stroke-dasharray-interpolation-talk/example2.html at master · petulla/stroke-dasharray-interpolation-talk · GitHub

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

path {
  fill: none;
  stroke: #000;
  stroke-width: 3px;
}

circle {
  fill: steelblue;
  stroke: #fff;
  stroke-width: 3px;
}
</style>
<script src="http://d3js.org/d3.v3.min.js"></script>
<script>

var points = [
  [480, 200],
  [480, 400],
  [680, 200],
  [680, 400]
];

var line = d3.svg.line()
    .tension(0)
    //.interpolate("linear-closed");
    .interpolate("basis-closed");

var svg = d3.select("body").append("svg")
    .attr("width", 960)
    .attr("height", 900);

svg.append("path")
    .datum(points)
    .style("stroke", "#ddd")
    .style("stroke-dasharray", "4,4")
    .attr("d", line);

var path = svg.append("path")
    .datum(points)
    .attr("d", line)
    .call(transition2);


var circle = svg.append("circle")
    .attr("r", 7)
    .attr("transform", "translate(" + points[0] + ")");

transition();
function transition() {

   circle.transition()
      .duration(7500)
      .attrTween("transform", translateAlong(path.node()));
}

function transition2(path) {
  path.transition()
      .duration(7500)
      .attrTween("stroke-dasharray", tweenDash);
}

function tweenDash() {
  var l = this.getTotalLength(),
      i = d3.interpolateString(0 + "," + l, l + "," + l);

  return function(t) { return i(t); };
}

function translateAlong(path) {
  var l = path.getTotalLength();
  return function(d, i) {
    return function(t) {
      var p = path.getPointAtLength(t * l);
      return "translate(" + p.x + "," + p.y + ")";
    };
  };
}

</script>