canvas
menu
  form(onsubmit='init(event)')
    input(
      type='text'
      id='textInput'
      maxLength='90'
      placeholder='Random text'
    )
    button Run
    br
    button.active(type='button' onClick='setSpeed(event, 40)') Fast
    button(type='button' onClick='setSpeed(event, 15)') Slow

body {
  font-family: Arial;
  padding: 0;
  margin: 0;
  overflow: hidden;
}
canvas {
  background: linear-gradient(
    to bottom,
    rgb(6,9,43) 0%,
    rgb(30,45,75) 100%
  );
}
canvas, menu {
  position: absolute;
  top: 0;
  color: white;
}
input, button {
  color: gray;
  font-size: 30px;
  background: transparent;
  border: 3px solid gray;
  padding: 5px;
  margin-top: 5px;
  transition: all 500ms;
}

button.active {
  color: aqua;
  border-color: aqua;
  box-shadow: 0 0 4px aqua;
  text-shadow: 0 0 14px aqua;
  transition: all 500ms;
}

label {
  display: inline-block;
  color: gray;
  padding: 10px;
}

const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');
const layers = 4;
let size = 0;
let particles = [];
let targets = [];
const lerp = (t, v0, v1) => (1 - t) * v0 + t * v1;
const fov = 2000;
const viewDistance = 200;
let targetRotationY = 0.5;
let rotationY = 0.5;
let speed = 40;
let animFrame;
const texts = [
  'hello.',
  '(╯°□°）╯︵ ┻━┻',
  'CodePen <3',
  '{ JavaScript }',
  'We are the robots',
  'C:\\>',
  'Get creative!',
  'I live in a giant bucket',
  'sudo rm -rf /*',
  'Eat your vegetables',
];
let textIndex = 0;

canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

class Vector3 {
  constructor(x, y, z) {
    this.x = x;
    this.y = y;
    this.z = z;
  }
  
  static fromScreenCoords(_x, _y, _z) {
    const factor = fov / viewDistance;
    const x = (_x - canvas.width / 2) / factor;
    const y = (_y - canvas.height / 2) / factor;
    const z = _z !== undefined ? _z : 0;
    
    return new Vector3(x, y, z);
  }
  
  rotateX(angle) {
    const z = this.z * Math.cos(angle) - this.x * Math.sin(angle);
    const x = this.z * Math.sin(angle) + this.x * Math.cos(angle);
    return new Vector3(x, this.y, z);  
  }
  rotateY(angle) {
    const y = this.y * Math.cos(angle) - this.z * Math.sin(angle);
    const z = this.y * Math.sin(angle) + this.z * Math.cos(angle);
    return new Vector3(this.x, y, z);
  }
  pp() {
    const factor = fov / (viewDistance + this.z);
    const x = this.x * factor + canvas.width / 2;
    const y = this.y * factor + canvas.height / 2;
    return new Vector3(x, y, this.z);
  }
}

function init(e) {
  if (e) e.preventDefault();
  cancelAnimationFrame(animFrame);
  const text = document.getElementById('textInput').value || texts[textIndex++ % texts.length];
  let fontSize = 150;
  let startX = window.innerWidth / 2;
  let startY = window.innerHeight / 2;
  particles = [];
  targets = [];
  // Create temp canvas for the text, draw it and get the image data.
  const c = document.createElement('canvas');
  const cx = c.getContext('2d');
  cx.font = `900 ${fontSize}px Arial`;
  let w = cx.measureText(text).width;
  const h = fontSize * 1.5;
  let gap = 7;
  
  // Adjust font and particle size to fit text on screen
  while (w > window.innerWidth * .8) {
    fontSize -= 1;
    cx.font = `900 ${fontSize}px Arial`;
    w = cx.measureText(text).width;
  }
  if (fontSize < 100) gap = 6;
  if (fontSize < 70) gap = 4;
  if (fontSize < 40) gap = 2;
  size = Math.max(gap / 2, 1);
  c.width = w;
  c.height = h;
  startX = Math.floor(startX - w / 2);
  startY = Math.floor(startY - h / 2);
  cx.fillStyle = '#000';
  // For reasons unknown to me, font needs to be set here again, otherwise font size will be wrong.
  cx.font = `900 ${fontSize}px Arial`; 
  cx.fillText(text, 0, fontSize);
  const data = cx.getImageData(0, 0, w, h);


  // Iterate the image data and determine target coordinates for the flying particles
  for (let i = 0; i < data.data.length; i += 4) {
    const rw = data.width * 4;
    const rh = data.height * 4;
    const x = startX + Math.floor((i % rw) / 4);
    const y = startY + Math.floor(i / rw);
    
    if (data.data[i + 3] > 0 && x % gap === 0 && y % gap === 0) {
      for (let j = 0; j < layers; j++) {
        targets.push(Vector3.fromScreenCoords(x, y, j * 1));
      }
    }
  }
  
  targets = targets.sort((a, b) => a.x - b.x);
  loop();
  return false;
}

function loop() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);

  // As long as there are targets, keep creating new particles.
  // Remove target from the targets array when it's been assigned to a particle.
  for (let i = 0; i < speed; i++) {
    if (targets.length > 0) {

      target = targets[0];
      x = (canvas.width / 2) + target.x * 10;
      y = canvas.height / 2;
      z = -10;

      const position = Vector3.fromScreenCoords(x, y, z);
      const interpolant = 0;

      particles.push({ position, target, interpolant });
      targets.splice(0, 1);
    }
  }

  particles
    .sort((pa, pb) => pb.target.z - pa.target.z)
    .forEach((p, i) => {
    if (p.interpolant < 1) {
      p.interpolant = Math.min(p.interpolant + .01, 1);
    
      p.position.x = lerp(p.interpolant, p.position.x, p.target.x);
      p.position.y = lerp(p.interpolant, p.position.y, p.target.y);
      p.position.z = lerp(p.interpolant, p.position.z, p.target.z);
    }
    const rotationX = Math.sin(Date.now() / 2000) * .8;
    rotationY = lerp(0.00001, rotationY, targetRotationY);
    const particle = p.position
      .rotateX(rotationX)
      .rotateY(rotationY)
      .pp();
    
    const s = 1 - (p.position.z / layers);
    ctx.fillStyle = p.target.z === 0
      ? 'rgb(114, 204, 255)'
      : `rgba(242, 101, 49, ${s})`;
    
    ctx.fillRect(particle.x, particle.y, s * size, s * size);
  });

  animFrame = requestAnimationFrame(loop);
}

init();

window.addEventListener('mousemove', e => {
  const halfHeight = window.innerHeight / 2;
  targetRotationY = (e.clientY - halfHeight) / window.innerHeight; 
})

function setSpeed(e, val) {
  document.querySelectorAll('button').forEach(el => {
   el.classList.remove('active'); 
  });
  e.target.classList.add('active');
  speed = val;
}