title: How to toggle preserveDrawingBuffer in three.js?
body: <p>Basically, I want the setup where I could go to preserveDrawingBuffer=true, render the scene once, grab the screenshot, and go back. However, this poses two problems:</p>
  
  <ul>
  <li>there is no method in renderer to dispose all the buffers,</li>
  <li><p>canvas goes black if I do</p>
  
  <p>renderer = new THREE.WebGLRenderer({canvas:renderer.domElement,preserveDrawingBuffer:true});</p></li>
  </ul>
  
  <p>How do I do this properly?</p>
  
  <p>EDIT: I did not find the way to toggle this, so I had to clone scene and create second renderer instead to make the screenshot. See <a href="https://github.com/mrdoob/three.js/issues/189" rel="noreferrer">https://github.com/mrdoob/three.js/issues/189</a></p>