Scrolling with keyboard

["D.Cortecchia" <d cortecchia specialvideo-eng com>]

I've written some callbacks to navigate through a GtkTree (contained in a
GtkViewPort) with keyword,
but I don't how to manage the scrolling of the GtkViewPort when an item not
visible got the focus.

1. How may I know if the focus is on a hidden item ?
2. There's a way to simply calculate the Adjustment to scroll GtkViewPort in
order to make the focused
item visible ?

Thanks.