Collision Detection (Canvas)

A fork of the SVG version. Mouseover to repel nodes. Adapted from my talk on force layouts.

<!DOCTYPE html>
<meta charset="utf-8">
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var width = 960,
    height = 500;

var nodes = d3.range(200).map(function() { return {radius: Math.random() * 12 + 4}; }),
    root = nodes[0];

root.radius = 0;
root.fixed = true;

var force = d3.layout.force()
    .gravity(0.05)
    .charge(function(d, i) { return i ? 0 : -2000; })
    .nodes(nodes)
    .size([width, height]);

force.start();

var canvas = d3.select("body").append("canvas")
    .attr("width", width)
    .attr("height", height);

var context = canvas.node().getContext("2d");

force.on("tick", function(e) {
  var q = d3.geom.quadtree(nodes),
      i,
      d,
      n = nodes.length;

for (i = 1; i < n; ++i) q.visit(collide(nodes[i]));

context.clearRect(0, 0, width, height);
  context.fillStyle = "steelblue";
  context.beginPath();
  for (i = 1; i < n; ++i) {
    d = nodes[i];
    context.moveTo(d.x, d.y);
    context.arc(d.x, d.y, d.radius, 0, 2 * Math.PI);
  }
  context.fill();
});

canvas.on("mousemove", function() {
  var p1 = d3.mouse(this);
  root.px = p1[0];
  root.py = p1[1];
  force.resume();
});

</script>

https://d3js.org/d3.v3.min.js