Path: chuka.playstation.co.uk!news
From: Craig Graham <c_graham@hinge.mistral.co.uk>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Poly Intersections
Date: Tue, 29 Dec 1998 23:34:55 +0000
Organization: PlayStation Net Yaroze (SCEE)
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Anyone got a quick(ish) way of doing polygon intersection calculation?
I'm adding constructive geometry to RsdANIM, and althought I've put
together some code that does the job, my code to calculate the ray/plane

intersection point is dismally slow. Checking that the point on the
plane
lies within a the poly is a much quicker, but actually getting the
intersection
between one poly edge and the plane of a 2nd poly is a lot slower than
I'd
like.

For those who've no idea what I'm on about, in order to subdivide a poly

where it crosses another poly I have to work out where the two poly's
intersect by projecting the edges of one poly to the point where they
meet the
plane that the 2nd poly lies in. Then I check to see if the point lies
within
the 2nd poly. If it does, then the first poly must be subdivided at that
point.

All clear? No, anyway, upshot is it'll allow the following new features
in
RsdANIM:
1) a smooth join of two objects (like the "Boolean-Union" operation in
3DS Max),
2) undisplayed faces removed from the model.
3) Directional and point source embedded lighting with proper shadow
casting
   (currently there's only point source support, and it doesn't cast
shadows).

Anyone got a nice quick way of doing the ray plane intersect?
(an O(1) algorithm would be good)

Laters,
Craig.