[Wayland-bugs] [Bug 90735] Touchpad does not feel "right", acceleration issue

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90735

--- Comment #19 from Peter Hutterer <peter.hutterer at who-t.net> ---
(In reply to Britt Yazel from comment #16)
> It's getting better, though not quite there yet. I am noticing that really
> minute touch movements are not registering as movements under libinput,
> whereas the same minute movements (I'm talking 1-2mm) do register under
> synaptic drivers. That might be a reason for a lack of perceived precision,
> or it could all be in my head.

libinput has a function to drop tiny movements (which I think is broken in
synaptics, or at least not as consistent across devices). but that's in the
sub-mm scale with libinput 0.18, on your device it should be 0.5mm.
the last patch, when applied to master doesn't have deceleration so the pointer
movement is what the touchpad sends.


> Also, it feels like the acceleration ramps up too quickly. There is a point
> right between the transition from slow movements and quick movements where
> the acceleration seems to take a jump, and it is a bit jarring. The only way
> to describe it is as if I am losing control of the cursor for a second. This
> leads you to a state where mentally the cursor is not where my mind thinks
> it should be, and I need to then cognitively reasses its location.

hmm, interesting. for me it's almost too slow here and I feel the accel doesn't
kick in when I think it does. You can play around with the parameters if you
feel like it. the curve is a simple step of baseline, then linear up to
max_accel. the parameters are:
baseline: basic speed of the device w/o accel
threshold: speed when accel starts kicking in
max_accel: maximum accel factor, will be relative to baseline (2 * baseline ==
twice as fast)
incline: the incline, the lower the longer it takes to reach max_accel.

In your case I guess you either need a smaller incline or a higher threshold.


(In reply to Britt Yazel from comment #18)
> For the cursor to move 100% across the screen, at a maximum touchpad
> velocity threshold that should equal 100% across the length of the touchpad.
> And, at the lowest velocity threshold, the distance moved on the screen
> should equal that of the distance moved on the touchpad.

we don't know the screen size in libinput and tbh I don't think this approach
works anyway. I'm using my laptop with an external monitor connected (LVDS
off), touchpads like the T650 are external, touchpads on the x220 was
significantly smaller at roughly the same screen resolution of the T440, etc.

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