[Wayland-bugs] [Bug 98800] Allow resting the thumb on the touchpad while performing multi-finger gestures

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98800

Peter Hutterer <peter.hutterer at who-t.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEEDINFO                    |RESOLVED
         Resolution|---                         |WONTFIX

--- Comment #6 from Peter Hutterer <peter.hutterer at who-t.net> ---
ok, basic problem here: your touchpad only supports 2 finger tracking. That's
common for all PS/2 touchpads, until we get the RMI4 patches into the kernel
this simply cannot work. The main problem is that we only get a bitflag to tell
us that 2, 3, 4 or even 5 fingers are down (the various BTN_TOOL_*TAP). The
actual position is only provided for the first two fingers down, so depending
on the situation this may be thumb+finger or just two fingers. We can't even do
thumb detection for 2+ fingers for that reason.

For the gestures that also means we have no idea if all fingers need to be
counted or not because we just don't know where some of them are (and thus
whether one of them could be a thumb or not).

As I said above, the RMI4 code hopefully in kernel 4.10 should fix that by
giving us full 5 finger tracking, but until then we can't do anything with your
touchpad.

But anyway, it brings us to the next issue: it's semantically quite ambiguous
to figure out when a thumb counts and when it doesn't. Thumb down + two-finger
scroll - is it a 2fg scroll or a three-finger pinch? Especially given the small
movements a thumb does while moving the other fingers, it's hard to determine
what should happen. With buttonareas we have the advantage of just ignoring a
part of the touchpad, but with clickfinger this doesn't work.

There are cases where it's reasonably clear (e.g. a thumb resting for ages on
some area) but we need to solve these ambiguities for all use-cases. And at
that point I rather not have the ability to do thumb + gestures, if for no
other reason than that it trains users not to try it in the first place. Sorry

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