FPS Drop with Chaos Flesh in Unreal Engine 5 for Complex Mesh – Optimization Help Needed

Question

I'm working on a VR project using Unreal Engine 5 with Chaos Flesh for simulating a complex human body mesh. However, I'm facing a significant FPS drop when using Chaos Flesh.

Currently, my numcell count is set to 40, which I cannot reduce further because lowering it compromises the structure of the mesh. Reducing the solver iteration count from 5 to 1 temporarily boosted performance to 60 FPS, but this affects the simulation's accuracy.

Another optimization I tried was activating the Chaos Flesh mesh properties only when the player is near the mesh. While this helps with performance, I can't seem to deactivate the mesh afterward, as the calculations have already been executed.

Has anyone else faced similar performance issues with Chaos Flesh, especially with complex meshes in VR? Are there any other optimization techniques I can try without sacrificing too much fidelity?

Answer 1

I don't develop with Unreal, but I was curious about the feature you're describing, so I tried researching it. I couldn't find much official information from the Unreal team, but did find this staff tutorial. Note this passage in the tutorial:

While the current intention of the Chaos Flesh system is to provide highly accurate simulation results that can be cached and then used to train a GPU based ML-Deformer, the 5.2 release will also support in-game deformations of low resolution tetrahedron.

In other words, it sounds like the system is expected to have a high performance impact and is better suited for simulation which doesn't need to be rendered in real time, rather than for real-time use in a game or other interactive experience. That's in line with what I'd expect for this type of feature.

Combining Chaos Flesh with VR, which already has a high performance cost, sounds like a recipe for performance issues. Some possible solutions:

• Accept a compromise on visual fidelity to maintain stable performance in VR.
• Try training a GPU-based ML-Deformer as the quoted passage suggests. If properly trained, this in theory would allow for a good approximation of the simulation with a lower performance cost.
• If your application content is more or less fixed (e.g. Chaos Flesh is used during cutscenes where the character always performs the exact same animation(s) in the exact same way), look into whether it's possible to bake the flesh simulation into an animation so that the end-user's device doesn't need to run the simulation in real-time.