title: Can't get three.js EffectComposer to work
body: <p>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?</p>
  
  <pre><code>&lt;!doctype html&gt;
  &lt;html&gt;
    &lt;head&gt;
      &lt;title&gt;game&lt;/title&gt;
      &lt;style type="text/css"&gt;
        html, body {        
          margin: 0px;
          width: 100%;
          height: 100%;
        }
  
        canvas {
          display: block;
        }
      &lt;/style&gt;    
    &lt;/head&gt;
    &lt;body&gt;
      &lt;canvas id="viewport"&gt;&lt;/canvas&gt;
      &lt;script type="text/javascript" src="three.js"&gt;&lt;/script&gt;
      &lt;script type="text/javascript" src="CopyShader.js"&gt;&lt;/script&gt;
      &lt;script type="text/javascript" src="ShaderPass.js"&gt;&lt;/script&gt;
      &lt;script type="text/javascript" src="EffectComposer.js"&gt;&lt;/script&gt;
      &lt;script type="text/javascript" src="RenderPass.js"&gt;&lt;/script&gt;
      &lt;script type="text/javascript" src="MaskPass.js"&gt;&lt;/script&gt;
      &lt;script type="text/javascript"&gt;
        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);
      &lt;/script&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>If I uncomment the last line I get something on the screen.</p>