UE5 "Exploding" Hair


https://forum.reallusion.com/Topic535847.aspx 		Print Topic | Close Window

By lightbearer - 2 Years Ago
I'm not sure how to solve this issue. The video below shows what's happening with standard cloth settings for hair. I have the same issue when I paint different weight maps and use the anim stiffness mask as shown on Reallusion's YouTube video. If I simulate the render and press play in the timeline, things work correctly. When I render with the legacy Movie Renderer things work fine, but when I use MRQ, the results are chaotic. Suggestions? Is there are a CVAR I need to use?
By StyleMarshal - 2 Years Ago
Did you try the cvar :  p.ChaosCloth.UseTimeStepSmoothing 0
Also AA can make trouble , especially the "Temporal Sample Count" should always be 1.

Here are 2 Sample Settings :

https://forum.reallusion.com/uploads/images/6b8fc15c-23f4-4996-a1b4-8687.jpg

https://forum.reallusion.com/uploads/images/0b001d05-43a6-41fe-986c-e00f.gif

and :

https://forum.reallusion.com/uploads/images/1c187eb8-85cd-4799-9f4e-a74e.jpg

https://forum.reallusion.com/uploads/images/a160190a-a32c-4fd2-a6e8-0f25.gif
By lightbearer - 2 Years Ago
Bassline303 (4/24/2023)
Did you try the cvar :  p.ChaosCloth.UseTimeStepSmoothing 0



I have not but surely will now. Thanks.
By lightbearer - 2 Years Ago
I swear this continues my love/hate relationship with UE - settings. Here's a "developer" link that talks about samples and the need to increase Temporal Sample Count for better motion blur:

Demystifying sampling in Movie Render Queue | Epic Developer Community (epicgames.com)

But that might be problem with the hair? I'm using CVARs from William Faucher's tutorial for AA and an odd number of temporal samples based on the article above. But, from your examples, it appears that is the issue (especially since the legacy render is fine, but MRQ shows "chaos"). 

Again, thanks for the heads up.
By StyleMarshal - 2 Years Ago

The Cloth simulation time step smoothing is interfering with the substepping fix for multi Temporal Samples by changing the very variable DeltaTime and causing some large errors in the cloth simulation due to increasing/decreasing convergence.

Simulating with p.ChaosCloth.UseTimeStepSmoothing 0 fixes the issue.

This Cvar needs to be added to the MovieRenderPipeline startup sequence to solve this issue for everyone.

Cloth or hair , it is the same Chaos Physics , Should be fixed in UE5.2 😁
By lightbearer - 2 Years Ago
Thanks for the help. I sincerely appreciate it.
By raitan2008 - 2 Years Ago
It is not fixed in 5.2