Wrong particle distribution #71731

New Issue

Julian Schmidt · 2019-11-21T14:50:54+01:00

Julian Schmidt commented

2019-11-21 14:50:54 +01:00

System Information
Operating system: Ubuntu 18.04 LTS
Graphics card: NVidia Quadro K2000D

Blender Version
version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: f6cb5f5449, type: Release

Short description of error
The density of randomly generated particles inside of a deformed mesh is not uniform.

This behaviour is unwanted for a random distribution and leads to visual artifacts as well as inconsistencies in simulations. ('even distribution' does not solve this, the distribution probably has to be normalized on the actual mesh volume)

Exact steps for others to reproduce the error
Set up a particle system in a cube volume and set the distribution to 'random' and generate all particles in the first frame. Take one edge of the cube pointing in z-direction and pull it further away. Press 7 on the numpad to see the effect in the distribution. The effect becomes prominent with around 5000 particles.

This is the top view of a cube with one vertical edge dragged out:

#71731-particleVolume.blend

**System Information** Operating system: Ubuntu 18.04 LTS Graphics card: NVidia Quadro K2000D **Blender Version** version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: f6cb5f54494e, type: Release **Short description of error** The density of randomly generated particles inside of a deformed mesh is not uniform. This behaviour is unwanted for a random distribution and leads to visual artifacts as well as inconsistencies in simulations. ('even distribution' does not solve this, the distribution probably has to be normalized on the actual mesh volume) **Exact steps for others to reproduce the error** Set up a particle system in a cube volume and set the distribution to 'random' and generate all particles in the first frame. Take one edge of the cube pointing in z-direction and pull it further away. Press 7 on the numpad to see the effect in the distribution. The effect becomes prominent with around 5000 particles. This is the top view of a cube with one vertical edge dragged out: ![image.png](https://archive.blender.org/developer/F8289972/image.png) [#71731-particleVolume.blend](https://archive.blender.org/developer/F8290012/T71731-particleVolume.blend)

Julian Schmidt commented

2019-11-21 14:50:54 +01:00

Added subscriber: @singularity

Sybren A. Stüvel commented

2020-01-20 18:14:04 +01:00

Added subscriber: @dr.sybren

Sybren A. Stüvel commented

2020-01-20 18:14:04 +01:00

@singularity wrote in the original report:
The density of randomly generated particles inside of a deformed mesh is not homogeneous/even and therefore not random.

That's not strictly true. You can have various distribution functions that produce clumped-up particles that are still random. It's not uniformly random, I'll certainly give you that ;-)

2.79 also seems to suffer from this, albeit less pronounced:

> @singularity wrote in the original report: > The density of randomly generated particles inside of a deformed mesh is not homogeneous/even and therefore not random. That's not strictly true. You can have various distribution functions that produce clumped-up particles that are still random. It's not *uniformly* random, I'll certainly give you that ;-) 2.79 also seems to suffer from this, albeit less pronounced: ![image.png](https://archive.blender.org/developer/F8290021/image.png)

Soumya Pochiraju commented

2021-01-08 08:17:22 +01:00

Added subscriber: @Forest1

Soumya Pochiraju commented

2021-01-10 08:58:58 +01:00

Hey! I'm a beginner, and I'm trying to work on this. I think I understand what needs to be done, but I can't seem to find where grid_res of the ParticleSettings is being computed. Could anyone guide me on the same?

Sybren A. Stüvel commented

2021-01-11 12:34:33 +01:00

Hi @Forest1, thanks for helping out here. It's probably more useful for you to pop over to https://blender.chat/channel/blender-coders and ask around there. Your question(s) will be seen by more people, who will be able to help you better than the few who are subscribed to this particular report.

Soumya Pochiraju commented

2021-01-12 04:54:09 +01:00

@dr.sybren A. Stüvel (sybren) Sure, I will do that. Thanks for the tip!!

Philipp Oeser removed the

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Wrong particle distribution #71731