title: Where does TrackballControls come from?
body: <p>I am trying to have some camera control in a threejs scene.</p>
  
  <p>I looked at <a href="http://threejs.org/examples/#webgl_octree_raycasting" rel="noreferrer">this example</a> and it seems that it is completely handled with those lines : </p>
  
  <pre><code>controls = new THREE.TrackballControls( camera );
  controls.rotateSpeed = 1.0;
  controls.zoomSpeed = 1.2;
  controls.panSpeed = 0.8;
  controls.noZoom = false;
  controls.noPan = false;
  controls.staticMoving = true;
  controls.dynamicDampingFactor = 0.3;
  </code></pre>
  
  <p>Those lines use <code>THREE.TrackballControls</code> which comes from <code>js/controls/TrackballControls.js</code></p>
  
  <p>My question is : what exactly is <code>TrackballControls.js</code>? I cannot find it in the threejs download bundle. Is it an extension? Where can I find it? (Apart from taking it directly from <a href="http://threejs.org/examples/js/controls/TrackballControls.js" rel="noreferrer">the example's file</a>)</p>