OSG嵌入QT的簡明總結

charlee44發表於2019-06-16
QT

目錄

1.解決方案

不得不說關於OSG的資料實在太零散了，搜尋了很多關於OSG在QT下的解決方案，都是各有各的說法，有的說的不是很清楚，有的已經過時了。這裡提供一下自己的解決方案吧。
在遠古的OSG裡面，應該是提供對QT的支援的；不過應該是由於QT版本變動比較大，現在的OSG版本應該已經沒有了。但是在GitHub上又有了新的osgQt專案（地址：https://github.com/openscenegraph/osgQt） 用來解決這個問題。
osgQt是個簡單的小專案，其實沒有必要額外的編譯，最核心的是個名為GraphicsWindowQt的類，只需要複製GraphicsWindowQt.h和GraphicsWindowQt.cpp到QT工程裡面就可以使用了。同時osgQt給出了一個名為osgviewerQt的樣例，也僅僅只是個cpp檔案。結合兩者，一個簡單的示例就出來了。
QT工程如下：
OSG嵌入QT的簡明總結
編譯執行後如下：
OSG嵌入QT的簡明總結

2.存在問題

1) 警告提示

上述專案直接執行，會出現諸如“QOpenGLContext::swapBuffers() called with non-exposed window, behavior is undefined”的警告。查閱網上的英文資料，大意說是因為OpenGL環境未初始化產生的。在osgviewerQt中繫結了一個定時器，每隔10ms就呼叫frame()來繪製一幀，而這個定時器是在建構函式的時候就開始呼叫了，沒有等待QT中OpenGL環境的生成。在這裡我把定時器的部分給改進了一下，等待OSG的環境初始化完成在啟動定時器，這個警告就沒有了。osgviewerQt改進後的程式碼如下：

#include <QTimer>
#include <QApplication>
#include <QGridLayout>

#include <osgViewer/CompositeViewer>
#include <osgViewer/ViewerEventHandlers>

#include <osgGA/MultiTouchTrackballManipulator>

#include <osgDB/ReadFile>

#include "GraphicsWindowQt"

#include <iostream>

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("D:/Work/OSGBuild/OpenSceneGraph-Data/cow.osgt") );
        QWidget* widget2 = addViewWidget( createGraphicsWindow(0,0,100,100), osgDB::readRefNodeFile("D:/Work/OSGBuild/OpenSceneGraph-Data/glider.osgt") );
        QWidget* widget3 = addViewWidget( createGraphicsWindow(0,0,100,100), osgDB::readRefNodeFile("D:/Work/OSGBuild/OpenSceneGraph-Data/axes.osgt") );
        QWidget* widget4 = addViewWidget( createGraphicsWindow(0,0,100,100), osgDB::readRefNodeFile("D:/Work/OSGBuild/OpenSceneGraph-Data/fountain.osgt") );
//        QWidget* popupWidget = addViewWidget( createGraphicsWindow(900,100,320,240,"Popup window",true), osgDB::readRefNodeFile("D:/Work/OSGBuild/OpenSceneGraph-Data/dumptruck.osgt") );
//        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<osg::Node> 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) );

        // set the draw and read buffers up for a double buffered window with rendering going to back buffer
        camera->setDrawBuffer(GL_BACK);
        camera->setReadBuffer(GL_BACK);

        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<osg::GraphicsContext::Traits> 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(); }

    //定時器事件
    void timerEvent(QTimerEvent* )
    {
        frame();
    }

    //啟動定時器繪製
    void show()
    {
        QWidget::show();
        _timerID = startTimer(10);
    }


protected:

    //QTimer _timer;
    int _timerID;               //定時器ID
};

int main( int argc, char** 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

    QApplication app(argc, argv);
    ViewerWidget* viewWidget = new ViewerWidget(0, Qt::Widget, threadingModel);
    viewWidget->setGeometry( 100, 100, 800, 600 );
    viewWidget->show();
    return app.exec();
}

2) 多執行緒問題

在OSG中提供了諸如CullDrawThreadPerContext等多執行緒模式，但是在這裡是沒辦法支援這些多執行緒模式的，只能支援單執行緒。在網上查閱了一些解決方案，但是最後都不是很完美，有空再把其解決方案寫出來。

3) 其他

GraphicsWindowQt最終繼承的還是QT中的QGLWidget類，提供OpenGL功能。而在新版本的QT中，這個類已經被廢棄了，取而代之的是一個叫做QOpenGLWidget的類。所以這裡面問題還是不少的，好在內容相對較少，以後有空可以自己改進。

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