you ever look at something in the real world and be like "damn, that's a nice shader"

so anyway yesterday i was admiring the subsurface scattering on a watermelon

@chr what does that mean?

@Felthry subsurface scattering is when you can see light from a source behind something through it, like when you put a light up behind your skin and it kinda glows red

@chr @Felthry that's a "bad" example, 'cause a hand has a constant scattering value, it's easier to understand with things like plants, fungus and crystals, or fluids like honney, it's just easier to find real examples =P

@Efi @Felthry yeah i was just looking for an image which showed the same object under several different levels of scattering

@chr @Felthry wich is not a thing that can happen, that's my point =3

@Efi @chr I don't know that I follow

@Felthry @chr do you know the refraction index of water? it's constant, the same for all water
the subsurface property is also part of the material, so the same material has always the aame value, just tha
the hand example is a virtual prop, not a real thing

@Efi @chr why does this mean that the same thing under different levels of scattering can't happen? Is it not dependent partly on the color and intensity of the light?

@Felthry @chr the idea is the scattering value doesn't change
the scattering value tells you how deep the ligh can travel in the material before being absorbed at a constant intensity
sorry for technical stuff, it's a very obscure physics thing XD

@Efi @chr I can handle technical!

Would it not have any difference with wavelength? I feel like it would, because I know for a fact that x-rays can penetrate much further

@Felthry @chr different radiation permeates differently, but the material keeps its index, it's the same concept as lead radiation shielding, the material absorbs a quantity per thickness
when you set a value for subsurface scattering the value is the depth where a white light of intensity 1 (in the relative scale of the software) is completely absorbed
if you double the intensity the penetration doubles (it's actually quadratic, but shhh)
but the number you set is the same

@Efi @chr there's no dispersion at all? and no nonlinearity at all? this has the feel of over-idealized stuff to me

@Felthry @chr 3D rendering always assumes uniform material distribution on meshes, but there are volumetric renderers that do that kind of thing
irl, it depends on the needs you have, but for example, regular crystals are known to have very stable absorption rates, so you can measure cracks in the inside by the way light traverses them

@Efi @chr there are nonlinear optical materials used for things like optical amplifiers though, I know that

@Felthry @chr yeah, but that's out of the scope of anything the subsurface scattering index is used for

@Efi @chr are we talking about a physical, measured quantity or something in computer graphics, anyway?

@Felthry @chr pretty sure it is both
it is used irl to talk about translucent materials, but I've only seen it in art, and it follows that it's used in cgi, because cgi tries to imitate nature
I don't know how physicists look at it, but I know it's a shorthand property for a very specific and human-scale use

@chr i like that this cognitive experience predates shaders

@chr but is like, enriched by the existence of shaders

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