[Radiance-general] usage of rtrace within a material

[Greg Ward]

I should have said specifically that the source calculation doesn't work if the light bends and stays bent.  In a more typical situation where the dielectric is in two parallel planar surfaces, the ray straightens out again and everything works just fine.  Radiance started out only having the dielectric material -- glass and trans types were added much later.

Cheers,
-Greg

> From: Greg Ward <gregoryjward at gmail.com>
> Date: January 31, 2013 9:08:04 AM PST
> 
> Hi Lars,
> 
> The physics of this situation is unusual, and the Radiance source code does apply a correction for the "solid angle ratio" caused by lensing at the surface.  However, Radiance doesn't track source directions properly inside a dielectric or through a refracting object -- it naively sends rays in a straight line towards the source, missing it in cases where significant refraction occurs.  This is why a straight ambient calculation works but the direct calculation does not.
> 
> Cheers,
> -Greg
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