D3 Examples - Snowflake Simplification

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
.koch {
  fill: #eee;
  stroke: #000;
}
​
.overlay {
  fill: none;
  pointer-events: all;
}
​
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>
​
var width = 960,
    height = 500;
​
var area = 1, simplify = d3.geo.transform({
  point: function(x, y, z) {
    if (z >= area) this.stream.point(x, y);
  }
});
​
var x = d3.scale.sqrt()
    .domain([0, 1e4])
    .range([0, width]);
​
var path = d3.geo.path()
    .projection(simplify);
​
var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);
​
svg.append("rect")
    .attr("class", "overlay")
    .attr("width", width)
    .attr("height", height)
    .on("mousemove", mousemoved);
​
d3.json("snowflake.json", function(error, topo) {
  if (error) throw error;
​
  svg.insert("path", ".overlay")
      .datum(topojson.feature(topojson.presimplify(topo), topo.objects.snowflake))
      .attr("class", "koch")
      .attr("d", path);
});
​
function mousemoved() {
  area = x.invert(d3.mouse(this)[0]);
  svg.select(".koch").attr("d", path);
}
​
</script>
​
    