multi pass rendering

[farfromrefug]

i got this

I would like to apply a post process effet to the terrain but not the texts and lines.
I think this can be achieve with multiple passes and the fact that a pass can decide which layer to render. but i dont really know where to start.
Let say i want to blur the terrain layer but not the TextLayer. Is there any code or sample code i could base my self on to achieve that?