title: THREE.js Skybox not working
body: <p>i am trying to do my own version of a planetarium based on the book Up and running and i am getting a problem when trying to make a skybox. </p>
  
  <p>I am using Chrome and the javascript console bring up an error "Uncaught TypeError: undefined is not a function" in the line where the material is defined. </p>
  
  <p>Am i missing some library? Or is it some change in three.js? I am using r55. The code is the following:</p>
  
  <p>Thank you!</p>
  
  <pre><code>var urlPrefix   = "images/skybox/";
  var urls = [ 
  urlPrefix + "skyboxmid.jpg", urlPrefix + "skyboxback.jpg",
  urlPrefix + "skyboxleft.jpg", urlPrefix + "skyboxfront.jpg",
  urlPrefix + "skyboxright.jpg", urlPrefix + "skyboxtop.jpg" ];
  
  var textureCube = THREE.ImageUtils.loadTextureCube( urls );
  var shader  = THREE.ShaderLib['normalmap'];
  shader.uniforms["tNormal"].texture = textureCube;
  var material = new THREE.MeshShaderMaterial({
      fragmentShader  : shader.fragmentShader,
      vertexShader    : shader.vertexShader,
      uniforms    : shader.uniforms
  });
  
  skybox  = new THREE.Mesh( new THREE.CubeGeometry( 100000, 100000, 100000, 1, 1, 1, null, true ), material );
  scene.addObject( skybox ); 
  </code></pre>