Mapping GameCube Z button to BACK/Select button is problematic

[InquisitiveCoder]

The GameCube's Z button is currently mapped to XInput's BACK button and Switch's minus button. This is an unfortunate choice since it doesn't match the default button layouts used by Super Smash Bros. Ultimate or recently-released Smash Bros. Melee clone, Rivals of Aether 2. What's worse, neither game allows binding actions to BACK/-, so the current GameCube mode renders the Z button entirely unusable.

The current mapping doesn't seem to have much in the way of upsides either. As far as I know Steam's Big Picture Mode doesn't use the BACK button for anything and RetroArch only uses BACK as the equivalent of PageDown. Back/Select/- is far more likely to go unused in any given game than the bumpers as well. If someone uses GameCube controllers on MiSTer for whatever reason they can change the OSD hotkey to another button combination that doesn't involve Select.

My proposal is simple: map Z to RB (XInput)/R (Switch). This makes the GameCube mode work perfectly with Smash Ultimate and - if the Use Nintendo Button Layout option is enabled on Steam - also Rivals 2. From poking around in Input_GameCube.h it even looks like this was already considered, since there's commented out code lines doing just that.

[bryanparadis]

Trying to think what the reason for the current mapping is. No good history/blame hints unfortunately.

[bryanparadis]

N64 is mapped the same way? https://github.com/misteraddons/Reflex-Adapt/blob/main/ReflexMPG/Input_N64.h#L342C1-L342C107