;;; Scheme Recursive Art Contest Entry
;;;
;;; Please do not include your name or personal info in this file.
;;;
;;; Title: Falling
;;;
;;; Description:
;;;   Even though there is
;;;   inverse-square force, these are not
;;;   isopotentials


;;; NOTE: Since I had to do a lot of refactoring to get this code into the lightweight division, a lot of comments
;;;       were cut out and a lot of constants were replaced by their values


(define (square n) (* n n))

(define (arc_helper angle_left r)
    (if (<= angle_left 0)
        ()
        (begin (forward (* 2 r 0.008726646259971648))
               (rt 1)
               (arc_helper (- angle_left 1) r))
        )
    )

(define (gray_helper n last_color)
	(if (zero? n)
    	()
    	(let ((new_gray (map (lambda (x) (- x 3)) last_color)))
    		 (cons new_gray (gray_helper (- n 1) new_gray)))
    	)
	)

; because why the heck is it scaled 0 to 1???
(define (to_rgb c)
	(rgb (/ (car c) 255) (/ (car (cdr c)) 255) (/ (car (cdr (cdr c))) 255))
	)

; Draws a bunch of gray stuff
(define (drawbg r scale colors)
	(if (null? colors)
		()
		(begin (begin_fill)
               (color (to_rgb (car colors)))
		       (setpos (- r) -200)
		       (pendown)
		       (seth 0)
		       ; When the remaining angle is 0, stop recursion
		       (arc_helper 360 (+ 200 r))
			   (end_fill)
			   (penup)
			   (drawbg (- r scale) scale (cdr colors)))
		)
	)

(define (orbit_update x y vx vy c dt)
	(cond ((< x -420) ())
		  ((> y 395) ())
		  (else
		  	(let ((angle (atan (/ (+ y 1800) (+ x 1000))))
			  	  (k (/ 8 (+ (square (+ x 1000)) (square (+ y 1800))))))
				(setpos x y)
				(pendown)
				(color (to_rgb c))
				(orbit_update (+ x (* dt vx)) (+ y (* dt vy))
					(+ vx (* dt k (abs (cos angle)) (if (> x -1000) -1 1))) (+ vy (* dt k (abs (sin angle)) (if (> y -1800) -1 1)))
					(map (lambda (n) (if (>= n 254) 255 (+ 0.15 n))) c)
					dt
					)
				)
			)
		)
	)

; Draws n orbits with starting velocity v, angle from 180° angle0, and cw change adj
(define (draworbits n vx vy r)
	(if (zero? n)
		()
		(begin (penup)
			   (orbit_update 420 -393.5 vx vy '(120 0 0) 30)
			   (draworbits (- n 1) (* vx 0.89) (+ vy 0.003) r)
			)
		)
	)

(define (draw)
    ; YOUR CODE HERE
    (speed 0)
    (bgcolor "#c0c8d2")
    (drawbg 630 9 (gray_helper 64 '(192 200 210)))
    (draworbits 60 -0.08 0.01 0)
    (hideturtle)
    (exitonclick))

; Please leave this last line alone.  You may add additional procedures above
; this line.
(draw)