title: how do you enable compatibility mode in HLSL?
body: <p>how do you enable compatibility mode in HLSL? I'm using Visual studio and xna.</p>
  
  <p>I want to be able to change global variables from within the pixel shader and then retrieve them from the pixel shader after a pass of the pixel shader, but I can't change the global variables from within the pixel shader without getting an error that tells me they are constant and that I must enable compatibility mode.</p>
  
  <p>So how do I enable this?</p>