SVG Performance with paths and rounded coordinates

<!DOCTYPE html>
<meta charset="utf-8">
<title>SVG Swarm</title>
<style>

svg {
  position: absolute;
  top: 0;
}

circle {
  fill: steelblue;
  stroke: #666;
  stroke-width: 1.5px;
}

</style>
<div id="fps">FPS: <span>?</span></div>
<script src="https://d3js.org/d3.v2.min.js?2.9.1"></script>
<script>

var data = d3.range(4000).map(function() {
  return {xloc: 0, yloc: 0, xvel: 0, yvel: 0};
});

var width = 960,
    height = 500;

var x = d3.scale.linear()
    .domain([-5, 5])
    .range([0, width]);

var y = d3.scale.linear()
    .domain([-5, 5])
    .range([0, height]);

var time0 = Date.now(),
    time1;

var fps = d3.select("#fps span");

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

var p = svg.append("path")
    .data([data])
    .attr("d", function(d) {
        return 'M' + d.map(function(x) { return [x.xloc, x.yloc]; }).join('L');
    });

var fpsqueue = [];

d3.timer(function() {

data.forEach(function(d) {
    d.xloc += d.xvel;
    d.yloc += d.yvel;
    d.xvel += 0.04 * (Math.random() - .5) - 0.05 * d.xvel - 0.0005 * d.xloc;
    d.yvel += 0.04 * (Math.random() - .5) - 0.05 * d.yvel - 0.0005 * d.yloc;
  });

p.attr("d", function(d) {
      return 'M' + d.map(function(a) { return [~~x(a.xloc), ~~y(a.yloc)]; }).join('L');
  });

time1 = Date.now();
  if (fpsqueue.length === 100) { fps.text(d3.mean(fpsqueue).toFixed(3)); fpsqueue.pop(); }
  fpsqueue.push(Math.round(1000 / (time1 - time0)));
  time0 = time1;
});

</script>

Modified http://d3js.org/d3.v2.min.js?2.9.1 to a secure url

https://d3js.org/d3.v2.min.js?2.9.1