ABX wrote:
>On Wed, 12 Nov 2003 17:03:10 +0100, sascha <sas### [at] userssourceforgenet>
>wrote:
>Somehow I missed 'fresnel' keyword, sorry. In case of 'fresnel' there was a
>problem related to equation I also found. This is a line:
>
>  g = sqrt(Sqr(ior) + Sqr(cos_angle) - 1);
>
>in lighting.cpp (in determine_reflectivity()). For some cases (also official
>benchmark) it caused evaluation of sqrt for negative values. Depending on
>compiler it could behave different.
>
>And this is _not_ fixed yet. Any ideas would be appreciated for sure.
>
>ABX
>

That line appears to be calculating the cosine of the angle of refraction
from the cosine of the angle of incidence - you can derive the expression by
writing Snell's law of refraction in terms of cosines. Negative values in
that sqrt will correspond to total internal reflection, I think. I don't see
a simple solution (unless you trap internally reflected rays somewhere
already?)

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