Function libeyelink_sys::set_write_image_hook

pub unsafe extern "C" fn set_write_image_hook(
    hookfn: Option<unsafe extern "C" fn(outfilename: *mut c_char, format: c_int, bitmap: *mut EYEBITMAP) -> c_int>, 
    options: c_int
) -> c_int

@ingroup bitmap_save Use this function to set function pointer, so that the call to el_bitmap_save and el_bitmap_save_and_backdrop will use the passed in function to write the image to disk.