[Wayland-bugs] [Bug 101051] Two-finger scrolling is unreliable, hard to trigger

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101051

            Bug ID: 101051
           Summary: Two-finger scrolling is unreliable, hard to trigger
           Product: Wayland
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: libinput
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: stark3y at gmail.com

Created attachment 131364
  --> https://bugs.freedesktop.org/attachment.cgi?id=131364&action=edit
udev info, evemu info, xinput props

libinput version: 1.7.1
Device:           Lenovo Thinkpad 13 "ETPS/2 Elantech Touchpad"
DMI:             
dmi:bvnLENOVO:bvrR0CET27W(1.15):bd09/05/2016:svnLENOVO:pn20GJCTO1WW:pvrThinkPad13:rvnLENOVO:rn20GJCTO1WW:rvrSDK0J40697WIN:cvnLENOVO:ct10:cvrNone:

See attached udev info, evemu device description, xinput props


Hi,

Two-finger scrolling on my touchpad became very, very hard to trigger after
updating from 1.5.3-1 to 1.7.1-1 (Arch package version). My guess would be
it's related to the pressure-based touch detection introduced in 1.7.0, but
that's just a guess.

Normal, single-finger touch events work fine, it's only two finger scrolling
which doesn't. I have to press very hard and deliberately to get two finger
scrolling to trigger at all - but even trying to do that it is pretty hard to
trigger.

Before the update, two-finger scrolling was as easy to trigger as normal mouse
movement, with very light finger pressure.

I've tried to collect evemu data showing the problem. See attached three
evemu logs:

one-finger.txt:
   Normal cursor movement

two-finger-noscroll.txt:
   Two fingers with similar applied pressure as one-finger.txt.
   Scrolling was not triggered.
   In fact, usually, this results in zero libinput events being generated
   (as reported by libinput-debug-events), but sometimes normal mouse movement
   is triggered.

two-finger-scroll.txt:
   Two fingers, on an attempt that did trigger two-finger scrolling.
   The pressure is very high.

I tried tweaking the pressure settings as described here[1], but it didn't
help (and mostly made one-finger movement worse).

I've also attached plotted evemu stats (as described in [1] again), for the
same movements (20 swipes upwards) with one and two fingers. The pressure for
two fingers appears to be lower than one, and there are significantly fewer
PRESSURE events for two fingers.

Let me know if there's anything more I can provide.

[1] https://wayland.freedesktop.org/libinput/doc/latest/touchpad_pressure.html

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