POV-Ray : Newsgroups : povray.binaries.images : using 'object pattern' as media : Re: using 'object pattern' as media Server Time
7 Jul 2022 01:02:14 EDT (-0400)
  Re: using 'object pattern' as media  
From: Bald Eagle
Date: 29 Apr 2022 19:50:00
Message: <web.626c7935ac9c0ae11f9dae3025979125@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:

> My understanding of mesh/mesh2 objects and bicubic_patch objects is that they
> are *both* just zero-thickness 'shells' -- so I still don't quite understand why
> one works as an object pattern, while the other does not. I still have the
> thought that it is due to a missing inside_vector(?). OR, the problem could be
> due to the particular bicubic model I used. It is just a union of patches, but
> is not a completely 'closed' one.

The issue isn't whether it's closed or not, it's what takes place under-the-hood
in POV-Ray.  Meshes are geared toward making "solid" objects by defining the
object's surface, and has the code to support such an extrapolation.  Bicubic
patches are only ever interpreted as surfaces, no matter what you do.

What you'll likely have to do is take the control points of your patches, and
run them through the Bernstein polynomial stuff that TOK, and later I did to get
the <x, y, z> of any point on the surface of the patch.

Then you can use the points and the normals, and make a mesh object.

I did that in the Bezier monograph.

I'll probably have to give you a zip of the scene and any includes, and then it
would have to be extended to create a mesh from multiple patches.

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