On this page:
5.1 Spiral with changing pen color
5.2 Spiral with changing pen color and size
5.3 Flower spiral with changing sizes and colors
5.4 Star spiral with changing sizes and colors
7.1

5 Racket Turtle examples with recursion

5.1 Spiral with changing pen color

Spiral created by recursively increasing the distance that turtle moves. Pen colors are changed according to a list of colors.

(define COLORS1 (list "red" "green" "yellow" "purple"))
 
(define (spiral a x times)
  (if (< times 0)
      empty
      (append (list (forward x)(turn-left a))
              (spiral a (+ x 2)(sub1 times)))))
 
(define spiral-image
  (list (change-pen-size 2)
        (change-bg-color "black")
        (change-color COLORS1)
        (spiral 91 1 152)))

(draw spiral-image)

5.2 Spiral with changing pen color and size

Spiral created by recursively increasing the distance that turtle moves. Pen colors are changed according to a list of colors and pen size increases each time.

(define COLORS2 (list "red" "blue" "green" "yellow" "purple"))
 
(define (side x w a)
  (list (change-pen-size w)(forward x)(turn-left a)))
 
(define (spiral2 x w a times)
  (if (<= times 0)
      empty
      (cons (side x w a)
            (spiral2 (+ x 5) (+ w 1) a (sub1 times)))))
 
(define spiral-image2 (list (change-bg-color "black")
                            (change-color COLORS2)
                            (spiral2 1 1 45 45)))

(draw spiral-image2)

5.3 Flower spiral with changing sizes and colors

Flower spiral programmed using the stamper functionality. The colors of the flowers change randomly.

(define (leaf size color)
  (ellipse (* 8 size) size "solid" color))
 
(define (leafs size color)
  (overlay (leaf size color)
           (rotate 90 (leaf size color))))
 
(define (draw-flower size color)
  (overlay (circle (/ size 2) "solid" "white")
           (leafs size color)
           (rotate 45 (leafs size color))))
 
(define (flower-spiral a x times)
  (if (< times 0)
      empty
      (append (list (forward x)(turn-left a))
              (flower-spiral a (+ x 6)(sub1 times)))))
 
(define (draw-flowers n size)
  (if (<= n 0)
      empty
      (cons (rotate size (draw-flower size (make-color (random 255)
                                                     (random 255)
                                                     (random 255))))
            (draw-flowers (sub1 n)(add1 size)))))
 
(define spiral-image3 (list (stamper-on (draw-flowers 20 1))
                            (pen-up)
                            (flower-spiral 25 1 20)))

(draw spiral-image3)

5.4 Star spiral with changing sizes and colors

Star spiral programmed using the stamper functionality. The colors of the stars change randomly.

(define (draw-stars n size)
(if (<= n 0)
    empty
    (cons (rotate size (star size "solid" (make-color (random 255)
                                                      (random 255)
                                                      (random 255))))
(draw-stars (sub1 n)(add1 size)))))
 
(define spiral-image4 (list (stamper-on (draw-stars 100 1))
                            (pen-up)
                            (spiral 91 1 100)))

(draw spiral-image4)