https://bugs.freedesktop.org/show_bug.cgi?id=103208
--- Comment #18 from Peter Y. Chuang <[email protected]> ---
I want to expand a bit on the idea of using orientation to distinguish between
a palm and a finger around the edges. I've uploaded two evemu-records. One of
which is the recording of my left palm moving along the left edge and sideway
within probably 1 or 2 cm from the left edge. The second is the recording of
the same movements, but with one single finger.
By my count (not sure if iI've counted correctly), when a palm touches the left
edge, orientation is a positive number about 96% of the time. In my
observation, orientation on the left edge is correct (i.e. positive) even when
the contact point is very small and way before touch-size-based palm detection
can kick in.
When a finger touches the edge area, the result is less consistent. By my
count, around 70% of time the orientation is not positive (i.e. either zero,
negative, or nothing).
Given touch-size-based palm detection is not possible around the edges,
orientation may be helpful, even if not 100% reliable (mostly, a single finger
would be falsely identified as a palm; a palm falsely identified as a finger is
much less of a problem). Since most real touch inputs aren't initiated within,
say, 3mm from the edge anyway, perhaps orientation-based palm detection doesn't
have to be 100% accurate. If this could work good enough, perhaps tapping and
tracking could be enabled within the edge exclusion zone.
One of the downsides of it, other than being not 100% reliable, especially with
single finger input, is that if one of the fingers in two-finger scrolling is
placed within the zone where orientation-based palm detection is enabled,
initiating two-finger scrolling will become less reliable too.
I'm also not sure if those measures are good in other touchpads.
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