Bug in particle system - missing particles representations #81103

New Issue

Sebastian · 2020-09-23T19:14:32+02:00

Sebastian commented

2020-09-23 19:14:32 +02:00

System Information
Operating system: Linux-5.4.0-47-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX TITAN X/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 440.44

Blender Version
Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: 3e85bb34d0
Worked: potentially never, does also not work with 2.80

Short description of error
When creating a particle system with instance objects and using more than ~15.000 particles, not all particles are represented with the instance object. The more particles the particle system contains, the more instance objects are missing.
The following images illustrate the problem.

Example with 120 x 120 = 14.400 particles. All particles are represented with the instance object (in this case a cube) - except for the first particle at the top left corner. This particle is always missing - even for small particle systems.

For slightly bigger particle systems (e.g. 150 x 150 = 22500 particles), a few particles at random positions in the particle system do not contain an instance object (see the black dots)

For way bigger particle systems (e.g. 200 x 200 = 40000 particles) the last particles (i.e. the particles at the bottom right with the biggest indices are missing)

The presence of particles without instance objects also affects other particles when using specific nodes. For example, when using the index output of the Particle Info Node to compute a texture coordinate for each particle used to compute individual colors for the particles produced strange results.

Here a working example for 120 x 120 particles (as reference)

And here a non-working example for 200 x 200 particles (zoomed on the bottom-right corner)

Side note: In all the examples, the particles are there, but the instance object representation is missing.

Exact steps for others to reproduce the error

Execute the following Python script within Blender's text editor. Or, when using Jacques Lucke's VSCode Plugin: execute the script (again) when Blender is already opened (since it does not work with a restricted context)

particle_sys.py

Blend file with the an incorrect particle system

particle_sys.blend

**System Information** Operating system: Linux-5.4.0-47-generic-x86_64-with-debian-buster-sid 64 Bits Graphics card: GeForce GTX TITAN X/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 440.44 **Blender Version** Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: `3e85bb34d0` Worked: potentially never, does also not work with 2.80 **Short description of error** When creating a particle system with `instance objects` and using more than ~15.000 particles, not all particles are represented with the instance object. The more particles the particle system contains, the more instance objects are missing. The following images illustrate the problem. Example with 120 x 120 = 14.400 particles. All particles are represented with the instance object (in this case a cube) - except for the first particle at the top left corner. This particle is always missing - even for small particle systems. ![image.png](https://archive.blender.org/developer/F8912462/image.png) For slightly bigger particle systems (e.g. 150 x 150 = 22500 particles), a few particles at random positions in the particle system do not contain an instance object (see the black dots) ![image.png](https://archive.blender.org/developer/F8912479/image.png) For way bigger particle systems (e.g. 200 x 200 = 40000 particles) the last particles (i.e. the particles at the bottom right with the biggest indices are missing) ![image.png](https://archive.blender.org/developer/F8912492/image.png) The presence of particles without instance objects also affects other particles when using specific nodes. For example, when using the `index` output of the `Particle Info Node` to compute a texture coordinate for each particle used to compute individual colors for the particles produced strange results. Here a working example for 120 x 120 particles (as reference) ![image.png](https://archive.blender.org/developer/F8912504/image.png) And here a non-working example for 200 x 200 particles (zoomed on the bottom-right corner) ![image.png](https://archive.blender.org/developer/F8912501/image.png) Side note: In all the examples, the particles are there, but the instance object representation is missing. **Exact steps for others to reproduce the error** Execute the following Python script within Blender's text editor. Or, when using Jacques Lucke's VSCode Plugin: execute the script (again) when Blender is already opened (since it does not work with a restricted context) [particle_sys.py](https://archive.blender.org/developer/F8912521/particle_sys.py) Blend file with the an incorrect particle system [particle_sys.blend](https://archive.blender.org/developer/F8912511/particle_sys.blend)

Sebastian commented

2020-09-23 19:14:32 +02:00

Added subscriber: @sbcv

Jer Bot commented

2020-09-23 22:18:17 +02:00

Added subscriber: @JerBot

Sebastian changed title from ~~Bug in particle system - missing object instances representations of particles results in incorrect node behavior~~ to Bug in particle system - missing particles representations

2020-09-29 10:46:31 +02:00

Richard Antalik commented

2020-09-30 13:35:28 +02:00

Added subscriber: @iss

Richard Antalik commented

2020-09-30 13:35:28 +02:00

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

Richard Antalik commented

2020-09-30 13:35:28 +02:00

I can reproduce this even when I duplicate vertices manually, so script should not influence the result.

Jacques Lucke commented

2021-01-07 12:00:55 +01:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2021-01-07 12:00:55 +01:00

The error seems to be unrelated to the instancing itself. It happens in particle_distribute.c:

See that line 1227 is not executed the expected 39999 times. Instead it is only executed 39967 times. The missing iterations are responsible for the misplaced instances.

There have been multiple attempts to fix this in the past: 950acb0ced, 35ee9ff7a0.
It's a bit crazy that the simplest kind of distribution (one particle per vertex) is hard to implement, currently. The main issue is that this tries to incorporate weights, even if there are none, leading to floating point accuracy issues.

The error seems to be unrelated to the instancing itself. It happens in `particle_distribute.c`: ![image.png](https://archive.blender.org/developer/F9554094/image.png) See that line 1227 is not executed the expected 39999 times. Instead it is only executed 39967 times. The missing iterations are responsible for the misplaced instances. There have been multiple attempts to fix this in the past: 950acb0ced, 35ee9ff7a0. It's a bit crazy that the simplest kind of distribution (one particle per vertex) is hard to implement, currently. The main issue is that this tries to incorporate weights, even if there are none, leading to floating point accuracy issues.

hujin commented

2021-03-14 05:32:40 +01:00

Added subscriber: @2046411367

Philipp Oeser removed the

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Bug in particle system - missing particles representations #81103