visual-modeling/fig_13.1.svg

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<ludus>

fn ngon! (n, edge) -&gt; {
  repeat n {
    forward! (edge)
    right! (inv (n))
  }
}

fn cngon! (n, radius) -&gt; {
  let angle = add (inv (4), inv (mult (2, n)))
  let edge = mult (2, radius, sin (inv (mult (2, n))))

  penup! ()
  forward! (radius)
  right! (angle)
  pendown! ()
  ngon! (n, edge)
  left! (angle)
  penup! ()
  back! (radius)
  pendown! ()
}

fn twisty_nonagons! (times, iter, radius, growth) -&gt; {
  if gte? (iter, times) then :ok
  else {
    cngon! (9, radius)
    right! (inv (times))
    twisty_nonagons! (times, inc (iter), add (radius, growth), growth)
  }
}

&amp; twisty_nonagons! (10, 0, 100, 3)

fn centre_squares! (times, radius, growth) -&gt; {
  if lt? (times, 1) then :ok
  else {
    cngon! (4, radius)
    centre_squares! (dec (times), add (radius, growth), growth)
  } 
}

right! (0.125)
centre_squares! (10, 100, 4)

fn twisty_triangles! (times, radius, angle, growth) -&gt; {
  if lt? (times, 1) then :ok
  else {
    cngon! (3, radius)
    right! (angle)
    twisty_triangles! (dec (times), sub (radius, growth), angle, growth)
  }
}

&amp; right! (inv (6))
&amp; twisty_triangles! (8, 100, inv (120), 10)

hideturtle! ()

</ludus>
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