How to position text labels on a Sunburst chart with d3.js

Question

I am facing a problem trying to position text inside the wedges of a Sunburst chart which is based on d3.js.The text elements seem to be not positioned as desired even on zooming..

Here is the brief snippet of the code that i tried, but unsuccessfully :

    var slices = svg.selectAll(".form")
            .data(function(d) { return data_slices; })
            .enter()
            .append("g");

        slices.append("path")
            .attr("d", arc)
            .attr("id",function(d,i){return d[2]+""+i;})
            .style("fill", function(d) { return color(d[2]);})
            .on("click",animate)
            .attr("class","form")
            .append("svg:title")
            .text(function(d) { return Math.round(d[0]*100)/100 +" , "+ Math.round(d[1]*100)/100; });

       //Something needs to change below....
      slices.append("text")
            .style("font-size", "10px")
            .attr("x", function(d) { return y(d[1]); })
            .attr("transform", function(d) { return "rotate(" + this.parentNode.getBBox().width + ")"; })
            .attr("dx", "6") // margin
            .attr("dy", ".35em") // vertical-align
            .text(function(d){return d[2]})
            .attr("pointer-events","none");

Here is the Fiddle of the chart

Fiddle

What can be possible problem ? and can anyone please tell me or guide me as to how to position the <text> inside svg <path>.Looks like the solution is a minor tweak to this, but i am not able to get to it even after trying for a long time..

Any help/comment in the direction of a solution would be greatly appreciated...Thanks in Advance..

Answer 1

I think this comes close to what you aimed to achieve: http://jsfiddle.net/4PS53/3/

The changes needed are the following:

function getAngle(d) {
    // Offset the angle by 90 deg since the '0' degree axis for arc is Y axis, while
    // for text it is the X axis.
    var thetaDeg = (180 / Math.PI * (arc.startAngle()(d) + arc.endAngle()(d)) / 2 - 90);
    // If we are rotating the text by more than 90 deg, then "flip" it.
    // This is why "text-anchor", "middle" is important, otherwise, this "flip" would
    // a little harder.
    return (thetaDeg > 90) ? thetaDeg - 180 : thetaDeg;
}

slices.append("text")
    .style("font-size", "10px")
    .attr("x", function(d) { return d[1]; })
     // Rotate around the center of the text, not the bottom left corner
    .attr("text-anchor", "middle")
     // First translate to the desired point and set the rotation
     // Not sure what the intent of using this.parentNode.getBBox().width was here (?)
    .attr("transform", function(d) { return "translate(" + arc.centroid(d) + ")" + "rotate(" + getAngle(d) + ")"; })                                    
    .attr("dx", "6") // margin
    .attr("dy", ".35em") // vertical-align
    .text(function(d){return d[2]})
    .attr("pointer-events","none");

Now to make it work with zooming, where the reference point changes, we need a bit more infrastructure.

1. Make the g.form-container and not only the path.form visible/invisible. This means that we do not have to worry about making the labels disappear separately. (I have added the form-container class.)

2. Calculate the new point and calculate the centroid and rotation for it. This is a bit more tricky, but not too difficult:

   function change_ref(data_point, reference_point) {
       return [
           get_start_angle(data_point, reference_point),
           get_stop_angle (data_point, reference_point),
           data_point[2],
           get_level      (data_point, reference_point)
       ];
   }
   
   // And while doing transitioning the `text.label`:
   
   svg.selectAll('.label')
   .filter(
       function (b)
       {
           return b[0] >= new_ref[0] && b[1] <= new_ref[1] && b[3] >= new_ref[3];
       }
   ).transition().duration(1000)
    .attr("transform", function(b) {
        var b_prime = change_ref(b, d);
        return "translate(" + arc.centroid(b_prime) + ")" + 
               "rotate("    + getAngle(b_prime) +     ")"; 
    })
   

   I have added the class label to the text.

Updated Demo: http://jsfiddle.net/4PS53/6/

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However, I have argued that there might be better ways of presenting this data, esp. if you are allowing zooming and panning: D3 put arc labels in a Pie Chart if there is enough space