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Re: [help-3dldf] Fwd: Re: button-hole problem
From: |
Laurence Finston |
Subject: |
Re: [help-3dldf] Fwd: Re: button-hole problem |
Date: |
Sun, 24 Apr 2005 22:08:20 +0200 |
User-agent: |
IMHO/0.98.3+G (Webmail for Roxen) |
> Take, for example, two parallel triangles.
>
> A B
> /\ /\
> / \/ \
> / /\ \
> / C/__\___\D
> /________\
> E F
>
> If AEF is in front of BCD, then
>
> A B
> /\ /\
> / \/g \
> / \ \
> / \h__\D
> /________\
> E F
>
> the plan containing A, F and Focus::position has cut BCD in two parts.
> Cgh is occluded and BghD is not.
Thanks for the explanation. The case I'm having difficulty with is where the
triangles lie in a plane parallel to the x-z plane, the line Focus::position
-- Focus::direction also lies in a plane parallel to the x-z plane, and the
triangles as seen from above look something like this, but rotated about plus
or minus 75°:
______
| /|
| / |
| / |
| A / |
| / B |
| / |
| / |
I / |
| / |
|/_____|
I've implemented routines for "self-decomposition" of polygons, but I'm afraid
that no matter how many pieces I break them into, simply sorting by their
max-z, min-z, or mean-z values will fail for some of them. I may try
projecting a ray from Focus::position through each of the vertices and testing
the distance from Focus::position to the first intersection point of each of
the polygons. I think this will work for convex polygons.
I don't know what to do about conic sections yet.
Thanks.
Laurence