Hashing Points by mbostock

index.html

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

.bar {
  fill: steelblue;
}

.axis line,
.axis path {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.axis text {
  display: none;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>

var m = 256,
    bins = d3.range(m).map(function() { return 0; });

var margin = {top: 20, right: 30, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var x = d3.scale.ordinal()
    .domain(d3.range(m))
    .rangeBands([0, width], .1);

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

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom")
    .tickSize(4, 0);

var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

svg.append("g")
    .attr("class", "bar")
  .selectAll("rect")
    .data(bins)
  .enter().append("rect")
    .attr("y", height)
    .attr("width", x.rangeBand())
    .attr("x", function(d, i) { return x(i); });

svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis);

var bars = svg.selectAll(".bar rect")[0].map(d3.select);

d3.json("/mbostock/raw/4090846/us.json", function(error, us) {
  if (error) throw error;

  var collection = topojson.feature(us, us.objects.counties), points = [];

  collection.features.forEach(function(f) {
    var g = f.geometry;
    if (g) switch (g.type) {
      case "MultiPolygon": g.coordinates.forEach(polygon); break;
      case "Polygon": g.coordinates.forEach(ring); break;
    }
  });

  function polygon(coordinates) {
    coordinates.forEach(ring);
  }

  function ring(coordinates) {
    coordinates.forEach(point);
  }

  function point(coordinates) {
    points.push(coordinates);
  }

  y.domain([0, points.length / m * 2]);

  d3.timer(function() {
    for (var k = 0, p; k < 100; ++k) {
      if (!(p = points.pop())) return true;
      var i = Math.abs(hash2(p[0], p[1]) % m), j = ++bins[i];
      bars[i].attr("y", y(j)).attr("height", height - y(j));
    }
  });
});

var buffer = new ArrayBuffer(8),
    floats = new Float64Array(buffer),
    ints = new Int32Array(buffer);

function hash1(x) {
  floats[0] = x;
  x = ints[1] ^ ints[0];
  x ^= (x >>> 20) ^ (x >>> 12);
  x ^= (x >>> 7) ^ (x >>> 4);
  return x;
}

function hash2(x, y) {
  return (hash1(x) + 31 * hash1(y)) | 0;
}

</script>