Draw on a QTableWidget

[Corran]

I'm reletively new to Qt so I'm still learning the best ways to do thing. Quite often I guess there's a simple solution which I don't know about.

Anyway, I have a QTableWidget which I've set up so that each cell is square. However, I want to delineate blocks of cells to make it clearer. I want blocks of 3x3 cells to have a darker border around them as in the picture attached.

As far as I can tell, to do this I will have to subclass QTableWidget and reimplement its paintevent() function and draw the lines there. However, if I do this I don't know how to make it draw the table, text, etc as usual. The lines are static and just have to sit atop the table so is there any easier way do do this?

Many thanks