Qt & OpenGl, calling gl-commands within other classes

hi, I've searched for this already long time, but couldn't find any solution so far.

The problem is the following thing:

I created a GLWidget which is derived from QGLWidget, in this class I have overriden the method paintGL(), in which I can successfully call the gl commands like glVertex3f(..) and so on. So that works fine.

Now I am trying to make a Cube class, in which I want to make a method like drawCube(...), in which the glCommands for exactly a cube are called. I then want to call the drawCube method in the QGLWidget e.g:
Code:

public GLWidget::paintGL() { mycube.drawCube(this); // I am not sure which parameter I should give the cube }
The problem I get is I don't know how to reference the GLWidget, to the Cube class, so I can actually call there its methods. (the glVertex3f(..) for example)

I hope I described my problem clear enough to understand.

Any help is very appreciated, since it would be horrible to writing all the glPaint code in only one method

thanks in advance