Network Wavy Path - I

Make link paths wavy for randomly-generated network.

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

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

.nodes circle {
  stroke: #fff;
  stroke-width: 1.5px;
}
</style>
<svg width="900" height="600"></svg>
<script src="https://d3js.org/d3.v4.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 svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height");

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
  var step = 0.7, amp = 3, cpi = step*Math.PI
  var dist = Math.hypot(p2.y - p1.y, p2.x - p1.x)
  var angle = Math.atan2(p2.y - p1.y, p2.x - p1.x)
  var ca = Math.cos(angle), sa = Math.sin(angle)
  var arr = []
  for (x=0; x<=dist; x+=step){
    var y = amp * Math.sin(x/cpi)
    var x2 = p1.x + x*ca - y*sa
    var y2 = p1.y + x*sa + y*ca 
    arr.push({x:x2, y:y2})
  }
  var line = d3.line().curve(d3.curveBasis)
    .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>

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