Unreal lightMass Broken on UE 5.1, 5.2 and 5.3 on M1 Mac?

[EmmadIlyas]

A few Days ago the Unreal Lightmass Failed on my UE 5.2 Build, I cloned and Built the latest 5.3 from code but I’m still receiving this message when I try to build the lighting

[SeriousIHitman]

This is because UnrealLightmass uses SSE instructions to create lightmaps which are not supported on ARM processors. Arm processors use NEON instructions that are not implemented yet in unreal engine as far as i know. To fix this error, you need to force build the lightmass for intel processors only.

Select the UnrealLightmass project and make these changes in the architecture tab in the build settings like on the screenshot.

Add the x86_64 in the project build settings

Add the x86_64 in ARCHS and VALID_ARCHS in the UnrealLightmass_Build build settings like on the screenshot

Build the UnrealLightMass and make sure that its building for the [Intel] and not [Apple].

After that build should be successful, run the editor and try to build lighting again, see if it works.

[dzeevg]

Thank you so much for this! I tried this fix but I’m still failing to build (MacBook Pro M1 Max Ventura)

Any ideas?? Did I miss something?

Log attached and here: Pastery - The sweetest pastebin in the world!

Thanks!

Build UnrealLightmass_2023-09-08T14-45-19.txt (82.5 KB)

[CosmicLobster]

@SeriousIHitman

x86_64

Worked for me, thank you very much!

(UE 5.3.1, Mac M chip, XCode 15.0.1)

[david.gillespie]

Has anyone tried this with Unreal 5.5 from Source on a M3 running Sequoia? I’ve built the intel version and still get “Lighting build failed” after exporting the scene completes in editor