Modifying a Force Layout with Voronoi Polygons for Dragging and Mouseover of Grouped Elements

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    path {
      pointer-events: all;
      fill: none;
      stroke: #666;
      stroke-opacity: 0.2;
    }

.active path {
      fill: #111;  
      opacity: 0.05;
    }

.active text {
  		visibility: visible;
		}

.active circle {
      stroke: #000;
      stroke-width: 1.5px;
    }

svg {
      border: 1px solid #888;  
    }

.links {
      stroke: #000;
      stroke-width: 1.5;
    }

.nodes {
      stroke-width: 1.5;
    }

text {
      pointer-events: none;
      font: 1.8em sans-serif;
      visibility: hidden;
    }
  </style>
</head>

<body>
  <script>
    var svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 500);

var width = +svg.attr("width"),
      height = +svg.attr("height"),
      color = d3.scaleOrdinal(d3.schemeCategory10);

var a = {id: "a"},
      b = {id: "b"},
      c = {id: "c"},
      data = [a, b, c],
      links = [];

var simulation = d3.forceSimulation(data)
      .force("charge", d3.forceManyBody().strength(-10))
      .force("link", d3.forceLink(links).distance(200))
      .force("center", d3.forceCenter(width / 2, height / 2))
      .alphaTarget(1)
      .on("tick", ticked);

var link = svg.append("g").attr("class", "links").selectAll(".link"),
      node = svg.append("g").attr("class", "nodes").selectAll(".node");

var voronoi = d3.voronoi()
      .x(function(d) { return d.x; })
      .y(function(d) { return d.y; })
      .extent([[-1, 1], [width + 1, height + 1]]);

update();

d3.timeout(function() {
      links.push({source: a, target: b}); // Add a-b.
      links.push({source: b, target: c}); // Add b-c.
      links.push({source: c, target: a}); // Add c-a.
      update();
    }, 1000);

d3.interval(function() {
      data.pop(); // Remove c.
      links.pop(); // Remove c-a.
      links.pop(); // Remove b-c.
      update();
    }, 5000, d3.now());

d3.interval(function() {
      data.push(c); // Re-add c.
      links.push({source: b, target: c}); // Re-add b-c.
      links.push({source: c, target: a}); // Re-add c-a.
      update();
    }, 5000, d3.now() + 1000);

function update() {

node = node.data(data, function(d) { return d.id; });
      node.exit().remove();
      var nodeEnter = node.enter().append("g")
        .attr("class", "node")
        .on("mouseover", mouseover)
        .on("mouseout", mouseout);
      nodeEnter.append("circle").attr("fill", function(d) { return color(d.id); }).attr("r", 8);
      nodeEnter.append("text")
        .attr("dx", 12)
        .attr("dy", ".35em")
        .text(function(d) { return d.id; });
      nodeEnter.append("path").attr("class", "path");
      nodeEnter.call(d3.drag()
                     .on("start", dragstarted)
                     .on("drag", dragged)
                     .on("end", dragended));
      node = node.merge(nodeEnter);

// Apply the general update pattern to the links.
      link = link.data(links, function(d) { return d.source.id + "-" + d.target.id; });
      link.exit().remove();
      link = link.enter().append("line").merge(link);

// Update and restart the simulation.
      simulation.nodes(data);
      simulation.force("link").links(links);
      simulation.alpha(1).restart();
    }

function mouseover(d) {
      d3.select(this).raise().classed("active", true);
    }

function mouseout(d) {
      d3.select(this).raise().classed("active", false);
    }

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

function dragged(d) {
      d3.select(this).select("circle").attr("cx", d.fx = d3.event.x).attr("cy", d.fy = d3.event.y);
    }

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

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

node.select("path")
        .data(voronoi.polygons(data))
        .attr("d", function(d) { return d == null ? null : "M" + d.join("L") + "Z"; });

node.select("text")
        .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")" });

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; });
    }

</script>
</body>

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