UE5.6+ - Mutable - IDPrefix crash when combining Child Objects, Add to Mesh Component and Extend Mesh Section.

Development Programming & Scripting
, ,
1

So the issue seems to be a combination of Add To Mesh Component and Extend Mesh Section.

I’ve tried this in Epic Launcher 5.6, 5.6 in-house modified engine as well as ue5-main 5.7 from git (editor built 14th of July) and they all produce the same crash.

This seemed to work perfectly fine for us in 5.5.x

The repro-steps I provided does stack 2x of LOD0 Section 0 of Manny but that isn’t important. In a normal use-case, you’d use multiple meshes sharing the core skeleton but for simplicity of the repro I stuck to only using Manny.

2

Steps to Reproduce

Reproduction Steps:

Should only need Third-Party Template, base Mutable plugin loaded and no specific changes to the editor.

You will need at least 2 Customizable Object (CO) graphs, with one being attached to the other.

In my example setup, I got the following COs:

  • CO_Parent (aka. Parent)
  • CO_Child (aka. Child)

For skeletal mesh, any should do but for this example I use SKM_Manny_Simple as the Skeleton Reference as well as the Skeletal Mesh.

Setup Parent graph:

  1. Add and wire up the following nodes:
    1. Mesh Component
      1. Name: MC_Parent
      2. Reference Skeletal Mesh: SKM_Manny_Simple
    2. Mesh Section
      1. Material: Any (e.g. WorldGridMaterial)
      2. Enable Tags: MyTag
    3. Skeletal Mesh
      1. Mesh: SKM_Manny_Simple - Mesh section: Any (e.g. LOD0 Section 0)
    4. Object Group
      1. Name: IN_Child
      2. Type: All Options

Setup Child graph:

  1. Add and wire up the following nodes:
    1. Add To Mesh Component
      1. Component Name: MC_Parent
    2. Mesh Section
      1. Material: Any (e.g. WorldGridMaterial)
    3. Extend Mesh Section
      1. Required Tags: MyTag
    4. Skeletal Mesh
      1. Mesh: SKM_Manny_Simple
      2. LOD0 Section 0 to Mesh Section
      3. LOD0 Section 1 to Extend Mesh Section
    5. Attach the Base Object, named OUT_Child, to the IN_Child Object Group within Parent.
    6. Compile
    7. Crash

Note:

3

Hey there,

Can you send along your test files? I’m unable to repro your issue even with the images and repro steps. There were some changes recently, but as you say you’re getting source from July 15th, we made those changes on 5-29 and 5-21 respectively. My goal is to get a good repro over to the the dev team.

[Content removed]

Dustin

4

Sure, give this a go. This was packaged from base UE5.6 from the launcher.

It should just crash when opening CO_Parent in the root Content folder.

Thanks for having a look!

5

Thanks,

This repro here as well. I’ve logged an issue that you can follow: https://issues.unrealengine.com/issue/UE-306133. I will say it is not typical to have the case where the child CO trys to add the same mesh (LOD0 of simple manny in your test case here) to the parent. Are you seeing this in your projects and are your CO’s trying to do this action?

Dustin

6

No we’re not merging the same mesh multiple times (LOD0 as you mentioned), that was only to simplify the setup with as few meshes as possible as well as using UE native skeletal meshes. It still caused the same crash so I figured it was easier to set it up that way.

The action however, of having other skeletal meshes in child objects getting added to a component that lives outside of the child-graph as well as extending to mesh section that lives in other object(s) is something we’re doing (and have been doing successfully pre-5.6)

7

Yep understood. the team is looking at the issue but I don’t have a resolution yet. I’m going to mark this case as pending for now. I’ll let you know once I have more info.

8

Hey there,

This cl from github has the fix.https://github.com/EpicGames/UnrealEngine/commit/0bd4e6208fc40ed83d350eb4c2caa3116a9ff981.

The CO, will need to be recompiled afterwards.

Dustin