[Mantaflow] Generating a huge number of particles as substeps increase #81968

New Issue

Pavel Blend · 2020-10-22T17:30:18+02:00

Pavel Blend commented

2020-10-22 17:30:18 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: AMD Radeon HD 7560D ATI Technologies Inc. 4.5.13399 Core Profile Context 15.201.1151.1008

Blender Version
Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: 3e85bb34d0
Worked: (newest version of Blender that worked as expected)

Short description of error
The number of particles increases as the number of substeps increases.

Exact steps for others to reproduce the error
Bake the liquid from this scene.
substeps_bug.blend
You will see the following:

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: AMD Radeon HD 7560D ATI Technologies Inc. 4.5.13399 Core Profile Context 15.201.1151.1008 **Blender Version** Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: `3e85bb34d0` Worked: (newest version of Blender that worked as expected) **Short description of error** The number of particles increases as the number of substeps increases. **Exact steps for others to reproduce the error** Bake the liquid from this scene. [substeps_bug.blend](https://archive.blender.org/developer/F9036211/substeps_bug.blend) You will see the following: ![particles_count.jpg](https://archive.blender.org/developer/F9036216/particles_count.jpg)

Pavel Blend commented

2020-10-22 17:30:18 +02:00

Added subscriber: @Pavel_Blend

Richard Antalik commented

2020-10-23 20:05:19 +02:00

Added subscriber: @iss

Richard Antalik commented

2020-10-23 20:05:19 +02:00

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

Richard Antalik commented

2020-10-23 20:05:19 +02:00

By "number of substeps" Do you mean timesteps?

I can confirm that, but I would think, that this is correct behavior - it will lead to smoother result.

By "number of substeps" Do you mean timesteps? I can confirm that, but I would think, that this is correct behavior - it will lead to smoother result.

Pavel Blend commented

2020-10-26 16:13:14 +01:00

Yes, substeps are timesteps (I confused the terminology used in flip fluids).

I think timesteps shouldn't affect the number of particles. Timesteps should only affect precision. If you set timesteps to 64, then the simulator will generate too many particles that will be layered on top of each other. This amount of particles will be excessive. I think there is a bug in the simulator code that causes the simulator to emit particles at every step. The simulator should only emit particles if there are no other particles nearby.

Yes, substeps are timesteps (I confused the terminology used in flip fluids). I think timesteps shouldn't affect the number of particles. Timesteps should only affect precision. If you set timesteps to 64, then the simulator will generate too many particles that will be layered on top of each other. This amount of particles will be excessive. I think there is a bug in the simulator code that causes the simulator to emit particles at every step. The simulator should only emit particles if there are no other particles nearby.

Richard Antalik commented

2020-10-27 06:23:46 +01:00

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

Richard Antalik commented

2020-10-27 06:23:46 +01:00

Added subscriber: @sebbas

Richard Antalik commented

2020-10-27 06:23:46 +01:00

I am really not sure. Behavior is consistent from 2.82 so this isn't regression.

@sebbas Should liquid sim with more timesteps procude more particles?

I am really not sure. Behavior is consistent from 2.82 so this isn't regression. @sebbas Should liquid sim with more timesteps procude more particles?

Pavel Blend commented

2020-12-01 10:31:05 +01:00

How can I increase the accuracy of the simulator without increasing the number of particles? By precision, I mean calculating particle velocities using shorter time steps. For example, instead of 0.01 seconds per step, use 0.002 seconds, without increasing the number of particles.

Ankit Meel commented

2021-05-17 19:45:37 +02:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Philipp Oeser removed the

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[Mantaflow] Generating a huge number of particles as substeps increase #81968