d3 v4 - zoom with buttons in conflicts with zoom behaviour

d3.js, javascript, pan, zooming

Solution

The key thing to remember is that the zoom transform is stored on the `node`, NOT in the `_zoom` object.

In your case you set the mouse listener on the `svg` node,

svg.call(_zoom);

When a zoom event is triggered on the `svg` element, you then take the updated zoom transform of the `svg` node and apply it to the `g` node,

g.attr("transform", d3.event.transform);

All you need to do when updating the zoom of the g element on the button click is grab the correct transform, in your case that of the `svg` node,

 _zoom.scaleBy(svg, 0.5);

Which will trigger the zoom event on the `svg` node correctly, updated in full below,

var svg = d3.select("svg"),
  width = +svg.attr("width"),
  height = +svg.attr("height");
svg.style("border", "solid 1px black");
var points = d3.range(2000).map(phyllotaxis(10));
var g = svg.append("g");

var _zoom = d3.zoom()
  .scaleExtent([1 / 2, 8])
  .on("zoom", function() {
    g.attr("transform", d3.event.transform);
  });
svg.call(_zoom);

var container = g.selectAll("circle")
  .data(points)
  .enter().append("circle")
  .attr("cx", function(d) {
    return d.x;
  })
  .attr("cy", function(d) {
    return d.y;
  })
  .attr("r", 2.5)

function phyllotaxis(radius) {
  var theta = Math.PI * (3 - Math.sqrt(5));
  return function(i) {
    var r = radius * Math.sqrt(i),
      a = theta * i;
    return {
      x: width / 2 + r * Math.cos(a),
      y: height / 2 + r * Math.sin(a)
    };
  };
}
var gui = d3.select("#gui");
gui.append("span")
  .classed("zoom in", true)
  .text("+")
  .on("click", function() {
    _zoom.scaleBy(svg, 2);
  });
gui.append("span")
  .classed("zoom out", true)
  .text("-")
  .on("click", function() {
    _zoom.scaleBy(svg, 0.5);
  })

<svg width="960" height="500"></svg>
<div id="gui"></div>
<script src="https://d3js.org/d3.v4.min.js"></script>

Problem

Original source