Arnold for Houdini 5.5.1: subsurfacce + displacement + bump?

[lumogas]

Hi, I have no problem getting the Standard Surface to render with a bump map (RGB), ditto displacement, but once I turn on SSS to 1, the bump map vanishes (displacement stays). If I set SSS to, say 0.85, I get some bump. I would prefer to keep the SSS at 1.

Am I supposed to get any surface normal alteration exclusively through displacement when I use full SSS on the Standard Surface?

Apologies if it's a known thing, I remember being able to get bump and displacement with Maya. Reposting the question.

[lee_griggs]

I see some bump with sss_weight: 1. It is more noticeable when it is lower than 1.

Is autobump enabled?

Can you post some images?

[lumogas]

..thanks for the reply. I enclose an image. The one on the left has SSS set to 0.85. The one on the right has the exact same settings, bump + displacement, but the bump map is no longer visible. The SSS is at 1.

Except for colour and maps (both procedural, in this case) the SSS settings are default.

I also enclose the sample file as an attachment. I can probably hack a map that combines the bump into the displacement, but I don't want to have to crank the subdivisions so high to get the extra detail. In the sample autobump is off, but I have not noticed a difference when I switch it on.

Thanks again.

bump_disp_example_to_send.zip

[lee_griggs]

Have you tried this?

[lumogas]

Thanks for the quick reply. That link is for Arnold for Maya. Where do I find that toggle in HtoA?

I have not been able to find an "sss use autobump" toggle in HtoA.

I have enabled this, on the "obj" context:

...but the bump remains invisible once I set SSS to 1.

[Stephen.Blair]

You use the User Options like this:

[lumogas]

Thanks for the answer. Interesting to discover that setting. Unfortunately, the results don't change, more's the pity.

The odd thing is that I don't recall having this problem in Maya. I would need to crank the subdivisions very high to get that detail in displacement, which will make the render even slower.

Anyway, here's a picture, SSS at 0.85 on the left, SSS at 1 on the right, new setting active. The problem is that lowering SSS to 0.85 on the actual mesh I want to render radically changes the appearance, which is not what I want.

Thanks again for your help. I also enclose the sample file, just in case.

bump_disp_example.zip

[thiago.ize]

Are you using autobump (displacement does the bump) or are you manually applying a bump map. I suspect only autobump supplied bump would work?

[lumogas]

Yes, Thiago, I'm aplying a bump map separately. Your observation is interesting, since I had also understood that "autobump" was a way of getting the displacement to offload extra detail onto a bump map, as it were, as opposed to getting the SSS to accept independent bump maps on top of the displacement.

So I'm guessing, the answer is, currently, on Arnold SSS at 1 and bump maps, is a no?

[thiago.ize]

right, autobump will apply the rest of the displacement onto the triangle faces as a bump (the triangle vertices were displaced, but inside the triangle it's of course still flat). SSS+bump is only enabled for the autobump case and then only if you toggle that special flag.

The only workaround that I can think of at the moment is to move your bump into the displacement slot.