NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/comp/sys/sgi/11227

Text File | 1992-07-22 | 1.7 KB | 38 lines

Newsgroups: comp.sys.sgi
Path: sparky!uunet!snorkelwacker.mit.edu!thunder.mcrcim.mcgill.edu!panisset
From: [e-mail] (Jean-Francois Panisset)
Subject: RealityEngine texturing question
Message-ID: <[e-mail]>
Summary: How are the texture coordinates computed?
Keywords: texture VGX RealityEngine
Organization: McGill Research Centre for Intelligent Machines
Date: Thu, 23 Jul 92 03:57:52 GMT
Lines: 22


I saw the glossies for RealityEngine, and I would sure want one... My
question is the following: on VGX/VGXT, the texture coordinates are specified
at the vertices of a polygon using the t2?() commands. The intermediate
s,t texture coordinates are then computed for the pixels inside the polygon
using linear interpolation between the "real" values at the vertices.
Since this does not yield the exact texture coordinates (you need to
do a per-pixel division to get those), you end up having to subdivide
your polygons (the name of the call to do this automatically escapes
me at this point), which is not always a satisfying solution. So the
question is: does RealityEngine do a per-pixel division to get the
exact s,t coordinates, or does it still rely on polygon subdivision
to approximate the real answer? Also, does it do any form of directional
filtering in the mip-map for edge-on polygons, and if not, how does
it determine the level of detail from which to fetch the texture pixels:
does it select it based on the largest or smallest dimension of the pixel
once projected on the polygon?

Thanks in advance for all answers...

JF Panisset
--
Jean-Francois Panisset
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