Zoom Transitions

This example demonstrates smooth zoom transitions using d3-zoom. Every 2.5 seconds, a point is randomly selected, and the transform to position the selected point at the center of the viewport is computed:

function transform() {
  return d3.zoomIdentity
      .translate(width / 2, height / 2)
      .scale(8)
      .translate(-point[0], -point[1]);
}

Then, transition.call is used to invoke zoom.transform with the new transform, initiating a smooth zoom transition from the current transform.

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

var canvas = d3.select("canvas"),
    context = canvas.node().getContext("2d"),
    width = canvas.property("width"),
    height = canvas.property("height"),
    radius = 2.5;

var points = d3.range(1000).map(phyllotaxis(10)),
    point = points.pop();

var zoom = d3.zoom()
    .on("zoom", zoomed);

canvas
    .call(zoom.transform, transform)
    .call(transition);

function zoomed() {
  context.save();
  context.clearRect(0, 0, width, height);
  context.translate(d3.event.transform.x, d3.event.transform.y);
  context.scale(d3.event.transform.k, d3.event.transform.k);
  drawPoints();
  context.restore();
}

function drawPoints() {
  context.beginPath();
  points.forEach(drawPoint);
  context.fillStyle = "#000";
  context.fill();

context.beginPath();
  drawPoint(point);
  context.fillStyle = "#f00";
  context.fill();
  context.stroke();
}

function drawPoint(point) {
  context.moveTo(point[0] + radius, point[1]);
  context.arc(point[0], point[1], radius, 0, 2 * Math.PI);
}

function transform() {
  return d3.zoomIdentity
      .translate(width / 2, height / 2)
      .scale(8)
      .translate(-point[0], -point[1]);
}

function transition(canvas) {
  var n = points.length,
      i = Math.random() * n | 0,
      c = points[i]; // Pick a random point.

points[i] = points[n - 1];
  points[n - 1] = point;
  point = c;

canvas.transition()
      .delay(500)
      .duration(3000)
      .call(zoom.transform, transform)
      .on("end", function() { canvas.call(transition); });
}

function phyllotaxis(radius) {
  var theta = Math.PI * (3 - Math.sqrt(5));
  return function(i) {
    var r = radius * Math.sqrt(i), a = theta * i;
    return [
      width / 2 + r * Math.cos(a),
      height / 2 + r * Math.sin(a)
    ];
  };
}

</script>

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