In a QLWidget you can make OGL calls. I have no experience on it but the doc may show yiou the way.

If you want to derived a QGraphicsItem that manages an OGL texture, you can use QImage as a wrapper of a buffer of char, to prevent from copying texture data. Then it is easy to draw it with in painter. QPainter::draw can draw a part of the image inside a part of your item, doing the scaling automatically, without any pre computed transformation.

S.Cascio