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Many time I've seen some material using mixing of two same nodes like this:

this

Is there any difference from using this?

this method

gandalf3
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Alexander Pukhalski
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    The roughness value is different – J Sargent Nov 09 '15 at 20:36
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    @Alexander Pukhalski think it's in case of altering the other shader at a later on (a normal map on the bottom one, for example). Or when you change the shader in the materials panel, some settings are preserved from the old one and this is a good example of that. – Vladimir Nov 09 '15 at 20:44

3 Answers3

22

They are not equivalent. Mixing two different roughnesses produces a subtly different distribution of angles at which light can be scattered:

enter image description here

Note the shaper highlights on the right hand example (mixed roughness).

To visualize what is going on, take this (very approximate) example:

enter image description here

The length of the arrows represents the amount of light that gets scattered in that direction.

gandalf3
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7

Late to the party but the example with suzanne is not very clear.

Let me over-exaggerate and demonstrate - these are the 2 shaders that will participate - glossy sphere with a perfect point light in front (0.0 size):

enter image description here

Now let's mix the roughnesses into 1 shader ((0.01+0.91)/2 = 0.465) and also mix the shaders to see the difference:

enter image description here

The mixed shaders doesn't produce a single "material" (no physically correct material has this roughness distribution), but they produce (simulate) two materials - a material with a glossy clear coat. That's what it is used for.

Jaroslav Jerryno Novotny
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6

In your given example the roughness value is different. This is a common method to add two otherwise identical shaders that have different values.

enter image description here

J Sargent
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