Merge Actors (Simplify) is broken with Substrate Shader Models Node

Development Asset Creation
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Material Baking is not working with Substate authored materials, as used by the Mesh Simplify pipeline, including HLOD.

You need to use the Substrate Shading Models node to see this artifact.

Base Color, Roughness, Metal, Specular and Opacity render out as Black

Normal renders ok!

Simplification is the only HLOD poly-reduction scheme giving us good silhouette, and having no materials is not allowing us to use that.

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Steps to Reproduce
In the attached ZIP file you will find a minimal Unreal Project to exhibit this issue.

- In the root folder is the level L_MergeTest

- This contains two cubes

- One cube is mapped to the material M_Legacy

- The other cube is mapped to the material M_Substrate

- Select both cubes

- Select Tools -> Merge Actors -> Simplify and choose the defaults and save your merged static mesh somewhere

- Observe that only “Normal” is saved from M_Substrate

- Base Color is black, (as are Metal, Roughness, Specular, Opacity if you choose to render them)

The only difference between these materials is the use of the Substate Shading Models Node

This project is a default UE5 project, with r.Substrate=True added to the DefaultEngine.ini

We are blocked from making HLOD with Substate in 5.6, as Simplify is the only poly-reduction that is doing a good job of decimating our world.

I have verified this issue is still present on Epic’s //UE5/Main/…@46012423

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Hello,

Thank you for reaching out.

I have been assigned this ticket and will be looking into the merge actors issue for you.

Have you also tried the “Approximate” setting in the merge actors and HLOD settings?

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Hey Kevin, fancy finding you here!

Thank you for getting back to me.

I can confirm that Mesh Approximation is producing a baked material with the same in-game geometry; fascinating!

Where do those two pipelines diverge?

I’ve done a pile of bakes today, and I have some settings which unblock our HLOD pipeline on Approximation. I’m not actually sure what the difference is between these two any more, as they both voxelize - I think it’s just termination rules.

I see over the weekend that Substrate is moving to production in 5.7. Can we get the Simplify fix into the Release please?

Cheers

Andy

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We could not open the assets in your test project within a vanilla version of 5.7. I am thinking there might be an engine version mismatch there.

However, we were able to reproduce the issue in 5.7 as well using a minimal test project of our own.

I will create a bug report for the issue and get back to you with a tracker once it is made.

Please keep in mind, we cannot provide an ETA for the fixes.

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Thanks Kevin for the follow-up.

I’m pretty sure those assets were against //UE5/Main/…[Content removed] and therefore notionally 5.8.

I’m glad the repro steps were enough for you to make your own version.

Cheers

Andy

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Here is the public tracker link for the bug report: