[Wayland-bugs] [Bug 98839] Trackpad cursor movement feels sluggish at very slow speeds and does not move at all when you pivot your finger around a spot

[bugzilla-daemon at freedesktop.org]

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

--- Comment #4 from Peter Hutterer <peter.hutterer at who-t.net> ---
Have we checked the size of your touchpad yet? 105x97mm - is that accurate? If
not, please run the touchpad-edge-detector tool (check that the axis ranges are
correct anyway please).

>From what I can tell, the issue is that your touchpad's deltas for this
particular recording are extremely small - in the 1-4 device unit range. At the
device's x/y resolutions that's 0.027/0.016mm precision. Our hysteresis code
uses 0.5mm to avoid pointer wobble, so most of your movements fall into that
code.

This is even further amplified by the issue that the hysteresis works ok while
moving in the same direction, but whenever you change directions the margin
takes effect. so rolling a finger left/right would show the worst effect,
continuing in one direction should be fine. And indeed the delta shows a lot of
back/forth movement at the device-unit level.

Either way, I think this also explains why the movement feels like it snaps to
one axis, the hysteresis is calculated separately so you can get one axis
suppressed back and the other axis move on normally. *maybe* this could be
fixed by changing the hysteresis to use hypot() but that's quite expensive to
run over every delta. Feel free to try this though locally.

We tried removing the hysteresis but it caused pointer wobbles for a lot of
people. Did you ever use synaptics on this touchpad? Did that behave better?

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