calling Qt's QGraphicsView::setViewport with a custom QGLWidget

Question

I've derived from QGLWidget before, like so:

class MyGLWidget : public QGLWidget
{
public:
   // stuff...

   virtual void initializeGL() { /* my custom OpenGL initialization routine */ }

   // more stuff...
};

However, I find that if I try to initialize a QGraphicsView with my custom QGLWidget as the viewport, initializeGL doesn't get called (setting a breakpoint within the Qt library, neither does QGLWidget::initializeGL() when created plain).

// initializeGL, resizeGL, paintGL not called
ui.graphicsView->setViewport(new MyGLWidget(QGLFormat(QGL::DoubleBuffer)));

// initializeGL, resizeGL, paintGL *still* not called
ui.graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::DoubleBuffer)));

Where is the correct location to place the code that currently resides in MyGLWidget::initializeGL()?

Answer 1

The setupViewport slot of a custom QGraphicsView could be used to call updateGL() on the QGLWidget, which will cause initializeGL() to be called.

class MyGraphicsView : public QGraphicsView
{
    //... The usual stuff

protected slots:
    virtual void setupViewport(QWidget *viewport)
    {
        QGLWidget *glWidget = qobject_cast<QGLWidget*>(viewport);
        if (glWidget)
            glWidget->updateGL();
    }

};