Blend Material request for bump mapping

[FakeShamus]

I am wondering if it would be possible to retain the bump characteristics of each individual material used in a blend. right now it seems that one of the blended materials (the B material, maybe because it's last?) overrides the bump of the other material. I understand this might be complicated to solve for some materials, like for 50/50 mix or opacity blends. but, for example, if you want to have a smooth metal with rust patches, it would be great to only have to control where the rust patches show through, using an image texture or ISL to blend, and let each material in the blend retain it's own bump characteristics.

any developer thoughts on this?

[Mor4us]

what host app are you working on? seems to work fine with cindigo.

best regards

[FakeShamus]

I'm actually talking about what seems to be a limitation of Indigo itself. If you check out my "snowy rock" material, for example: http://www.indigorenderer.com/materials/materials/1132
The bump for the rock uses a different and more detailed texture than the bump for the snow material, but the snow material bump which is blurred seems to override that of the rock.

I'm realizing right now that it must be kind of tricky to evaluate with the ISL shader like I have it, where the blend is controlled by the shading normal, cause how exactly would Indigo decide which bump to use to evaluate the normal?
But maybe there's another way to approach this?

[OnoSendai]

The bump mapping is blended in the same way that the colour is.

[Polinalkrimizei]

Remark from a technical dummy: Do your bumps have more or less the same heigth? If I mix two mats in my head, one with a very fine detailed strucure, and one with huge bumps, the one with the bigger (=higher) bumps will more or less override the other one when blended 50/50.
I am not at home in front of Indigo, but this should be quite easily tested...

[FakeShamus]

ok, this should demonstrate what I mean. again, taking the example of the snowy rock material. first image shows close up of the rock material basically by itself (snow cover parameter is set to 1.0, meaning no snow) you see the sharper, more detailed bump on the rock as expected. as soon as you begin to mix the snow into the material (anything less than 1.0 on the snow cover parameter) the softer, more blurred bump map takes over the whole material.

so ideally I would like to be able to see the softer bump just on the snow parts and the sharper bump on the rock parts. but as I mentioned I don't really know how this would work, seeing as how the bump is affecting the shading normal, and therefore the blend of the 2 materials - it becomes a chicken and egg situation: the bump affects the normal, which controls the blend, which determines the bump...etc.

so probably not doable in this situation, but I thought I'd ask about it anyway.

[OnoSendai]

Hi FakeShamus,
Thanks for the report.
I have improved this behaviour a bit. The pre-bump shading normal is now passed into the ISL shader (available as normalWS() ), to control the blending factor. This allows the effect you were going for, I think. (see image)
The changes will be available in 3.8.3.

cheers!

[FakeShamus]

yes! so awesome - thanks Ono!

[OnoSendai]

np