Question

D3 has a force directed layout here. Is there a way to add zooming to this graph? Currently, I was able to capture the mouse wheel event but am not really sure how to write the redraw function itself. Any suggestions?

var vis = d3.select("#graph")
  .append("svg:svg")
  .call(d3.behavior.zoom().on("zoom", redraw)) // <-- redraw function
  .attr("width", w)
  .attr("height", h);

Answer 1

Update 6/4/14

See also Mike Bostock’s answer here for changes in D3 v.3 and the related example. I think this probably supersedes the answer below.

Update 2/18/2014

I think @ahaarnos’s answer is preferable if you want the entire SVG to pan and zoom. The nested g elements in my answer below are really only necessary if you have non-zooming elements in the same SVG (not the case in the original question). If you do apply the behavior to a g element, then a background rect or similar element is required to ensure that the g receives pointer events.

Original Answer

I got this working based on the zoom-pan-transform example – you can see my jsFiddle here: http://jsfiddle.net/nrabinowitz/QMKm3/

It was a bit more complex than I had hoped – you have to nest several g elements to get it to work, set the SVG’s pointer-events attribute to all, and then append a background rectangle to receive the pointer events (otherwise it only works when the pointer is over a node or link). The redraw function is comparatively simple, just setting a transform on the innermost g:

var vis = d3.select("#chart")
  .append("svg:svg")
    .attr("width", w)
    .attr("height", h)
    .attr("pointer-events", "all")
  .append('svg:g')
    .call(d3.behavior.zoom().on("zoom", redraw))
  .append('svg:g');

vis.append('svg:rect')
    .attr('width', w)
    .attr('height', h)
    .attr('fill', 'white');

function redraw() {
  console.log("here", d3.event.translate, d3.event.scale);
  vis.attr("transform",
      "translate(" + d3.event.translate + ")"
      + " scale(" + d3.event.scale + ")");
}

This effectively scales the entire SVG, so it scales stroke width as well, like zooming in on an image.

There is another example that illustrates a similar technique.