POV-Ray : Newsgroups : povray.binaries.images : using 'object pattern' as media : Re: using 'object pattern' as media Server Time
26 Sep 2022 01:28:36 EDT (-0400)
  Re: using 'object pattern' as media  
From: Kenneth
Date: 30 Apr 2022 13:30:00
Message: <web.626d70edac9c0ae18d86850a6e066e29@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
> "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...
> 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.

Oh, I get it now.

There are two aspects of this problem that initially threw me off: The docs
about bezier_patches repeatedly refer to 'triangles', as if the patch or model
is converted to a smooth-triangle mesh 'under the hood'. At least, that's what I
took to be the meaning there... which is probably a misconception on my part(?).
The other odd thing during my render trials is that POV-ray *seems* to be
evaluating my bicubic_patch model 'successfully' in the same way it treats the
Bunny model-- that is, the render likewise slows down while evaluating the media
container shape, and the render times are about identical. Except that no
media-effect is produced. This behavior made me blame the problem simply on the
'missing inside_vector.'
> 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'll take a look at the files you sent; thanks!

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