[Wayland-bugs] [Bug 105963] Lenovo P50 - Slow fine touchpad movement makes it jump (bug 2)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105963

--- Comment #13 from Peter Hutterer <peter.hutterer at who-t.net> ---
[This was typed in response to comment #8, but bugzilla didn't take it first
time round]

Also look into bug 101139, that is the current bug for the "way too fast"
behaviour.

As for debugging this in general: touchpad_accel_profile_linear() is the
acceleration profile and the returned factor is applied to the deltas. The
threshold and incline are affected by the configured speed, see
touchpad_accelerator_set_speed() which is called when you change the property.

Note that if you're using libinput debug-events or any other tools, the context
is *not* the one your X server has, it's always a new context and changes don't
go across. Think of it as two different processes reading the same byte stream,
you can change how you process data in one process but the other one still
receives the unmodified byte stream and is thus unaffected. So any changes in X
don't affect libinput debug-events and vice versa.

libinput debug-gui has a hidden feature, cursor keys up/down change the pointer
acceleration by ±0.1 with each press. That's going to be helpful for testing
because you see the immediate effects on the cursor.

Also note that in calculate_acceleration() we're using simpson's rule to smooth
things a bit. So that may affect things a bit as well.

> I think sharing a flag with other quirks causes problems

It shouldn't, the flags are just that and libinput doesn't care about them
beyond the usual handling. That particular T450 flag is only used in one place,
so re-using it is safe.

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