Refraction - GrabPass in Forward Rendering

Hi,

I am trying to create a refraction effect in Unity 4 Pro.
First, I use GrabPass for a simple transparency effect. Next, I will apply the bump refraction effect. But I have some questions.

  • What is the difference between the two GrabPass syntax ? GrabPass { } and GrabPass { “TextureName” }. I don’t get why one is optimized and the other isn’t.
  • Another important question is why GrabPass doesnt work in forward rendering ? Is there a way to implement GrabPass in forward rendering ?

Thanks a lot for your answers !

It seems that it is possible to use GrabPass with Forward but it needs to be rendered last.

But even if I change de RenderQueue greater than Geometry, the GrabPass Texture seems to be empty. Any ideas ?

[EDIT] My bad, if you change the RenderQueue in the SubShader it works.

Thanks !