[tom]

Fact8: Fact7 sometimes fakes Fact6

[David Solito]

[Half Life]

The best way I was able to understand this is to think of a the surface as being divided by whatever ratio the BSDF's are set to -- so if we are doing 50/50 then every even numbered surface unit would be roughness 90% and every odd numbered surface unit would be roughness 10%. Since we are not able to percieve at that small a scale they visually look like they are right on top of each other, but in fact are residing next to one another at intervals.

As I said the specifics of the math I'm cloudy on... no mathematician here

Best,
Jason.

[Mihnea Balta]

The part with 100/100 being the same as 50/50 is easy to explain: Maxwell divides each weight to the sum of all weights within a layer (this is called normalization). It's the proportion of the numbers which matters, not the absolute values. For example 70/30 is the same as 35/15, 7/3 or about 100/43. It does this because it's easier for the user to tweak the weights that way - it would be pretty user-unfriendly to force you to change all the weights when you adjust one, to make them add up to 100. On the other hand, it needs to perform this normalization because the weights it ends up using can't exceed 1, or you would have a material which reflects more lights than it receives, which is physically impossible and creates all sort of problems in an engine like Maxwell.

Half Life: your intuition of the process is correct. When you have two BSDFs with weights X and Y in percentages, X% of the rays that hit the object will be computed with the first BSDF and Y% will be computed with the second BSDF. You can think of the object as being made of many small bits which are distributed evenly over the surface, but each bit retains its properties. If the first BSDF is diffuse and the other is a mirror, you'll get some reflections from the mirror bits and a lambert look from the other bits; our brains see this as a diffuse material with a clear coat on top. Making a material with a roughness value in between would not be the same, since it won't have the sharp reflections that the mirror bits produce. It's like the flakes in car paint, but on a much smaller scale. Putting flakes in the paint is not the same as making the paint a bit more reflective, which would be the equivalent of blending the roughness factors.

[David Solito]

it's like putting a black/withe checker texture in infinite low scale ?

[Half Life]

yep, except you can controls the checks to be whatever ratio and properties you want... Offset Lithography works on some similar principles to create what we perceive as full color continuous tone images but are simply small dots of Cyan, Magenta, Yellow, and Black arranged accordingly.

Best,
Jason.

[David Solito]

Offset Lithography works on some similar principles to create what we perceive as full color continuous tone images but are simply small dots of Cyan, Magenta, Yellow, and Black arranged accordingly.

Best,
Jason.

This is my every day's job