; Devil's Pitchfork in Dr. Scheme

(define the-view-port '())

(define (init-graph)
  (open-graphics)
  (set! the-view-port 
  (open-viewport "chaos" 80 80 10)))

(define (close-graph)
  (if (not (null? the-view-port)) (close-viewport the-view-port)
  (close-graphics)))

;(define (put-pixel x y)
  ;((draw-pixel the-view-port) 
   ;(make-posn (* 100 (car x)) (+ 400 (* 100 (cdr x))))))

(define (put-pixel x y)
  (define color (make-rgb 0 0 0))
  ((draw-solid-ellipse the-view-port) 
   (make-posn (* 130 (car x)) (+ 400 (* 150 (cdr x))))
   4 4 color))

  

; = next state of system S
(define (logistic state)
  (* const (- 1 state) state))

; = displays attractor of logistic procedure
(define (show-log-attractor const)
  
  ; the logistic function
  (define (logistic state) 
    (* const (- 1 state) state))
  
  ; 0 <= init-state <= 1 & init-state <> .5
  (define init-state .2)
  
  ; control-loop:
  (do ((cycle 0 (+ cycle 1))
       (state init-state (logistic state)))
    ((> cycle 620) 'done)
    (if (> cycle 500)
	(show-state const state))))



;(define (show-state const state)
 ; (display (cons const state))
 ; (newline))

(define (show-state const state)
  (put-pixel (cons const state) 'white))

(define (pitchfork start finish)
  
  (define slices 75)   ; # of attractors shown
  
  (define delta (/ (- finish start) slices))
  
  (init-graph)      ; enter graphics mode
  
  (do ((const start (+ const delta)))
    ((< finish const) 'done)
    (show-log-attractor const)))