Transparent background

Questions
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2

I think there are a couple things missing there:

  1. You do need alpha: true on the scene, as you mention.
  2. Don’t change setClearColor.
  3. If you’re using EffectComposer, there is some extra work required to make it allow a transparent background, see these comments. three.js - How do I stop EffectComposer from destroying my transparent background? - Stack Overflow

I’d recommend starting with renderer.render( scene, camera ) instead of composer.render() just to make sure you have the first two parts working.