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From: mg@ (Mike Gigante)
Newsgroups: comp.graphics
Subject: Re: Triangles in uniform spatial subivision
Keywords: 3DDDA, uniform spatial subdivision, ray-tracing
Message-ID: <mg.671526645@godzilla>
Date: 13 Apr 91 07:10:45 GMT
Article-I.D.: godzilla.mg.671526645
References: <1991Apr11.144339@disuns2.epfl.ch>
Sender: @minyos.xx.rmit.oz.au
Organization: RMIT Computer Centre, Melbourne Australia.
Lines: 17

What I do is for each voxel overlapping bbox of triangle substitute
each corner of voxel into plane eqn of triangle.  If sign of resultant
substitution is the same for all corners, then you can reject the
voxel (i.e. it lies entirely on one side of the triangle)

This gets rid of most of the obvious voxels, but you can still end up
with some voxels that cross the *plane* of the triangle, but not
containing the triangle. This is mostly a problem for long, thin
triangle that are not conveniently aligned with the coordinate system.
Further effort (eg performing clipping tests on the triangle for each
voxel), wasn't warranted in my case as all the triangles are the result of 
"nice" tesselations.

Now is it worth it? I am undecided, I suspect not tho' as long as you have
the raytag/ray-id/mailbox optimization...

Mike Gigante, RMIT