    // This shader program will highlight the selected object.
	// 着色器程序会使选中的object高亮
    VirtualProgram* vp = VirtualProgram::getOrCreate(stateSet);
    vp->setFunction( "checkForHighlight",  highlightVert, ShaderComp::LOCATION_VERTEX_CLIP );
    vp->setFunction( "highlightFragment",  highlightFrag, ShaderComp::LOCATION_FRAGMENT_COLORING );

    // Since we're accessing object IDs, we need to load the indexing shader as well:
	// 由于我们正在访问对象ID，因此还需要加载索引着色器：
    Registry::objectIndex()->loadShaders( vp );

    // A uniform that will tell the shader which object to highlight:
	// 通过uniform变量，告诉着色器哪个对象要被高亮
    app.highlightUniform = new osg::Uniform("objectid_to_highlight", 0u);
    stateSet->addUniform(app.highlightUniform );
}

//------------------------------------------------------------------------

// Configures a window that lets you see what the RTT camera sees.
// 配置一个窗口，使您可以看到RTT相机所看到的内容。
void
setupRTTView(osgViewer::View* view, osg::Texture* rttTex)
{
    view->setCameraManipulator(0L);
    view->getCamera()->setName( "osgearth_pick RTT view" );
    view->getCamera()->setViewport(0,0,256,256);
    view->getCamera()->setClearColor(osg::Vec4(1,1,1,1));
    view->getCamera()->setProjectionMatrixAsOrtho2D(-.5,.5,-.5,.5);// 二维正投影
    view->getCamera()->setViewMatrixAsLookAt(osg::Vec3d(0,-1,0), osg::Vec3d(0,0,0), osg::Vec3d(0,0,1));
    view->getCamera()->setProjectionResizePolicy(osg::Camera::FIXED);// 固定

	// v 和 t，都是通过绘制2个三角形拼接为正方形
    osg::Vec3Array* v = new osg::Vec3Array(6);
    (*v)[0].set(-.5,0,-.5); (*v)[1].set(.5,0,-.5); (*v)[2].set(.5,0,.5); (*v)[3].set((*v)[2]); (*v)[4].set(-.5,0,.5);(*v)[5].set((*v)[0]);

    osg::Vec2Array* t = new osg::Vec2Array(6);
    (*t)[0].set(0,0); (*t)[1].set(1,0); (*t)[2].set(1,1); (*t)[3].set((*t)[2]); (*t)[4].set(0,1); (*t)[5].set((*t)[0]);

    osg::Geometry* g = new osg::Geometry();
    g->setUseVertexBufferObjects(true);
    g->setUseDisplayList(false);
    g->setVertexArray( v );		// 几何顶点坐标
    g->setTexCoordArray( 0, t );// 纹理坐标
    g->addPrimitiveSet( new osg::DrawArrays(GL_TRIANGLES, 0, 6) );// 通过绘制三角形方式绘制

    osg::Geode* geode = new osg::Geode();
    geode->addDrawable( g );

    osg::StateSet* stateSet = geode->getOrCreateStateSet();
    stateSet->setDataVariance(osg::Object::DYNAMIC);// 动态的

    stateSet->setTextureAttributeAndModes(0, rttTex, 1);
    rttTex->setUnRefImageDataAfterApply( false );
    rttTex->setResizeNonPowerOfTwoHint(false);

    GLUtils::setLighting(stateSet, 0);
    stateSet->setMode(GL_CULL_FACE, 0);
    stateSet->setAttributeAndModes(new osg::BlendFunc(GL_ONE, GL_ZERO), 1);
    
    const char* fs =
    "#version " GLSL_VERSION_STR "\n"
    "void swap(inout vec4 c) { c.rgba = c==vec4(0)? vec4(1) : vec4(vec3((c.r+c.g+c.b+c.a)/4.0),1); }\n";
    osgEarth::Registry::shaderGenerator().run(geode);
    VirtualProgram::getOrCreate(geode->getOrCreateStateSet())->setFunction("swap", fs, ShaderComp::LOCATION_FRAGMENT_COLORING);

    view->setSceneData( geode );
}

void startPicker(App& app)
{
    // Note! Must stop and restart threading when removing the picker
    // because it changes the OSG View/Slave configuration.
	// 当移动拾取器时，必须停止并重置线程。
    app.viewer.stopThreading();

	// 创建rtt拾取器
    app.picker = new RTTPicker();
    app.mainView->addEventHandler(app.picker);

    // add the graph that will be picked.
	// 添加将要被拾取的mapNode
    app.picker->addChild(app.mapNode);

    // install a callback that controls the picker and listens for hits.
	// 安装回调方法，它控制拾取器并侦听命中。
    app.picker->setDefaultCallback(new MyPickCallback(app));

    // Make a view that lets us see what the picker sees.
	// 创建视景器，让我们看到拾取器看到了什么。
    if (app.rttView == NULL)
    {
        app.rttView = new osgViewer::View();
        app.rttView->getCamera()->setGraphicsContext(app.mainView->getCamera()->getGraphicsContext());
        app.rttView->getCamera()->setSmallFeatureCullingPixelSize(-1.0f);
        app.viewer.addView(app.rttView);  // 子视景器加入到主视景器中  
    }
    setupRTTView(app.rttView, app.picker->getOrCreateTexture(app.mainView));
    app.rttView->getCamera()->setNodeMask(~0);

    app.viewer.startThreading();// 开启主视景器线程
}

// 停止拾取
void stopPicker(App& app)
{
    // Note! Must stop and restart threading when removing the picker
    // because it changes the OSG View/Slave configuration.
    app.viewer.stopThreading();

    //app.viewer.removeView(app.rttView);
    app.rttView->getCamera()->setNodeMask(0);
    app.mainView->removeEventHandler(app.picker);
    app.picker = 0L;// 停止拾取的状态

    app.viewer.startThreading();
}

struct TogglePicker : public ui::ControlEventHandler
{
    App& _app;
    TogglePicker(App& app) : _app(app) { }
	// 点击拾取时，需要判断是否为拾取状态。处于停止状态，则开启；反之，则停止。
    void onClick(Control* button)
    {
        if (_app.picker == 0L)// 当前处于停止拾取的状态
            startPicker(_app);
        else
            stopPicker(_app);
    }
};

//-----------------------------------------------------------------------

int
usage(const char* name)
{
    OE_NOTICE 
        << "\nUsage: " << name << " file.earth" << std::endl
        << MapNodeHelper().usage() << std::endl;
    return 0;
}

int
main(int argc, char** argv)
{
    osg::ArgumentParser arguments(&argc,argv);
    if ( arguments.read("--help") )
        return usage(argv[0]);

    App app(arguments);

	// 创建主视景器
    app.mainView = new osgViewer::View();
    app.mainView->setUpViewInWindow(30, 30, 1024, 1024, 0);
    app.mainView->getCamera()->setSmallFeatureCullingPixelSize(-1.0f);
    
    app.viewer.addView(app.mainView);

    app.mainView->getDatabasePager()->setUnrefImageDataAfterApplyPolicy( false, false );
    app.mainView->setCameraManipulator( new EarthManipulator() );    

    // Made some UI components: 制作一些ui控件
    ui::VBox* uiContainer = new ui::VBox();
    uiContainer->setAlign( ui::Control::ALIGN_LEFT, ui::Control::ALIGN_TOP );
    uiContainer->setAbsorbEvents( true );
    uiContainer->setBackColor(0,0,0,0.8);

    uiContainer->addControl( new ui::LabelControl("RTT Picker Test", osg::Vec4(1,1,0,1)) );
    uiContainer->addControl( new ui::ButtonControl("Toggle picker", new TogglePicker(app)) );// 控制是否允许拾取
    app.fidLabel = new ui::LabelControl("---");
    uiContainer->addControl( app.fidLabel );
    app.nameLabel = uiContainer->addControl( new ui::LabelControl( "---" ) );

    // Load up the earth file. 加载earth文件
    osg::Node* node = MapNodeHelper().load( arguments, &app.viewer, uiContainer );
    if ( node )
    {
        app.mainView->setSceneData( node );

        app.mapNode = MapNode::get(node);

        // start with a picker running 开始拾取
        startPicker(app);

        // Highlight features as we pick'em.
        installHighlighter(app); // 高亮

        app.mainView->getCamera()->setName( "Main view" );

        return app.viewer.run();
    }
    else
    {
        return usage(argv[0]);
    }
}