Newsgroups:	comp.os.msdos.djgpp
From:	tob AT world DOT std DOT com
Subject:	Re: John Carmack <johnc AT idnewt DOT idsoftware DOT com>: Question about Doom.
Message-ID:	<E7MGEx.4yG@world.std.com>
Sender:	tob AT world DOT std DOT com (Tom Breton)
Reply-To:	tob AT world DOT std DOT com
Organization:	BREnterprises
References:	<199703250435 DOT WAA28704 AT mail DOT sockets DOT net>
Date:	Tue, 25 Mar 1997 23:11:21 GMT
Lines:	29
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

"Anthony Q. Bachler, BAS" <cwhizard AT sockets DOT net> writes:
> (Ray Tracing == Ray Casting) = True.  Just a different way of saying the
> same thing.  I use the term casting because it makes me think of fishing
> and the code is fishing for a structure.  Sounds stupid, but hey, we all
> need our little crutches.

Ooh, we're gonna hear this one being corrected forever.

Not the same. Ray casting shoots out generally once per vertical line,
and stops as soon as it gets something it can draw. With ray *casting*,
objects are "lit" in and of themselves.

Ray tracing generally shoots out once per pixel and bounces to hit more
stuff beyond the first object. With ray *tracing*, nothing is "lit" till
you trace it back to a light source.

This is why ray casting has been good enough for real time games for
some time, whereas ray casting still makes you wait for a single frame.

I am simplifying a lot here, of course. There are endless
qualifications, variations, and optimizations that make what I said not
precisely true. Like "raycasting can hit two things with
semi-transparency and explicit mirrors." or "if you combine raytracing
with radiosity, objects are lit."

PS: I like your .sig. Ain't it the truth.

        Tom

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