On Mon, 14 Aug 2000 22:49:46 +0200, Peter J. Holzer wrote:
>>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).

Or, you tesselate both spheres, ensure no triangles intersect, and perform 
the CSG operation on the resulting meshes.  If you can depend on the 
surfaces to be well-behaved, there are even shortcuts that can be taken to 
avoid testing insideness for every single vertex.

CSG is not the difficult thing to tesselate.  Things like julia objects
and infinite polys and other implicit objects are.

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
My opinions.  Mine.  Not anyone else's.

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