[Wayland-bugs] [Bug 104533] Hysteresis detection fails on the single-touch axes after a while

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104533

            Bug ID: 104533
           Summary: Hysteresis detection fails on the single-touch axes
                    after a while
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: libinput
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: peter.hutterer at who-t.net
                CC: benjamin.tissoires at gmail.com,
                    jcowgill+freedesktop at jcowgill.uk
        Depends on: 98839

Created attachment 136606
  --> https://bugs.freedesktop.org/attachment.cgi?id=136606&action=edit
evemu recording of a finger-hold

Spin-off of bug 98839, see the attachment (originally from attachment 136276).

When replayed, libinput leaves the hysteresis in place until the 6.799107
frame. That frame is 84ms after the previous one and disables the hysteresis.
At that point the pointer starts wobbling.

Noteworthy is: this only wobbles because it's a semi-mt where we disable MT and
look at ABS_X/ABS_Y only. And only ABS_X/Y events have wobbles because fuzz is
0 - the ABS_MT_POSITION_X/Y axes have a fuzz of 8 which makes the kernel
suppress the wobbles.

The mismatched fuzz is a result of input_mt_init_slots() in the kernel,
copy_abs() forces fuzz to zero. See kernel commit
352ce2b0575f195c8e6452a9802e6c186b39409a. But that commit seems to be a bug, at
least the synaptics driver doesn't use any in-kernel single-touch emulation but
sends ABS_X/Y directly (as opposed to calling
input_mt_report_pointer_emulation). Benjamin, can you have a look at that
please?


Referenced Bugs:

https://bugs.freedesktop.org/show_bug.cgi?id=98839
[Bug 98839] Somehow conditionalize hysteresis (hardware black/whitelist, device
property introspection, user-exposed setting, etc)
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