D3 Examples - Force-Directed Tree, fixing angles [UNLISTED]

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<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="300"></canvas>
<script src="https://d3js.org/d3.v4.0.0-alpha.49.min.js"></script>
<script>
var nodes = d3.range(400).map(function(i) {
  return {
    index: i
  };
});
​
var links = d3.range(nodes.length - 1).map(function(i) {
  return {
    source: Math.floor(Math.sqrt(i)),
    target: i + 1,
  };
});
​
var f = function(links) {
  var angles = new Array(links.length),
      anglef = function(link) {
        return Math.atan2(link.target.y - link.source.y, link.target.x - link.source.x);
      };
  function initialize() {
    for (var i=0, n=links.length, link; i<n; i++) {
      link = links[i];
      angles[i] = anglef(link);
    }
  }
  function force(alpha){
    var sum = 0;
    for (var i = 0, n = links.length; i < n; ++i) {
      var link = links[i],
          angle = anglef(link);
      dl = Math.sin(angle-angles[i]);
      sum += dl*dl;
      dl *= Math.sqrt(alpha);
      link.source.vx -= Math.sin(angle) * dl;
      link.source.vy += Math.cos(angle) * dl;
      link.target.vx += Math.sin(angle) * dl;
      link.target.vy -= Math.cos(angle) * dl;
    }
    console.log('sum', sum);
  }
  
  force.initialize = initialize;
  return force;
};
​
  
var simulation = d3.forceSimulation(nodes)
    .force("charge", d3.forceManyBody())
    .force("link", d3.forceLink(links).distance(20).strength(1))
    .force("x", d3.forceX())
    .force("y", d3.forceY())
    .force("f", f(links))
    .on("tick", ticked);
​
var canvas = document.querySelector("canvas"),
    context = canvas.getContext("2d"),
    width = canvas.width,
    height = canvas.height;
​
d3.select(canvas)
    .call(d3.drag()
        .container(canvas)
        .subject(dragsubject)
        .on("start", dragstarted)
        .on("drag", dragged)
        .on("end", dragended));
​
function ticked() {
  context.clearRect(0, 0, width, height);
  context.save();
  context.translate(width / 2, height / 2);
​
  context.beginPath();
  links.forEach(drawLink);
  context.strokeStyle = "#aaa";
  context.stroke();
​
  context.beginPath();
  nodes.forEach(drawNode);
  context.fill();
  context.strokeStyle = "#fff";
  context.stroke();
​
  context.restore();
}
​
function dragsubject() {
  return simulation.find(d3.event.x - width / 2, d3.event.y - height / 2);
}
​
function dragstarted() {
  if (!d3.event.active) simulation.alphaTarget(0.3).restart()
  simulation.fix(d3.event.subject);
}
​
function dragged() {
  simulation.fix(d3.event.subject, d3.event.x, d3.event.y);
}
​
function dragended() {
  if (!d3.event.active) simulation.alphaTarget(0);
  simulation.unfix(d3.event.subject);
}
​
function drawLink(d) {
  context.moveTo(d.source.x, d.source.y);
  context.lineTo(d.target.x, d.target.y);
}
​
function drawNode(d) {
  context.moveTo(d.x + 3, d.y);
  context.arc(d.x, d.y, 3, 0, 2 * Math.PI);
}
​
</script>
​
    