How to match text width to circle size in D3 circle pack

Question

Using D3 I display a bunch of circles in different sizes, each filled with text. I'm stuck with finding the correct font size so that the text fits correct in the circle, depending of it's size and the length of the text. Long text should possibly be broken up in more lines. Here is my code:

var data = {
    "name": "",
    "children": [
        { "name": "This is a tag", "value": 242 },
        { "name": "Circle", "value": 162 },
        { "name": "Tree", "value": 80 },
        { "name": "My sentence is very long and needs breaks", "value": 80 },
    ]
}

var diameter = 300,
    format = d3.format(",d");

var bubble = d3.layout.pack()
    .sort(null)
    .size([diameter, diameter])
    .padding(1.5);

var svg = d3.select("body").append("svg")
    .attr("width", diameter)
    .attr("height", diameter)
    .attr("class", "bubble");

d3.json(data, function(error, root) {
  var node = svg.selectAll(".node")
      .data(bubble.nodes(data)
      .filter(function(d) { return !d.children; }))
    .enter().append("g")
      .attr("class", "node")
      .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; });

  node.append("circle")
      .attr("r", function(d) { return d.r; })
      .style("fill", function(d) { return '#f88' });

  // text part
  node.append("text")
      .attr("dy", ".3em")
      .style("text-anchor", "middle")
      .style("font-size", function(d) { return Math.round(d.r/3)+'px'; })
      .text(function(d) { return d.name.substring(0, d.r / 3); });
});

d3.select(self.frameElement).style("height", diameter + "px");

I have created a fiddle as well on http://jsfiddle.net/L4nMx/ I think I should calculate the width of the text and modify the font size until it matches the circle's size or something like that. Or is there any "strech" function to do this the easy way?

Answer 1

This solution is fine for me for now. It's not accurate maths but fits anyway.

See it in action on http://jsfiddle.net/L4nMx/3/

  .style("font-size", function(d) {
      var len = d.name.substring(0, d.r / 3).length;
      var size = d.r/3;
      size *= 10 / len;
      size += 1;
      return Math.round(size)+'px';
  })
  .text(function(d) {
      var text = d.name.substring(0, d.r / 3);
      return text;
  });

Next step would be to break long text into multiple lines so you could enlarge font sizes in such cases but I didn't manage to solve this. It's not easy in SVG because simple line breaks are not possible. Maybe the wrapping solutions from the comments in the question can be added here - somehow...