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HTML

              
                <section>
  <canvas id="population" width="2000" height="1200"></canvas>
  <div class="info">
    <canvas id="graph" height="400" width="1500"></canvas>
    <ul>
      <li><span>Recovered</span><span id="recovered">0</span></li>
      <li><span>Healthy</span><span id="healthy">0</span></li>
      <li><span>Sick</span><span id="sick">0</span></li>
      <li><span>Dead</span><span id="dead">0</span></li>
    </ul>
  </div>
  <div id="overlay" class="active">
    <p>
      A social distance simulator based on <a href="https://www.washingtonpost.com/graphics/2020/world/corona-simulator/">the incredible work done by the Washington Post</a>.
      This simulator assumes a 1% mortality rate.
    </p>
    <div class="field is-grouped">
      <span class="select">
        <select id="quarantine">
          <option value="0" selected>No Social Distancing</option>
          <option value="0.1">One-Tenth Self-Quarantine</option>
          <option value="0.25">One Quarter Self-Quarantine</option>
          <option value="0.33">One Third Self-Quarantine</option>
          <option value="0.5">One Half Self-Quarantine</option>
          <option value="0.75">Three Quarters Self-Quarantine</option>
          <option value="1">Everyone Self-Quarantines</option>
        </select>
      </span>
      &nbsp;
      <button class="button is-primary" id="run">Run</button>
    </div>
  </div>
</section>
              
            
!

CSS

              
                html,
body {
  background: #111;
}
canvas {
  background: black;
  display: block;
  width: 100%;
  height: auto;
}

section {
  margin: 10vh auto;
  max-width: 1000px;
  width: 95%;
  position: relative;
}
#overlay {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 25%;
  padding: 3rem;
  box-sizing: border-box;
  width: 100%;
  transition: opacity 250ms ease-in-out;
  opacity: 0;
  color: white;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background: rgba(0, 0, 0, 0.9);
}
#overlay.active {
  opacity: 1;
}

#overlay p {
  margin-bottom: 1rem;
  text-align: center;
}
#overlay a {
  color: #00d1b2;
  text-decoration: none;
}

section > div.info {
  display: flex;
  align-content: center;
  align-items: center;
  flex-wrap: wrap;

  border-top: 1px solid #111;
  background: black;
}

section > div.info canvas {
  flex: 1;
  background: transparent;
}
section > div.info ul {
  list-style: none;
  margin: 0;
  padding: 0;

  text-align: center;
  color: white;
  padding: 1rem;
  width: 100%;
  box-sizing: border-box;
  font-size: 0.8rem;
  text-transform: uppercase;
}
@media (min-width: 600px) {
  section > div.info canvas {
    width: calc(100% - 200px - 1rem);
  }
  section > div.info ul {
    width: 200px;
  }
}

li {
  width: 100%;
  display: flex;
  justify-content: space-between;
}

              
            
!

JS

              
                console.clear();

const PI = Math.PI;
const PI2 = PI * 2;

const SPEED = 2;
const SICK_TIMEFRAME = 275;

const COLOR = {
  recovered: "violet",
  sick: "tomato",
  dead: "white",
  healthy: "#00d1b2"
};

const NORMAL = degrees => {
  const radians = (degrees * PI) / 180;
  return { x: Math.sin(radians), y: -Math.cos(radians) };
};

const WALLS = {
  N: { velocity: NORMAL(0) },
  S: { velocity: NORMAL(0) },
  E: { velocity: NORMAL(90) },
  W: { velocity: NORMAL(90) }
};

class Vector {
  constructor(x, y) {
    this.x = x;
    this.y = y;
  }
}

class Person {
  constructor(id, radius, width, height, sick, quarantined, vulnerable) {
    this.id = id;
    this.width = width;
    this.height = height;
    this.radius = radius;
    this.position = new Vector(
      Math.random() * (this.width - this.radius * 2) + this.radius,
      Math.random() * (this.height - this.radius * 2) + this.radius
    );
    this.quarantined = quarantined;
    this.sick = sick;
    this.vulnerable = vulnerable;
    this.sickFrame = 0;
    this.recovered = false;
    this.angle = Math.random() * 360;
    this.updateVelocity();
  }

  updateVelocity() {
    const radians = (this.angle * PI) / 180;
    this.velocity = {
      x: Math.sin(radians) * SPEED,
      y: -Math.cos(radians) * SPEED
    };
  }

  get edge() {
    return {
      bottom: this.position.y + this.radius,
      left: this.position.x - this.radius,
      right: this.position.x + this.radius,
      top: this.position.y - this.radius
    };
  }

  reflect({ velocity }) {
    const x = this.velocity.x * velocity.x;
    const y = this.velocity.y * velocity.y;
    const d = 2 * (x + y);
    this.velocity.x -= d * velocity.x;
    this.velocity.y -= d * velocity.y;
  }

  collide({ id, position }) {
    const dx = this.position.x - position.x;
    const dy = this.position.y - position.y;
    const d = Math.sqrt(dx * dx + dy * dy);
    return id !== this.id && d < this.radius * 2;
  }

  tick(population) {
    if (this.edge.left <= 0) this.reflect(WALLS.W);
    if (this.edge.right >= this.width) this.reflect(WALLS.E);
    if (this.edge.top <= 0) this.reflect(WALLS.N);
    if (this.edge.bottom >= this.height) this.reflect(WALLS.S);
    if (this.sick) {
      population.forEach(person => {
        if (!person.recovered && !person.sick && this.collide(person)) {
          person.sick = true;
        }
      });
    }
    if (!this.quarantined && !this.dead) {
      this.position.x += this.velocity.x;
      this.position.y += this.velocity.y;
    }
    if (this.sick) this.sickFrame++;
    if (this.sickFrame >= SICK_TIMEFRAME) {
      this.sick = false;
      this.recovered = true;
      if (this.vulnerable) this.dead = true;
    }
  }

  handleReflection(person) {
    if (this.edge.left <= person.edge.right) this.reflect(WALLS.W);
    if (this.edge.right >= person.edge.left) this.reflect(WALLS.E);
    if (this.edge.top <= person.edge.bottom) this.reflect(WALLS.N);
    if (this.edge.bottom >= person.edge.top) this.reflect(WALLS.S);
  }
}

class Population {
  constructor(size, quarantineRate, patientZeroes) {
    this.people = [];
    this.canvas = document.getElementById("population");
    this.context = this.canvas.getContext("2d");
    this.width = this.canvas.width;
    this.height = this.canvas.height;
    this.radius = size < 250 ? 12 : size < 500 ? 8 : 5;
    for (let i = 0; i < size; i++) {
      const sick = i > size - patientZeroes - 1;
      const quarantined = i / size <= quarantineRate;
      const vulnerable = Math.random() < 0.01;
      this.people.push(
        new Person(
          i,
          this.radius,
          this.width,
          this.height,
          sick,
          quarantined,
          vulnerable
        )
      );
    }
  }

  tick() {
    this.context.clearRect(0, 0, this.width, this.height);
    this.people.forEach(p => {
      this.draw(p);
      p.tick(this.people);
    });
  }

  draw({ dead, position, recovered, sick }) {
    this.context.fillStyle = sick
      ? COLOR.sick
      : dead
      ? COLOR.dead
      : recovered
      ? COLOR.recovered
      : COLOR.healthy;
    this.context.beginPath();
    this.context.arc(position.x, position.y, this.radius, 0, PI2);
    this.context.fill();
  }
}

class Graph {
  constructor(population) {
    this.population = population;
    this.canvas = document.getElementById("graph");
    this.context = this.canvas.getContext("2d");
    this.height = this.canvas.height;
    this.width = this.canvas.width;
    this.$recovered = document.getElementById("recovered");
    this.$healthy = document.getElementById("healthy");
    this.$sick = document.getElementById("sick");
    this.$dead = document.getElementById("dead");
    this.$recovered.style.color = COLOR.recovered;
    this.$healthy.style.color = COLOR.healthy;
    this.$sick.style.color = COLOR.sick;
    this.reset();
  }

  reset() {
    this.x = 0;
    this.done = false;
  }

  tick() {
    let recovered = 0;
    let healthy = 0;
    let sick = 0;
    let dead = 0;
    this.population.people.forEach(person => {
      if (person.dead) dead++;
      else if (person.recovered) recovered++;
      else if (person.sick) sick++;
      else healthy++;
    });
    const total = dead + recovered + healthy + sick;

    const recoveredH = (recovered / total) * this.height;
    const healthyH = (healthy / total) * this.height;
    const sickH = (sick / total) * this.height;
    const deadH = (dead / total) * this.height;

    this.$recovered.innerText = recovered;
    this.$healthy.innerText = healthy;
    this.$sick.innerText = sick;
    this.$dead.innerText = dead;

    this.context.strokeStyle = COLOR.recovered;
    this.context.beginPath();
    this.context.moveTo(this.x, 0);
    this.context.lineTo(this.x, recoveredH);
    this.context.stroke();

    this.context.strokeStyle = COLOR.healthy;
    this.context.beginPath();
    this.context.moveTo(this.x, recoveredH);
    this.context.lineTo(this.x, recoveredH + healthyH);
    this.context.stroke();

    this.context.strokeStyle = COLOR.sick;
    this.context.beginPath();
    this.context.moveTo(this.x, recoveredH + healthyH);
    this.context.lineTo(this.x, recoveredH + healthyH + sickH);
    this.context.stroke();

    this.context.strokeStyle = COLOR.dead;
    this.context.beginPath();
    this.context.moveTo(this.x, recoveredH + healthyH + sickH);
    this.context.lineTo(this.x, recoveredH + healthyH + sickH + deadH);
    this.context.stroke();

    this.x++;

    if (this.x >= this.width) this.done = true;
  }
}

const $overlay = document.getElementById("overlay");
const $quarantine = document.getElementById("quarantine");
const $run = document.getElementById("run");

$run.addEventListener("click", () => {
  const q = parseFloat($quarantine.value);
  const pop = new Population(1000, q, 3);
  const graph = new Graph(pop);
  graph.context.clearRect(0, 0, graph.width, graph.height);
  $overlay.classList.remove("active");

  function run() {
    pop.tick();
    graph.tick();
    if (graph.done) $overlay.classList.add("active");
    else requestAnimationFrame(run);
  }

  run();
});

              
            
!
999px

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