On 22 Aug 2000 05:28:40 -0400, Warp wrote:
>Ron Parker <ron### [at] povrayorg> wrote:
>: Depends on your definition of "necessary."
>
>  Well, suppose that we have two meshes consisting of 1 million triangles
>each and we make an intersection of them. In the intersection only 10
>triangles are visible.
>  We can:
>  a) Calculate a mesh which is the resulting intersection. This mesh would
>take something like 15-20 triangles.
>  b) Leave the meshes be and use just regular CSG intersection.
>
>  In the case a) we need memory for 15-20 triangles. In case b) we need
>memory for 2 million triangles (1999990 of them not affecting the scene
>in any way (except slowing the render)).

Perhaps you misunderstood.  I was not talking about using regular CSG 
intersection (that would be of no use in exporting something other software
could use, after all.)  I was talking about computing the intersection of
two arbitrary but well-behaved meshes.  That is a solvable problem, and
there may even be a paper out there from someone who's solved it and/or 
optimized it.  I have solved it myself, though I've never implemented or
published the solution.  (The margins of this post, etc...)  Once you know
how to compute the intersection of two meshes, you have CSG licked.

The memory usage in this case would be that of 2 million triangles, but the
exported data would contain only the 15-20 (or 10, whatever) in the result.

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

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