let u = 0,

    k = 4;

​

let d, max_d;

​

let x = [0, 0], 

    y = [0, 0];

​

function setup() {

  createCanvas(400, 400)

  colorMode(HSB)

  background(10)

  i = TWO_PI / 2000

  max_d = width*width/12 + height*height/12

}

​

function draw() {

  translate(width/2, height/2)

  d = x[1]*x[1] + y[1]*y[1]

  let h = map(d, 0, max_d, 0, 255)

  stroke(h, 200, 200)

  strokeWeight(4)

  let r = width * 0.49 * cos(k*u)

  x[1] = r * cos(u)

  y[1] = r * sin(u)

  if (u > 0) {

    line(x[0], y[0], x[1], y[1])

    if (floor(u / TWO_PI) >= 1) {

      noLoop()

      // restart, increase k

      // background(10)

      // u = 0

      // k += 2

    }

  }

  x[0] = x[1]

  y[0] = y[1]

  u += i

}