filter: drop delta-softening

filter: drop delta-softening

I doubt this does what we think it does. It doesn't soften the delta changes,
rather it introduces bumps in the smooth processing of the changes.

abs(delta) below 1.0 is untouched, and abs(delta) beyond 3 or 4 isn't
noticable much. But in the slow range around the 1/-1 mark there is a bump.

For example, if our last_delta is 1.0 and delta is 1.1, the "softened"
delta is set to 0.6. That is stored as last delta, so an input sequence of:
   0.8, 0.9, 1.0, 1.1, 1.2, 1.0, 0.8, 1.1

results in "softened" deltas that don't match the input:
   0.8, 0.9, 1.0, 0.6, 0.7, 1.0, 0.8, 0.6

A better approach at smoothing this out would be to calculate the softened as:
   current = current ± diff(last, current) * 0.5
or even weighted towards the new delta
   current = current ± diff(last, current) * 0.25

In tests, this makes little difference. Dropping this function altogether is
sufficient to make the pointer pointer behave slightly better at low speeds
though the increase is small enough to attribute to confirmation bias.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>