How to render links as elbow connectors in d3 force directed graph

  var width = 600,
    height = 148,
    constant = 10,
    color = "#BCD8CD"

  var scale = .75, w = 70*scale, h = 50*scale,
    nodes = [
    {label: '1st stage', x:   constant, y: 20*scale , width:w,height:h , color :color , stage: true },
    {label: '2nd stage', x: constant + 150*scale , y: 20*scale ,width:w,height:h ,color :color, stage: true },
    {label: '3rd stage', x: constant + 279*scale, y: 20*scale ,width:w,height:h, color :color, stage: false },
    {label: '4th stage', x: constant + 460*scale, y: 20*scale ,width:w,height:h, color :color, stage: false },
    {label: '5th stage', x: constant + 660*scale, y: 20*scale ,width:w,height:h ,color :color, stage: false },
    {label: '6th stage', x: constant + 350*scale, y: 100*scale ,width:w,height:h, color :color, stage: true }
    ].map(function(d, i){return (d.fixed = (i != 5), d)});

  var links = [
    { source: 0, target: 1 },
    { source: 1, target: 2},
    { source: 2, target: 3},
    { source: 3, target: 4},
    { source: 1, target: 5}
  ];

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

  var markerW = 4, markerH = 3,
    marker = svg.append('marker')
    .attr('id',"triangle")
    .attr('viewBox',"0 0 10 10")
    .attr('refX',"0")
    .attr('refY',5)
    .attr('markerUnits','strokeWidth')
    .attr('markerWidth',markerW)
    .attr('markerHeight',markerH)
    .attr('orient','auto')

  var path = marker.append('path')
    .attr('d',"M 0 0 L 10 5 L 0 10 z")

  var force = d3.layout.force()
    .size([width, height])
    .nodes(nodes)
    .links(links)
    .linkDistance(width/4)
    .on("tick", function(e){
      //hack to force IE to do it's job!
      link.each(function() {this.parentNode.insertBefore(this, this); });

      link.attr("d", linkPath);
      node.attr("transform", function (d) {
        return "translate(" + d.q.x + "," + d.q.y + ")";
      })
    });
    force.nodes().forEach(function(d) {
      d.q = {};
      Object.keys(d).forEach(function (p) {
        if (!isNaN(d[p])) Object.defineProperty(d.q, p, {
          get: function () {
            return Math.round(d[p])
          }
        });
      })
    });

  var connector = d3.svg.line().interpolate("linear")
    .x(function(d){return Math.round(d[0])})
    .y(function(d){return Math.round(d[1])});
  function linkPath(d){
    return connector([[d.source.x + d.source.width/2, d.source.y + d.source.height/2],
      [d.source.x + d.source.width/2, d.target.y + d.target.height/2],
      [d.target.x  - markerW - 4, d.target.y + d.target.height/2]]);
  }

  var link = svg.selectAll('.link')
    .data(links)
    .enter().append('path')
    .attr("stroke-width", "2")
    .attr('marker-end','url(#triangle)')
    .attr('stroke','black')
    .attr("fill", "none");

  var defs = svg.append("defs");

  // create filter with id #drop-shadow
  // height=130% so that the shadow is not clipped
  var filter = defs.append("filter")
    .attr("id", "drop-shadow")
    .attr({"height": "200%", "width": "200%", x: "-50%", y: "-50%"});

  // SourceAlpha refers to opacity of graphic that this filter will be applied to
  // convolve that with a Gaussian with standard deviation 3 and store result
  // in blur
  filter.append("feGaussianBlur")
    .attr("in", "SourceAlpha")
    .attr("stdDeviation", 3)
    .attr("result", "blur");

  // translate output of Gaussian blur to the right and downwards with 2px
  // store result in offsetBlur
  var feOffset = filter.append("feOffset")
    .attr("in", "blur")
    .attr("dx", 2)
    .attr("dy", 2)
    .attr("result", "offsetBlur");

  // overlay original SourceGraphic over translated blurred opacity by using
  // feMerge filter. Order of specifying inputs is important!
  var feMerge = filter.append("feMerge");

  feMerge.append("feMergeNode")
    .attr("in", "offsetBlur")
  feMerge.append("feMergeNode")
    .attr("in", "SourceGraphic");

  var node = svg.selectAll('.node')
    .data(nodes)
    .enter().append('g')
    .attr('class', 'node')
    .attr("transform", function(d){
      return "translate("+ d.q.x+","+ d.q.y+")";
    })
  .call(force.drag)

  node.append("rect").attr("class", "nodeRect")
    .attr("rx", 6)
    .attr("ry", 6)
    .attr('width', function(d) { return d.width; })
    .attr('height', function(d) { return d.height; })
    .style("fill", function(d) { return d.color; })
    .transition()
    .duration(1000) // this is 1s
    .delay(1000)
    .style("fill",function(d){if(d.stage) return "#FF9966"})
    .style("filter",function(d){if(d.stage) return "url(#drop-shadow)"})


  node.append("text").style("text-anchor", "middle")
    .style("pointer-events", "none")
    .style("font-weight", 900)
    .attr("fill", "white")
    .style("stroke-width", "0.3px")
    .style("font-size", 16*scale + "px")
    .attr("y", function (d){return d.height/2+6*scale;})
    .attr("x", function (d){return d.width/2;})
    .text(function (d) {return d.label;})

  force.start();

    link.attr("d", linkPath)
   .transition()
    .duration(1000) // this is 1s
    .delay(1000)
    .style("filter",function(d){if(d.source.stage) return "url(#drop-shadow)"});

  d3.select("svg").append("text").attr({"y": height - 20, fill: "black"}).text("drag me!")

svg { overflow: visible;}
.node {
  fill: #ccc;
  stroke: #fff;
  stroke-width: 2px;
}
.link {
  stroke: #777;
  stroke-width: 2px;
}
g.hover {
  background-color: rgba(0, 0, 0, .5);
}

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