Wasn't it Chris B who wrote:
>
>Interestingly on rendering the three solutions side-by-side I see that 
>Mike's solution is the only one that gets lit correctly.
>I'm not sure why this should be. I've adjusted the light in the SDL below to 
>emphasize the effect, in case anyone can shed light on this.

I think the CSG torus solver doesn't do quite the right thing with the
bit in the middle when the minor radius is greater than the major radius
and the major radius is positive. 

Once the surface normals are pointing the wrong way, "inverse" doesn't
fix them, it only fixes the situation where the inside is on the outside
and swaps the interior_texture for the texture.

Oddly, these work.

torus {-MajorRadius,MinorRadius 
  pigment {color rgb <0,1,1>}
  clipped_by {sphere {0,SphereRadius}}
}

difference {
  sphere {0,SphereRadius}
  torus {-MajorRadius,MinorRadius inverse}
  pigment {color rgb <1,0,1>}
}

-- 
Mike Williams
Gentleman of Leisure

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