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From: mmblom@cs.vu.nl (Marc Blom)
Newsgroups: comp.sys.amiga.programmer
Subject: Fast 3d Graphics
Keywords: fast 3d optimizing assembly cycles
Message-ID: <9529@star.cs.vu.nl>
Date: 2 Apr 91 21:24:30 GMT
Sender: news@cs.vu.nl
Lines: 34

'm wondering how fast 3D graphics can really go. I've written some rotation
and perspective routines (in assembly) and profiling shows that 60 % of the
time is spend in my routine RotatePoint. This routine rotates 1 point around
all three axes in only about 900 cycles minimum and about 1100 cycles maximum.
Is this fast ? Can someone do better ? (If so PLEASE mail me how you did it).
I won't include the source here because it's about 100 lines long but instead
i'll tell you what it does: It rotates a point x.word, y.word, z.word (signed)
using fixed point (14 bits behind the point) integer calculation. rotating
around each ax uses 4 muls, giving a total of 12 muls. (This is the variation
in clock cycles I mentioned above, about 900 for best case muls, about 1100
for worst case muls) By the way, these clock cycles are only valid for a plain
68000. (I don't know about 680x0 with x=1,2,3,(4?) I believe you then have to
play with cache-sizes etc. to get the best results).
I want to have the fastest possible rotation routine so I can concentrate on
kicking the Graphics Library AreaMove/Draw/End out (In a system friendly manner,
don't worry :-) ) And write a fast blitter routine.
The 60 % mentioned above was only relative to my routines part of the execution
time, of the total time involved, 15 % was spend in my routines, including
RotatePoint, Perspective etc and 85 % was consumed by those wonderfull (yuk,
did I say wonderfull ?) Graphics Library Calls. No wonder games writers kick
the OS out ! (I hope this doesn't provoke another TO OS OR NOT TO OS
discussion !)
If someone is interested in the source of RotatePoint, just drop me a line and
I will mail it to you.
 
	Marc Blom
 
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