donut.ix

(var W 80 H 25
     chars ".,-~:;=!*#$@"
     PI2 (* 2 PI)
     speed-A .05 speed-B .05 speed-I .05 speed-J .05
     a 0 b 0)

(var last-ms (time))

(function calculate-screen screen
  (let prev-ms last-ms)
  (str
    (- (var last-ms (time)) prev-ms) "ms between frames\n"
    (join "\n" (map (.. str) (partition W screen)))))

(while true
  (let grid  (times (* H W) " ")
       _grid (times (* H W) 0)
       j 0)
  (while (< j PI2)
    (let j (+ j speed-I) i 0)
    (while (< i PI2)
      (let i (+ i speed-I)
           [sa sb sc sd] (map sin [a b i j])
           [ca cb cc cd] (map cos [a b i j])
           cd+2 (+ cd 2)
           e (/ 1 (+ (* sc cd+2 sa) (* sd ca) 5))
           f (- (* sc cd+2 ca) (* sd sa))
           x (floor (+ (/ W 2) (* 30 e (- (* cc cd+2 cb) (* f sb)))))
           y (floor (+ (/ H 2) (* 15 e (+ (* cc cd+2 sb) (* f cb)))))
           index (+ x (* W y)))
      (when (and (< 0 y H) (< 0 x W) (< (index _grid) e))
        (let z (floor (* 8 (- (* (- (* sd sa) (* sc cd ca)) cb)
                              (* sc cd sa)
                              (* sd ca)
                              (* cc cd sb)))))
        (var _grid (set-at [index] e _grid)
             grid  (set-at [index] ((max z 0) chars) grid)))))
  (print (calculate-screen grid))
  (var a (+ a speed-A) b (+ b speed-B)))