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I'm trying to create a 'spiderwebbing' / 'swirl' effect caused by microscratches around highlights, but for some reason get triangular rays instead of a round halo. I've tried loads of scratch textures and they all have the same problem, even with different sizes/strengths.

The only solution I've found is to use a normal map instead of bump, which isn't ideal as I would need UVs for 100+ objects (or find a way for triplanar normal maps). I've seen other people create this effect with just a bump map, in cycles as well as some other render engines. One solution I've seen for 3dsMax/Vray was to change the "bitmap filtering to Pyramidal or Summed area", but changing Blender's texture filtering doesn't do much (it fixes for eevee, but not cycles).

(The screenshot is slightly exaggerated, but the rays appear with any bump value or texture size. From 2.92 cycles viewport)

EDIT: New images to show difference between normal and bump map. Both use the same texture and mapping setup:

Thanks for any help or tips you can offer

Using bump map: weird triangular highlights with bump map

Using normal map: correct highlight flow with normal map

Nodes: node setup for both normal and bump maps

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    $\begingroup$ Maybe it's aliasing in the height->normal conversion? (which AFAIK is a convolution) And maybe procedural scratches wouldn't have that, no pixels? I'll give it a shot, if no one else does first. $\endgroup$
    – Robin Betts ♦
    Commented Mar 4, 2021 at 21:07
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    $\begingroup$ I revisited an old attempt at procedural microscratches, and the distorted highlights are still there. Its a shame normal maps can't be procedural, it could just be that bump maps arent detailed enough $\endgroup$
    – stack64
    Commented Mar 5, 2021 at 21:04
  • $\begingroup$ .. contemplated procedural normal maps, but the result of height-normal conversion on my procedural height-scratches was exactly what I would have done for normals, and it didn't work. Now having a look at this approach, but using nodes. This changes roughness and anisotropy within the scratch-mask, rather than directly generating normals. $\endgroup$
    – Robin Betts ♦
    Commented Mar 5, 2021 at 21:24
  • $\begingroup$ That might be the solution. I've already done some tests with anisotropy for scratches, and the results are promising. Luckily there's a ton of resources for this online, and someone has even made it in blender. Thanks $\endgroup$
    – stack64
    Commented Mar 6, 2021 at 10:07

1 Answer 1

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I would reccomend trying to change your bump node settings. Set the strenght to 1 and the distance to 0.01 or anything sutable. Try to mix the displacement with the normals also. Attached below is an example low strength vs low distance.enter image description hereenter image description here

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  • $\begingroup$ Thanks for the tip, but sadly it doesn't solve the problem. The repeated/triangular highlights are still there, just a bit smaller. I'm not sure if this effect is even possible with a bump map anymore, at least not in cycles :/ $\endgroup$
    – stack64
    Commented Mar 4, 2021 at 13:41
  • $\begingroup$ Oh. Maybe it is a bug. Can you share your .blend file and textures? Maybe it is a problem in the displacement map. $\endgroup$
    – Yousuf Chaudhry
    Commented Mar 4, 2021 at 16:24
  • $\begingroup$ Here's one of the textures I've used, which causes the same problem: s3-us-east-2.amazonaws.com/rendermedia/wp-content/uploads/2018/… So far all the textures I have used/created have the same problem, unless converted to a normal map. $\endgroup$
    – stack64
    Commented Mar 4, 2021 at 19:01
  • $\begingroup$ @stack64 The texture you have attached actually has a lot of repeating triangles. Maybe those triangles are meant to be there, and if not sometimes you can skip the displacement because you have the normal map. Just as an experiment, try to mix the normal map with the displacement map by plugging the normal map node into the normal input of the bump node and the displacement map into the height input of the bump node. Set the distance to whichever is suitable for you (0.1 or 0.01 is best) and then connect the bump node into the normals input of the Principled BSDF $\endgroup$
    – Yousuf Chaudhry
    Commented Mar 5, 2021 at 5:41
  • $\begingroup$ You're right that texture isn't great, but even seamless textures from Substance Designer have the same problem. I tried mixing the normal and bump nodes, but without UVs the highlights are still broken. Thanks for the suggestion $\endgroup$
    – stack64
    Commented Mar 5, 2021 at 8:38

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