Function ncvisual_from_rgb_packed 

pub unsafe extern "C" fn ncvisual_from_rgb_packed(
    rgba: *const c_void,
    rows: c_int,
    rowstride: c_int,
    cols: c_int,
    alpha: c_int,
) -> *mut ncvisual

ncvisual_from_rgba(), but the pixels are 3-byte RGB. A is filled in throughout using ‘alpha’. It is an error if ‘rows’, ‘rowstride’, or ‘cols’ is not positive, if ‘rowstride’ is not a multiple of 3, or if ‘rowstride’ is less than ‘cols’ * 3.