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From: butch@hoss.unl.edu (Charles Rosecrans Jr.)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: 3D Graphics
Message-ID: <1991Mar10.183032.17717@hoss.unl.edu>
Date: 10 Mar 91 18:30:32 GMT
References: <91067.230242R18QC@CUNYVM.BITNET>
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Organization: University of Nebraska - Lincoln
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In <91067.230242R18QC@CUNYVM.BITNET> Jeannopoulos Alex <R18QC@CUNYVM.BITNET> writes:

>      Has anyone done any 3d graphics on the AMIGA. I have been some 3D program
>ming but I was wondering how I can calculate whether certain lines are removed
>ed or should be visible. Any info on hidden line removal would be greatly
>appreciated.               Thanks
>                              Alex Jeannopoulos
>                                 R18QC@CUNYVM

In my integer-based 3D code, I have a pre-computed surface normal (I use
this basically for my shading algorithm) that I use.  If the Z-element
of the normal vector is positive after rotation, then the face is pointing 
towards the viewer (or camera).  So far, this has given me very reliable
results.  Anyone know of a quick algorithm for depth cueing (I think
thats the word I'm looking for) the faces.  Right now I use the minimum Z 
value, but this goofs up from time to time.  Any help on this would be 
greatly appreciated.

    Also, I think someone mentioned a clock-wise algorithm, which works well 
too.  The reason why I choose the normal algorithm is the time it took to 
rotate the normal as opposed to the time it took to derive the value for the 
clock-wise test.  There is really a small difference for a few faces,
but when the numbers grow, the normal test gives better time performance.

Butch Rosecrans					butch at fergvax.unl.edu