   HLSL, screen alligned quad?
  Is there a way, purely in vertex/pixel shaders to make a polygon always face the screen?  Or is this usually done in the main engine code? (this is a game engine by the way).    ...I've only got access to HLSL to manipulate pixels, so was wondering if this was possible.Thanks!   
  inverse model-view-projection matrix   ;  Does it have to be defined in 3D?If you're trying to do "2D in 3D" type effects (e.g. post-processing, GUI's etc...) then you can just define the geometry in 2D and skip any complicated maths...A few more details and I (or someone else) can probably suggest a solution.hthJack   