How to draw an arc with module `graphics/turtles`?

[Killian Zhuo (KDr2)]

I am imitating the Logo API to draw some shapes with `graphics/turtles`, but in it I only find functions to draw lines, is there a way to draw an arc?



Greetings.

Killian Zhuo (KDr2, https://kdr2.com)

[making-a-racket]

Turtles can only turn or move forward with or without drawing. To draw an arc, you'll need to combine these methods to do that.

I highly recommend the book Turtle Geometry by Abelson and diSessa. Below you can find an excerpt of the book that talks about drawing circles and arcs.

Here's an implementation of a circle in Racket using the turtle library you referenced.

#lang racket

(require graphics/turtles)

(turtles #t)

(for ([i (in-range 360)])

  (draw 1)

  (turn 1))

[Killian Zhuo (KDr2)]

Thank you, I just implemented a UCBLogo compatible `arc`:

(define (arc angle radius)
  (let* ([alpha (* 2 (asin (/ 1 (* 2 radius))))]
         [rangle (* pi (/ angle 180))]
         [n (abs (/ rangle alpha))]
         [astep (if (> angle 0) (- alpha) alpha)])
    (tprompt
     (move radius)
     (turn (if (> angle 0) -90 90))
     (for ([i (in-range n)])
       (draw 1)
       (turn/radians astep)))
    (turn (- angle))))

Here's an implementation of a circle in Racket using the turtle library you referenced.

#lang racket

(require graphics/turtles)

(turtles #t)

(for ([i (in-range 360)])
  (draw 1)
  (turn 1))

On Monday, February 1, 2021 at 5:54:05 PM UTC-6 zhuo...@gmail.com wrote:
> I am imitating the Logo API to draw some shapes with `graphics/turtles`, but in it I only find functions to draw lines, is there a way to draw an arc?
>
>
>
> Greetings.
>
> Killian Zhuo (KDr2, https://kdr2.com)

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