title: What is the most efficient way to overlay a second camera with alpha?
body: <p>I have two cameras in my scene. </p>
  
  <ul>
  <li>Camera A needs to be 100% visible.  </li>
  <li>Camera B needs to be overlaid over Camera A at 50% opacity. </li>
  <li>Using texture maps is a bit messy because it requires scene geometry to match screen resolution and performance is hit. The texture resolution also needs to be taken into account. </li>
  </ul>
  
  <p>Is there an all shader way to pull two cameras together in a performant way that allows us to mix the opacity of the two cameras? </p>
  
  <p>Any help is appreciated</p>