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#lang sketching
(define (setup)
(size 200 200)
(frame-rate 1)
(loop))
(define iterations 14)
(define init-segment 400)
(define Line cons)
(define ->0 car)
(define ->1 cdr)
(define Point cons)
(define ->x car)
(define ->y cdr)
(define (draw/line my-line)
(let [ (p1 (->0 my-line)) (p2 (->1 my-line)) ]
(line (->x p1) (->y p1) (->x p2) (->y p2))))
(define (split-line my-line dir)
(let* [
(x1 (->x (->0 my-line)))
(y1 (->y (->0 my-line)))
(x2 (->x (->1 my-line)))
(y2 (->y (->1 my-line)))
(len (dist x1 y1 x2 y2))
(sidelen (sqrt (/ (* len len) 2)))
(theta (atan2 (- y2 y1) (- x2 x1)))
(slope (+ theta (* (/ pi 4) dir)))
(p3 (Point
(+ x1 (* sidelen (cos slope)))
(+ y1 (* sidelen (sin slope)))))
]
(cons (Line (->0 my-line) p3) (Line p3 (->1 my-line)))))
(define (dragon-curve my-line dir iteration)
(let [ (lines (split-line my-line dir)) ]
(if (<= iteration 0)
(list (->0 lines) (->1 lines))
(append
(dragon-curve (->0 lines) 1 (- iteration 1))
(dragon-curve (->1 lines) -1 (- iteration 1))))))
(define current-iteration 0)
(define (draw)
(background 150)
(let* [
(p1 (Point (- (/ width 2) (/ init-segment 2)) (/ height 2)))
(l1 (Line p1 (Point (+ (->x p1) init-segment) (->y p1))))
(lines (dragon-curve l1 1 current-iteration))
]
(stroke-weight 2)
(stroke 0 0 0)
(for-each draw/line lines)
(if (= current-iteration iterations)
(no-loop)
(set! current-iteration (+ current-iteration 1)))))
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