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Diffuse roughness is how you would simulate a powdery surface like dried clay or dust.  When roughness is 0.0,  LamaDiffuse uses the Lambertian model to calculate the diffuse response.  When roughness is > 0.0, the Oren Nayar model is used instead.

Normal / Bump

Here is where you supply a signal, either a texture or procedural pattern, to create a bump to the surface to "fake" surface details like small bumps or scratches. This means an artist doesn't have to model these tedious and often repetitious parts of a model.

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