world units for Cloth dynamics seems wrong by defaults #83578

New Issue

Libor Batek · 2020-12-09T09:20:37+01:00

Libor Batek commented

2020-12-09 09:20:37 +01:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06

Blender Version
Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash: 0f45cab862
Worked: (newest version of Blender that worked as expected)

Short description of error

Its pretty obvious that default settings for cloth dynamics are not working well. For ie making classic waving flag (about real world scale 1.5x1m doesnt behave naturally...one has to make it like 10x or 20x bigger to make it natural moving sim resulting in flag about 20 to 40 meters big cloth object.
It seems there is a Sim Scale ratio wrong by defaults like 100x times. To me its seems like problem introduced in some 2.8x release when first introduced possibility to switch unit systems and the cloth sim algorithms where not adjusted to take these units switching into account.

Exact steps for others to reproduce the error
Default world unit system (metric) keeped untouched.
Simply create a plane mesh about 2m scale, subdivide it to a reasonable detail and apply cloth and run a sim with default cloth properties (ideally with some force field and pinning) if self collisions are turned on its even more obvious that defaults doesnt give you reasonable output...
Also resulting in insane field strenghts like 150 - 200 values (defaults are value 1.0!) to make the force field affect the cloth somehow.

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06 **Blender Version** Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash: `0f45cab862` Worked: (newest version of Blender that worked as expected) **Short description of error** Its pretty obvious that default settings for cloth dynamics are not working well. For ie making classic waving flag (about real world scale 1.5x1m doesnt behave naturally...one has to make it like 10x or 20x bigger to make it natural moving sim resulting in flag about 20 to 40 meters big cloth object. It seems there is a Sim Scale ratio wrong by defaults like 100x times. To me its seems like problem introduced in some 2.8x release when first introduced possibility to switch unit systems and the cloth sim algorithms where not adjusted to take these units switching into account. **Exact steps for others to reproduce the error** Default world unit system (metric) keeped untouched. Simply create a plane mesh about 2m scale, subdivide it to a reasonable detail and apply cloth and run a sim with default cloth properties (ideally with some force field and pinning) if self collisions are turned on its even more obvious that defaults doesnt give you reasonable output... Also resulting in insane field strenghts like 150 - 200 values (defaults are value 1.0!) to make the force field affect the cloth somehow.

Libor Batek commented

2020-12-09 09:20:37 +01:00

Added subscriber: @LiborBatek

Robert Guetzkow commented

2020-12-09 11:47:21 +01:00

Added subscriber: @rjg

Robert Guetzkow commented

2020-12-09 11:47:21 +01:00

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

Robert Guetzkow commented

2020-12-09 11:47:21 +01:00

Could you please provide an example file that used to work properly in older Blender version and that doesn't in current versions? I've tested this and couldn't see anything obviously wrong.

Libor Batek commented

2020-12-09 13:16:35 +01:00

Hi,
here are 2 example scenes packed in ZIP archive.

scene_examples

Its more a comparison between scale used. Scene 01 is behaving weirdly at the defaults, 02 corrected by bigger scale (10x bigger cloth object, and 100x times stronger Wind force field). Its obvious the second one is much more
correct in behaviour than the previous uncorrected one.

I ve tried older version of Blender but I ve got same results as in the latest Blender 2.91 (been tested in previous oldest I ve got on my PC which was 2.83, so not sure how it behaves in older ones)

However its definetely not much of a use with default cloth preset(s) when using proper scene scale for ie. simulating character clothing (dimensions being around 1m). So I guess it need revision or at least set proper defaults for physics attribs values so one can use them straight as set.

Thank you for your interest and really quick response!

Libor

Hi, here are 2 example scenes packed in ZIP archive. [scene_examples ](https://1drv.ms/u/s!Ah8rk5bM3wcigqB5Xawsa5ffcEG10A?e=mBBwre) Its more a comparison between scale used. Scene 01 is behaving weirdly at the defaults, 02 corrected by bigger scale (10x bigger cloth object, and 100x times stronger Wind force field). Its obvious the second one is much more correct in behaviour than the previous uncorrected one. I ve tried older version of Blender but I ve got same results as in the latest Blender 2.91 (been tested in previous oldest I ve got on my PC which was 2.83, so not sure how it behaves in older ones) However its definetely not much of a use with default cloth preset(s) when using proper scene scale for ie. simulating character clothing (dimensions being around 1m). So I guess it need revision or at least set proper defaults for physics attribs values so one can use them straight as set. Thank you for your interest and really quick response! Libor

Robert Guetzkow commented

2020-12-09 13:24:23 +01:00

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

Richard Antalik commented

2020-12-11 19:11:21 +01:00

Added subscriber: @iss

Richard Antalik commented

2020-12-11 19:11:21 +01:00

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

Richard Antalik closed this issue

2020-12-11 19:11:21 +01:00

Richard Antalik commented

2020-12-11 19:11:21 +01:00

Same example doesn't behave much better in 2.79
0.015m self collision is too large to be used with such large number of subivisions, this pretty much kills whole simulation
Also mass of cloth is defined by kg per vertex, hence it is not really possible to make good defaults. I think usual workflow is to make relatively low-poly mesh for simulation and then apply subdivision.

So far I don't see any bug here.

Thanks for the report, but the issue reported here is a request for modified/improved behavior and not a bug in current behavior. Closing as this bug tracker is only for bugs and errors.
For user requests and feedback, please use other channels: https://wiki.blender.org/wiki/Communication/Contact#User_Feedback_and_Requests
For more information on why this isn't considered a bug, visit: https://wiki.blender.org/wiki/Reference/Not_a_bug

Same example doesn't behave much better in 2.79 0.015m self collision is too large to be used with such large number of subivisions, this pretty much kills whole simulation Also mass of cloth is defined by kg per vertex, hence it is not really possible to make good defaults. I think usual workflow is to make relatively low-poly mesh for simulation and then apply subdivision. So far I don't see any bug here. Thanks for the report, but the issue reported here is a request for modified/improved behavior and not a bug in current behavior. Closing as this bug tracker is only for bugs and errors. For user requests and feedback, please use other channels: https://wiki.blender.org/wiki/Communication/Contact#User_Feedback_and_Requests For more information on why this isn't considered a bug, visit: https://wiki.blender.org/wiki/Reference/Not_a_bug

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world units for Cloth dynamics seems wrong by defaults #83578