title: embedding an image via d3 does not work
body: <p>I am using an example from <a href="http://codepen.io/anon/pen/GJWqrL" rel="nofollow">here</a></p>
  
  <p>And I am trying to put an image into the white child node circles.
  So I made svg def, and pattern dom like the one below</p>
  
  <pre><code>var svg = d3.select("div.global-main-wrap").append("svg")
    .attr("width", window.innerWidth * 2)
    .attr("height", window.innerHeight * 2)
    .append("g")
    .attr("transform", "translate(" + diameter / 1.2 + "," + diameter / 2 + ")");
  
  var pattern = d3.select("svg")
    .append('svg:defs')
    .append('pattern')
      .attr('id', 'album')
      .attr("patternUnits", "userSpaceOnUse")
      .attr('width', '6')
      .attr('height', '6')
    .append('image')
      .attr("xlink:href", "/images/artist.jpg")
      .attr('x', 0)
      .attr('y', 0)
      .attr('width', 6)
      .attr('height', 6);
  </code></pre>
  
  <p>The image successfully imports, but does not attach to the circle.</p>
  
  <p>When i used it in here:</p>
  
  <pre><code>svg.selectAll(".node--leaf")
    .data(nodes)
    .style("fill", function(d){
      console.log("fuck this")
      return("url(#album)");
    })
  </code></pre>
  
  <p>The html(under svg) generated by d3 looks like this</p>
  
  <pre><code>&lt;svg width="3840" height="1232"&gt;
     &lt;g transform="translate(800,480)"&gt;
        &lt;circle class="node" transform="translate(113.71054875330515,-165.44378762634966)" r="81.17208760605139" style="fill: rgb(255, 201, 192);"&gt;
           &lt;title&gt;Hyukoh&lt;/title&gt;
        &lt;/circle&gt;
        &lt;circle class="node node--leaf" transform="translate(77.73322389314524,-134.28651033724577)" r="33.578560397369024" style="fill: url(#album);"&gt;
           &lt;title&gt;Hooka&lt;/title&gt;
        &lt;/circle&gt;
        &lt;circle class="node node--leaf" transform="translate(149.68787361346506,-134.28651033724577)" r="33.578560397369024" style="fill: url(#album);"&gt;
           &lt;title&gt;Wi ing Wi ing&lt;/title&gt;
        &lt;/circle&gt;
        &lt;circle class="node node--leaf" transform="translate(-139.849884911782,-131.45698460661947)" r="53.09236570260736" style="fill: url(#album);"&gt;
           &lt;title&gt;Gangnam Style&lt;/title&gt;
        &lt;/circle&gt;
        &lt;circle class="node node--leaf" transform="translate(-179.79062119212261,-44.78531265608177)" r="37.54197181754974" style="fill: url(#album);"&gt;
           &lt;title&gt;Gentleman&lt;/title&gt;
        &lt;/circle&gt;
        &lt;circle class="node node--leaf" transform="translate(-99.90914863144138,-44.78531265608177)" r="37.54197181754974" style="fill: url(#album);"&gt;
           &lt;title&gt;Champion&lt;/title&gt;
        &lt;/circle&gt;
        &lt;text class="label" font-family="sans-serif" dy=".35em" transform="translate(-9.852034042048786,139.01271989766576)" style="fill-opacity: 1; font-size: 18px;"&gt;Kim Kwang-Seok&lt;/text&gt;
        &lt;text class="label" font-family="sans-serif" dy=".35em" transform="translate(53.85251368137091,139.01271989766576)" style="fill-opacity: 0; display: none; font-size: 18px;"&gt;Yu Jae-Ha&lt;/text&gt;
        &lt;text class="label" font-family="sans-serif" dy=".35em" transform="translate(-77.2754011091547,139.01271989766576)" style="fill-opacity: 0; display: none; font-size: 18px;"&gt;Kim Hyun-Sik&lt;/text&gt;
        &lt;text class="label" font-family="sans-serif" dy=".35em" transform="translate(-217.33259300967237,-95.89634557387944)" style="fill-opacity: 1; font-size: 18px;"&gt;Pop&lt;/text&gt;
        &lt;text class="label" font-family="sans-serif" dy=".35em" transform="translate(-322.1393458205501,-95.89634557387944)" style="fill-opacity: 0; display: none; font-size: 18px;"&gt;Girl's Generation&lt;/text&gt;
        &lt;text class="label" font-family="sans-serif" dy=".35em" transform="translate(-139.849884911782,-95.89634557387944)" style="fill-opacity: 0; display: none; font-size: 18px;"&gt;Psy&lt;/text&gt; 
     &lt;/g&gt;
     &lt;defs&gt;
        &lt;pattern id="album" patternUnits="userSpaceOnUse" width="6" height="6"&gt;
           &lt;image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/images/artist.jpg" x="0" y="0" width="6" height="6"&gt;&lt;/image&gt;
        &lt;/pattern&gt;
     &lt;/defs&gt;
  &lt;/svg&gt;
  </code></pre>