gistfile1.hs

intersectDist :: Exp Ray -> Exp Sphere -> Exp SphereIntersect
intersectDist r s =
                let
                    v = (center s) -. (start r)
                    a = dot v (dir r)
                in
                (a <* 0) ? (
                    lift $ (constant False, s, constant (-1.0)),
                    let
                        b2 = dot v v - a * a
                        r2 = (radius s) * (radius s)
                    in
                    (b2 >* r2) ? (lift $ (cfalse, s, constant (-1.0)),
                                  let
                                        c = sqrt(r2 - b2)
                                        near = a - c
                                        far = a + c
                                        distance = (near <* 0) ? (far, near)
                                  in                    
                                  lift $ (constant True, s, distance))
                )