pub type PFNGLVDPAUSURFACEACCESSNVPROC = Option<unsafe extern "C" fn(surface: GLvdpauSurfaceNV, access: GLenum)>;
enum PFNGLVDPAUSURFACEACCESSNVPROC { None, Some(unsafe extern "C" fn(_: isize, _: u32)), }
No value.
Some value of type T.
T