Force-Directed Graph with hidden Voronoi

This is another version of this block: Force-Directed Voronoi Graph, but with the polygons hidden. This is an experiment in making it easier to drag the nodes. Clicking anywhere selects the closest node instead of having to click directly on the node.

From the previous block:

This is a fork of mbostock's block: Force-Directed Graph where I've added a voronoi overlay. This could have a practical use by not having to click directly on a node in order select it and drag it.

From the original block:

This simple force-directed graph shows character co-occurence in Les Misérables. A physical simulation of charged particles and springs places related characters in closer proximity, while unrelated characters are farther apart. Layout algorithm inspired by Tim Dwyer and Thomas Jakobsen. Data based on character coappearence in Victor Hugo's Les Misérables, compiled by Donald Knuth.

Compare this display to a force layout with curved links, a force layout with fisheye distortion and a matrix diagram.

<!DOCTYPE html>
<meta charset="utf-8">
<style>
  
body {
  margin:0;
  position:fixed;
  top:0;
  right:0;
  bottom:0;
  left:0; 
}

.links line {
  stroke: #999;
  stroke-opacity: 0.6;
}

.nodes circle {
  stroke: #fff;
  stroke-width: 1.5px;
}

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

var svg = d3.select("svg"),
    width = innerWidth,
    height = innerHeight;

svg.attr("width", width)
	.attr("height", height)

var color = d3.scaleOrdinal(d3.schemeCategory20);

var simulation = d3.forceSimulation()
    .force("link", d3.forceLink().id(function(d) { return d.id; }))
    .force("charge", d3.forceManyBody())
    .force("center", d3.forceCenter(width / 2, height / 2));

d3.json("miserables.json", function(error, graph) {
  if (error) throw error;

var link = svg.append("g")
      .attr("class", "links")
    .selectAll("line")
    .data(graph.links)
    .enter().append("line")
      .attr("stroke-width", function(d) { return Math.sqrt(d.value); });

var voronoi = d3.voronoi().extent([[0,0], [width, height]]);

var polygons = svg.append("g")
      .attr("class", "polygons")
    .selectAll("polygon")
      .data(graph.nodes)
      .enter().append("polygon")
        .style("fill-opacity", 0)
        .call(d3.drag()
          .on("start", dragstarted)
          .on("drag", dragged)
          .on("end", dragended));
      
  var node = svg.append("g")
      .attr("class", "nodes")
    .selectAll("circle")
    .data(graph.nodes)
    .enter().append("circle")
      .attr("r", 5)
      .attr("fill", function(d) { return color(d.group); })
      .call(d3.drag()
          .on("start", dragstarted)
          .on("drag", dragged)
          .on("end", dragended));

node.append("title")
      .text(function(d) { return d.id; });

simulation
      .nodes(graph.nodes)
      .on("tick", ticked);

simulation.force("link")
      .links(graph.links);

function ticked() {
    if (graph.nodes[0].x) {
      var polygonShapes = voronoi(graph.nodes.map(function(d) {return [d.x, d.y]})).polygons()
      
      polygons.attr("points", function(d, i) {return polygonShapes[i]})
    }

link
        .attr("x1", function(d) { return d.source.x; })
        .attr("y1", function(d) { return d.source.y; })
        .attr("x2", function(d) { return d.target.x; })
        .attr("y2", function(d) { return d.target.y; });

node
        .attr("cx", function(d) { return d.x; })
        .attr("cy", function(d) { return d.y; });
  }
});

function dragstarted(d) {
  if (!d3.event.active) simulation.alphaTarget(0.3).restart();
  d.fx = d.x;
  d.fy = d.y;
}

function dragged(d) {
  d.fx = d3.event.x;
  d.fy = d3.event.y;
}

function dragended(d) {
  if (!d3.event.active) simulation.alphaTarget(0);
  d.fx = null;
  d.fy = null;
}

</script>

https://d3js.org/d3.v4.min.js