Function set_input_descriptors 

pub unsafe fn set_input_descriptors(
    callback: retro_environment_t,
    descriptors: &[retro_input_descriptor],
) -> bool

Sets an array of retro_input_descriptors. It is up to the frontend to present this in a usable way. The array is terminated by retro_input_descriptor::description being set to NULL. This function can be called at any time, but it is recommended to call it as early as possible.