Text dissapears on QOpenGLWidget after undocking

Question

I'm trying to integrate Qt5 and OpenSceneGraph. I've found this minimal example of embedding.

When I encapsulate the widget, defined in the example, into a QDockWidget and add a simple text label to the example, the text dissapears when I undock the container window. When I redock the window the text is shown no more.

I've already ask this on the OpenSceneGraph forum without success. My guess is that it has something to do with the GL related methods and the internal reparenting of the widgets.

In my example only the constructor and the main function are modified from the original.

This is my modified example (main.cpp):

#include<QApplication> 
#include<QMainWindow> 
#include<QOpenGLWidget> 
#include<QMouseEvent> 
#include<QWheelEvent> 
#include<QDesktopWidget> 
#include<QScreen> 
#include<QtGlobal> 
#include<QWindow> 
#include<QWidget> 
#include<QDockWidget> 
#include<QVBoxLayout> 

#include<osg/ref_ptr> 
#include<osgViewer/GraphicsWindow> 
#include<osgText/Text> 
#include<osgViewer/Viewer> 
#include<osg/Camera> 
#include<osg/ShapeDrawable> 
#include<osg/StateSet> 
#include<osg/Material> 
#include<osgGA/EventQueue> 
#include<osgGA/TrackballManipulator> 

#include <iostream> 
#include <stdio.h> 

class QtOSGWidget : public QOpenGLWidget 
{

public: 
    QtOSGWidget(qreal scaleX, qreal scaleY, QWidget* parent = 0) 
      : QOpenGLWidget(parent) 
        , _mGraphicsWindow(new osgViewer::GraphicsWindowEmbedded( this->x(), this->y(), 
                                                                 this->width(), this->height() ) ) 
        , _mViewer(new osgViewer::Viewer) 
        , m_scaleX(scaleX) 
        , m_scaleY(scaleY) 
    { 
        osg::Cylinder* cylinder    = new osg::Cylinder( osg::Vec3( 0.f, 0.f, 0.f ), 0.25f, 0.5f ); 
        osg::ShapeDrawable* sd = new osg::ShapeDrawable( cylinder ); 
        sd->setColor( osg::Vec4( 0.8f, 0.5f, 0.2f, 1.f ) ); 
        osg::Geode* geode = new osg::Geode; 
        geode->addDrawable(sd); 

        // adding text to the visualization 
        osgText::Text * test = new osgText::Text(); 
        test->setDataVariance(osg::Object::DYNAMIC); 

        test->setCharacterSize(1.0); 
        test->setColor(osg::Vec4(0.0, 0.0, 0.0, 1.0)); 
        test->setAlignment(osgText::Text::CENTER_BOTTOM); 
        test->setAxisAlignment(osgText::TextBase::SCREEN); 
        test->setCharacterSizeMode(osgText::Text::OBJECT_COORDS); 
        test->setText("CYLINDER"); 
        geode->addDrawable(test); 
        // end adding text 

        osg::Camera* camera = new osg::Camera; 
        camera->setViewport( 0, 0, this->width(), this->height() ); 
        camera->setClearColor( osg::Vec4( 0.9f, 0.9f, 1.f, 1.f ) ); 
        float aspectRatio = static_cast<float>( this->width()) / static_cast<float>( this->height() ); 
        camera->setProjectionMatrixAsPerspective( 30.f, aspectRatio, 1.f, 1000.f ); 
        camera->setGraphicsContext( _mGraphicsWindow ); 

        _mViewer->setCamera(camera); 
        _mViewer->setSceneData(geode); 
        osgGA::TrackballManipulator* manipulator = new osgGA::TrackballManipulator; 
        manipulator->setAllowThrow( false ); 
        this->setMouseTracking(true); 
        _mViewer->setCameraManipulator(manipulator); 
        _mViewer->setThreadingModel(osgViewer::Viewer::SingleThreaded); 
       // _mViewer->realize(); 
    } 


    virtual ~QtOSGWidget(){} 

    void setScale(qreal X, qreal Y) 
    { 
        m_scaleX = X; 
        m_scaleY = Y; 
        this->resizeGL(this->width(), this->height()); 
    } 

protected: 

    virtual void paintGL() 
    { 
        _mViewer->frame(); 
    } 

    virtual void resizeGL( int width, int height ) 
    { 
        this->getEventQueue()->windowResize(this->x()*m_scaleX, this->y() * m_scaleY, width*m_scaleX, height*m_scaleY); 
        _mGraphicsWindow->resized(this->x()*m_scaleX, this->y() * m_scaleY, width*m_scaleX, height*m_scaleY); 
        osg::Camera* camera = _mViewer->getCamera(); 
        camera->setViewport(0, 0, this->width()*m_scaleX, this->height()* m_scaleY); 
    } 

    virtual void initializeGL()
    { 
        osg::Geode* geode = dynamic_cast<osg::Geode*>(_mViewer->getSceneData()); 
        osg::StateSet* stateSet = geode->getOrCreateStateSet(); 
        osg::Material* material = new osg::Material; 
        material->setColorMode( osg::Material::AMBIENT_AND_DIFFUSE ); 
        stateSet->setAttributeAndModes( material, osg::StateAttribute::ON ); 
        stateSet->setMode( GL_DEPTH_TEST, osg::StateAttribute::ON ); 
    } 

    virtual void mouseMoveEvent(QMouseEvent* event) 
    { 
      this->getEventQueue()->mouseMotion(event->x()*m_scaleX, event->y()*m_scaleY); 
    } 

    virtual void mousePressEvent(QMouseEvent* event) 
    { 
        unsigned int button = 0; 
        switch (event->button())
        { 
            case Qt::LeftButton: 
                button = 1; 
                break; 
            case Qt::MiddleButton: 
                button = 2; 
                break; 
            case Qt::RightButton: 
                button = 3; 
                break; 
            default: 
                break; 
        } 
        this->getEventQueue()->mouseButtonPress(event->x()*m_scaleX, event->y()*m_scaleY, button); 
    } 

    virtual void mouseReleaseEvent(QMouseEvent* event) 
    { 
        unsigned int button = 0; 
        switch (event->button())
        { 
            case Qt::LeftButton: 
                button = 1; 
                break; 
            case Qt::MiddleButton: 
                button = 2; 
                break; 
            case Qt::RightButton: 
                button = 3; 
                break; 
            default: 
                break; 
        } 
        this->getEventQueue()->mouseButtonRelease(event->x()*m_scaleX, event->y()*m_scaleY, button); 
    } 

    virtual void wheelEvent(QWheelEvent* event) 
    { 
        int delta = event->delta(); 
        osgGA::GUIEventAdapter::ScrollingMotion motion = delta > 0 ? 
                  osgGA::GUIEventAdapter::SCROLL_UP : osgGA::GUIEventAdapter::SCROLL_DOWN; 
        this->getEventQueue()->mouseScroll(motion); 
    } 

    virtual bool event(QEvent* event) 
    { 
        bool handled = QOpenGLWidget::event(event); 
        this->update(); 
        return handled; 
    } 

private: 

    osgGA::EventQueue* getEventQueue() const 
    { 
        osgGA::EventQueue* eventQueue = _mGraphicsWindow->getEventQueue(); 
        return eventQueue; 
    } 

    osg::ref_ptr<osgViewer::GraphicsWindowEmbedded> _mGraphicsWindow; 
    osg::ref_ptr<osgViewer::Viewer> _mViewer; 
    qreal m_scaleX, m_scaleY; 
}; 

int main(int argc, char** argv) 
{ 
    // This was necessary for keeping the context when undocking
    // without it nothing is shown on the widget when gets undocked 
    QApplication::setAttribute(Qt::AA_ShareOpenGLContexts); 

    QApplication qapp(argc, argv); 

    QMainWindow window; 

    // Here starts code to put the QtOSGWidget inside a dock area 
    QDockWidget * visDock = new QDockWidget(&window); 
    visDock->setFloating(false); 
    visDock->setFeatures(QDockWidget::DockWidgetFloatable | QDockWidget::DockWidgetMovable); 
    visDock->setAllowedAreas(Qt::TopDockWidgetArea); 

    QWidget * dockWidgetContent = new QWidget(); 

    QVBoxLayout * verticalLayout = new QVBoxLayout(dockWidgetContent); 
    verticalLayout->setSpacing(6); 
    verticalLayout->setContentsMargins(11, 11, 11, 11); 

    QWidget * containerWidget = new QWidget(dockWidgetContent); 
    QHBoxLayout * horizontalLayout = new QHBoxLayout(containerWidget); 
    horizontalLayout->setSpacing(0); 
    horizontalLayout->setContentsMargins(11, 11, 11, 11); 
    horizontalLayout->setContentsMargins(0, 0, 0, 0); 

    QtOSGWidget* widget = new QtOSGWidget(1, 1, containerWidget); 

    horizontalLayout->addWidget(widget); 

    verticalLayout->addWidget(containerWidget); 

    visDock->setWidget(dockWidgetContent); 

    window.addDockWidget(static_cast<Qt::DockWidgetArea>(4), visDock); 

    // No central widget is used for the example 
    window.setCentralWidget(Q_NULLPTR); 
    window.show(); 

    return qapp.exec(); 
}

Answer 1

After _mViewer->setSceneData(geode); add this:

_mGraphicsWindow->init();
initializeGL();

and change the method

virtual void paintGL() { 
    _mViewer->frame(); 
}

to

virtual void paintGL() {
    _mGraphicsWindow->decrementContextIDUsageCount(_mGraphicsWindow->getMaxContextID());
    _mGraphicsWindow->releaseContext();
    _mGraphicsWindow->init(); 
    _mViewer->frame(); 
}

And add thins on main function:

QApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);

will solve your problem.