//chaos game (https://en.wikipedia.org/wiki/Chaos_game)
//parameters: n = 5, r = 2 & cannot pick same vertex twice
//demo:       https://editor.p5js.org/RichardJohnn/sketches/VxFo5o_Yv
//image:      https://i.imgur.com/iBFEZDO.png

let w ;
let h ;
let x = 0;
let y = 0;
let anchors = [];
let n = 5;
let r = 2;
let step = 700;
let sliceAngle = 0;

let current;
let currentI = 0;

let colour = "#ffffff";

function mid(first, second, r) {
  return [
    floor((first[0] + second[0]) / r),
    floor((first[1] + second[1]) / r)
  ]
}

function polar2rectangular(theta, radius) {
  return [
    radius * cos(theta) + (w/2),
    radius * sin(theta) + (h/2)
  ];
}

function setup() {
  w = displayWidth / 3;
  h = displayHeight / 3;
  createCanvas(w, h);
  background("#000");
  stroke("#444"); //grey
  angleMode(DEGREES);
  blendMode(SCREEN); //so multiple grey points in the same position become lighter
  sliceAngle = floor(360 / n);

  current = [floor(random(w)), floor(random(h))];
  //place 'anchors' (corners, verticies) on a circle 
  for (let theta = 0; theta < 360; theta += sliceAngle) {
    let anchor = polar2rectangular(theta - 90, h / 2);
    anchors.push(anchor);
  }
  strokeWeight(1);
}

function getIndex() {
  let i = floor(random(anchors.length));
  //not allowing the same vertex to be chosen twice can yield very different results!
  if (currentI != i)
    return i
  else
    return getIndex();
}

function draw() {
  for (let x = 0; x < step; x += 1) { //add more dots per render to speed things up 
    let i = getIndex();
    currentI = i;
    current = mid(current, anchors[i], r);
    point(current[0], current[1]);
  }
}