D3 Examples - Hexbin Canvas Transitions

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
html, body {
  background: #222;
}
canvas {
  position: absolute;
  top: 0;
  left: 0;
}
</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="d3.canvas-hexbin.js"></script>
<script>
​
var width = 960,
    height = 500;
​
var hexbin = d3.canvasHexbin()
    .size([width, height])
    .radius(4);
​
var color = d3.scale.linear()
   .domain([0, 14, 15, 35, 132])
   .range(["#050505", "#222", "#d7191c", "#ffffbf", "#2c7bb6"])
   .interpolate(d3.interpolateHcl);
​
var canvas = d3.select("body").append("canvas")
    .attr("width", width)
    .attr("height", height);
​
var context = canvas.node().getContext("2d");
var points = [];
var hexagons = [];
​
hexbin.context(context);
​
getImage("readme.png", function(image) {
  context.drawImage(image, 0, 0, width, height);
  image = context.getImageData(0, 0, width, height);
​
  // Rescale the colors.
  for (var c, i = 0, n = width * height * 4, d = image.data; i < n; i += 4) {
    points.push([i/4%width, Math.floor(i/4/width), d[i]]);
  }
​
  hexagons = hexbin(points);
  hexagons.forEach(function(d) {
    d.min = d3.min(d, function(p) { return p[2]; });
    d.max = d3.max(d, function(p) { return p[2]; });
    d.mean = d3.mean(d, function(p) { return p[2]; });
  });
​
  // optimization: filter out sea level
  hexagons = hexagons.filter(function(d) {
    return d.max > 16 || d.min < 10;
  });
​
  var interpolated = d3.interpolate(
    hexagons.map(function(d) { return d.min; }),
    hexagons.map(function(d) { return d.max; })
  );
​
  function toggle() {
    d3.timer(function(t) {
      if (t > 9000) return true;
      if (t > 4500) t = 9000 - t;
​
      context.clearRect(0,0,width,height);
​
      interpolated(t/4500).forEach(function(d,i) {
        context.save();
        context.fillStyle = color(d);
        context.translate(hexagons[i].x, hexagons[i].y);
        hexbin.hexagon(4.5);
        context.fill();
        context.restore();
      });
    });
  };
​
  loop(toggle, 9000);
​
  function loop(f,t) {
    f();
    setTimeout(function() {
      loop(f,t);
    },t)
  };
});
​
​
function getImage(path, callback) {
  var image = new Image;
  image.onload = function() { callback(image); };
  image.src = path;
}
​
</script>
​
    