Volumetric Fog causing Black Artifacts around Mesh Edges

Development Rendering
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1

I got this issue when rendering cinematics. The volumetric fog is causing these strange jittery black blobs around edges of meshes that are close to the camera (left side of the stone edges). Spent hours trying to fix it, but nothing helped so far, apart from just deactivating volumetric fog, which isn’t really a solution. Increasing the volumetric quality just slows down rendering but doesn’t really make it much better.


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1698×633 49.2 KB

I’m on 5.5.
Any ideas?

2

Hi @srswntr,

Could you try using the following cvars and see if it avoids that bug?

  1. r.VolumetricFog.ConservativeDepth=0
  2. r.Forward.LightGridHZBCull=0

It would be great if you could also provide some more info to help identify the root cause:

  1. Are you able to reproduce with a static camera or only when the camera is moving?
  2. Is the volumetric fog in that area affected by local lights or only the directional light?
  3. Is this project using MegaLights?
  4. If the cvars prevent the issue could you check whether you need both to fix it or just one of them is enough, and if so which?

Or even better if you are able to share a project that reproduces the issue with us for further debugging and addressing the issue.

Thanks!

3

Thanks for your answer and suggestions.

I’ve tested it with both commands, the issue still persists.
It definitely only happens with the camera moving. I’ve tried it both with local lights included and not, no effect on the issue.
MegaLights are used, but have no effect on it, if turned off. I struggled with the very same issues back with UE5.3 already. Made a thread back then already as well, no one knew a working solution: Weird shadowy blobs around mesh

I found this official thread, which I believe is about that exact issue.

The suggested workarounds in there didn’t do much for me either though.
“Our study concluded that the most effective solution to this problem is to switch from Lumen to Ray Tracing GI lighting” - I wouldn’t even know if this is still possible to do in 5.5, global illumination method of “ray tracing GI lighting” isn’t listed as option in my project settings.

Here are two more displays:

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11920×1056 125 KB

2
21920×1056 113 KB

I can literally watch the black areas disappearing in viewport, by going from one frame to another.

4

This is a huge general volumetrics issue, I’m having trouble believing that it seems to be of no priority at all…

5

@srswntr are you able to share a small project that reproduces this issue for further investigation?

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I will try to do so whenever I find the time. But it really shouldn’t be hard to reproduce in my opinion, it seems like a very widespread, common volumetric fog issue.