How to determine a widget is visible or not within a scrollw?

[yanxin <ycui wmsvision com>]

I have a layout in a scrolled window, and some widgets inside the
layout. My question is, when I hit a tab key, the focus may go to a
widget which is not inside the current viewable area, how do I determine
this and automatically adjust the scrollbar and show the widget that has
just got the focus?

Thanks

Yanxin