MatX Furnace Test

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I've set up a furnace test between Karma/MatX and Octane/Universal material, with varying results. The most disappointing for me is the all-important micro-surface test with normal map, which MatX didn't do very well on. All images have a default of Diffuse = 1/Spec = 1 - with additional channels added or removed as needed.

Baseline diffuse 1/spec 1 Note: we can see Karma MatX outline here in the base test.
Edited by Danny McGrath - 2024年7月22日 09:31:13

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diffuse_spec1.jpg (360.3 KB)

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Metalness = 1

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diffuse_spec_M1.jpg (354.1 KB)

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Metaness =1 Roughness = 1

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diffuse_spec_M1R1.jpg (363.5 KB)

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Normal map micro-surface

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diffuse_spec_normalmap.jpg (355.0 KB)

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Normal map Roughness = 50%
Edited by Danny McGrath - 2024年7月22日 09:28:26

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diffuse_spec_normalmap_R05.jpg (368.4 KB)

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And for an additional direct comparison, this is normal map + Roughness = 50% using the Octane Standard Surface Material

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diffuse_spec_OR_SS_NM_R05.jpg (195.5 KB)

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Roughness = 1 Metalness = 0

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diffuse_spec_R1M0.jpg (358.6 KB)

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And finally this is with all 3 spec layers at 1: spec/coat/sheen

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diffuse_spec_S1C1.jpg (358.2 KB)

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Overall, I think MatX performed very poorly. This has been a known issue in Arnold for quite some time,due to Standard Surface Material leaking energy because of the lack of multiple scattering reflections and the use of classic normal mapping. These issues have possibly carried across to MaterialX? Even Blender at this stage has implemented multi-scatter GGX. Hopefully this will be improved in futures versions of MatX.
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Currently, the Rombo 3rd-party Arnold material is the only model I know of that implements microfacet normal mapping, based on this paper. I expect Octane does too, based on the results above.

https://www.researchgate.net/publication/321233843_Microfacet-based_normal_mapping_for_robust_Monte_Carlo_path_tracing [www.researchgate.net]
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In the meantime, I've found this in the docs, so I'll run the test again. Great news if this is what I hope it is.

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It turns out that XPU doesn't support building your own materials from the BSDF nodes. They only render on CPU.

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diffusesp.jpg (165.0 KB)

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The result using the Schlick BSDF - diffuse/spec/metal + normal map

This result is better than MatX Standard Surface, but still quite a way off the Octane Universal Material.
Edited by Danny McGrath - 2024年7月22日 12:46:51

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diffuse_spec_schlick.jpg (135.3 KB)

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