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From: mmblom@cs.vu.nl (Marc Blom)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Fast 3d Graphics
Keywords: fast 3d optimizing assembly cycles
Message-ID: <9576@star.cs.vu.nl>
Date: 6 Apr 91 18:33:53 GMT
Article-I.D.: star.9576
References: <9529@star.cs.vu.nl> <1047@cbmger.UUCP> <20338@cbmvax.commodore.com> <1073@cbmger.UUCP>
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Newsgroups: comp.sys.amiga.programmer
Subject: Re: Fast 3d Graphics
Summary: 
Expires: 
References: <20338@cbmvax.commodore.com> <9554@star.cs.vu.nl> <1073@cbmger.UUCP>
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Organization: Fac. Wiskunde & Informatica, VU, Amsterdam
Keywords: fast 3d optimizing assembly cycles

In article <1073@cbmger.UUCP> peterk@cbmger.UUCP (Peter Kittel GERMANY) writes:
>In article <9554@star.cs.vu.nl> mmblom@cs.vu.nl (Marc Blom) writes:
>>
>> 
>>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.
>

Yes, I know and i am using this, i just forgot it.


>> 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.
>

I think i misunderstood you, I am allready using tables for the sin/cos
values, I thought you meant tables for the multiplies, then the coordinate
system's size is very important, the larger your coordinate system, the
larger the multable.

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


--
Marc Blom, Vrije Universiteit Amsterdam, Email: mmblom@cs.vu.nl | short .sig