Bug 98799

Please record your touchpad with evemu-record and rest your thumb on the touchpad a few times (only the thumb, no other fingers to avoid interference). Then do the same thing again with normal finger operation. That should give us an idea of how to detect the thumb.

Gladly! One thing that I notice from the recordings is that I get pressure values that are around 40-60 when the thumb is resting on the bottom edge, but 80-110 when the thumb is resting somewhere away from an edge. Fingers, by contrast, register as 40-60 when away from an edge. That might be a good way to detect a resting thumb.

The recordings I'm about to attach show the problem: with the thumb resting on the bottom of the pad, pointing occasionally triggers two-finger scroll behavior, and two-finger sctolling almost always does nothing (perhaps it's interpreting it as some kind of three-finger gesture?)

Created attachment 128133 [details]
evemu recording of my thumb sitting on various places on the touchpad

Created attachment 128134 [details]
evemu recording of my thumb resting on the bottom of the pad and my fingers pointing and scrolling

Here is a use case that illustrates the problem 100% of the time for me:

1. Move just your pointer finger horizontally along the pad.
2. While the finger is moving, put your thumb on the bottom of the pad, in the area that should be ignoring thumbs.

With "Areas" behavior, the cursor continues moving, albeit with a slight stutter the moment the thumb hits the bad (boo)

With "Clickfinger" behavior, the cursor stops moving the moment the thumb hits the pad.

(In reply to Nate Graham from comment #5)
> Here is a use case that illustrates the problem 100% of the time for me:
> 
> 1. Move just your pointer finger horizontally along the pad.
> 2. While the finger is moving, put your thumb on the bottom of the pad, in
> the area that should be ignoring thumbs.

fwiw, this work here on my T440, as long as the thumb is on the very edge/bottom of the touchpad. Run libinput-debug-events --verbose --set-click-method=clickfinger and it'll show when the thumb is detected.

Admittedly, there's a short scroll event if the thumb is put down while the other finger is moving, but it works. if the finger is held still until thumb detection kicks in. That's a separate bug we should address at some point.

(In reply to Nate Graham from comment #3)
> Created attachment 128133 [details]
> evemu recording of my thumb sitting on various places on the touchpad

I ran a touch-pressure from here https://github.com/whot/input-data-analysis/:
./touch-pressure-deltas.py ~/tmp/today/thumb.evemu | cut -d ' ' -f 1,2 | sort | uniq

The values start at 24 and top out at 102. between 40 and 98 almost every value is present. your second recording has values from 19 to 71. So there's likely some overlap between the pressure values. but I don't have the script to analyse this just yet. Note that pressure is just a function of contact surface area, so it's less at the edges because your thumb hangs off the touchpad then.

meanwhile feel free to tinker with tp_init_thumb(), there's a comment about the pressure. Your level is clearly lower, if you tweak that your thumb detection should work better too.

a script to print a 3d graph of pressure values on a touchpad recording is here:
https://github.com/whot/input-data-analysis/blob/master/touch-pressure/touch-pressure.py

run it against a long-term touchpad data recording and it should show you the various pressure values in a mesh graph. Not perfect, but good enough to recognise the interesting ranges.

FWIW changing the thumb detection pressure value to 70 works great for me. But this doesn't solve the true problem: https://bugs.freedesktop.org/show_bug.cgi?id=99268

We can probably close this out in favor of that, since if that solution I proposed there gets implemented, then the problem in this bug disappears.

Or the reverse. Probably don't need two bugs tracking the same thing.

Closing this because of comment #8 and bug 99268 that is closed now, please re-open if there are leftover issues.