   Famous nVidia 8-stage hack?
  I''ve heard of this as some way to get extra functionality on (I think) the early Geforce range but what is it? 
  It's not exactly extra functionality. It's just that the 8 stages aren't general purpose, and - as far as I know - to use all 8 stages you should know what ops and arguments to use with each stage.Your best bet would be:1. Search the nVidia website2. Google3. Mail nVidia's developer relations4. Wait until someone like Donavon Keithly, Herb Marselas or Simon O'Connor sees this post  Peace,Muhammad Haggag   [edited by - Coder on July 31, 2003 3:14:50 PM];  It exposes the register combiners directly, i.e. "that fixed equation" in my reply to your post on why anything other than 2 stage setups can be problematic on GeForce256's. That should explain *WHAT* it is.They were originally exposed by an nVidia specific OpenGL vendor extension. No doubt after a few people asked for that in D3D they came up with the (nVidia specific) hack/method.There's a paper that explains everything you need to know on developer.nvidia.comIt's actually also known as the "TNT 8-stage setup" because it was originally exposed on the nVidia Riva TNT. The GeForce version doesn't expose anything over the TNT one using that setup.Looking back over some of my ancient source code (actually an enhanced version of the Pac-Man:AIT engine for the GeForce2 Ultra launch), the TNT combiners exposed the following equation:TC0 = a * b OP1 c * dTC1 = e * f OP2 g * hfor both the scalar (alpha) and vector (colour) pipes.TC0 and TC1 were the texture units, i.e. only being able to use 2 unique textures at the same time is a FIXED limit. IIRC OP1&OP2 are limited to very simple ops, maybe + and *.The inputs are also limited. Some have special settings to introduce constants like 1 and 0 into the equation.   --Simon O'Connorex    -Creative AsylumProgrammer &Microsoft MVP [edited by - s1ca on July 31, 2003 7:21:04 PM]