pub type PFNGLGETTEXENVXVPROC = Option<unsafe extern "C" fn(env: GLenum, pname: GLenum, params: *mut GLfixed)>;
enum PFNGLGETTEXENVXVPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: *mut i32)), }
No value.
Some value of type T.
T