I want to start doing some postprocessing on my renders with the EffectComposer but I can't get the most basic setup to render to the screen. It just stays blank. I must be looking over something. Does anybody have an idea?

```
<!doctype html>
<html>
  <head>
    <title>game</title>
    <style type="text/css">
      html, body {        
        margin: 0px;
        width: 100%;
        height: 100%;
      }

      canvas {
        display: block;
      }
    </style>    
  </head>
  <body>
    <canvas id="viewport"></canvas>
    <script type="text/javascript" src="three.js"></script>
    <script type="text/javascript" src="CopyShader.js"></script>
    <script type="text/javascript" src="ShaderPass.js"></script>
    <script type="text/javascript" src="EffectComposer.js"></script>
    <script type="text/javascript" src="RenderPass.js"></script>
    <script type="text/javascript" src="MaskPass.js"></script>
    <script type="text/javascript">
      var width = document.body.clientWidth;
      var height = document.body.clientHeight;      
      var canvas = document.querySelector('#viewport');
      var renderer = new THREE.WebGLRenderer({canvas: canvas});
      renderer.setSize(width, height);

      var scene = new THREE.Scene();

      var cube = new THREE.Mesh(
        new THREE.CubeGeometry(30, 30, 30), 
        new THREE.MeshPhongMaterial({color: 0xFF0000}));
      scene.add(cube);

      var camera = new THREE.PerspectiveCamera(45, width / height, 0.1, 1000);
      camera.position = new THREE.Vector3(60, 60, 60);
      camera.lookAt(cube.position);
      camera.updateMatrix();
      scene.add(camera);      

      var pointLight = new THREE.PointLight(0xFFFFFF);
      pointLight.position = new THREE.Vector3(100, 80, 20);
      scene.add(pointLight);

      var renderPass = new THREE.RenderPass(scene, camera);
      renderPass.renderToScreen = true;      
      var composer = new THREE.EffectComposer(renderer);
      composer.addPass(renderPass);
      renderer.clear();
      composer.render();

      //renderer.render(scene, camera);
    </script>
  </body>
</html>

```

If I uncomment the last line I get something on the screen.