D3 Examples - World Tour with color bitmap

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
h1 {
  position: absolute;
  top: 280px;
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  font-size: 18px;
  text-align: center;
  width: 960px;
  pointer-events: none;
}
​
</style>
<h1></h1>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="https://d3js.org/queue.v1.min.js"></script>
<script src="https://d3js.org/topojson.v1.min.js"></script>
<script>
​
var width = 960,
    height = 500;
​
var projection = d3.geo.orthographic()
    .scale(248)
    .clipAngle(90);
​
var canvas = d3.select("body").append("canvas")
    .attr("width", width)
    .attr("height", height);
​
var c = canvas.node().getContext("2d");
​
// this is our "bitmap" image for color lookups
var hidden = document.createElement("canvas"),
    c2 = hidden.getContext('2d');
hidden.width = width;
hidden.height = height;
​
// comment this out to hide the bitmap
document.body.appendChild(hidden);
​
var colorToFeature = {};
​
var path = d3.geo.path()
    .projection(projection)
    .context(c);
​
var title = d3.select("h1");
​
queue()
    .defer(d3.json, "world-110m.json")
    .defer(d3.tsv, "world-country-names.tsv")
    .await(ready);
​
function ready(error, world, names) {
  var globe = {type: "Sphere"},
      land = topojson.feature(world, world.objects.land),
      countries = topojson.feature(world, world.objects.countries).features,
      borders = topojson.mesh(world, world.objects.countries, function(a, b) { return a !== b; }),
      i = -1,
      n = countries.length;
​
  var hexFormat = d3.format('06x'),
      nextColor = (function() {
        var c = 512, step = 2048;
        return function() {
          return '#' + hexFormat(c += step);
        };
      })();
​
  countries = countries.filter(function(d) {
    return names.some(function(n) {
      if (d.id == n.id) return d.name = n.name;
    });
  })
  .sort(function(a, b) {
    return a.name.localeCompare(b.name);
  });
​
  countries.forEach(function(d) {
    d.color = nextColor();
    colorToFeature[d.color] = d;
  });
​
  var overFeature, mouse;
  d3.selectAll('canvas')
    .on('mousemove', function() {
      mouse = d3.mouse(this);
      draw();
    });
​
  function draw() {
    path.context(c);
    c.clearRect(0, 0, width, height);
    c.fillStyle = "#bbb", c.beginPath(), path(land), c.fill();
    c.fillStyle = "#f00", c.beginPath(), path(countries[i]), c.fill();
    c.strokeStyle = "#fff", c.lineWidth = .5, c.beginPath(), path(borders), c.stroke();
    c.strokeStyle = "#000", c.lineWidth = 2, c.beginPath(), path(globe), c.stroke();
​
    if (mouse) {
      var color = c2.getImageData(mouse[0], mouse[1], 1, 1).data;
      var hex = '#' + hexFormat(color[0] << 16 | color[1] << 8 | color[2]);
      var feature = colorToFeature[hex];
      if (feature != overFeature) {
        console.log('over:', hex, feature ? feature.name : 'none');
        overFeature = feature;
      }
    }
​
    c2.clearRect(0, 0, width, height);
    countries.forEach(function(d) {
      if (d === overFeature) {
        c.strokeStyle = '#fff';
        c.lineWidth = 1;
        drawFeature(c, d, '#6f0');
        c.stroke();
      }
      c2.strokeStyle = '#fff';
      c2.lineWidth = 1;
      drawFeature(c2, d, d.color);
      c2.stroke();
    });
  }
​
  function drawFeature(ctx, d, fill) {
    ctx.fillStyle = fill || d.color;
    ctx.beginPath();
    path.context(ctx)(d);
    ctx.fill();
  }
​
  (function transition() {
    d3.transition()
      .duration(1250)
      .each("start", function() {
        title.text(countries[i = (i + 1) % n].name);
      })
      .tween("rotate", function() {
        var p = d3.geo.centroid(countries[i]),
            r = d3.interpolate(projection.rotate(), [-p[0], -p[1]]);
        return function(t) {
          projection.rotate(r(t));
          draw();
        };
      })
      .transition()
        .each("end", transition);
  })();
}
​
d3.select(self.frameElement).style("height", (height * 2) + "px");
​
</script>
​
    