Re: pfMatrix question

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Jim Helman (jimh++at++surreal)
Tue, 07 Nov 95 14:56:31 -0800

If I had a nickel for every time someone has been confused by
this (including engineers at SGI), I could retire in luxury......
well almost.

The OpenGL spec and reference book simply use a different
notation, i.e. the one more commonly used in linear algebra
courses. Basically OpenGL docs use post-multiplication by
column vectors rather than pre-multiplication by row vectors.
Or phrased another way OpenGL docs specify matrices in column-
major order whereas C stores them in row major order.

So if you see:

                Vout = PROJ * MODELVIEW * Vin

you should still code exactly as in IRIS GL:

                Vout' = Vin' * MODELVIEW' * PROJ'

where the primes indicate transposition of the vectors
and matrices.

rgds,

-jim helman

jimh++at++surreal.asd.sgi.com
415/933-1151

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