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From: peterk@cbmger.UUCP (Peter Kittel GERMANY)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Fast 3d Graphics
Keywords: fast 3d optimizing assembly cycles
Message-ID: <1073@cbmger.UUCP>
Date: 5 Apr 91 12:14:08 GMT
References: <9529@star.cs.vu.nl> <1047@cbmger.UUCP> <20338@cbmvax.commodore.com> <9554@star.cs.vu.nl>
Reply-To: peterk@cbmger.UUCP (Peter Kittel GERMANY)
Organization: Commodore Bueromaschinen GmbH, West Germany
Lines: 39

In article <9554@star.cs.vu.nl> mmblom@cs.vu.nl (Marc Blom) writes:
>
>peterk@cbmger.UUCP (Peter Kittel GERMANY) wrote:
>>All I hear permanently is, use tables, tables, tables instead of real
>>(or integer) calculations. At least for the sin and cos calculations.
>>Estimations about real-life situations show that you don't need tremendous
>>precision normally (but that depends on your real project). 
> 
>I wish I knew how to use tables without taking too much memory: I'm using
>360 degrees around each angle, so to multiply a coordinate with a sin/cos
>(this is one table) value i would need 360 words PER coordinate,

No, you can cut down this by a factor of 4 by making use of the identities
of sin and cos for offsets of n*90 degrees. This is common technique.

> I'm now
>using coordinates that range from -16K to + 16K. I don't even want to
>calculate this ! (22.5 meg !) Offcourse i could use less percision, for
>instance only rotating by an even number of degrees (0,2,4...,360) and
>don't use such a large a coordinate system, but i don't want to compromise
>between speed/presicion just yet !

Hmm, why is the size of the coordinate system important?
In first attempt I would only make a table of sin and cos values in some
arbitrary stepping. If you need high precision, then for only one quadrant
in small steps; else for the whole circle in bigger steps. In this system
you save the sin/cos evaluation, but you have still to multiply your
coordinates with these factors.

Another thought: If you don't have so many objects, would it be of
advantage to build tables of every object coordinate already multiplied
with all these sin/cos values? That should save you some more multipli-
cations in the innermost loops. But the number of stored table entries
has squared, now there you would have to choose very carefully.
Anyone already done this?

-- 
Best regards, Dr. Peter Kittel  // E-Mail to  \\  Only my personal opinions... 
Commodore Frankfurt, Germany  \X/ {uunet|pyramid|rutgers}!cbmvax!cbmger!peterk