Path: utzoo!attcan!uunet!husc6!think!bloom-beacon!apple!well!ewhac
From: ewhac@well.UUCP (Leo L. Schwab)
Newsgroups: comp.graphics
Subject: Re: Raytracing speedups....
Summary: It's been done.
Message-ID: <10083@well.UUCP>
Date: 22 Dec 88 08:28:39 GMT
References: <907@cmx.npac.syr.edu>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Organization: The Digital-Watches-With-Millions-Of-Useless-Features Company.
Lines: 39
Quote: "I am not interested in trying to compensate for your amazing lack of
	observation."  -- Orac

In article <907@cmx.npac.syr.edu> gefuchs@top.cis.syr.edu (Gill E. Fuchs) writes:
>   The following paragraphs describe an idea of mine.  This idea describe
>a possible algorithm for improving speed for raytracing...
> [ ... ]
>    This process describes a possible improvement for raytracing....
>This method uses bounding boxes instead of bounding volumes to speed up
>intersection tests of objects.
>
	Basically, he's proposing 2D boxes in screen space rather than 3D
voxels in world space.

	There's a commercial raytracer for the Amiga that uses precisely the
method you outlined.  It works well enough for matte objects, but falls
far short of optimal for anything that might redirect the ray.

	If you have a silver sphere, and you bounce a ray off it, your
screen space subdivision is now useless, and you must check against every
object/polygon in the scene to see what you've hit, which might be another
mirrored object...

	The other disadvantage is less obvious.  Suppose I have 10,000
polygons all lined up, and I position my camera to look straight down the
line.  Rays cast toward the center will test positive for far more polygons
than necessary.  It may be possible to optimize this by sorting the box test
results by Z, but you'll still be making more tests than necessary.

	Scenes on the aforementioned raytracer inevitably take longer to
render than on a competing raytracer that uses voxels (using equivalent
hardware and software configurations).  The voxel tracer usually finishes no
less than 25% faster than the boxel tracer.  Of course, your mileage may
vary.

	Disclaimer:  I'm just parroting this stuff...

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Leo L. Schwab -- The Guy in The Cape	INET: well!ewhac@ucbvax.Berkeley.EDU
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O----^o	      The Only Way To Fly.	      hplabs / (pronounced "AE-wack")
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