title: How to apply 2-pass postprocessing without using EffectComposer?
body: <p>I need to post-process the scene that I rendered previously on textureA (as render target), with my custom shader and save the result to textureB (input:textureA, output:textureB). Therefore, I don't need a scene and a camera. I think it's too simple to even bother with three.js classes like EffectComposer, Shaderpass, CopyShader, TexturePass, etc.</p>
  
  <p>So, how do I setup this computing-like post-processing in a simple way?</p>