Handle collide with a d3.js multi foci force layout
<p>I'm new with d3.js, what I'm trying to do is close to this : <a href="http://codepen.io/fabiobiondi/pen/nFxyD" rel="nofollow">http://codepen.io/fabiobiondi/pen/nFxyD</a></p>

<pre><code>// GROUPS:  0 Web | 1: Adobe | 2: hybrid
var data = [
  {"id": 0, "name": "AngularJS", "r": 50 },
  {"id": 0, "name": "HTML5", "r": 40 },
  {"id": 0, "name": "Javascript", "r": 30 },
  {"id": 0, "name": "NodeJs", "r": 30 },
  {"id": 0, "name": "D3.js", "r": 40 },
  {"id": 0, "name": "CreateJS", "r": 45 },
  {"id": 0, "name": "Cordova", "r": 40 },
  {"id": 0, "name": "CSS", "r": 40 },
  {"id": 0, "name": "SVG", "r": 20 },
  {"id": 0, "name": "PHP", "r": 20 },
  {"id": 0, "name": "jQuery", "r": 30 },

  {"id": 1, "name": "Actionscript", "r": 50 },
  {"id": 1, "name": "Flash", "r": 32 },
  {"id": 1, "name": "Flex", "r": 50 },
  {"id": 1, "name": "AIR", "r": 40 },
  {"id": 1, "name": "Photoshop", "r": 30 },
  {"id": 1, "name": "Illustrator", "r": 30 },

  {"id": 2, "name": "Node Webkit", "r": 40 },
  {"id": 2, "name": "Chrome App", "r": 30 },
  {"id": 2, "name": "Cordova", "r": 45 },
];

var width = window.innerWidth,
    height = 450;

var fill = d3.scale.category10();

var nodes = [], labels = [],
    foci = [{x: 0, y: 150}, {x: 350, y: 150}, {x: 200, y: 150}];

var svg = d3.select("body").append("svg")
    .attr("width", "100%")
    .attr("height", height)
    //.attr("domflag", '');

var force = d3.layout.force()
    .nodes(nodes)
    .links([])
    .charge(-400)
    //.chargeDistance(200)
    .gravity(0.1)
    .friction(0.8)
    .size([width, height])
    .on("tick", tick);

//var node = svg.selectAll("circle");
var node = svg.selectAll("g");

var counter = 0;

function tick(e) {
  var k = .1 * e.alpha;

  // Push nodes toward their designated focus.
  nodes.forEach(function(o, i) {
    o.y += (foci[o.id].y - o.y) * k;
    o.x += (foci[o.id].x - o.x) * k;
  });

  node.attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; });

}


var timer = setInterval(function(){

  if (nodes.length &gt; data.length-1) { clearInterval(timer); return;}

  var item = data[counter];
  nodes.push({id: item.id, r: item.r, name: item.name});
  force.start();

  node = node.data(nodes);

  var n = node.enter().append("g")
      .attr("class", "node")
      .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; })
      .style('cursor', 'pointer')
      .on('mousedown', function() {
         var sel = d3.select(this);
         sel.moveToFront();
      })
      .call(force.drag);

  n.append("circle")
      .attr("r",  function(d) { return d.r; })
      .style("fill", function(d) { return fill(d.id); })

  n.append("text")
      .text(function(d){
          return d.name;
      })
      .style("font-size", function(d) {
          return Math.min(2 * d.r, (2 * d.r - 8) / this.getComputedTextLength() * 16) + "px"; 
       })
      .attr("dy", ".35em")

  counter++;
}, 100);


d3.selection.prototype.moveToFront = function() {
  return this.each(function(){
    this.parentNode.appendChild(this);
  });
};

function resize() {
  width = window.innerWidth;
  force.size([width, height]);
  force.start();
}

d3.select(window).on('resize', resize);
</code></pre>

<p>What I don't understand is how can I control the way the circles can or can't collide.</p>

<p>I have tried collide function like this <a href="https://bl.ocks.org/mbostock/1804919" rel="nofollow">https://bl.ocks.org/mbostock/1804919</a> but I  don't get how it works. When I change padding value, circles keep avoiding themselves. What I would like is to allow collide but not too much (let's say 10px), to be sure that the text inside is never hidden.</p>