Apex cloth and animated Morph Target mesh crashes UE4

I was trying to test clothing on a character with animated morph targets, but once I select an animation to play, Unreal crashes.
I tested two apex files- both made from the character with morphs (one was with the cut out mesh with the required material, the other was the full mesh), then I cross tested the apex files on the same character (one with morphs active in the animations, the other without) in UE4.9.2. The cutout apex worked on the non-active mesh and appear to work on the active morph mesh, but crash animation. The full mesh apex would compress the cloth to the origin on both meshes, but only crash when the active morph animated (it remained compressed for the non-active mesh during animation).
Hopefully there is a fix in the works?

Hi KMClough,

This is a rather isolated crash, but I’ve entered a bug in our system (UE-22446).

It has a much higher likelihood of getting fixed if we are able to reproduce it internally. Would you mind sending me a test project with the assets needed to reproduce the crash here? You can upload the files to a cloud service and PM me a link on the forums if you’re not comfortable attaching them here.


Thanks! I’ve sent the link in a message to you. I’ll keep working on finding a solution here as well.

I figured it out! It kept crashing because my blendshapes were affecting the same verts that the apex cloth was. Separating the cloth geo out as a different mesh and having the blends only on the body mesh solved it.
Thanks for looking into it, though!

Thanks for updating us. Wish I had been able to help sooner. The crash is still a bug, so I’ve attached the assets you sent to UE-22446 with some repro steps. That should help get a fix much quicker.

I didn’t see the crash in the latest version of the code. But it does look like the cloth graphics section is messed up. The underlying cloth simulation mesh (white wireframe) appears to be ok. (see attached pictures)

as you’ve already concluded, for any cloth vert that is simulated, dont have it affected by morphs. Additionally, for any fixed vert that is connected to any free cloth vert, be sure that these aren’t affected by morphs. Then it will be more likely that both codepaths for physx/apex simulation and graphics render path will be putting things in the same place. Also ensure that no skinned vertex (that is connected to cloth) is affected by more than 4 bones.