Re: Non-square clipmaps

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Philip Nemec (nemec++at++sgi.com)
Tue, 10 Mar 1998 11:23:49 -0800

The only current graphics hardware capable of running clipmapping is infinite
Reality. And it has a requirement that cliptextures be square.

The examples given of how to pad out a non-square cliptexture to a square one
are the correct solutions, although there are also a few cases where the best
thing to do is make 2 square cliptextures.

caveats with these techniques:

Padding up a non-square cliptexture may cost you a level. In other words if
you have 2 square cliptextures you can achieve a higher number of levels (a
larger sized cliptexture) than with one square one containing a rectangular
cliptexture.

2 cliptextures take up roughly twice the texture memory as 1. Other resources
are increased as well, but this is the most painful one to me...

-------

Angus's suggestion of using the texture matrix to scale texture coords to make
the square cliptexture look like a rectangle sounds reasonable, but hopefully
Don Hatch can clarify if this interferes any with Performer's cliptexture
munging (and precision issues).
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