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From: lance@motcsd.csd.mot.com (lance.norskog)
Newsgroups: sci.virtual-worlds
Subject: Re: Real-time raytrace and some related "ramblings"
Message-ID: <1991May31.040232.26702@milton.u.washington.edu>
Date: 31 May 91 00:18:42 GMT
References: <1991May13.193721.5473@milton.u.washington.edu> <1991May14.
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You're right, I misspoke myself.  I meant to say that ray-tracing
is inherently scan-line-first, whereas radiosity is inherently 
object-first.  For VR, ray-tracing is useless because you can't 
compute anything up-front and then re-use it.  You want to precompute
as viewpoint-independent information much as possible, then recycle 
it from the current viewpoint.  Maintaining BSP trees of unchanging
objects has this effect, and radiositizing immovable unchanging
objects

My application (5D, a 3D real-time multi-media window system) 
is not intended for making movie special effects or falsifying 
evidence, so I don't give a damn about realism.  I want to create
a new interactive medium for information presentation and
manipulation.  

The scene can be abstract instead of physical objects, with
the 3D effect used to convey relationships between those objects.
Shading is useful for reinforcing the 3D effect,
and helping your visual system build a 3D map from a scene.
If stuff closer to you is more important, that's a form of
intellectual depth-cuing.

The problem with making all polygons less than a pixel is that
they can all be varying distances from the viewpoint.  So, I'm supposed
to make them all smaller than a pixel from (say) 6 inches away
in world space, because maybe someday I'll get that close?
That's a lot of polygons!  Reyes-style micropolygonization
is really not a feasible strategy for VR.

What just popped into my head is to do shaded polygons with a light
source and an ambient value, with one batch of math doing both the
viewpoint transform and the normal transform intertwingled.  
GG1 has a gem on how to do this.  I'm doing this on a 486 with VGA, 
and reports are that my FP will grossly outstrip my video bandwidth.
This may be feasible cheap shading.  

Lance

Note use of the word "interwingled": the new edition of
Computer Lib/Dream Machines is my current breakfast book.
I highly recommend it to computer dreamers.