pub type PFNGLGETTEXTURESAMPLERHANDLENVPROC = Option<unsafe extern "C" fn(texture: GLuint, sampler: GLuint) -> GLuint64>;
enum PFNGLGETTEXTURESAMPLERHANDLENVPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32) -> u64), }
No value.
Some value of type T.
T