Almonds

(use data-structures srfi-1)

(define height 900)
(define width 900)
(define escape-value 700)

(define (->integer n)
  (inexact->exact (floor (exact->inexact n))))

(define (hsb->rgb h s b)
  (let* ((c (* b s))
         (x (* c (- 1 (abs (sub1 (modulo (->integer (/ h 60)) 2))))))
         (m (- b c))
         (rgb*
          (cond ((and (<= 0 h) (< h 60))
                 (list c x 0))
                ((and (<= 60 h) (< h 120))
                 (list x c 0))
                ((and (<= 120 h) (< h 180))
                 (list 0 c x))
                ((and (<= 180 h) (< h 240))
                 (list 0 x c))
                ((and (<= 240 h) (< h 300))
                 (list x 0 c))
                ((and (<= 300 h) (< h 360))
                 (list c 0 x)))))
    (map (lambda (c) (->integer (* 255 (+ m c)))) rgb*)))

(define (color-mapping i)
  (hsb->rgb (- 359 (modulo i 360)) 1 (/ i (+ 8 i))))

(define colors (map color-mapping (iota (add1 escape-value))))

(define (mandelbrod/real real img)
  (define (x* x y)
    (+ (- (* x x) (* y y)) real))
  (define (y* x y)
    (+ (* 2 x y) img))
  (let iterate ((x 0)
                (y 0)
                (count 0))
    (if (or (>= (+ (* x x) (* y y)) 4)
            (>= count escape-value))
        count
        (iterate (x* x y) (y* x y) (add1 count)))))

(define (infinity-trap/instant-draw acorner bcorner side #!key (formula mandelbrod/real))
  (let ((h-gap (/ side height))
        (w-gap (/ side width)))
    (fprintf (current-error-port) "Gap: ~a, ~a~%" h-gap w-gap)
    (let loop ((i 0))
      (if (>= i (* height width))
          'done
          (begin
            (let* ((c (formula (+ acorner (* w-gap (remainder i width)))
                               (+ bcorner (* h-gap (quotient i width)))))
                   (colors (if (>= c escape-value)
                               '(0 0 0)
                               (list-ref colors (->integer c)))))
              (printf "~a ~a ~a~%" (car colors) (cadr colors) (caddr colors)))
            (loop (add1 i)))))))

(print "P3")
(printf "~a ~a~%" width height)
(print 255)
(infinity-trap/instant-draw -2 -1.25 2.5 formula: mandelbrod/real)