Good morning and thank you for your answers.

To norobro:
vertical_scroll is effectively called from graphicsview when its vertical (and horiz.) scroll bar's value changes. As you suggest, setPos(x,y) is probably what I need to call instead of moveBy(x, y);
( I will try this as soon as I get back from work ;-) )

To Wysota:
You have now spurred my curiosity about the graphicsview's viewport. If its top is always 0 when the view is scrolled up or down, does it mean that it is the scene which is moving ? (I was under the impression that the viewport should be the one moving)
In other words, what happens to the viewport when a user scrolls down/up?

The item is derived from QGraphicsItem as usual and it is added to scene as one would expect.
class my_graphics_item: public QGraphicsItem
....
my_graphics_item* test = new m_graphics_item(parent);
pscene->addItem(test);


(I will post my results later tonight)

Thanks,
Jean