Please help: TScrollbox question

Hi all,

I need to use a Scrollbox component on my form to scroll a large
Paintbox. When I scroll the paintbox the picture I drawed disappears.
I think I need to redraw my picture when there has been scrolled, but
there seems to be no OnScroll event as there is for normal scrollbars.

How can I detect when the user has scrolled the scrollbox ?

Any help would be greatly appreciated.