Grab key scrolling

[Marco Pesenti Gritti]

Hello,

we have the grab key on the keyboard which, when pressed, should
activate the scrolling mode. It should work like this:

1 The user press the grab key on the keyboard.
2 The scrollbars of the current view are highlighted.
3 Movements on the trackpad (both resistive and not resistive) scrolls
the view. The mouse pointer is "locked" and does not change position.

We are having problems with the X side of this but I think Jim said to
Eben it was possible. Can someone with more with more X knowledge than
me suggest a good way of implementing it?

What I tried is to detach the pointer device from the core pointer.
(XChangePointerDevice). But then how do I get notified about trackpad
movements?

Thanks,
Marco