(define turtle-draw! 
  (lambda (turtle distance turn counter width n) 
    (if (> counter 80) (turtle-down! turtle)) 
    (cond ((< (* distance counter) (* width 80)) 
           (turtle-forward! turtle distance) 
           (turtle-turn! turtle turn) 
           (turtle-draw! turtle distance (modulo (+ n turn) 80) (+ counter 1) width (+ (* n 2) 1))) 
          (else (display "turtle is finnished!") (newline)))))

(define go-go-go! 
  (lambda (canvas n) 
    (let ((width (image-width canvas)) 
          (height (image-height canvas))) 
      (image-compute-pixels! 
       canvas 0 0 (- (image-width canvas) 1) (- (image-height 
                                                 canvas) 1) 
       (lambda (pos) 
         (let* ((xpos (position-col pos)) 
                (ypos (position-row pos)) 
                (xin (* xpos (/ 3 width))) 
                (yin (* ypos (/ 3 height))) 
                (zval (* (+ (- (* xin xin xin) (* 3 xin)) (- (* yin 
                                                                yin yin) (* 3 yin))) (cos (* xin yin yin (+ (modulo n 2) 1)))))) 
           (cond  ((and (< zval (* 5.5 (sqrt (/ n 27)))) (> zval (* 4.5 (sqrt (/ n 27))))) 
                   (rgb-new (* 200 (/ xpos width)) (* 100 (/ ypos height)) 0)) 
                  
                  ((and (> zval (* -5.5 (sqrt (/ n 27)))) 
                        (< zval (* -4.5 (sqrt (/ n 27))))) 
                   (rgb-new (* (* 100 (/ (mod n 28) 27)) (/ xpos width)) 
                            0 
                            (* (* 200 (/ (mod n 28) 27)) (/ ypos height)))) 
                  
                  ((negative? zval) 
                   (rgb-new 0 (/ (abs (* 44 zval)) 2) 0)) 
                  (else 
                   (rgb-new 0 0 (/ (abs (* 44 zval)) 2))))))))))

(define circle-draw! 
  (lambda (canvas xcent ycent rad type) 
    (image-select-ellipse! canvas type 
                           (- xcent rad) (- ycent rad) 
                           (* 2 rad) (* 2 rad))))

(define symbol! 
  (lambda (canvas n width height) 
    (context-set-fgcolor! (rgb-new (+ (modulo (* n n) 100) 100) (modulo (* n n n) 68) (modulo (* n n n) 250))) 
    (define rad  (quotient (quotient (+ height width) 2) 20)) 
    
    (circle-draw! canvas (quotient width 2) (quotient height 2) rad selection-add)
    
    (context-set-brush! "Sparks") 
    (image-stroke! canvas) 
    ;(image-stroke! canvas) 
    (image-select-nothing! canvas) 
    (context-update-displays!) 
    ))

(define image-series 
  (lambda (n width height) 
    (define n (+ n 1)) 
    (define canvas (image-new width height)) 
    (image-show canvas)
    
    ;***********************sets up turtle 
    (define distance (+ (* (+ (modulo n 2) 1) (/ width 40)) 1))  
    (define pen1 (turtle-new canvas)) 
    (turtle-teleport! pen1 
                      (+ (modulo n (quotient width 3)) (quotient width 6)) (+ (modulo n (quotient height 3)) (quotient height 6)))    
    (turtle-set-color! pen1 (rgb-new 255 255 255)) 
    ;***********************sets up turtle 
    
    ;@@@@@@@@@@@@@@@@@@@@@@@renders background 
    (display "Rendering background") 
    (newline) 
    ;(define layer (image-get-drawable canvas)) 
    ;(drawable-begin-caching! layer) 
    ;(go-go-function! canvas layer 0 0 n width height) 
    ;(drawable-end-caching! layer) 
    (go-go-go! canvas n) 
    (display "Background complete!") 
    (newline) 
    ;@@@@@@@@@@@@@@@@@@@@@@@renders background 
    
    ;&&&&&&&creates small shape 
    (symbol! canvas n width height) 
    ;&&&&&&&creates small shape 
    
    ;******************runs turtle 
    (turtle-up! pen1) 
    (turtle-draw! pen1 distance 0 0 width n) 
    ;******************runs turtle 
    
    (define n (- n 1)) 
    ;(display n) 
    (if (or (equal? n 2) (equal? n 4) (equal? n 8) (equal? n 16) (equal? n 32) (equal? n 64) (equal? n 128) (equal? n 256) (equal? n 512) (equal? n 1024) (equal? n 2048) (equal? n 4096)) (((image-transform! canvas rgb-complement))))
    
    
    (display "COMPLETE!")  ;occassionally, an image will create successfully, but the next will not.  Its sometimes necessary to hit the run button                                                  ;between images.  I'm not sure why.  Everything should take between 5 and 10 minutes for a desktop background size image (thanks in large part to help from Sam Rebelsky in the efficiency department)
    
    (newline)    
    ))