pub type PFNGLCOLOR4UBVERTEX3FVSUNPROC = Option<unsafe extern "C" fn(c: *const GLubyte, v: *const GLfloat)>;
enum PFNGLCOLOR4UBVERTEX3FVSUNPROC { None, Some(unsafe extern "C" fn(_: *const u8, _: *const f32)), }
No value.
Some value of type T.
T