van Wijk Smooth Zooming

A demo of d3.interpolateZoom. Added in release 3.3, zoom interpolation is now supported automatically for the zoom behavior. See also the zoom transitions and map zooming examples.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.mesh {
  fill: none;
  stroke: #000;
  stroke-width: .25px;
}

.start {
  fill: none;
  stroke: brown;
}

.end {
  fill: none;
  stroke: steelblue;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="d3.hexbin.min.js"></script>
<script>

var width = 960,
    height = 500,
    radius = 10;

var p0 = [250, 200, 60],
    p1 = [560, 300, 120];

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height)
  .append("g")
    .call(transition, p0, p1);

svg.append("path")
    .attr("class", "mesh")
    .attr("d", d3.hexbin()
      .size([width, height])
      .radius(radius)
      .mesh);

svg.selectAll("circle")
    .data([p0, p1])
  .enter().append("circle")
    .attr("class", function(d, i) { return i ? "end" : "start"; })
    .attr("cx", function(d) { return d[0]; })
    .attr("cy", function(d) { return d[1]; })
    .attr("r", function(d) { return d[2] / 2 - .5; });

function transition(svg, start, end) {
  var center = [width / 2, height / 2],
      i = d3.interpolateZoom(start, end);

svg
      .attr("transform", transform(start))
    .transition()
      .delay(250)
      .duration(i.duration * 2)
      .attrTween("transform", function() { return function(t) { return transform(i(t)); }; })
      .each("end", function() { d3.select(this).call(transition, end, start); });

function transform(p) {
    var k = height / p[2];
    return "translate(" + (center[0] - p[0] * k) + "," + (center[1] - p[1] * k) + ")scale(" + k + ")";
  }
}

</script>

https://d3js.org/d3.v3.min.js