Lumen Hardware Raytracing with nanite and splitscreen

Development Rendering
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1

I noticed that hardware raytracing lumen reflection is now enabled even in splitscreen, since the github Commit 7dc6fb9. However when I try to run a 5.7 packaged game with nanite and lumen hwrt reflections, a lot of actors in the 3d view disappear. Is there any known issues?

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2

Steps to Reproduce
Enable lumen reflections with hardware raytracing in a scene with a lot of nanite meshes and start a splitscreen game on a packaged game.

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3

Hello,

This doesn’t appear to be a known issue. Does the mesh only disappear from reflections or disappear entirely? Does it only occur in splitscreen or outside of splitscreen also?

It’s possible the fallback meshes used for RT have been stripped in the shipping build and is causing them to disappear but that’s just a guess, we’ll need more details, or a sample project with a repro to make sure we’re using the same settings. bGenerateNaniteFallbackMeshes controls whether those fallback meshes are generated/stripped.

By default Lumen just supports 2 views in splitscreen - see LUMEN_MAX_VIEWS in Engine/Shaders/Shared/LumenDefinitions.h and we haven’t tested more than 2.

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4

Hello,

Apologies for the delay. I’ve been unable to reproduce this error in a UE 5.7 first person template with r.SplitscreenDebug.Enable 1. Does the issue only occur in a packaged game, or does it also occur in PIE when using the game client?

If you’re able to provide a simple repro project that would help us troubleshoot the issue further.

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5

Thanks for providing the project to reproduce the issue, we’ve got a fix in testing and will provide an issue link for tracking likely tomorrow.

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6

Here’s the issue link for tracking: https://issues.unrealengine.com/issue/UE\-380600, it should be visible soon and the fix changelist is 54263913 in the 5.8 release branch and will be merged to //UE5/Main later.

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7

Meshes disappear from both 2-players main 3d views. Skeletal meshes are correctly rendered. This happens on 2 players mode only (I don’t know if the issue is on 3/4 players too).

I may try to ask about a small repro project, but I think it will be a bit difficult to create it.

Thanks.

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8

I attached a small project

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9

To add more context, we managed to reproduce the issue by adding several niagara mesh emitters in the scene, in a project based on the Third Person template.

Upon opening the project linked above (built with Unreal 5.7.4 as available on the Epic Games Launcher) and hitting the play button you should see a situation similiar to the following: the only changes we made to the level are that:

  1. we added several Niagara systems to the level;
  2. the level’s level blueprint is setup to to spawn a second local player at BeginPlay;
  3. the level’s Tick resets the particle systems every 3 seconds by calling each NiagaraComponent’s Activate()

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The issue does not appear if we set r.RayTracing.Geometry.NiagaraMeshes to 0 before starting a play-in-editor session

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