Draggable Blob

Drag the blob to deform it. Press the shift key to show the underlying force simulation's nodes and links.

Uses d3-shape's line() and curveBasisClosed() functions to draw a blob from a graph.

Inspired by Mike Bostock's Force Dragging III example.

<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="500"></canvas>
<script src="https://d3js.org/d3.v4.0.0-alpha.44.min.js"></script>
<script>

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

var numPoints = 5
var radius = 200
var nodes = d3.range(numPoints).map(function(d) {
  return {
    id: d,
    x: width / 2 + radius * Math.cos(Math.PI * 2 / numPoints * d) + Math.random() * 30 - 15,
    y: height / 2 + radius * Math.sin(Math.PI * 2 / numPoints * d) + Math.random() * 30 - 15
  };
});

var links = nodes.map(function(n) {
  return {
    source: n.id,
    target: n.id + 1 === nodes.length ? 0 : n.id + 1
  }
});

var drawShape = d3.line()
  .x(function(d) { return d.x; })
  .y(function(d) { return d.y; })
  .curve(d3.curveBasisClosed)
  .context(context)

render({
  nodes: nodes,
  links: links
});

function render(graph) {
  simulation
      .nodes(graph.nodes)
      .on("tick", ticked);
  simulation.force("link")
      .links(graph.links);
  d3.select(canvas)
      .call(d3.drag()
          .container(canvas)
          .subject(dragsubject)
          .on("start", dragstarted)
          .on("drag", dragged)
          .on("end", dragended));

d3.select("body")
    .on("keydown", toggleDebug)
    .on("keyup", toggleDebug);

function ticked() {
    context.clearRect(0, 0, width, height);

context.beginPath();
    // Draw the shape from all nodes 
    drawShape(graph.nodes);
    context.fillStyle = "#f55";
    context.fill();

if (debug) {
      context.beginPath();
      graph.links.forEach(drawLink);
      context.strokeStyle = "#003B5C";
      context.stroke();

context.beginPath();
      graph.nodes.forEach(drawNode);
      context.fillStyle = "#003B5C";
      context.fill();
      context.strokeStyle = "#fff";
      context.stroke();      
    }
  }
  function toggleDebug() {
    debug = d3.event.shiftKey;
    ticked();
  }
}
function dragsubject() {
  return simulation.find(d3.event.x, d3.event.y);
}
function dragstarted() {
  if (!d3.event.active) simulation.alphaTarget(0.5).restart()
  simulation.fix(d3.event.subject);
}
function dragged() {
  simulation.fix(d3.event.subject, d3.event.x, d3.event.y);
}
function dragended() {
  if (!d3.event.active) simulation.alphaTarget(0);
  simulation.unfix(d3.event.subject);
}
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.v4.0.0-alpha.44.min.js