Particle Hair Physics - 30 fps vs 60 fps produces very different physics #98062

New Issue

cmto · 2022-05-12T02:19:00+02:00

cmto commented

2022-05-12 02:19:00 +02:00

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

Blender Version
Broken: 3.0.1, dc2d180181, 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.blend
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:

**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.blend](https://archive.blender.org/developer/F13069718/hair_30fps.blend) 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: ![b2949a82e9dae85e9e51e91c21fc57b830223bc4_2_323x500.jpeg](https://archive.blender.org/developer/F13069719/b2949a82e9dae85e9e51e91c21fc57b830223bc4_2_323x500.jpeg) 60 fps, frame 36: ![8965a14ab7189757bc237c98dbafb0b51d866ba0.jpeg](https://archive.blender.org/developer/F13069721/8965a14ab7189757bc237c98dbafb0b51d866ba0.jpeg)

cmto commented

2022-05-12 02:19:00 +02:00

Added subscriber: @CHARLES-MURRAY

cmto changed title 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

2022-05-12 02:22:46 +02:00

Omar Emara commented

2022-05-12 09:08:30 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-05-12 09:08:30 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Omar Emara commented

2022-05-12 09:08:30 +02:00

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 #68627.

Philipp Oeser removed the

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Particle Hair Physics - 30 fps vs 60 fps produces very different physics #98062