HISM flickering when any character is visible

Development Rendering
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1

Hello,

since updating from UE 5.4 to UE 5.6 we’ve an issue with flickering HISM objects when some character is visible. The characters are Metahumans. It only appears for some LODs of the characters. You can find a video in the attachment.

What can be the reason for these flickerings? Is there anything we can try?

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2

Hello,

Thank you for reaching out.

I’ve been assigned this issue, and we will be looking into the HISM flickering for you.

Can you please send us a minimal test project that demonstrates this flickering, and include a recording from that test project?

The guide for test projects:

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3

Hi,

I’m Max trying to figure out the issue together with Mathias.

As I also saw a report on the unreal forums Instanced Static Mesh + Groom Flickering we were hoping that a similar issue might have already been encountered.

We’ve narrowed it down to some LOD’s of our Groom components and that it also happens in PIE. I’ll try to make a reproduction but any hints as to how to find what could cause this would be appreciated.

Regards,

Max

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4

After realizing the error also occurs without PIE, I’ve discovered that disabling RBF Interpolation on the groom asset seems to fix the issue. Unsure how that is related to HISMs.

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5

Hello,

We attempted to reproduce this based on your description, and could not. Thank you for working on a reproduction case - it will make it much easier to investigate on our side.

A few questions to help us understand the issue better:

  1. Can you please check if disabling “r.CullInstances” prevents the issue?
  2. Is the LOD on the Groom asset a Strand, Card, or Mesh LOD?
  3. Is the flickering applying to Nanite, non-Nanite, or both types of meshes in the HISM?
  4. Does the flickering happen with a regular ISM as well?

Please let us know if this helps.

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6

Hi,

  1. r.CullDistances 0/1 has no effect.
  2. In my current test case it only happens in Mesh LODs, though I’m pretty sure I had it with cards as well.
  3. We have Nanite disabled in our project. A quick test shows that ISMs with nanite do not flicker.
  4. yes

I’m looking into creating a test project, however I wasn’t able to reproduce in a first attempt where I stripped almost all assets except the hair. Will try again next year.

Regards,

Max

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7

Hello,

We were still unable to reproduce the flickering with this extra information. We have a couple more questions to narrow it down further, and they might also help you create a reproduction case:

  1. Does the Groom component cause the flickering with or without a binding to a skeletal mesh, or both?
  2. Does the bound skeletal mesh (if needed) have to be animating to cause the flickering?
  3. Are any of the objects involved (groom, skeletal mesh, and ISM) using World Position Offset in the relevant Materials?

To clear up one thing, the CVar we mentioned above is “r.CullInstances”, not “r.CullDistances”. Can you confirm the test you performed used “r.CullInstances”? Thank you.

If this ticket auto-closes before the new year, feel free to reopen it by replying.

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8

Hi,

  1. groom alone does not cause the flickering
  2. no, happens in editor without PIE or simulate
  3. They do in our case, but its not required to reproduce the issue

Double checked. r.CullInstances 0/1 does not have any effect.

I’ve also managed to finally create a reproduction case. To reproduce load the test map and look at the instanced cubes and the character. Then move backwards until the cubes flicker.

Had to copy over our defaultengine.ini so likely there is a setting that causes this to appear.

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9

Hello,

Thank you for reporting this. I can confirm this issue can be reproduced as described in the latest CL, and have opened a bug report:

The tracker will be visible after it is approved internally at Epic Games and is publicly accessible.

If you have any further questions, please let us know.

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