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From: scofield@apollo.uucp (Cary Scofield)
Newsgroups: comp.graphics
Subject: Re: Ray tracing and caustics.
Message-ID: <36098418.352b@apollo.uucp>
Date: Mon, 13-Jul-87 12:07:00 EDT
Article-I.D.: apollo.36098418.352b
Posted: Mon Jul 13 12:07:00 1987
Date-Received: Tue, 14-Jul-87 05:48:23 EDT
References: <219@sugar.UUCP>
Reply-To: scofield@apollo.UUCP (Cary Scofield)
Organization: Apollo Computer, Chelmsford, MA
Lines: 39
Keywords: ray-tracing caustics algorithm reality

In article <219@sugar.UUCP> peter@sugar.UUCP (Peter DaSilva) writes:
>
>It has occurred to me that I have never seen such an effect in ray-traced
>images. It shouldn't be too hard: you would have to reverse ray-trace from
>the light source for each transparent object and add the caustic to the
>texture map for each matte object it eventually falls on. Has anyone
>considered doing this?
>

See:

    "Backward ray tracing" by James R. Arvo

    "Reflection and refraction model for ray tracing" by Masa Inakage

both of the above papers are in the 1986 SIGGRAPH Course Notes volume
entitled "Developments in Ray Tracing".


Also see:

    "The Rendering Equation" by James T. Kajiya from the 1986 SIGGRAPH
    Proceedings, pp. 143-150.


Arvo's paper describes, in detail, an algorithm pretty close to your idea.
In Kajiya's paper, the caustics were a natural by-product of the 
his terra-flop rendering algorithm.   If you're inclined to "cheat", use Arvo's 
method -- it's much faster, even if a little cumbersome to implement.





-- 
Cary Scofield - Graphics Software          decvax!wanginst!apollo!scofield
Apollo Computer Inc.
270 Billerica Road
Chelmsford, MA 01824