"MidiPlay" <ast### [at] yahoocouk> wrote:
> I have 2 polygons, they're 200 units apart and they're identical apart from 1
> vertex being moved 1 unit.  They're displayed with different colours.  Why?  I'm
> using version 3.7.0.msvc10-sse2.win32.
>
> #version 3.5;
> #include "colors.inc"
> global_settings { assumed_gamma 1.0 }
> background { rgb 0.0500 }
> light_source { <0, +10000, 0> rgb 1 }
> #declare Pigment1 = texture { pigment { color rgb < 1 , 0 , 0 > } }
> #declare Pigment2 = texture { pigment { color rgb < 0 , 1 , 0 > } }
> polygon
> {
>     11,
>     < 192 , 0 , -126 >
>     < 152 , 0 ,   23 >
>     < 145 , 0 ,   53 >
>     < 124 , 0 ,   77 >
>     <  96 , 0 ,   88 >
>     <  65 , 0 ,   84 >
>     <  50 , 0 ,   79 >
>     <  50 , 0 ,  126 >
>     < 200 , 0 ,  126 >
>     < 200 , 0 , -126 >
>     < 192 , 0 , -126 >
>     texture { Pigment1 } interior_texture { Pigment2 }
> }
> polygon
> {
>     11,
>     < 392 , 0 , -126 >
>     < 353 , 0 ,   23 >
>     < 345 , 0 ,   53 >
>     < 324 , 0 ,   77 >
>     < 296 , 0 ,   88 >
>     < 265 , 0 ,   84 >
>     < 250 , 0 ,   79 >
>     < 250 , 0 ,  126 >
>     < 400 , 0 ,  126 >
>     < 400 , 0 , -126 >
>     < 392 , 0 , -126 >
>     texture { Pigment1 } interior_texture { Pigment2 }
> }
> plane
> {
>     y, -0.1
>     pigment
>     {
>         checker rgbf <0.6,0.6,0.6, 1.0>, rgbf <1,1,1, 0.6>
>     }
>     scale 100
> }
> camera
> {
>     location < 200 , 8000 , 0 >
>     right 1.778 * x
>     angle 6.5000
>     look_at < 200 , 0 , 0 >
> }

The surface normal points the other way. A polygon has no real "inside" and at
the end of the day, "interior_texture" does nothing else but look at the sign of
the surface normal because in objects with a volume, it is properly defined (in
POV-Ray anyway) in a consistent way. As there is no way to set the surface
normal
of polygons in POV, you might want to try reversing the order of points to
invert the surface normal.

Either way, it is not a bug.

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