<svg viewBox="0 0 1170 1650" width="1170" height="1650" xmlns="http://www.w3.org/2000/svg" version="1.1" >
  <!--
  Johan Karlsson, 2020
  https://twitter.com/DonKarlssonSan
  MIT License, see Details View
  A3 paper size: 1650 x 1170 
  -->
</svg>

html, body {
  height: 100%;
  margin: 0;
  cursor: pointer;
  background-color: white;
}

svg {
  position: absolute;
  width: 100%;
  height: 100%;
}

/*
  Johan Karlsson, 2020
  https://twitter.com/DonKarlssonSan
  MIT License, see Details View
*/

const svgNs = "http://www.w3.org/2000/svg";
const w = 1170;
const h = 1650;
let svg;
let circles;
let imageBuffer;

class Circle {
  constructor(x, y) {
    this.x = x;
    this.y = y;
    this.r = 8;
    this.done = false;
  }
  
  draw(groupElement) {
    let circle = document.createElementNS(svgNs, "circle");
    circle.setAttribute("cx", this.x);
    circle.setAttribute("cy", this.y);
    circle.setAttribute("r", this.r);
    groupElement.appendChild(circle);
  }  
}

function setup() {
  svg = document.querySelector("svg");
  document.addEventListener("click", draw);
  document.addEventListener("keydown", onKeyDown);
  
  let canvas = document.createElement("canvas");
  let ctx = canvas.getContext("2d");
  canvas.width = w;
  canvas.height = h;
  storeTextInBuffer(ctx);
}

function storeTextInBuffer(ctx) {
  ctx.textAlign = "center";
  ctx.textBaseline = "middle";
  ctx.font = `bold 440px sans-serif`;
  ctx.fillText("LEXI", w / 2, h * 0.2);
  ctx.font = `bold 1200px sans-serif`;
  ctx.fillText("5", w / 2, h * 0.7);
  let image = ctx.getImageData(0, 0, w, h);
  imageBuffer = new Uint32Array(image.data.buffer);
}

function onKeyDown (e) {
  if(e.code === "KeyD") {
    download();
  }
}

function download() {
  let svgDoc = svg.outerHTML;
  let filename = "packed-circles.svg";
  let element = document.createElement("a");
  element.setAttribute("href", "data:image/svg+xml;charset=utf-8," + encodeURIComponent(svgDoc));
  element.setAttribute("download", filename);
  element.style.display = "none";
  document.body.appendChild(element);
  element.addEventListener("click", e => e.stopPropagation());
  element.click();
  document.body.removeChild(element);
}

function dist(x1, y1, x2, y2) {
  return Math.hypot(x1 - x2, y1 - y2);
}

function addCircles() {
  let nrOfTries = 0;
  let wasAdded;
  do {
    wasAdded = false;
    let x = Math.random() * w;
    let y = Math.random() * h;
    if(validPos(x, y)) {
      wasAdded = true;
      let c = new Circle(x, y);
      circles.push(c);
    }
    nrOfTries++;
  } while (!wasAdded && nrOfTries < 10)
}

function validPos(x, y) {
  let index = Math.round(y) * w + Math.round(x);
  let isInside = index < imageBuffer.length && imageBuffer[index];
  if(isInside) {
    return false;
  }
  for(let i = 0; i < circles.length; i++) {
    let current = circles[i];
    let d = dist(x, y, current.x, current.y);
    if(d - 8 < current.r) {
      return false;
    }
  }
  return true;
}

function canGrow(circle) {
  for(let i = 0; i < circles.length; i++) {
    let current = circles[i];
    if(circle !== current) {
      let d = dist(circle.x, circle.y, current.x, current.y);
      if(d - 4 <= circle.r + current.r) {
        return false;
      } 
    }
  }
  return true;
}

function resetCircles() {
  circles = [];
  let nrOfTries = w * h / 1800;
  for(let i = 0; i < nrOfTries; i++) {
    addCircles();
  }
}
  
function packCircles() {
  let nrOfTries = w * h / 400;
  for(let i = 0; i < nrOfTries; i++) {
    addCircles();
    circles.filter(c => !c.done).forEach(c => {
      if(canGrow(c)) {
        c.r += 1;
      } else {
        c.done = true;
      }
    });
  }
}
  
function drawCircles() {
  let group = document.querySelector("#container");
  if(group) {
    group.remove();
  }
  
  group = document.createElementNS(svgNs, "g");
  group.setAttribute("id", "container");
  group.setAttribute("fill", "none");
  group.setAttribute("stroke", "black");
  
  circles.forEach(c => c.draw(group));
  
  svg.appendChild(group);
}
  
function draw() {
  console.clear();
  resetCircles();
  packCircles();
  drawCircles();
}
  
  

setup();
draw();