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If one has a closer look at Iridescence, the results are devastating.
Take the scene below, for instance:
- We have two spheres, one with "irid" and one without.
- The non-iridescent sphere is set to be 100% white, the brightest you
can realistically have. The iridescent one is set to pitch black except
for the iridescence contribution.
- We have two very dim light sources, one of which is a spotlight with
smooth falloff.
What's wrong?
- The iridescent sphere is brighter than the white one!
- The iridescence effect breaks the smooth spotlight.
If you toy around more with lighting, you'll notice that the iridescence
effect perfectly ignores how bright the light of any particular source
is - as long as it isn't zero.
What else?
- Try setting the "thickness" value to something extremely low;
theoretically, this should kill off any interference at visible
wavelengths; yet the iridescence effect adds some plain grey.
- If you toy around with camera perspective, you may notice that it has
no influence on the iridescence effect; theoretically, it should be
influenced by both the light source *and* observer position.
To make a long story short: Iridescence is badly broken (and has always
been, by the way). I suggest to give it a major overhaul - even at the
cost of breaking compatibility with 3.6.
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camera {
location <0.0, 0.5, -4.0>
direction 1.5*z
right x*image_width/image_height
look_at <0,0,0>
}
light_source { <0,30,-30> color rgb 0.2
spotlight point_at 0.0 radius 0.5 falloff 1.0
}
light_source { <-30,30,-30> color rgb 0.1 }
default {
finish { ambient 0 diffuse 1 specular 0 }
}
plane { y, -1
pigment { checker color rgb 1 color rgb 0.5 rotate y*30 }
}
sphere { -x, 1
pigment { color rgb 1 }
}
sphere { x, 1
pigment { color rgb 0 }
finish { irid { 0.5 thickness 1 turbulence 0.5 } }
}
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