Force with Springy Links

Make link paths wavy for randomly-generated network.

wave function creates a wavy-like path between source and target link, using coordinate transforamtions.

I just updated the wave function so that the step variable is dependent upon the distance between nodes, so the link looks like a spring.

<!DOCTYPE html>
  <head>
    <meta charset="utf-8">
    <style>
      body {
        margin: 0;
      }
      .links path {
        fill: none;
        stroke: #999;
        stroke-opacity: 0.6;
      }

.nodes circle {
        stroke: #fff;
        stroke-width: 1.5px;
      }
    </style>
  </head>
  <body>
    <script src="https://d3js.org/d3.v4.min.js"></script>
    <script src="https://unpkg.com/d3-marcon/build/d3-marcon.min.js"></script>
    <script>
      var nodes = d3.range(100).map(function(i) {
        return { index: i }
      });

var links = d3.range(nodes.length - 1).map(function(i) {
        return { source: Math.floor(Math.sqrt(i)), target: i + 1}
      });
        
      var graph =  {nodes: nodes, links: links};

var m = d3.marcon().width(window.innerWidth).height(window.innerHeight);
      m.render();
      var width = m.innerWidth(),
        height = m.innerHeight(),
        svg = m.svg();

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

var simulation = d3.forceSimulation()
          .force("link", d3.forceLink().distance(50).strength(1))
          .force("charge", d3.forceManyBody())
          .force("center", d3.forceCenter(width / 2, height / 2));

var link = svg.append("g")
            .attr("class", "links")
          .selectAll("path")
          .data(graph.links)
          .enter().append("path")

var node = svg.append("g")
            .attr("class", "nodes")
          .selectAll("circle")
          .data(graph.nodes)
          .enter().append("circle")
            .attr("r", function(d) { return 4 + 6*Math.random(); })
            .attr("fill", function(d) { return color(Math.floor(Math.sqrt(d.index))); })
            .call(d3.drag()
                .on("start", dragstarted)
                .on("drag", dragged)
                .on("end", dragended));

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

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

function ticked() {
          link.attr("d", wave);

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

// Create wavy path between source and target
      function wave(d) {
        
        var p1 = d.source
          p2 = d.target,
          amp = 2,
          dist = Math.hypot(p2.y - p1.y, p2.x - p1.x),
          step = dist / 120,
          cpi = step * Math.PI,
          angle = Math.atan2(p2.y - p1.y, p2.x - p1.x),
          ca = Math.cos(angle),
          sa = Math.sin(angle),
          arr = [];

for (x = 0; x <= dist; x += step){
          var y = amp * Math.sin(x / cpi),
            x2 = p1.x + x * ca - y * sa,
            y2 = p1.y + x * sa + y * ca;

arr.push({x: x2, y: y2})
        }

var line = d3.line()
          .x(function(d) { return d.x; })
          .y(function(d) { return d.y; })

return line(arr);
      }

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>
  </body>
</html>

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

https://unpkg.com/d3-marcon/build/d3-marcon.min.js