Square lattice spring network

This demonstrates forceLink.iterations, which strengthens d3-force’s link constraint by applying the constraint multiple times per simulation step.

forked from mbostock's block: Force-Directed Lattice

created in blockbuilder.

<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="960"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var n = 20;

var nodes = d3.range(n * n).map(function(i) {
  return {
    index: i,
    x: 20*(i % n),
    y: 20*Math.floor(i / n)-450
  };
});

var links = [];

for (var y = 0; y < n; ++y) {
  for (var x = 0; x < n; ++x) {
    if (y > 0) links.push({source: (y - 1) * n + x, target: y * n + x});
    if (x > 0) links.push({source: y * n + (x - 1), target: y * n + x});
  }
}

var simulation = d3.forceSimulation(nodes)
//    .force("charge", d3.forceManyBody().strength(-30))
    .force("link", d3.forceLink(links).strength(1).distance(20).iterations(10))
    .on("tick", ticked);

var canvas = document.querySelector("canvas"),
    context = canvas.getContext("2d"),
    width = canvas.width,
    height = canvas.height;

d3.select(canvas)
    .call(d3.drag()
        .container(canvas)
        .subject(dragsubject)
        .on("start", dragstarted)
        .on("drag", dragged)
        .on("end", dragended));

function ticked() {
  context.clearRect(0, 0, width, height);
  context.save();
  context.translate(width / 2, height / 2);

context.beginPath();
  links.forEach(drawLink);
  context.strokeStyle = "#aaa";
  context.stroke();

context.beginPath();
  nodes.forEach(drawNode);
  context.fill();
  context.strokeStyle = "#fff";
  context.stroke();

context.restore();
}

function dragsubject() {
  return simulation.find(d3.event.x - width / 2, d3.event.y - height / 2);
}

function dragstarted() {
  if (!d3.event.active) simulation.alphaTarget(0.3).restart();
  d3.event.subject.fx = d3.event.subject.x;
  d3.event.subject.fy = d3.event.subject.y;
}

function dragged() {
  d3.event.subject.fx = d3.event.x;
  d3.event.subject.fy = d3.event.y;
}

function dragended() {
  if (!d3.event.active) simulation.alphaTarget(0);
  d3.event.subject.fx = null;
  d3.event.subject.fy = null;
}

function drawLink(d) {
  context.moveTo(d.source.x, d.source.y);
  context.lineTo(d.target.x, d.target.y);
}

function drawNode(d) {
  context.moveTo(d.x + 3, d.y);
  context.arc(d.x, d.y, 3, 0, 2 * Math.PI);
}

</script>

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