// http://paulbourke.net/geometry/butterfly/

​

const e = Math.E;

let u, r, speed, count;

let prev_x = 0,

    prev_y = 0;

​

function setup() {

  const length = min(innerWidth, innerHeight)

  createCanvas(length, length)

  background(40)

  u = 0

  r = width * 0.10

  speed = PI / 100

  count = 0 

}

​

function draw() {

  translate(width/2, height/2)

  rotate(-PI/2)

  stroke(count % 100, count % 300 + 100, count % 200 + 100)

  strokeWeight(3)

  let x = r * cos(u) * (pow(e, cos(u)) - 2*cos(4*u) - pow(sin(u/12), 5))

  let y = r * sin(u) * (pow(e, cos(u)) - 2*cos(4*u) - pow(sin(u/12), 5))

  if (count > 0) {

    line(prev_x, prev_y, x, y)

  }

  prev_x = x

  prev_y = y

  u += speed

  count += 1

}