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From: zap@lysator.liu.se (Zap Andersson)
Newsgroups: comp.graphics
Subject: Re: Question (silly?)
Keywords: raytrace, etc.
Message-ID: <490@lysator.liu.se>
Date: 20 Jan 91 09:22:12 GMT
References: <79641@unix.cis.pitt.edu> <5427@idunno.Princeton.EDU> <1991Jan16.200924.6784@dartvax.dartmouth.edu>
Sender: news@isy.liu.se (Lord of the News)
Organization: Lysator Computer Club, Linkoping University, Sweden
Lines: 37

npw@eleazar.dartmouth.edu (Nicholas Wilt) writes:

>>	We have 480000 pixels, each one of which has a single ray.  According
>>	to my book, the fastest sphere intersector I have is around 16 adds,
>>	13 multiplies, and one square root, for a total of 30 floating point
>>	ops.  Since we are not using a hierarchy, we have 6 * 30 floating
>>	point operations, or 180 per ray, per bounce.  Since we trace
>>	rays to level k, we have 2^k * as many rays per pixel, or 180 * 2^k.
>>	Since we wanted real time (lets assume the video rate of 30fps),
>>	then we have 
>>		800*600*30*180*2^k = 2,592,000,000 * 2^k floating point ops
>>			per second.
>>	And this doesn't even take into account shading.

>Or color quantization; the problem stated 256 colors.  So you'd have to
>quantize on the fly, as well, or figure out a clever way to do it
>incrementally.

VERY true. My raytracer does Quant-on-ze-fly, and for a simple test image
with a plane, a cylinder and a sphere with a LOT of pretty shading, reflects
e.t.c: Well total time was 8 minutes, but when doing it in black'n'white
(i.e. skipping quant code) it was a 5 minute job.... :-(

>A PC would have a heck of a time doing the real time display even if the 
>frames and color mappings were precomputed and compressed.

Ahem: Here we have total dissagrement. Have you never seen Autodesk Animator?
70 Frames/Sec best case (Ok, MAY skip a vertical blank worst case) but does
a really neat job of decompressing and displaying animations in realtime!

>--Nicholas Wilt
>  npw@eleazar.dartmouth.edu
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