How to create cavities?

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Hi all,
I’m a relative newcomer to Houdini (after a few years away) and although I’m getting back into a lot of areas I’ve a roadblock.
I’m trying to work out how to create a particular look, where the outmost parts of an object have one material but recessed and cavities have another. See attached as an example. Basically a tortoise shell kind of thing.

Any ideas to point me in the right direction?

Cheers all.

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363520B5-9BFA-4C08-8484-88DCF3491151.jpeg (99.8 KB)

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If you have “cutter” geometry that has a different material than the core geometry, the new Boolean SOP can transfer the shop_materialpath and uv attributes correctly. People have done a bunch of neat things with that sort of approach, so it might be helpful in your case.
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Thanks for that!
Would this work for using meshes generated by vdbs?
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Boolean works on any polygons, so as long as you convert the relevant VDBs to polygons, (e.g. using Convert VDB set to convert to polygons), it'll work.

If you're already working with SDF VDBs, though, you could alternatively use VDB Combine with Operation set to SDF Union, SDF Intersection, or SDF Difference. However, then transferring attributes (like shop_materialpath and uv) afterward would be very difficult. Boolean is often good for avoiding going through VDBs for a bunch of modelling operations that people would have done with VDBs before we had a robust Boolean.
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Thank you. I think maybe I wasn’t clear in my question.
I’m pretty happy using polygonal Boolean and vdb combines.
My real issue is possibly more shader based.
In the image it’s the gold areas I’m trying to replicate. Is there a way to make a selection based on cavities/recesses sovthat I can apply a different material?
Or, in that image is it more likely to be a noise driving a displacement and the same noise masking the gold?
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pariahrob
Is there a way to make a selection based on cavities/recesses sovthat I can apply a different material?
I'd recommend applying the material to the cutting geometry, then do a Boolean, so that you don't need to figure out how to select those polygons after the fact. It'll automatically transfer the shop_materialpath attribute correctly.

Alternatively, if you have to do material assignments afterward, you can create a different primitive attribute or group on the cutting geometry, then do a Boolean, and apply the material afterward based on that attribute or group.
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Do you have a new publication in Patreon [twitter.com] from Entagma, and I think they explain that process. I haven't seen it yet. I've been curious about how to do it.
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