Nieminen Juha wrote:
>   Answer: I'm not sure, but I have an idea. Perhaps someone could give it a
> try?
>   The shading could be calculated this way:
>   If the actual normal of the surface is pointing away from the light source
> while the modified normal is pointing at it, then we ignore the first
> intersection of the current object and the shadow ray calculated for this
> point.

I should've responded a few days ago but kept putting it off.

This solution would only compound the problem.  If you let the ray
ignore the first intersection, then it will be inside the sphere and
simply hit the other side going out, causing the same problem as
before.  Currently at least the transparency would work right, but if
the sphere were translucent, you would only see the one side filtering
the light in a band at the shadow line!

I think the only solution to this problem now and forever would be if
these faked surfaces were actually modeled.  I've been thinking that if
the point were moved after the intersection detected and that point
used, the place where the distorted normal actually works, then it would
avoid this shadow and allow other effects.  But I don't know how much
distortion that would leave on the objects.

For example, a polygon would be in two places at once.  An object
drawing close could "intersect" this virtual position and cause a
distinct shadow line long before it physically touches.  I'll add this
feature to my raytracer and leave it dead until I'm willing to play with
it.  Perhaps if the virtual distortion decreased as the angle between
the surface and the camera increased.  But then that would look like the
textures were not perspective correct.

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