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Fredi Walker avatar image
Fredi Walker asked ·

Creating anisotrophic scratches/spider web scratches?

Wondering how to recreate this effect in MtoA. Any clues?

shaderslightshading
swirlines.jpg (255.2 KiB)
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Zeno Pelgrims avatar image
Zeno Pelgrims answered ·

Directly quoting Lorne here, but note that it is for alsurface which has different ranges for the anisotropy parameters.

"Shader time...I'll go full details here since you guys might want to try this out for yourselves.

  • Bring in the <scratch.exr> map, set the mipmap bias to -10 or just turn off filtering, and you'll want to tile it a bunch too.
  • Multiply it by 0.5, because right now it's between -1 and 1...but those would rotate the anisotropy a full 180 and we only want 90. You could also have just done this in Houdini before rendering so it's baked in. Plug this in to your specular2_anisotropy_rotation (leave specular1 free as a clear coat).
  • Do a fit range on the alpha channel from <scratch.exr> so that it's between 0.5 and 1. Plug this in to your specular2_anisotropy.
  • Set your specular2_roughness to ~0.1
  • Set your specular1_roughness to ~0.06
  • Let it rip!"

As for the image, here's a new link, looks like the one he posted expired: https://www.dropbox.com/s/sim6ts2935dj8fj/scratch_test_v010.exr?dl=0

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Lee Griggs avatar image
Lee Griggs answered ·

OSL shader examples here.

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Mr Baiking avatar image
Mr Baiking answered ·

What those math node doing ? can adopt to any scratch map?

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Fredi Walker avatar image
Fredi Walker answered ·

Thank you for the answers, everyone.
@Zeno Pelgrims that's exactly the result I'm looking for. I already tried the high frequency bump map route but like you said the AA was getting hefty. I'd really like to see what Lorne Kwechansky came up with. (But the dropbox link doesn't seem to work. Could be permissions?)

Just one question, I assume the +1 and *0.25 is to normalise the specular rotation?

Also, great work on POTA ;)

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Zeno Pelgrims avatar image
Zeno Pelgrims answered ·

This is a technique Lorne Kwechansky shared on the mailing list somewhere last year, adapted for the standard_surface shader (his was for alsurface, RIP). In my opinion this is the best approach I've seen so far, using the anisotropy instead of relying on high frequency bump maps which need very high AA levels to clear up.

You can push this much further for metals (increase the outputmax value), this is just for a latex material I was working on.

The scratch map he created by scattering curves in Houdini can be found here: https://www.dropbox.com/s/sim6ts2935dj8fj/scratch_test_v010.exr?dl=0


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Girijashankar Senapati avatar image
Girijashankar Senapati answered ·

once you done with the brushed metal, assign a scratches texture map to specular roughness through blend colors.

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rachid Hadj Abderrahmane avatar image
rachid Hadj Abderrahmane answered ·
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