[PATCH libinput] touchpad: fix tapping that happens after a moving thumb

[Peter Hutterer]

On Thu, May 10, 2018 at 12:46:02AM +0200, Friedrich Schöller wrote:
> On 09.05.2018 06:34, Peter Hutterer wrote:
> > On Sat, May 05, 2018 at 03:49:32AM +0200, Friedrich Schöller wrote:
> > thanks, patch looks good and is merged locally. Any chance I can convince
> > you to write a test case for this? :)
> > Would make sure that we're not breaking this again.
> 
> Nice to hear! I wrote a test and will post it on the mailing list. However,
> there is a problem with it and all the other tests of thumb detection:
> 
> Thumb detection is triggered by setting the pressure to 75. Now this
> pressure is high enough to trigger palm detection as well. That means that
> all the thumb detection tests currently succeed, no matter if thumb
> detection works or not.

oh, oops. That's a by-product of the thumb detection existing before the
pressure-based palm detection.

> To avoid triggering palm detection, a pressure of 51 or lower is required.
> But this value is too low to trigger thumb detection on all devices.
> 
> Should we somehow disable palm detection during the thumb tests?

Nah, we should fix thumb pressure detection. Basically add another parameter
to the hwdb LIBINPUT_ATTR_THUMB_PRESSURE_THRESHOLD and use that as the
reference value . The current approach cannot work anyway due to the varying
pressure values. I forgot that was in there, I already switched the palm and
normal pressure to use the hwdb values.

I filed https://bugs.freedesktop.org/show_bug.cgi?id=106458 for this so it
doesn't get lost, feel free to start working on it. It would be a fairly
straightforward patchset.

Cheers,
   Peter