Delaunay Triangulation by mbostock

index.html

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

.triangles {
  fill: none;
}

.links {
  stroke: #000;
}

.sites {
  fill: #000;
  stroke: #fff;
}

.triangles .primary {
  fill: #f00;
}

.links .primary {
  stroke: #fff;
}

.sites :first-child {
  fill: #fff;
}

</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var svg = d3.select("svg").on("touchmove mousemove", moved),
    width = +svg.attr("width"),
    height = +svg.attr("height");

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

var voronoi = d3.voronoi();

var triangle = svg.append("g")
    .attr("class", "triangles")
  .selectAll("path")
  .data(voronoi.triangles(sites))
  .enter().append("path")
    .call(redrawTriangle);

var link = svg.append("g")
    .attr("class", "links")
  .selectAll("line")
  .data(voronoi.links(sites))
  .enter().append("line")
    .call(redrawLink);

var site = svg.append("g")
    .attr("class", "sites")
  .selectAll("circle")
  .data(sites)
  .enter().append("circle")
    .attr("r", 2.5)
    .call(redrawSite);

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

function redraw() {
  var diagram = voronoi(sites);
  triangle = triangle.data(diagram.triangles()), triangle.exit().remove();
  triangle = triangle.enter().append("path").merge(triangle).call(redrawTriangle);
  link = link.data(diagram.links()), link.exit().remove();
  link = link.enter().append("line").merge(link).call(redrawLink);
  site = site.data(sites).call(redrawSite);
}

function redrawTriangle(triangle) {
  triangle
      .classed("primary", function(d) { return d[0] === sites[0] || d[1] === sites[0] || d[2] === sites[0]; })
      .attr("d", function(d) { return "M" + d.join("L") + "Z"; });
}

function redrawLink(link) {
  link
      .classed("primary", function(d) { return d.source === sites[0] || d.target === sites[0]; })
      .attr("x1", function(d) { return d.source[0]; })
      .attr("y1", function(d) { return d.source[1]; })
      .attr("x2", function(d) { return d.target[0]; })
      .attr("y2", function(d) { return d.target[1]; });
}

function redrawSite(site) {
  site
      .attr("cx", function(d) { return d[0]; })
      .attr("cy", function(d) { return d[1]; });
}

</script>