[Wayland-bugs] [Bug 89683] Two finger scrolling isn't smooth

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89683

--- Comment #1 from Peter Hutterer <peter.hutterer at who-t.net> ---
This is weird. In the recording, your fingers move in opposite directions for a
number of events. In libinput, we average the movement of all fingers so the
movement cancels out. The jumps come from when the fingers move in the same
direction.

I put printf statements in libinput before replaying and this is the output:
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/10.42
Touch 1 0.00/-10.42
Delta 0.00/0.00
----
Delta after filter: 0.00/0.00
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/9.92
Touch 1 0.00/-9.92
Delta 0.00/0.00
----
Delta after filter: 0.00/0.00
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/9.92
Touch 1 0.00/-9.92
Delta 0.00/0.00
----
Delta after filter: 0.00/0.00
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/9.43
Touch 1 0.00/-9.43
Delta 0.00/0.00
----
Delta after filter: 0.00/0.00
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/8.43
Touch 1 0.00/19.35
Delta 0.00/13.89
----
Delta after filter: 0.00/5.62
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/7.94
Touch 1 0.00/49.61
Delta 0.00/28.78
----
Delta after filter: 0.00/13.06


That's the first couple of events, up to probably E: 0.389343 in the recording.
This repeats itself, with the jumps in between where the delta goes to
something normal. The movements aren't always identical, there is a later set
like this:
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/9.43
Touch 1 0.00/-7.44
Delta 0.00/0.99
----
Delta after filter: 0.00/0.35
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/8.43
Touch 1 0.00/-8.43
Delta 0.00/0.00
----
Delta after filter: 0.00/0.00
---- tp_gesture_post_twofinger_scroll:123
Touch 0 0.00/7.44
Touch 1 0.00/-7.44
Delta 0.00/0.00

This looks very odd. Unless you're doing this intentionally this would point at
some hw or firmware issue. Or a kernel bug. Can you confirm that you're moving
the fingers in the same direction here?

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