libinput: Thumb detection based on ABS_MT_WIDTH

[Friedrich Schöller]

Dear all, dear Peter,

As you know, bcm5974 touchpads do not report ABS_MT_PRESSURE, but ABS_MT_WIDTH 
instead. Since libinput does not currently use ABS_MT_WIDTH, thumb detection is 
inaccurate on those devices. When I switched from Mac OS to Linux, I stopped 
using the Magic Trackpad solely for that reason. Now I decided it would be time 
to get my favorite pointing device back. To do this, I would like to implement 
thumb detection based on ABS_MT_WIDTH. Using these values has the additional 
benefit of making thumb detection significantly more reliable, since the 
eccentricity of a thumb can be deduced, which is typically much larger than that 
of a finger.

Now I am wondering if this would be a welcome addition to libinput. When looking 
through the mailing list I found the patch "touchpad: add touch-size based touch 
handling". This would probably be a good basis to build on. Are you still 
considering committing the patch to git?

Thanks for all your great work.

Best,

Friedrich