Ok, this has me puzzled: what’s the fastest way to render a full-screen nailboard? Nailboards are RGBZ images, which encode the depth as well as color info. I need to render one full-screen nailboard for a survival-horror kind of thing… I know how to paint the RGB part, but how can I get decent performance with an RGBZ image?
Stefan Röttger has a pretty neat algorithm to render RGBA images with Alpha being the height (sounds like your nailboards), borrowing some of his experience with volume rendering, which he calls Terrain Slicing. Take a look at his publications page at http://wwwvis.informatik.uni-stuttgart.de/~roettger/ for details.
Note that this works best for views with large angles between image normal and view direction. If you want to look directly onto the image you can try tricks with RegisterCombiners and maniulating the Z component.
What exactly yre you trying to do?
If you’re redrawing a static background with depth, you might want to look into ARB_buffer_region (or KTX_buffer_region) I think it can help. You might have to do an initial slow update with DrawPixels though.