Delta-based scroll events

[David De La Harpe Golden]

Peter Hutterer wrote:

> true scrolling events are nothing but events on axes other than x/y. the X
> server doesn't really care what the semantics are (i.e. scrolling). And here
> is where the actual issue lies, there is no standard. The third axis is
> generally assumed to be pressure, beyond that it's anyone's guess. 

AFAIK wacom tablets use (numbering from one):

1 = x pos
2 = y pos
3 = pressure
4 = x tilt (of stylus)
5 = y tilt (of stylus)
6 = [rate] wheel (typically for airbrush)

Current XInput apps typically provide an interface for the axis numbers
to app-meaningful quantities though, e.g. in gimp preferences I could
set axis 2 to x-tilt if I wanted (though it would be pretty useless and
annoying of course).