Canvas Voronoi by mbostock

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="500"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var canvas = d3.select("canvas").on("touchmove mousemove", moved).node(),
    context = canvas.getContext("2d"),
    width = canvas.width,
    height = canvas.height;

var sites = d3.range(100)
    .map(function(d) { return [Math.random() * width, Math.random() * height]; });

var voronoi = d3.voronoi()
    .extent([[-1, -1], [width + 1, height + 1]]);

redraw();

function moved() {
  sites[0] = d3.mouse(this);
  redraw();
}

function redraw() {
  var diagram = voronoi(sites),
      links = diagram.links(),
      polygons = diagram.polygons();

  context.clearRect(0, 0, width, height);
  context.beginPath();
  drawCell(polygons[0]);
  context.fillStyle = "#f00";
  context.fill();

  context.beginPath();
  for (var i = 0, n = polygons.length; i < n; ++i) drawCell(polygons[i]);
  context.strokeStyle = "#000";
  context.stroke();

  context.beginPath();
  for (var i = 0, n = links.length; i < n; ++i) drawLink(links[i]);
  context.strokeStyle = "rgba(0,0,0,0.2)";
  context.stroke();

  context.beginPath();
  drawSite(sites[0]);
  context.fillStyle = "#fff";
  context.fill();

  context.beginPath();
  for (var i = 1, n = sites.length; i < n; ++i) drawSite(sites[i]);
  context.fillStyle = "#000";
  context.fill();
  context.strokeStyle = "#fff";
  context.stroke();
}

function drawSite(site) {
  context.moveTo(site[0] + 2.5, site[1]);
  context.arc(site[0], site[1], 2.5, 0, 2 * Math.PI, false);
}

function drawLink(link) {
  context.moveTo(link.source[0], link.source[1]);
  context.lineTo(link.target[0], link.target[1]);
}

function drawCell(cell) {
  if (!cell) return false;
  context.moveTo(cell[0][0], cell[0][1]);
  for (var j = 1, m = cell.length; j < m; ++j) {
    context.lineTo(cell[j][0], cell[j][1]);
  }
  context.closePath();
  return true;
}

</script>