[Wayland-bugs] [Bug 105727] libinput-1.10.3: two-finger-scrolling snaps back when lifting fingers

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105727

            Bug ID: 105727
           Summary: libinput-1.10.3: two-finger-scrolling snaps back when
                    lifting fingers
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: libinput
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: main.haarp at gmail.com

Created attachment 138333
  --> https://bugs.freedesktop.org/attachment.cgi?id=138333&action=edit
evemu log showing behavior

Hello.

I'm currently using libinput 1.10.3 with a SynPS/2 Synaptics TouchPad on a
Thinkpad W530. A recent update of libinput, I think either 1.10.2 or 1.10.3
introduced uncomfortable scrolling behavior.

When two-finger-scrolling, very often the scroll operation "snaps back" when I
lift my fingers. By that I mean a scroll event in the opposite direction is
generated.

Here's a debug-events example:

 event12  POINTER_AXIS      +4.64s      vert 2.52* horiz 0.25* (finger)
 event12  POINTER_AXIS      +4.67s      vert 6.83* horiz 0.25* (finger)
....
 event12  POINTER_AXIS      +5.16s      vert 0.36* horiz 0.00 (finger)
 event12  POINTER_AXIS      +5.24s      vert 0.18* horiz -0.25* (finger)
** lifting fingers around now **
 event12  POINTER_AXIS      +5.36s      vert 0.18* horiz -0.25* (finger)
 event12  POINTER_AXIS      +5.41s      vert -13.31* horiz -20.35* (finger)
 event12  POINTER_AXIS      +5.42s      vert 0.00* horiz 0.00* (finger)

The negative vert and horiz event is obvious.

I am also attaching an evemu log that shows how I scroll. It contains three
attempts, the first and third exhibited a snap-back, the second one did not.


It seems I can avoid snap-back by first lifting one finger and then the other.

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