On Mon, 14 Aug 2000 10:55:41 -0500, Chris Huff wrote:
>In article <slr### [at] tealhhjpat>, 
>hjp### [at] SiKituwsracat (Peter J. Holzer) wrote:
>
>> (what's "Kalotte" in English? - calotte seems to be some kind of hat)
>
>Well, what does it mean?

    intersection {
	sphere { ... }
	plane { ... }
    }

:-)


>> I think there is even a (low quality) macro for this, but it needs 
>> MegaPOV.
>
>Tesselating a sphere is pretty easy, and wouldn't require MegaPOV.

Yes. But even for such a simple CSG as in the example I gave (difference
of two spheres) it isn't that simple any more. There are already three
cases:
1) The spheres don't intersect at all (easy - just tesselate the first one)
2) The second is completely inside the first (also easy - tesselate both
   but invert the normals of the second).
3) Their surfaces intersect (a bit more complicated - you have to
    compute the circle where they intersect, then tesselate two partial
    spheres).

Now think of a CSG composed of an arbitrary number of objects. Coding
all possible combinations would be clearly infeasible. 

>I think the macro you are referring to is one which uses trace() to
>scan the surface of an object, it can tesselate almost any object, but
>doesn't always give great results.

Yup. Finding the best points for the triangles isn't trivial. I haven't
looked at the macro yet, but I'd guess that it uses a rather simple
algorithm.

	hp


-- 
   _  | Peter J. Holzer    | Nicht an Tueren mangelt es,
|_|_) | Sysadmin WSR       | sondern an der Einrichtung (aka Content).
| |   | hjp### [at] wsracat      |    -- Ale### [at] univieacat
__/   | http://www.hjp.at/ |       zum Thema Portale in at.linux

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