Touchpad acceleration

[Hans de Goede]

Hi,

On 04/10/2015 11:15 AM, Stefanos A. wrote:
> Hello,
>
> I recently started testing Gnome 3.16 over Wayland 1.7.0 & libinput
> 0.13.0 and came across the following interesting behavior on my
> touchpad. In short, the pointer feels as if it lagging on the monitor
> compared to my finger movement. The result is that I consistently
> overshoot small targets, such as the "X" button to close a window.
>
> Now, I understand that there is a familiarity effect going on here,
> but I have to say that I am not seeing this behavior when using Xorg
> or Windows on the same hardware (or OS X on different hardware.)
>
> Moving the "touchpad acceleration" slider to the "slowest" setting
> appears to remove this lag, at the cost of a too-slow-to-be-usable
> pointer. Moving the slider to the "fastest" setting appears to make
> things worse, in the sense that I find it impossible to hit any screen
> target reliably.
>
> My theory is that the libinput acceleration curve starts with a <1.0
> acceleration for slow movements and moves to a >1.0 acceleration for
> faster movements and the lag is a placebo caused by the <1.0 part of
> the curve.
>
> Is there a way (configuration or tool) I could use to test this
> theory? My gut feeling is that I would prefer to remove or make the
> <1.0 part of the acceleration curve less aggressive and keep the >1.0
> part, if that makes sense.
>
> `cat /proc/bus/input/devices` returns the following:
>
> I: Bus=0011 Vendor=0002 Product=0007 Version=01b1
> N: Name="SynPS/2 Synaptics TouchPad"
> P: Phys=isa0060/serio1/input0
> S: Sysfs=/devices/platform/i8042/serio1/input/input9
> U: Uniq=
> H: Handlers=event12 mouse0
> B: PROP=9
> B: EV=b
> B: KEY=6420 30000 0 0 0 0
> B: ABS=260800011000003

Do you happen to have a x230 laptop ? That one is know to have a couple
of issues with the libinput pointer accel code.

Regards,

Hans