From: Vic <tudor AT cam DOT org>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: "Are Allegro's routines fast enough to write Quake-like games?" - No. HUH?
Date: Wed, 04 Jun 1997 16:46:44 -0400
Organization: Communications Accesibles Montreal
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Roberto Henriquez Laurent wrote:
>     Another question: I know the Quake engine is good. But, what are the
> big differences between Quake's and Descent's engines? Because Descent
> gave real 3D just as Quake does, but at a decent speed in my 486... Why
> is Quake's engine so superior? (that would explain the CPU time it
> costs)
Descent and Quake use different techniques: Quake uses BSP trees while
Descent uses portals and interconected segments.
In Descent: You are in a room made out of segments. Now you have the
position in that room (the segment). Each segment has 6 faces. Those
faces can be solid (wall, door etc) or 'empty'-a link to another
segment. If you do a simple backface culling on the faces of the segment
you will find which ones are visible. Then you verify each face: if
visible you pass it to the renderer, if it is 'empty' it meand you can
see in another segment, you find out which segment and repeat this stuff
with that segment. Even in a big level your frame rated will remain
constant as the numbe of polys to check and draw will be little.
You can also use portals in descent. Check
http://www.rhumba.net/milo/3dgames/index.html for segment explanations
and http://www.geocities.com/CapeCanaveral/5402/ for portal stuff. 

In quake: you traverse most of the BSP tree. This is somewhat slower.
-- 
http://www.cam.org/~tudor
"I INSERTED THE DISK INTO THE COMPUTER, AND TURNED IT ON. LET THERE BE
DOS,I SAID! AND THERE WAS DOS." -- Bill Gates, 1977