Maniphest T98062

Particle Hair Physics - 30 fps vs 60 fps produces very different physics
Confirmed, Normal
Actions

Assigned To
None
Authored By
Charles (mtoronto)
May 12 2022, 2:19 AM
Tags
  • BF Blender
  • Nodes & Physics
Subscribers
Charles (mtoronto)
Omar Emara (OmarSquircleArt)

Description

System Information
Operating system: WIN 10
Graphics card: 3080 TI

Blender Version
Broken: 3.0.1, dc2d18018171, master, 2022-01-25
Worked: N/A

Short description of error
Baking particle 'hair dynamics' physics in 60 fps does not produce same physics results as 30 fps. Hair barely moves in 60 fps.

Exact steps for others to reproduce the error

hair_30fps.blend4 MBDownload

Open hair_30fps.blend
Bake hair. Go to frame 18 and place 3d cursor on furthest movement of hair. Note location of 3d cursor to compare later.
Scale Bone keyframes x2 in dope sheet
Change timeline range to 0-48
Change FPS to 60
Change hair's particle baking range to -24 to 48 (with disk cache enabled, so that frame 0 can bake)
Bake hair. Go to frame 36 and place 3d cursor on furthest movement of hair, compare to previous.

You will notice that the hair barely moves when baked in 60 fps, it does not receive the same physics as 30 fps does.

Example pictures below, pay attention to location of 3D cursor.

30 fps, frame 18:

60 fps, frame 36:

Related Objects

Mentioned Here
T68627: Simulations do update animations on frame rate change
rBdc2d18018171: Bump version to 3.0.1 release

Event Timeline

Charles (mtoronto) created this task.May 12 2022, 2:19 AM
Charles (mtoronto) renamed this task from Particle Hair Physics - 30 fps vs 60 fps produces different physics to Particle Hair Physics - 30 fps vs 60 fps produces very different physics.May 12 2022, 2:22 AM
Charles (mtoronto) updated the task description.
Charles (mtoronto) updated the task description.May 12 2022, 2:48 AM
Charles (mtoronto) updated the task description.
Omar Emara (OmarSquircleArt) changed the task status from Needs Triage to Confirmed.May 12 2022, 9:08 AM
Omar Emara (OmarSquircleArt) added a project: Nodes & Physics.
Omar Emara (OmarSquircleArt) added a subscriber: Omar Emara (OmarSquircleArt).

I can confirm the difference even with half the simulation steps for the 60 FPS cases to avoid divergence issues. The simulation should be independent of the FPS. Maybe related to T68627.