Collision

by Celia Siu

HTML

<script src="https://d3js.org/d3.v3.js"></script>

This example is modified from <a href="https://bl.ocks.org/mbostock/3231298">https://bl.ocks.org/mbostock/3231298</a>

<body></body>

JavaScript

var width = 500,
  height = 500;

var nodes = d3.range(200).map(function() {
    return {
      radius: Math.random() * 12 + 4
    };
  }),
  root = nodes[0],
  color = d3.scale.category10();

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

var force = d3.layout.force()
  .gravity(0.05)
  .charge(function(d, i) {
    return i ? 0 : -1500;
  })
  .nodes(nodes)
  .size([width, height]);

force.start();

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

svg.selectAll("circle")
  .data(nodes.slice(1))
  .enter().append("circle")
  .attr("r", function(d) {
    return d.radius;
  })
  .style("fill", function(d, i) {
    return color(i % 3);
  });

force.on("tick", function(e) {
  var q = d3.geom.quadtree(nodes),
    i = 0,
    n = nodes.length;

  while (++i < n) q.visit(collide(nodes[i]));

  svg.selectAll("circle")
    .attr("cx", function(d) {
      return d.x;
    })
    .attr("cy", function(d) {
      return d.y;
    });
});

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

function collide(node) {
  var r = node.radius + 16,
    nx1 = node.x - r,
    nx2 = node.x + r,
    ny1 = node.y - r,
    ny2 = node.y + r;
  return function(quad, x1, y1, x2, y2) {
    if (quad.point && (quad.point !== node)) {
      var x = node.x - quad.point.x,
        y = node.y - quad.point.y,
        l = Math.sqrt(x * x + y * y),
        r = node.radius + quad.point.radius;
      if (l < r) {
        l = (l - r) / l * .5;
        node.x -= x *= l;
        node.y -= y *= l;
        quad.point.x += x;
        quad.point.y += y;
      }
    }
    return x1 > nx2 || x2 < nx1 || y1 > ny2 || y2 < ny1;
  };
}