From: Kostya Vasilyev <kostik@verio.com>
  To  : ggi-develop@eskimo.com
  Date: Thu, 20 Aug 1998 21:41:25 -0700

RE: LibGGI3D RFC

: > 	That's what I had in mind.  After, all the texture is a 2D bitmap.
: > Yes, you need u, v values, but only one u,v offset (and offset
: angle?) per
: > triangle patch.  Unless you want to tile more than one texture per patch
: > or do multitexturing, in which case you need more info.  But the info is
: > still per-patch, not per-triangle.

This is only true in case of affine texture mapping. Granted, this is most
common case, but not 100%.

What you really need is u,v per vertex. This also makes interpolation (for
clipping) easy -- when clipping, the primitive operation is to interolate
and edge that intersects a clipping plane and make new vertex out of the
intersection.

: There's other ways of fixing up perspective-correction too...  I'll take a
: peek at how the HW people do it...  Maybe basing the lib on a hw-reference
: WOULD be the best way?

Perspective correction is done by interoplating s/z, t/z and 1/z as you walk
the scans, and diving at each pixels to get back s and t.

This is almost irrelevant, since HW does this (only relevance is for
clipping in Z, where you need to interpolate s/z and t/s, and not s and t).

~kostik