From:	"Thomas Harte" <*T DOT Harte AT btinternet DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Allegro perspective-correct texture mapping
Date:	15 Mar 1997 15:02:00 GMT
Organization:	BT Internet
Lines:	24
Message-ID:	<01bc3151$d8ca9b80$102549c2@default>
References:	<5fg3s0$hob$1 AT troll DOT powertech DOT no> <331F047A DOT 271F AT cam DOT org> <01bc2ff7$739c9340$14621ecb AT homer DOT effect DOT net DOT au>
NNTP-Posting-Host:	host-73-37-16.btinternet.com
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Josh McDonald <os-dev AT effect DOT net DOT au> wrote in article
<01bc2ff7$739c9340$14621ecb AT homer DOT effect DOT net DOT au>...
> 
> HAHAHAHAHAHAHAHAA ROTFL...... How can we tell _everybody_ the truth
> about doom so we don't get these messages anymore?
> 
> Doom does _not_ use raycasting, or raytracing. It draws polygons, 
> which are sorted through a bsp. Sheesh..
> 
> -Josh

	Actually, DooM looks at a table of which walls are displayed from where
you are standing (it has a massive pre-calculated look up table), and then
draws these walls by a simplified method of ray casting. It sends out one
ray per a vertical display line (ie 320 in graphics mode 320x200, or 640 in
the newer DooM95), which dictates how far away that part of the wall is.
The texture is broken into vertical lines, and each vertical line is scaled
individually to be drawn on the display at the size specified by the cast
ray. You cannot look up and down because of the dependence on the lines
being exactly vertical.

		-Thomas

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