pub type dTriCallback = Option<unsafe extern "C" fn(TriMesh: dGeomID, RefObject: dGeomID, TriangleIndex: c_int) -> c_int>;
pub enum dTriCallback { None, Some(unsafe extern "C" fn(*mut dxGeom, *mut dxGeom, i32) -> i32), }
No value.
Some value of type T.
T