[Qt-interest] QGLWidget: initializeGL not executed

[Samuel Rødal]

Oliver Demetz wrote:
> Hi!
> 
> I've got a QGraphicsView and scene, and the viewport of my vie is an 
> QGLWidget. Everything works fine, also I am sure that the OpenGL 
> subsystem is definitely used.
> 
> Now I want to use my own subclassed QGLWidget as the viewport in order 
> to check some properties of the opengl subsystem:
> 
> Instead of
> 
>      my_view.setViewport(new QGLWidget(...));
> 
> I state
> 
>      my_view.setViewport(new GLWidget(...));
> 
> where my GLWidget is:
> 
> class GLWidget : public QGLWidget
> {
> public:
> 	GLWidget(const QGLFormat & format, QWidget * parent = 0, const 
> QGLWidget * shareWidget = 0, Qt::WindowFlags f = 0 )
> 	: QGLWidget(format, parent, shareWidget, f)
> 	{
> 
> 	}
> protected:
> 	void glInit()
> 	{
> 		QGLWidget::glInit();
> 		qDebug() << "glinit";
> 	}
> 	void initializeGL()
> 	{
> 		QGLWidget::initializeGL();
> 
> 		QString strextensions((char*)glGetString(GL_EXTENSIONS));
> 		QStringList extlist = strextensions.split(" ");
> 		foreach(QString s, extlist)
> 			qDebug() << s;
> 
> 	}
> };
> 
> If I execute the code, I would expect to see at least the list of 
> extensions or the debugstring "glinit".
> 
> BUT NOTHING APPEARS!!!
> why are thos methods not executed?????
> 
> Note that the functionality still is as it was with the original QGLWidget!
> Only the functions are not executed (also not paintGL).
> 
> Thanks in advance,
> Olli

Hello,

initializeGL() etc are called by the default paintEvent() in QGLWidget. 
When a QGLWidget is used as a viewport in a QGraphicsView then 
QGLWidget::paintEvent() never gets called, as QGraphicsView does the 
painting in its paintEvent().

Instead you can call initializeGL() on your own right after creating the 
widget, like this:

GLWidget *viewport = new GLWidget(...);
my_view.setViewport(viewport);
viewport->makeCurrent();
viewport->initializeGL();

You'll need to make initializeGL() public, or alternatively create a 
different public function that does the initialization.

Regards,
Samuel