[Wayland-bugs] [Bug 98839] Somehow conditionalize hysteresis (hardware black/whitelist, device property introspection, user-exposed setting, etc)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98839

--- Comment #58 from Daniel van Vugt <daniel.van.vugt at canonical.com> ---
It feels like the tests you asked us to record are not indicative of normal
use. Under normal laptop use there is apparently not a period of 5 pressure
change events early enough. You start using the laptop and it feels awful -
can't put the cursor anywhere you want it to go. Hysteresis is at least 5mm and
the cursor refuses to move in natural curves -- only vertically or
horizontally. Only by staying still for a short while does it switch over.
Although it _should_ theoretically by the time you get to the first button
click. Maybe we need to spend more time testing the branch...

On that note, I'm still suspicious as to why hysteresis is so large -- around
5mm on multiple different machines. The only theory we have that explains that
is hardware hysteresis having an additive effect, because you say it should be
less than 1mm. Actually I have a second theory that weird unsmooth acceleration
curves [1] also contribute to the unnatural feel and poor pointer control but
that's a different bug. Perhaps also default acceleration curves are
decelerating for minimal velocities, which changes the hysteresis distance??

Long term I feel the only reliable options for hysteresis are to:
  (a) Hard code hysteresis off for some hardware; and
  (b) Make it a user-visible option.

I've spent more time using a Macbook and Chromebooks and they are dramatically
better, for various reasons. There is no noticeable hysteresis there -- the
tiniest finger movement is responded to.

P.S. X1 Carbon gen 3 is very different to gen 4 and 5. Gen 3's touchpad is just
wonderful and amazing (although also works best without software hysteresis). I
can provide stats from that one too if you are curious.

[1]
https://wayland.freedesktop.org/libinput/doc/latest/pointer-acceleration.html

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