This is an enumerated type for controller axes. Things are a bit gross here because it needs to correspond with the enum SDL_GameControllerAxis in SDL_gamecontroller.h. We skip the invalid axis one and the max one (Who would ever want to check those anyway?). This means that we start with an index 0 instead of -1, so that's nice at least. Make sure that the indices of the included axis matches with the values in the enum in native code. (i.e. that A is 0 in both, B is 1 in both, etc.).