Collision Detection by mbostock

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="960"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var canvas = document.querySelector("canvas"),
    context = canvas.getContext("2d"),
    width = canvas.width,
    height = canvas.height,
    tau = 2 * Math.PI;

var nodes = d3.range(1000).map(function(i) {
  return {
    r: Math.random() * 14 + 4
  };
});

var simulation = d3.forceSimulation(nodes)
    .velocityDecay(0.2)
    .force("x", d3.forceX().strength(0.002))
    .force("y", d3.forceY().strength(0.002))
    .force("collide", d3.forceCollide().radius(function(d) { return d.r + 0.5; }).iterations(2))
    .on("tick", ticked);

function ticked() {
  context.clearRect(0, 0, width, height);
  context.save();
  context.translate(width / 2, height / 2);

  context.beginPath();
  nodes.forEach(function(d) {
    context.moveTo(d.x + d.r, d.y);
    context.arc(d.x, d.y, d.r, 0, tau);
  });
  context.fillStyle = "#ddd";
  context.fill();
  context.strokeStyle = "#333";
  context.stroke();

  context.restore();
}

</script>