[Wayland-bugs] [Bug 94236] Palm detection: ignore moves over a pressure threshold

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94236

            Bug ID: 94236
           Summary: Palm detection: ignore moves over a pressure threshold
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: libinput
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: lagoon42 at gmail.com

libinput's palm detection is well described in the documentation and works
pretty well for the listed use cases. However, I've found that palms are
frequently not detected in other cases, basically when the palms are not in the
palm exclusion zones.

This is slightly annoying, and neither Windows 10 (on the same hardware, a Dell
XPS 9350 [1]) nor OS X (on a different hardware, a Macbook Air) suffer from
that issue.

I've tested a trivial patch (added a condition in tp_touch_active) to libinput
1.1.7 which ignores moves when the pressure is over 100, and I've found that it
resolves the issue. All my palms are correctly detected wherever they are, and
I haven't had false positives. The detection is now as good as Windows or OS X.

The threshold value (100) is good for my fingers and my touchpad, but maybe
that should be configurable. My legitimate moves are in the between 50 and 55.

The synaptics driver includes a similar feature with the PalmMinZ option.

[1] the touchpad has to be in PS/2 mode to report pressure, as it doesn't in
I2C mode.

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