pub type PFNGLTEXTUREPARAMETERIVPROC = Option<unsafe extern "C" fn(texture: GLuint, pname: GLenum, param: *const GLint)>;
enum PFNGLTEXTUREPARAMETERIVPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: *const i32)), }
No value.
Some value of type T.
T