[Wayland-bugs] [Bug 101139] Acceleration still too slow with medium finger movements

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101139

--- Comment #22 from Peter Hutterer <peter.hutterer at who-t.net> ---
Some notes after another afternoon of playing around with this:

The script that produces the output above measures *physical* movements on the
touchpad, thus the 'speed' on the right column represent 10mm/s physical
movement, not pointer movement. IMO it makes sense that the majority comes in
at below 20mm/s. Slow movements generate more events, fast movements are
*short* movements with few events.

I played around with a bunch of acceleration curves similar to attachment
136584. I used a linear curve instead for simplicity with varying inclines,
starting acceleration at 40mm/s, inclines from 'roughly parallel to current' to
'roughly like attachment 136584'. They showed the same thing every time: the
pointer is uncontrollable once we hit accel factor 3 [1] at anything but very
low speeds. The fast pointer movement is multiplied by a high factor, resulting
in ridiculous deltas and unpredictable pointers.

A fixed factor 3 is just about controllable but would cause RSI after 5 min.

I have in front of me: Lenovo T440s, Lenovo T450s, Dell XPS 13 9365, Asus
E402S. All with Fedora 27, up-to-date (libinput 1.10.1). The touchpad behaviour
is effectively identical [2] on all four machines.

Bug 105375 is the next step here, once that's implemented we can at least
compare full output. But right now, I know just as much as before :(


All that aside, please confirm that you do *not* have a hidpi screen though.


[1] factor 3 not accounting for the TP_MAGIC_SLOWDOWN, so effective factor 3 *
0.37
[2] The XPS has a hidpi screen and is slow under X, GNOME on wayland makes up
for this but that's not a libinput issue.

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