https://bugs.freedesktop.org/show_bug.cgi?id=101139
--- Comment #12 from Greg Reichow <gdr3...@me.com> ---
Created attachment 136585
--> https://bugs.freedesktop.org/attachment.cgi?id=136585&action=edit
Accel profile comparison patch at -0.75 vs nominal
Hi Peter,
After some further investigation, I think I have a better idea what is
happening. The good news is that I don't think there is some bug causing a
difference in performance between our machines.
To start, I confirmed that my touchpad was not doing something odd like
reporting a bad DPI or size. Everything looked good. (DPI is 92 device
units/mm or about 2300 per inch). Did a bunch of verification and everything
seemed to make sense.
I then used your speed measuring tool and found something interesting to me.
It turns out that my typical speeds for normal operation of the touchpad range
from 0 to 200 (99th percentile). I then compared this to the nominal accel
profiles (set at speed 0) and noticed that 99% of my operational speeds never
even get to the part of the curve where accel ramps up in the libinput profile.
This created what I felt was no acceleration and a "dead middle" to high end.
I also felt that at very slow speeds, it did not have the accuracy I needed.
If I cranked up the speed setting to pull in the threshold of the acceleration
ramp, it made the low end speed even worse (meaning even harder to control). I
then looked at the curve from the patch and noticed that within my operational
range, it addressed both of these problems for me. The low end is slower and
more accurate, and the acceleration starts at about the midpoint and ramps up.
(Completely agree that at much higher speeds the raw accel factor gets crazy
high in my patch, but it would seem I never get there with my touchpad speed.)
I have attached plots that show both the nominal and the patched accel profile
plots at a speed setting of zero.
I also then did a comparision on the patch at the setting that Nate mentioned
feeling good (-0.75). See attached graph that compares it to the zero speed
setting of the nominal accel profile. It actually seems very close yet
addresses the slow speed problem and also has a bit more acceleration early and
smoothly from the middle to the high end.
I will take another swing at a new profile / patch that moves the current
patch's -0.75 setting and moves this up to 0 to slow things down overall.
Thanks,
Greg
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