pub unsafe extern "C" fn CVDisplayLinkSetOutputCallback(
display_link: &mut DisplayLinkRef,
callback: CVDisplayLinkOutputCallback,
user_info: *mut c_void
) -> i32pub unsafe extern "C" fn CVDisplayLinkSetOutputCallback(
display_link: &mut DisplayLinkRef,
callback: CVDisplayLinkOutputCallback,
user_info: *mut c_void
) -> i32