Add text/label onto links in D3 force directed graph

Question

I've been working on modified force directed graph and having some problems with adding text/label onto links where the links are not properly aligned to nodes. How to fix it?

And how I can add an event listener to an SVG text element? Adding .on("dblclick",function(d) {....} just doesn't work.

Here's the code snippet:

<style type="text/css">
    .link { stroke: #ccc; }
    .routertext { pointer-events: none; font: 10px sans-serif; fill: #000000; }
    .routertext2 { pointer-events: none; font: 9px sans-serif; fill: #000000; }
    .linktext { pointer-events: none; font: 9px sans-serif; fill: #000000; }
</style>

<div id="canvas">
</div>

<script type="text/javascript" src="d3/d3.js"></script>
<script type="text/javascript" src="d3/d3.layout.js"></script>
<script type="text/javascript" src="d3/d3.geo"></script>
<script type="text/javascript" src="d3/d3.geom.js"></script>


<script type="text/javascript">

var w = 960,
    h = 600,
    size = [w, h]; // width height    
var vis = d3.select("#canvas").append("svg:svg")
  .attr("width", w)
  .attr("height", h)
  .attr("transform", "translate(0,0) scale(1)")
  .call(d3.behavior.zoom().on("zoom", redraw))
  .attr("idx", -1)
  .attr("idsel", -1)
  ;

var routers = {
    nodes: [
        {id:0, name:"ROUTER-1", group:1, ip: "123.123.123.111",
            x:394.027, y:450.978,outif:"ge-0/1/0.0",inif:""},
        {id:1, name:"ROUTER-2", group:1, ip: "123.123.123.222",
            x:385.584, y:351.513,outif:"xe-4/2/0.0",inif:"ge-5/0/3.0"},
        {id:2, name:"ROUTER-3", group:1, ip: "123.123.123.333",
            x:473.457, y:252.27,outif:"ae1.0",inif:"xe-1/0/1.0"},
        {id:3, name:"ROUTER-4", group:2, ip: "123.123.123.444",
            x:723.106, y:266.569,outif:"as0.0",inif:"ae1.0"},
        {id:4, name:"ROUTER-5", group:3, ip: "123.123.123.555",
            x:728.14, y:125.287,outif:"so-4/0/2.0",inif:"as1.0"},
        {id:5, name:"ROUTER-6", group:3, ip: "123.123.123.666",
            x:738.975, y:-151.772,outif:"",inif:"PO0/2/2/1" }
    ],
    links: [
        {source:0, target:1, value:3, name:'link-1',speed:"1000mbps",
            outif:"ge-0/1/0.0",nextif:"ge-5/0/3.0"},
        {source:1, target:2, value:3, name:'link-2',speed:"10Gbps",
            outif:"xe-4/2/0.0",nextif:"xe-1/0/1.0"},
        {source:2, target:3, value:3, name:'link-3',speed:"20Gbps",
            outif:"ae1.0",nextif:"xe-1/2/1.0"},
        {source:3, target:4, value:3, name:'link-4',speed:"1Gbps",
            outif:"as0.0",nextif:"as1.0"},
        {source:4, target:5, value:3, name:'link-5',speed:"OC3",
            outif:"so-4/0/2.0",nextif:"PO0/2/2/1"}
    ]
};  

var force = d3.layout.force()
      .nodes(routers.nodes)
      .links(routers.links)
      .gravity(0)
      .distance(100)
      .charge(0)
      .size([w, h])
      .start();

var link = vis.selectAll("g.link")
      .data(routers.links)
      .enter().append("svg:g");

  link.append("svg:line")   
      .attr("class", "link")
      .attr("title", function(d) { return "From: "+d.outif+", To: "+d.nextif })
      .attr("style", "stroke:#00d1d6;stroke-width:4px")
      .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; });

  link.append("svg:text")
      .attr("class", "linktext")
      .attr("dx", function(d) { return d.source.x; })
      .attr("dy", function(d) { return d.source.y; })
      .text("some text to add...");

  var node = vis.selectAll("g.node")
      .data(routers.nodes)
     .enter()
      .append("svg:g")
      .attr("id", function(d) { return d.id;})
      .attr("title", function(d) {return d.ip})
      .attr("class", "node")
      .attr("x", function(d) { return d.x; })
      .attr("y", function(d) { return d.y; })
      .on("dblclick",function(d) {
           alert('router double-clicked'); d3.event.stopPropagation();
      })
      .on("mousedown", function(d) {
          if (d3.event.which==3) {
              d3.event.stopPropagation();
              alert('Router right-clicked');
          }
      })
      .call(force.drag);

  node.append("svg:image")
      .attr("class", "node")
      .attr("xlink:href", "router.png")
      .attr("x", -24)
      .attr("y", -18)
      .attr("width", 48)
      .attr("height", 36);

  node.append("svg:text")
      .attr("class", "routertext")
      .attr("dx", -30)
      .attr("dy", 20)
      .text(function(d) { return d.name });

  node.append("svg:text")
      .attr("class", "routertext2")
      .attr("dx", 0)
      .attr("dy", -20)
      .attr("title", "some title to show....")
      .text(function(d) { return d.outif })
      .on("click", function(d,i) {alert("outif text clicked");})
      .call(force.drag);

    node.append("svg:text")
      .attr("class", "routertext2")
      .attr("dx", -40)
      .attr("dy", 30)
      .text(function(d) { return d.inif });

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

  function redraw() {
    vis.attr("transform",
      "translate(" + d3.event.translate + ")"
      + "scale(" + d3.event.scale + ")");
  };

</script>

Solution 1

Use a smaller example outside of D3 to see how the SVG stuff works. Then just rebuild this structure using D3 and your custom data.

<html>
    <body>

<svg width="600px" height="400px">

    <defs>
        <!-- DEFINE AN ARROW THAT WE CAN PLACE AT THE END OF EDGES. -->
        <!-- USE REFX TO MOVE THE ARROW'S TIP TO THE END OF THE PATH. -->
        <marker
            orient="auto"
            markerHeight="12"
            markerWidth="12"
            refY="0"
            refX="9"
            viewBox="0 -5 10 10"
            id="ARROW_ID"
            style="fill: red; fill-opacity: 0.5;">

            <path d="M0, -5L10, 0L0, 5"></path>

        </marker>
    </defs>

    <!-- DEFINE A PATH. SET ITS END MARKER TO THE ARROW'S ID. -->
    <!-- SET FILL NONE TO DRAW A LINE INSTEAD OF A SHAPE. -->
    <path
        d="M100,100 A300,250 0 0,1 500,300"
        style="fill:none; stroke:grey; stroke-width:2px;"
        id="PATH_ID"
        marker-end="url(#ARROW_ID)" />

    <!-- DEFINE A TEXT ELEMENT AND SET FONT PROPERTIES. -->
    <!-- USE DY TO MOVE TEXT ABOVE THE PATH. -->
    <text
        style="text-anchor:middle; font: 16px sans-serif;"
        dy="-12">

        <!-- DEFINE A TEXT PATH FOLLOWING THE PATH DEFINED ABOVE. -->
        <!-- USE STARTOFFSET TO CENTER TEXT. -->
        <textPath
            xlink:href="#PATH_ID"
            startOffset="50%">Centered edge label</textPath>
    </text>

</svg>

    </body>
</html>

Solution 2

Have you experimented with creating text elements separately in a standalone (simpler) example? It should give you a better feeling for how the different attributes control positioning.

For vertical alignment, use the "dy" attribute:

• by default, the baseline of the text is at the origin (bottom-aligned)
• a dy of .35em centers the text vertically
• a dy of .72em places the topline of the text at the origin (top-aligned)

Using em units is nice because it will scale automatically based on the font size. If you don't specify units (such as -20 in your code), it defaults to pixels.

For horizontal alignment, use the "text-anchor" attribute:

• the default is "start" (left-aligned for left-to-right languages)
• "middle"
• "end"

There's also the "dx" attribute, which is tempting to use for padding. However, I wouldn't recommend it because there is a bug in Firefox and Opera that cause it to not work as expected in conjunction with text-anchor middle or end.

Solution 3

Created JS fiddle example for showing labels over links in D3 Forced layout chart

See working demo in JS Fiddle: http://jsfiddle.net/bc4um7pc/

Give Id's to your path like below

var path = svg.append("svg:g").selectAll("path")
    .data(force.links())
  .enter().append("svg:path")
    .attr("class", function(d) { return "link " + d.type; })
    .attr("id",function(d,i) { return "linkId_" + i; })
    .attr("marker-end", function(d) { return "url(#" + d.type + ")"; });

Use SVG textPath element for associating labels with above links by specifying its 'xlink:href' attribute to point to its respective link/path.

 var linktext = svg.append("svg:g").selectAll("g.linklabelholder").data(force.links());
     linktext.enter().append("g").attr("class", "linklabelholder")
     .append("text")
     .attr("class", "linklabel")
     .style("font-size", "13px")
     .attr("x", "50")
     .attr("y", "-20")
     .attr("text-anchor", "start")
     .style("fill","#000")
     .append("textPath")
    .attr("xlink:href",function(d,i) { return "#linkId_" + i;})
     .text(function(d) { 
         return "my text"; //Can be dynamic via d object 
     });

Solution 4

I am using an arch as a link between nodes with a label text placed in the middle. Here is a code snippet:

    var vis = d3.select("body")
     .append("svg")
     .attr("width", 600)
     .attr("height", 400)
     .append("g");

    var force = d3.layout.force()
     .gravity(.05)
     .distance(120)
     .charge(-100)
     .size([600, 400]);
    var nodes = force.nodes(), links = force.links();

    // make an arch between nodes and a text label in the middle
    var link = vis.selectAll("path.link").data(links, function(d) {
       return d.source.node_id + "-" + d.target.node_id; });
    link.enter().append("path").attr("class", "link");

    var linktext = vis.selectAll("g.linklabelholder").data(links);
    linktext.enter().append("g").attr("class", "linklabelholder")
     .append("text")
     .attr("class", "linklabel")
     .attr("dx", 1)
     .attr("dy", ".35em")
     .attr("text-anchor", "middle")
     .text(function(d) { return "my label" });

    // add your code for nodes  ....

    force.on("tick", tick); force.start();

    function tick () {   
     // curve
     link.attr("d", function(d) {
      var dx = d.target.x - d.source.x,
      dy = d.target.y - d.source.y,
      dr = Math.sqrt(dx * dx + dy * dy);
     return "M" + d.source.x + "," + d.source.y + "A" + dr + "," 
         + dr + " 0 0,1 " + d.target.x + "," + d.target.y;
     });    
     // link label
     linktext.attr("transform", function(d) {
      return "translate(" + (d.source.x + d.target.x) / 2 + "," 
      + (d.source.y + d.target.y) / 2 + ")"; });
     // nodes 
    node.attr("transform", function(d) {
        return "translate(" + d.x + "," + d.y + ")"; });
    }

View more solutions

Comments

[dchang]

This will center text within a node, but I believe the question is asking to center text on a link.

[ᴠɪɴᴄᴇɴᴛ]

Like with textPath, SVG is case-sensitive (at least in Chrome), so the attribute should read startOffset.