Alps Touchpad does not detect three-or-four-finger gestures
Summary
libinput does not detect multi-finger gestures due to missetting of num_slots
by max value of ABS_MT_SLOT
+1 (see evdev-mt-touchpad.c#L2789).
The kernel will always report max value of ABS_MT_SLOT
3 for Alps devices (which implies 4 slots maximum, see alps.h#L25). However, the actuall number of slots for my Alps device is 2. Therefore, by setting tp->num_slots = absinfo->maximum + 1
, it will lead libinput unable to detect three or four fingers gestures.
On my own computer, changing tp->num_slots = 2
solves the issue.
libinput version you encountered the bug on
Latest master branch
Hardware information:
udev information: see here
Computer model: Lenovo Ideapad 310S-14ISK (modalias: dmi:bvnLENOVO:bvr0VCN31WW(V1.15):bd06/19/2018:svnLENOVO:pn80UA:pvrLenovoideapad310S-14ISK:rvnLENOVO:rnLNVNB161216:rvrSDK0K09938WIN:cvnLENOVO:ct10:cvrLenovoideapad310S-14ISK:
)
Other log output:
see here