Clothsim pressure depends on mesh position #119288

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opened 2024-03-10 17:52:50 +01:00 by Max Mustermann · 4 comments

Max Mustermann commented

2024-03-10 17:52:50 +01:00

System Information
Operating system: Fedora Linux
Graphics card: AMD

Blender Version
Broken: 4.0.2
Worked: (newest version of Blender that worked as expected)

Short description of error
The clothsim pressure seems to depend heavily on the mesh position when I don't see a reason for it to do that.
I have seen it be affected only by the X axis or only by Y and Z like in the video. Crossing the 0 mark on an affected axis always makes the simulation explode.
Could be related to #106562.

Exact steps for others to reproduce the error
Open the file clothsim-position.blend and move or duplicate the object.
Play animation.

**System Information** Operating system: Fedora Linux Graphics card: AMD **Blender Version** Broken: 4.0.2 Worked: (newest version of Blender that worked as expected) **Short description of error** The clothsim pressure seems to depend heavily on the mesh position when I don't see a reason for it to do that. I have seen it be affected only by the X axis or only by Y and Z like in the video. Crossing the 0 mark on an affected axis always makes the simulation explode. Could be related to #106562. **Exact steps for others to reproduce the error** Open the file [clothsim-position.blend](/attachments/f3bef827-0b4d-413b-8858-e4beabdd9372) and move or duplicate the object. Play animation. <video src="/attachments/54d76bc7-70ee-43aa-9bfa-b664259d2e5e" title="clothsim-position.webm" controls></video>

clothsim-position.webm

3.1 MiB

clothsim-position.blend

342 KiB

Max Mustermann added the

labels 2024-03-10 17:52:51 +01:00

Iliya Katushenock added the

Nodes & Physics

labels 2024-03-10 18:03:52 +01:00

Iliya Katushenock added

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and removed

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labels 2024-03-10 18:22:16 +01:00

Weikang-Qiu commented

2024-03-23 00:08:24 +01:00

Contributor

Looks like it is caused by

f235990009/source/blender/simulation/intern/SIM_mass_spring.cc (L94-L97)

It calculates the fluid gradient force on each vertex based on the vertex's global coordinates. I'd like to make PR for it but I am confused about the intention of the function.

@mod_moder May I get any suggestions?

Looks like it is caused by https://projects.blender.org/blender/blender/src/commit/f235990009f2980680d7e6cdda71fee8fa4d9758/source/blender/simulation/intern/SIM_mass_spring.cc#L94-L97 It calculates the fluid gradient force on each vertex based on the vertex's global coordinates. I'd like to make PR for it but I am confused about the intention of the function. @mod_moder May I get any suggestions?

Iliya Katushenock commented

2024-03-23 13:29:23 +01:00

Member

Well, its first time i see this function at all. Not sure if there is active developer which is know something about concept of this functions. You know, legacy physic.. If you can make sure this is right solution and this will not cause regressions, feel free to fix that. If this will be trivial fix (like just subscruct positions..), this can be reviewed without the developer of this physics i guess.

Well, its first time i see this function at all. Not sure if there is active developer which is know something about concept of this functions. You know, legacy physic.. If you can make sure this is right solution and this will not cause regressions, feel free to fix that. If this will be trivial fix (like just subscruct positions..), this can be reviewed without the developer of this physics i guess.

Max Mustermann commented

2024-03-24 04:17:20 +01:00

Author

Could its purpose be the fluid distribution within the mesh?
Like in this screenshot, the fluid sinks to the bottom when it's working correctly.

Maybe it could use the coordinates of the bounding box of the currently deformed mesh or local coordinates instead if that's the case?

I'll upload a simple file if you want to test the fluid distribution with those lines removed or changed.

Assuming this is what this is for:

The problem with using local coordinates is that unconnected meshes within a single object will share a fluid volume and the fluid will flow from the upper mesh into the lower mesh with not physical connection between them. This is what already happens currently too.

Could its purpose be the fluid distribution within the mesh? Like in this screenshot, the fluid sinks to the bottom when it's working correctly. ![fluid.png](/attachments/a3afca14-a904-4cd5-9048-704b73a286ab) Maybe it could use the coordinates of the bounding box of the currently deformed mesh or local coordinates instead if that's the case? I'll upload a simple file if you want to test the fluid distribution with those lines removed or changed. Assuming this is what this is for: The problem with using local coordinates is that unconnected meshes within a single object will share a fluid volume and the fluid will flow from the upper mesh into the lower mesh with not physical connection between them. This is what already happens currently too.

fluid-distribution.blend

14 MiB

71 KiB

Weikang-Qiu commented

2024-03-24 18:29:50 +01:00

Contributor

The problem with using local coordinates is that unconnected meshes within a single object will share a fluid volume and the fluid will flow from the upper mesh into the lower mesh with not physical connection between them. This is what already happens currently too.

I agree. Looks like the current implementation only considers the simplest setting.

> The problem with using local coordinates is that unconnected meshes within a single object will share a fluid volume and the fluid will flow from the upper mesh into the lower mesh with not physical connection between them. This is what already happens currently too. I agree. Looks like the current implementation only considers the simplest setting.

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