Being more specific (for the gurus!)....

Ok, my question - if I can sum up correctly is as follows:

How to generate a heightfield from the alpha component of a texture map, where parts of the map will be removed via. alpha test to leave holes (at some threshold - say zero in the alpha channel = invisible), without the alpha test removing bits of geometry that are `above sea level’ because the fragment is larger than the texel!

Thanks - !!!

[This message has been edited by Robbo (edited 04-03-2002).]

If you use interpolation, then only fragments that interpolate to 0 alpha will be culled.

However, I’ve found it better to do sea-level clipping or tinting by using a second 2x1 texture in NEAREST mode and using TexGen to get the correct texel based on height.