From:	Paul Furber <paul AT sprintlink DOT co DOT za>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: John Carmack <johnc AT idnewt DOT idsoftware DOT com>: Re: Question about Doom.
Date:	Thu, 27 Mar 1997 10:42:55 +0200
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M. Edward Kiser wrote:
> Oh, and PVS stands for _Potentially_ Visible Set, not Partial.

Michael Abrash defines it as such in his Quake discussions on the Dr
Dobbs site.

> Those are my guesses. Now the dumb question. What is ray casting? Is
> it a form of ray tracing?

Yes, but simplified. From the eye or camera you just fire out a number
of rays from -1/2 the field of view to +1/2 the field of view. When a
ray intersects a wall (as calculated on a 2d map) you compute the
distance from the eye to the wall and draw a line segment vertically. Do
it for all rays in the field of view and you have a 3d representation of
a 2D map.
Tricks of the Game Programming Gurus, SAMS, has an excellent dicussion
of ray-casting.


Paul.

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