The scroll wheel on Intuos4 devices currently sends bogus values. This is
largely caused by us trying to keep the pad as a relative device and doing
deltas. The scroll wheel is special in that it's easy to change from max →
min (71 -> 0), which looks like a large delta when in fact it is only a few
units.

The reason the pad is relative is historical. As Ping pointed out elsewhere,
it used to be relative if configured as core device and absolute otherwise.
The relative mode was to avoid movement of the pointer (x/y is always 0/0
for the pad and would lead to cursor jumps to the origin of the screen).

Now, I don't know how much of that was a server bug but there was definitely
a driver bug in there. first_valuator was always 0, so posting this as
absolute coordinates will always reset the pointer to 0/0. This patchset
came about by headbanging (not the good kind, I'm talking about the one
where a wall is involved), so it's not in the most straightforward order.
The interesting bits are in 05/14 where we start posting only the relvant
valuators (for proximity and motion events) and then patches 07/14 and 12/14
where the change over to use first+num valuators is completed. So the whole
lot may be a bit complicated to understand in this sequence.

The effect is for pad events we never send x/y coordinates, so we can switch
the pad back into absolute mode and not bother about delta-ing them.
Rule for changing the mode stays the same, a client cannot change the
mode of the pad tool, even though that mode is now different to before.

Tested with I4 and I3 on git master, I4 on 1.9.3 and 1.8.2.
Available for testing on the scroll-wheel branch on
git://people.freedesktop.org/~whot/xf86-input-wacom.git 

Cheers,
  Peter


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