Cloth simulation randomly breaks down when scrubbing timeline #99913

New Issue

Alexander · 2022-07-22T14:54:41+02:00

Alexander commented

2022-07-22 14:54:41 +02:00

System Information
Operating system: Ubuntu 20.04
Graphics card: Geforce MX230

Blender Version
Broken: 3.2.1
Worked: (newest version of Blender that worked as expected)

Short description of error
When scrubbing the timeline , the cloth simulation may cause the mesh to become distorted even with the existence of cache. The video below will show a quick way to break the simulation, however, I first stumbled upon the problem when I set the keys for the bones.

2022-07-22 15-48-43.mp4

Exact steps for others to reproduce the error

Create cloth simulation.
Scrub the timeline. After some time, a situation will arise where the mesh will be distorted.

**System Information** Operating system: Ubuntu 20.04 Graphics card: Geforce MX230 **Blender Version** Broken: 3.2.1 Worked: (newest version of Blender that worked as expected) **Short description of error** When scrubbing the timeline , the cloth simulation may cause the mesh to become distorted even with the existence of cache. The video below will show a quick way to break the simulation, however, I first stumbled upon the problem when I set the keys for the bones. [2022-07-22 15-48-43.mp4](https://archive.blender.org/developer/F13308149/2022-07-22_15-48-43.mp4) **Exact steps for others to reproduce the error** 1. Create cloth simulation. 2. Scrub the timeline. After some time, a situation will arise where the mesh will be distorted.

Alexander commented

2022-07-22 14:54:41 +02:00

Added subscriber: @sanek2005

Omar Emara commented

2022-07-22 15:31:34 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-07-22 15:31:34 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Omar Emara commented

2022-07-22 15:31:34 +02:00

I can't replicate the issue on a simple cloth simulation I created. Can you attach this particular file?

Alexander commented

2022-07-22 15:46:24 +02:00

flag_canat.blend
I noticed that this bug is faster and more noticeable on my file. again, I repeat, the error happens absolutely by accident, it may take some time to reproduce it

[flag_canat.blend](https://archive.blender.org/developer/F13308284/flag_canat.blend) I noticed that this bug is faster and more noticeable on my file. again, I repeat, the error happens absolutely by accident, it may take some time to reproduce it

Omar Emara commented

2022-07-22 16:07:08 +02:00

Changed status from 'Needs User Info' to: 'Confirmed'

Omar Emara commented

2022-07-22 16:07:08 +02:00

I can reproduce, though it very unreliably and requires multiple tries to reproduce.

Omar Emara changed title from ~~cloth simulation randomly breaks down when manipulating timeline~~ to Cloth simulation randomly breaks down when scrubbing timeline

2022-07-22 16:08:51 +02:00

Lukas Tönne commented

2022-08-01 12:30:11 +02:00

Added subscriber: @LukasTonne

Lukas Tönne commented

2022-08-01 12:30:11 +02:00

This seems to be a problem with the point cache mixing up the two cloth sim objects in the scene. One of them has a cache length of 100 frames, the other has 250. On loading the file the 250 frame cache is fully populated, but during scrubbing at some point it gets chopped off to the 100 frames of the other cache. After that the cloth sim sees skipped frames and tries to simulate with large time steps or backward time steps, which (unsurprisingly) causes the exploding behavior.

CORRRECTION
The 250 frame cache (Plane.001) is already limited to 100 cached frames initially, which is correct because of the scene frame range being set to 0..100. So the cache is not actually modified incorrectly by the point cache itself.

What is happening is that the cloth sim will request will try to find a valid cache frame before simulating. Usually if a frame outside the cached range is requested this will just return the last valid cache frame, but in this case the cloth sim sets the no_extrapolate_old flag to true. https://developer.blender.org/diffusion/B/browse/master/source/blender/blenkernel/intern/cloth.c$368-371

This causes the point cache to return 0 ("no frame found") and this triggers an invalidation of the entire cache.

~~This seems to be a problem with the point cache mixing up the two cloth sim objects in the scene. One of them has a cache length of 100 frames, the other has 250. On loading the file the 250 frame cache is fully populated, but during scrubbing at some point it gets chopped off to the 100 frames of the other cache. After that the cloth sim sees skipped frames and tries to simulate with large time steps or backward time steps, which (unsurprisingly) causes the exploding behavior.~~ **CORRRECTION** The 250 frame cache (`Plane.001`) is already limited to 100 cached frames initially, which is correct because of the scene frame range being set to 0..100. So the cache is not actually modified incorrectly by the point cache itself. What is happening is that the cloth sim will request will try to find a valid cache frame before simulating. Usually if a frame outside the cached range is requested this will just return the last valid cache frame, but in this case the cloth sim sets the `no_extrapolate_old` flag to true. https://developer.blender.org/diffusion/B/browse/master/source/blender/blenkernel/intern/cloth.c$368-371 This causes the point cache to return 0 ("no frame found") and this triggers an invalidation of the entire cache.

Philipp Oeser removed the

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Cloth simulation randomly breaks down when scrubbing timeline #99913