Impress <yha### [at] nospamhotmailcom> wrote:
> I mean, if by
> computing the normal length and check if it's zero or greater, the surface
> receive the texture, otherwise interior_texture...?

  AFAIK, triangles are assigned a normal vector at parse time.
  At render time it's enough to check the sign of the dot-product of the
incoming ray and the normal vector to see if the incoming ray hit the
inner or the outer side of the triangle.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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