"Chris R" <car### [at] comcastnet> wrote:
> I am working on a scene that will include some glasses with colored liquids
> inside of them.  While working on the model for the liquid, I noticed that
> something odd was happening when I used interior fading to color the liquid.
>
> The image on the left is the shape of the liquid rendered with a solid texture:
> pigment { color rgb 0.5 } interior { ior 1.34 }
>
> The image on the right is the same shape rendered with a transparent texture and
> fading:
>
> pigment { color rgbf 1 } interior { ior 1.34 fade_color <1, 0, 0> fade_distance
> 1 }
>
> From this viewpoint, in the solid version you can see the curve of the liquid
> object bowing upwards as expected.  In the transparent version, there is a sharp
> horizontal line where the fade_color ends, below that curve.  You can see the
> interior is still applying to the space above that line, as the vertical green
> cylinder is broken where the ior changes, but the fade color is completely
> missing in that segment.
>
> I would expect to see some variation in the color in that region due to light
> traveling different distances based on the camera angle, but not a complete drop
> out.
>
> Any idea why this might be happening?
>
> -- Chris R.

I should have included this in the initial post.  Here is a version using a
transparent colored pigment and no fading.  This is more what I would expect
from a completely transparent version with fading.  The lighter region on the
top in this version is where the viewing angle sends the light through a shorter
distance in the liquid, and corresponds to the completely transparent section in
the version with the fade_color.

-- Chris R.

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