Right, that’s functionality that does/can exist in QGC, but is disabled/hidden at the moment for vehicles that can be controlled with a Joystick. There’s a Github Issue about potentially re-enabling that (for a different purpose), but the proposal there is to hopefully come up with some kind of better system of mixing controls between QGC actions and vehicle actions from a single joystick, since it’s quite clunky at the moment.
That said, it does seem to function there, so if you want to try that approach you should hopefully also be able to add your own custom functionalities by copying the approach for the existing functionalities. The QGroundControl Joystick docs don’t seem to discuss the assignable functionalities much, but after a search on the QGroundControl github repo it seems like the
src/Joystick/Joystick.cc file is where most of the relevant code is, although I expect you’ll also need to update
Joystick.h, and possibly some other places (I’m not sure, as I haven’t needed to add something here before).