var N = 1 << order; // 2**order

var npts = N * N;

const path = [];

​

function setup() {

  createCanvas(512, 512);

  var L = width / N;

  // console.log(pts[0]);

  for (let i = 0; i < npts; i++) {

    path[i] = hilbert(i);

    path[i].mult(L);

    path[i].add(L/2, L/2);

  }

  noLoop();

}

​

function draw() {

  background(220);

  stroke(20);

  strokeWeight(3);

  noFill();

  beginShape();

  for (let i = 0; i < npts; i++) {

    vertex(path[i].x, path[i].y);

  }

  endShape();

}

​

function hilbert(p) {

  const pts = [

  new p5.Vector(0,0),

  new p5.Vector(0,1),

  new p5.Vector(1,1),

  new p5.Vector(1,0)];

  let index = p & 3;

  let v = pts[index].copy();

  let i = p >>> (2 * (order - 1));

  if (i == 0) {

    let tmp = v.x;

    v.x = v.y;

    v.y = tmp;

  }

  if (i == 3) {

    let tmp = -1-v.x;

    v.x = 1-v.y;

    v.y = tmp;

  }

  v.add(pts[i].mult(2));

  return v;

}