So it was brought to my attention that Viscorbel had found a problem with the custom brdf method I’ve been teaching in the Mastering V-Ray course. You can read more here. http://viscorbel.com/vray-materials-part-3-metals/ Image taken from his blog post: [image] So I did some testing and I hone…

The Falloff map works with the cosine of the angle, and not with the actual angle. The curve that viscorbel shows above is the graph of its inverse (the arccos function). Best regards, Vlado

It kind of does, but it’s not… Here’s an overlay I’ve tried correcting the falloff map with gamma or reverse gamma, but that doesn’t fix it, just distorts it differently

I knew someone smarter would figure out the math behind it :slight_smile:

That’s exactly what I thought but I can’t make the maths to fit. 255 * (0.5^2.2) = 55.5 I’m getting a value of approximately 76 at 45 degrees.

Use cos/arccos instead… Best regards, Vlado

Feel free :slight_smile: That’s what OSL is for. Best regards, Vlado

Hehe, yeah I’m trying to do so, but my maths skills are just not good enough. I got the part with the facing ratio, but I can’t get the arccos-thing to work: shader facing_ratio_linear ( output color Col_Out = color(0.5) ) { float facing = 1 - (dot(normalize(N), normalize(I))* -1); …

Try acos(1-x)/(pi*0.5) Best regards, Vlado

Yes, that does it: facing_ratio_linear.osl shader facing_ratio_linear ( output color Col_Out = color(0.5) ) { float floatOut = acos (1.0 - (1 - (dot(normalize(N), normalize(I))* -1)))/(M_PI * 0.5); Col_Out = color(floatOut , floatOut , floatOut ); } Thanks Vlado! facing_rat…

Determining correct falloff

V-Ray V-Ray for 3ds Max General

Wobi April 20, 2015, 3:45pm 11

Maybe this could be implemented with an OSL-Texture, so that we could use it with the gradient remap like Viscorbel mentioned here:

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Determining correct falloff

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