Sticky keys allow to trigger key combinations one key at a time.
This is an accessibility feature used by people that cannot press multiple keys simultaneously.
On X11 this is handled by the X server, configured via kaccess.
On Wayland we get to handle this ourselves.
wl_keyboard events already carry the modifier's latched/locked state, so all we need to do is to make sure the right state is set
Xkb gains a new method to set the state. The business logic is implemented in a new plugin that filters for keys and sets the Xkb state accordingly.
This is a barebones implementation. Some aspects are missing:
-
Locking modifiers -
Disabling when two keys are held down -
Notify when locked/latched