Static Foliage Lightmapping issue

Development Rendering
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1

When I rebuild lighting, the lighting on the foliage looks correct. So I save the map and close the editor.

When I reopen the map in another editor session, I notice that the lighting on the foliage is wacked out and looks like this:

[Image Removed]

So I don’t know what the problem is, for it to look correct when I save it but totally different and wrong when I load it, leads me to believe its an engine bug.

2

Steps to Reproduce
The attached static mesh FBX can be used to repro it.

Import it and set the lightmap index to 1 and the res to 128, turn of lightmap uv generation.

Add it to a map as foliage set to static so that it will get lightmap, add some static lights in the scene as well.

Build lighting and save the map, note how the lighting looks correct on the foliage.

Close and reopen the editor and the map, now note how the lighting on the foliage looks different and incorrect.

3

Hi,

Thank you for providing the FBX file to use for testing. Are you able to please provide the Material used in game and/or a minimal project that reproduces the issue. Also, a before and after screenshot would be beneficial to ensure we are experiencing the same results.

Kind Regards

4

Hi,

To attempt to reproduce the issue that you have reported I have performed the following steps in a launcher build of UE 5.5.4 :

  • Import the provided FBX file with ‘Source Lightmap Index’ set to 1, ‘Destination Lightmap Index’ set to 1, ‘Min Lightmap Resolution’ set to 128 and ‘Generate Lightmap UVs’ disabled.
  • Add the asset as Foliage via Foliage Mode
  • Paint the Foliage asset onto a Landscape
  • Build static lighting
  • Save the map and close down the editor
  • Re-open the editor

Following is a screen capture of my results:

[Image Removed]

I am currently unable to reproduce the results that you are experiencing. This could mean that our projects are out of sync, I have attached my test project for you to confirm the results at your end.

As a follow up question, does the issue still occur of you place the asset into a basic map with only a landscape and default lighting?

Kind Regards

5

I took the time to repro the issue with the mesh’s material unspecified making it use the default material, and it repros exactly the same, thus ruling out anything material related:

[Image Removed]

6

I’m just pinging this thread to keep it open.

I don’t have time to try to narrow down a repro for you any time soon. Part of the reason for posting was to see if anyone had a clue on how to narrow it down.

7

Hello there,

Is this happening on CPU Lightmass or GPU Lightmass, and are the Lightmaps using VirtualTexture?

Secondly, what hardware are you building on?

Best regards,

Chris

8

CPU lightmass, no.

The scene doesn’t have a landscape so no RVT either.

Our project configuration is basically UE4 features only, avoiding pretty much all UE5 rendering features, no nanite, no lumen.

In other words trying to keep it simple!

Ryzen threadripper 3970x and Radeon RX 7900 xtx

9

Is this a stock 5.5 engine? I’d like to rule out any changes to the way the lightmaps are being loaded. Potentially, clearing the DDC may also be worthwhile, but the Threadripper line are stable CPUs, so I’m doubtful over corruption there.

What settings are you using in WorldSettings for Lightmass?

I’m seeing some odd colouration, but nothing like the artefacting you mention. This may be due to the proximity of the cards to their rear-facing cards.

Best regards,

Chris

10

Having the same issue.

In my case, the baked foliage lightmap looks fine in editor, but totally a mess in playalone.

Any idea how to fix this?

Ps. Yes, all my foliages use the same lightmap uv for all lod.