Feature request: Trackpad zones for layer switching using thumbs

[nahuel]

Is your feature request related to a problem? Please describe.

Laptop keyboards don't have thumb buttons or at least a split spacebar (only Thinkpads have integrated mouse buttons that can be used as such).

Describe the solution you'd like.

Similar to #108 , IMHO it will be very useful and ergonomic to use the trackpad to switch layers using thumbs (without requiring Thinkpad-like mouse buttons). This can be done by listening for trackpad touchs (not clicks). So when the thumb starts touching the trackpad, kanata can emit some key-down event that can be mapped to a layer switch, and when the thumb stops touching the trackpad, the key-up event will be emitted and the layer will be disabled.

Note that this doesn't conflict with normal trackpad usage if an unused keycode is chosen (or if there is no keycode at all and is only mapped to an internal kanata event), because you usually don't use the keyboard while using the trackpad for pointer movement, so it doesn't matter if a layer switch happens while moving the pointer using the trackpad.

This functionality can be extended by defining multiple trackpad zones for multiple keys/layers, that can be used simultaneously with the two thumbs. E.g.

┌───┐
│   │  Single zone, whole trackpad "button"
└───┘
┌─┬─┐
│ │ │  Split in half, one half for each thumb, three possible "button" combinations/layers
└─┴─┘
┌─┬─┐
├─┴─┤  Three possible "buttons"
└───┘
┌─┬─┐
├─┼─┤  Advanced user :)
└─┴─┘

Will be nice to give the user the possibility of defining arbitrary zones by configuring rectangle zones using touchpad coordinates. Additionally you can put some stickers over the trackpad to have more visual trackpad "buttons" :)

Describe alternatives you've considered.

Additional context

[jtroo]

On Linux seems EV_ABS might be usable if the touchpad emits the event.

https://docs.kernel.org/input/event-codes.html

Unsure about Windows and macOS.

[mayurankv]

Haven't worked with it so unfamiliar with how it works, but Karabiner has a multitouch extension which I understand works off the same daemon: https://karabiner-elements.pqrs.org/docs/manual/misc/multitouch-extension/

This could hopefully help with Mac mouse actions too. Unfortunately I'm not familiar with Karabiner so I'm not able to contribute this myself :((. Will try and take a look but unlikely to be much help.