"Sprouting Arms" animation for an UE5 game asset

Question

I'm making an entity for a game in Unreal Engine 5, it's basically a floating paiting that sprouts arms, I need to be able to do 2 things:

1. Have the arms drift out of the painting and have them both be part of the same object, the problem here is that I don't know how the armature would behave for that since the arm bones and painting frame are both parented to the root bone.

2. Hide the parts of the arms that would be "behind" the painting, the frame is too narrow to fit the arms inside and scaling the arms in a shape key doesn't work when the arms are posed. I also don't know if I can use a boolean to bake the animation with.

Whatever method I can use to accomplish this must be exportable to Unreal, and must be real time (not in a cinematic).

The Cephalos sprouting out of bodies in Resident Evil 5 are an example of this effect done perfectly.

Answer 1

Modifying a mesh on the fly as you do with the boolean modifier isn't something that can be exported as is.

If you really want to export a mesh being cut like this, AFAIK the only option is to export it into alembic. That's the standard industry format for physic simulations, among other things. Though it's essentially taking snapshots of your mesh at each frame and exporting shapekeys out of it, so it will be heavy.

The other - probably - lighter non-destructive way is to just export your full mesh as is, and then make a shader in your target renderer that fades into transparent at a specific position in space.
I don't think it is something that can be exported from Blender, so you will have to refer to Unreal Engine 5's documentation for that. But it's nothing unheard of.