"Harry Peverell" <har### [at] 163com> wrote:
>
> Could you please provide some guidance on how to apply textures to the interior
> and exterior in Povray? I'm looking forward to implementing your suggestion of
> using a dark texture with a bright interior_texture to check for flipped
> triangles and to illuminate the dark areas in the center of the render.
>

Like this example (in case you are not using any light sources):

object{ ...your mesh object...
// a dark texture...
texture{pigment{rgb .2} finish{ambient 1 emission 0 diffuse 0}}
                      // or   {ambient 0 emission 1 diffuse 0}}

interior_texture{pigment{rgb <1,0,0>}finish{ambient 1 emission 0 diffuse 0}}
                                     // or {ambient 0 emission 1 diffuse 0}}
                }
      }

(ambient 1 will cause a non-fatal warning message, so use emission 1 instead.)
By the way: The first or main texture is actually applied to both the inner AND
outer surfaces of the mesh object-- unless an interior_texture is added.

IF the problem with your mesh is indeed flipped normals in certain places, the
bright red interior_texture will show them. That's because the 'inside' surfaces
of those triangles are actually facing outward.

(Instead of using an interior_texture, you *could* place a red light_source
*inside* the mesh object, and the lighting on the bad triangles would show up on
the outside. I think!)

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"Kenneth" <kdw### [at] gmailcom> wrote:

> (Instead of using an interior_texture, you *could* place a red light_source
> *inside* the mesh object, and the lighting on the bad triangles would show up on
> the outside. I think!)

Very nice insight, Kenneth.
An interesting experiment would be to place 2 light sources of different color
on either side of the mesh.

I also wonder what that would yield if smooth_triangles were rendered, with 1
vertex set "up" or "toward", one perpendicular to the direction / parallel to
the view plane, and one "down" or "away".

- BW

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Le 2024-10-14 à 13:38, Bald Eagle a écrit :

> I also wonder what that would yield if smooth_triangles were rendered, with 1
> vertex set "up" or "toward", one perpendicular to the direction / parallel to
> the view plane, and one "down" or "away".
> 
> - BW
> 

In that case, I would expect the normal to get interpolated between the 
two, causing part of the triangle to be treated as outside and part to 
be treated as inside. So, smaller red triangle or a red trapezoid to be 
visible depending if 1 or 2 of the normals are pointing the wrong way.

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