Link nodes to avoid node/link overlap

This gist demonstrates the inserting of link nodes to avoid node/link overlap.



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](http://www.csse.monash.edu.au/~tdwyer/) and [Thomas Jakobsen](http://web.archive.org/web/20080410171619/http://www.teknikus.dk/tj/gdc2001.htm). Data based on character coappearence in Victor Hugo's *Les Misérables*, compiled by [Donald Knuth](http://www-cs-faculty.stanford.edu/~uno/sgb.html).

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

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

.link {
  stroke: #999;
  stroke-opacity: .6;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>

var width = 960,
    height = 500;

var color = d3.scale.category20();

var force = d3.layout.force()
    .charge(-120)
    .linkDistance(30)
    .size([width, height]);

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

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

var linkNodes = [];

graph.links.forEach(function(link) {
    linkNodes.push({
      source: graph.nodes[link.source],
      target: graph.nodes[link.target]
    });
  });

force
      .nodes(graph.nodes.concat(linkNodes))
      .links(graph.links)
      .start();

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

var node = svg.selectAll(".node")
      .data(graph.nodes)
    .enter().append("circle")
      .attr("class", "node")
      .attr("r", 5)
      .style("fill", function(d) { return color(d.group); })
      .call(force.drag);

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

var linkNode = svg.selectAll(".link-node")
      .data(linkNodes)
    .enter().append("circle")
      .attr("class", "link-node")
      .attr("r", 2)
      .style("fill", "#ccc");

force.on("tick", function() {
    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; });

linkNode.attr("cx", function(d) { return d.x = (d.source.x + d.target.x) * 0.5; })
        .attr("cy", function(d) { return d.y = (d.source.y + d.target.y) * 0.5; });
  });
});

</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js