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Am 17.04.2018 um 05:51 schrieb Sven Littkowski:
> Okay, I started to add reflection, fresnel, and conserve_energy to the
> wood texture. But i don't see any difference to how it was before. The
> ior goes into the interior, but does solid lumber have an interior?
Why, yes, of course solid lumber does. Ask any woodworm ;)
No, seriously: /all/ materials have a refractive index.
In most materials -- even apparently totally opaque ones -- light /does/
enter the bulk of the object; there, it is scattered somewhat randomly a
couple of hundred times by impurities or irregularities, until it is
either absorbed or happens to find its way out again. While in the
material, light waves travel slower than in vacuum, which is what gives
it a non-unity refractive index, and does cause refraction at the
boundary, and also a bit of specular reflection.
(The internal scattering process is what causes the diffuse reflection
to be virtually completely independent of the direction of incoming
light, and the absorption process is what gives colour to the material.)
Metals are a kind of exception: There, light is indeed reflected or
absorbed directly at the boundary. Yet technically even they have a
refractive index, although theirs is a complex number.
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