Multi-Foci Force Layout

<!DOCTYPE html>
<meta charset="utf-8">
<style>

rect{
  fill: white;
}

circle {
  stroke: #000;
  stroke-opacity: .5;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var width = 960,
    height = 500;

var nodes = d3.range(5).map(function(i) {
  return {
    type: Math.random() * 5 | 0,
    radius: 30,
    fixed: true,
    type: i,
    x: (i + 1) * (width / 6),
    y: height / 2
  };
});

var color = d3.scale.category10();

var force = d3.layout.force()
    .gravity(0)
    .charge(0)
    .nodes(nodes)
    .size([width, height])
    .on("tick", ticked);

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

svg.append("rect")
    .attr("width", width)
    .attr("height", height);

svg.selectAll("circle")
    .data(nodes)
  .enter().append("circle")
    .attr("r", function(d) { return d.radius - 2; })
    .style("fill", function(d) { return color(d.type); });

var p0;

force.start();

function mousemoved() {
  var p1 = d3.mouse(this);
  p0 = p1;

var node = {
    radius: Math.random() * 12 + 4,
    type: Math.random() * 5 | 0,
    x: p1[0],
    y: p1[1],
    px: (p0 || (p0 = p1))[0],
    py: p0[1]
  };

svg.append("circle")
      .data([node])
      .attr("cx", function(d) { return d.x; })
      .attr("cy", function(d) { return d.y; })
      .attr("r", function(d) { return d.radius - 2; })
      .style("fill", function(d) { return color(d.type); })
    .transition()
      .delay(3000)
      .attr("r", 1e-6)
      .each("end", function() { nodes.splice(6, 1); })
      .remove();

nodes.push(node);
  force.resume();
}

function ticked(e) {
  var q = d3.geom.quadtree(nodes),
      k = e.alpha * 0.1,
      i = 0,
      n = nodes.length,
      o;

while (++i < n) {
    o = nodes[i];
    if (o.fixed) continue;
    c = nodes[o.type];
    o.x += (c.x - o.x) * k;
    o.y += (c.y - o.y) * k;
    q.visit(collide(o));
  }

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

</script>

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