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how to render grass properly?

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Re: how to render grass properly?

Unread postby sam » Mon Feb 08, 2021 5:59 pm

So just so you know SSS needs a geometry defining a volume to work properly. So unless your grass has a thickness like in real life (and not a flat polygon) it won't work. This is why you need to use diffuse backlighting on geometries that don't have any thickness.
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Re: how to render grass properly?

Unread postby sam » Wed Feb 10, 2021 8:18 pm

Just a disclosure about SSS. SSS is an approximation to render objects that have a volume. Today the best approximation to SSS on very thin surfaces is diffuse backlighting since it actually evaluates everything coming behind: lights, emission, diffuse reflection etc...

SSS (diffusion or random walk) is a way to approximate what's inside a geometry from the entry color of the surface. In a way that's reverse rendering. To do so, it considers the inside of a geometry to be an homogenous volume with fixed set of physical properties (attenuation...). It doesn't evaluate objects within nor the light it receives or reflects/scatter inside.

True SSS would be transmission scattering, but you would need to actually model the different layers down to the bones. Obviously that would be insanely slow to render, not to mention difficult to model. So all we do is a (smart) approximation of an effect.

BxDFs are also approximations of a microfacet surface etc... everything is. So contrary to what you say diffuse backlighting IS the way to go when using flat geometries that have no thickness like grass.
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Re: how to render grass properly?

Unread postby RayCaster » Fri Feb 12, 2021 4:37 pm

is he trying this with opacity maps or clip maps?
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