利用 MSYS2 及osgEarth 构建三维地球模型(2) osgEarth 与 Qt的结合

上一篇中，我们已经使用傻瓜化的 pacman -S 安装了 openSceneGraph 与 osgEarth 。为了在Qt中导入osgEarth 的窗口，需要安装 osgQt 模块。
注意，这个包分32位、64位，同时，也分 release, debug，下载下来还是不小的，需要好几个GB的空间

pacman -S --needed  mingw-w64-i686-osgQt-debug mingw-w64-x86_64-osgQt-debug  mingw-w64-i686-osgQt  mingw-w64-x86_64-osgQt 
pacman -S --needed mingw-w64-i686-osgearth mingw-w64-x86_64-osgearth mingw-w64-i686-osgearth-debug mingw-w64-x86_64-osgearth-debug

安装完毕后，即可启动 qtcreator，或者直接命令行qmake例子了。例子在
https://github.com/openscenegraph/osgQt/blob/master/examples/osgviewerQt/osgviewerQt.cpp
为其准备一个pro文件

QT       += core gui opengl
debug:LIBS+=  -losgViewerd -losgDBd -losgd -lOpenThreadsd -losgGAd -losgQtd
release:LIBS+=  -losgViewer -losgDB -losg -lOpenThreadsd -losgGA -losgQt
TARGET = osgviewerQt
TEMPLATE = app
DEFINES += QT_DEPRECATED_WARNINGS
SOURCES += osgviewerQt.cpp

而后把本地OSM数据源改写到 cpp 中:

#include 
#include 
#include 

#include 
#include 

#include 

#include 

#include 

#include 

class ViewerWidget : public QWidget, public osgViewer::CompositeViewer
{
public:
    ViewerWidget(QWidget* parent = 0, Qt::WindowFlags f = 0, osgViewer::ViewerBase::ThreadingModel threadingModel=osgViewer::CompositeViewer::SingleThreaded) : QWidget(parent, f)
    {
        setThreadingModel(threadingModel);

        // disable the default setting of viewer.done() by pressing Escape.
        setKeyEventSetsDone(0);

        QWidget* widget1 = addViewWidget( createGraphicsWindow(0,0,100,100), osgDB::readRefNodeFile("openstreetmap.earth") );
        QWidget* widget2 = addViewWidget( createGraphicsWindow(0,0,100,100), osgDB::readRefNodeFile("openstreetmap.earth") );
        QWidget* widget3 = addViewWidget( createGraphicsWindow(0,0,100,100), osgDB::readRefNodeFile("openstreetmap.earth") );
        QWidget* widget4 = addViewWidget( createGraphicsWindow(0,0,100,100), osgDB::readRefNodeFile("openstreetmap.earth") );
        QWidget* popupWidget = addViewWidget( createGraphicsWindow(900,100,320,240,"Popup window",true), osgDB::readRefNodeFile("openstreetmap.earth") );
        popupWidget->show();

        QGridLayout* grid = new QGridLayout;
        grid->addWidget( widget1, 0, 0 );
        grid->addWidget( widget2, 0, 1 );
        grid->addWidget( widget3, 1, 0 );
        grid->addWidget( widget4, 1, 1 );
        setLayout( grid );

        connect( &_timer, SIGNAL(timeout()), this, SLOT(update()) );
        _timer.start( 10 );
    }

    QWidget* addViewWidget( osgQt::GraphicsWindowQt* gw, osg::ref_ptr scene )
    {
        osgViewer::View* view = new osgViewer::View;
        addView( view );

        osg::Camera* camera = view->getCamera();
        camera->setGraphicsContext( gw );

        const osg::GraphicsContext::Traits* traits = gw->getTraits();

        camera->setClearColor( osg::Vec4(0.2, 0.2, 0.6, 1.0) );
        camera->setViewport( new osg::Viewport(0, 0, traits->width, traits->height) );
        camera->setProjectionMatrixAsPerspective(30.0f, static_cast<double>(traits->width)/static_cast<double>(traits->height), 1.0f, 10000.0f );

        view->setSceneData( scene );
        view->addEventHandler( new osgViewer::StatsHandler );
        view->setCameraManipulator( new osgGA::MultiTouchTrackballManipulator );
        gw->setTouchEventsEnabled( true );
        return gw->getGLWidget();
    }

    osgQt::GraphicsWindowQt* createGraphicsWindow( int x, int y, int w, int h, const std::string& name="", bool windowDecoration=false )
    {
        osg::DisplaySettings* ds = osg::DisplaySettings::instance().get();
        osg::ref_ptr traits = new osg::GraphicsContext::Traits;
        traits->windowName = name;
        traits->windowDecoration = windowDecoration;
        traits->x = x;
        traits->y = y;
        traits->width = w;
        traits->height = h;
        traits->doubleBuffer = true;
        traits->alpha = ds->getMinimumNumAlphaBits();
        traits->stencil = ds->getMinimumNumStencilBits();
        traits->sampleBuffers = ds->getMultiSamples();
        traits->samples = ds->getNumMultiSamples();

        return new osgQt::GraphicsWindowQt(traits.get());
    }

    virtual void paintEvent( QPaintEvent* /*event*/ )
    { frame(); }

protected:

    QTimer _timer;
};

int main( int argc, char** argv )
{
    QApplication app(argc, argv);

    osg::ArgumentParser arguments(&argc, argv);

#if QT_VERSION >= 0x050000
    // Qt5 is currently crashing and reporting "Cannot make QOpenGLContext current in a different thread" when the viewer is run multi-threaded, this is regression from Qt4
    osgViewer::ViewerBase::ThreadingModel threadingModel = osgViewer::ViewerBase::SingleThreaded;
#else
    osgViewer::ViewerBase::ThreadingModel threadingModel = osgViewer::ViewerBase::CullDrawThreadPerContext;
#endif

    while (arguments.read("--SingleThreaded")) threadingModel = osgViewer::ViewerBase::SingleThreaded;
    while (arguments.read("--CullDrawThreadPerContext")) threadingModel = osgViewer::ViewerBase::CullDrawThreadPerContext;
    while (arguments.read("--DrawThreadPerContext")) threadingModel = osgViewer::ViewerBase::DrawThreadPerContext;
    while (arguments.read("--CullThreadPerCameraDrawThreadPerContext")) threadingModel = osgViewer::ViewerBase::CullThreadPerCameraDrawThreadPerContext;

#if QT_VERSION >= 0x040800
    // Required for multithreaded QGLWidget on Linux/X11, see http://blog.qt.io/blog/2011/06/03/threaded-opengl-in-4-8/
    if (threadingModel != osgViewer::ViewerBase::SingleThreaded)
        QApplication::setAttribute(Qt::AA_X11InitThreads);
#endif

    ViewerWidget* viewWidget = new ViewerWidget(0, Qt::Widget, threadingModel);
    viewWidget->setGeometry( 100, 100, 800, 600 );
    viewWidget->show();

    return app.exec();
}

编译运行，即可见到效果了。
要注意的是，这里连接的是release库，因此必须在 release 配置下运行。debug需要链接 debug库，否则虽然编译通过了，运行却报错的。如果报错，要检查一下，osg相关的debug库是不是都安装了，运行

pacman -Ss osg

检查。
最后，编译、运行效果：

当然，能够这样顺利，还是站在伟大、辛勤、无私、可敬的MSYS2工具链维护者的肩膀上。到底怎样嵌入自己的场景呢？估计要从 OpenSceneGraph 而不是 osgEarth 开始入手了。毕竟 osgEarth 是 OpenSceneGraph 的一个扩展包，场景渲染、添加自己的模型（比如玩具飞机）应该是OpenSceneGraph 的工作。目前姑且这样理解吧！