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

I’m going to go ahead and answer my own question. This isn’t optimal, but this is how I’ve gotten around the problem.

Instead of

ui.graphicsView->setViewport(new MyGLWidget(QGLFormat(QGL::DoubleBuffer)));

I’ve got this instead:

ui.graphicsView->setViewport(new QGLWidget(new CustomContext(QGLFormat(QGL::SampleBuffers))));

CustomContext is a class that derives from QGLContext. I’ve overridden the create member, like so:

virtual bool create(const QGLContext *shareContext = 0)
{
    if(QGLContext::create(shareContext))
    {
        makeCurrent();

        /* do my initialization here */

        doneCurrent();

        return true;
    }

    return false;
}

I don’t think this is the optimal way to do this, but it’s better than the alternative of not having a specific initialization step at all. I’d still be happy to have someone leave a better answer!