[ltp] Smooth trackpoint acceleration

[Richard]

>
> Thanks for the tips.  I tried out your settings.  It's a different from what I
> settled on using, but addresses the problem with about the same
> effectiveness.  I still feel like something is missing.
>
> So it doesn't seem to me that it's facile to calculate for acceleration in the
> kernel driver.  I'm not sure I want to parse through the raw data to figure
> out what's going on.  I don't even know its format.  Perhaps X.org /is/ the
> natural place for an acceleration algorithm because the parsing and
> abstraction has already been done by that point.

I do think this belongs in xorg, because it would be generally useful for 
all mice, not just for trackpoints. Also, xorg already has the "normal" 
mouse acceleration code, so you'd just have to modify that a bit.

The current gain model is
    output_num_pixels = input_num+pixels * k
where
    normally,
      k=1
   but if input_num_pixels/second > $threshold
      k=$accel

This graph has 2 gradients, with a sharp bend in the middle. I think that 
if you smoothed it to 4 lines, you'd never be able to tell it wasn't true 
exponential.

Anyway, good luck!

Richard