Poisson Disk Seed Repeats distribution every 125 values #87217

New Issue

Erindale · 2021-04-05T19:10:28+02:00

Erindale commented

2021-04-05 19:10:28 +02:00

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 461.92

Blender Version
Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-04-03 16:32, hash: 8681504f06
Worked: (newest version of Blender that worked as expected)

Short description of error
Poisson Disk distribution isn't properly randomising. Every 125 values or so the pattern will repeat with a slight offset. Changing the seed value doesn't change the distribution so much as slide the pattern over the surface.
This only seems to be an issue particularly with a subdivided mesh either via subdiv modifier or the subdivide nodes.

Exact steps for others to reproduce the error
Open a new file, add a plane and add a geo node tree.
Add a Point Distribute node set to poisson disk and change the Seed value.

2021-04-05 18-02-00.mp4
PoissonSeedBug.blend

**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 461.92 **Blender Version** Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-04-03 16:32, hash: `8681504f06` Worked: (newest version of Blender that worked as expected) **Short description of error** Poisson Disk distribution isn't properly randomising. Every 125 values or so the pattern will repeat with a slight offset. Changing the seed value doesn't change the distribution so much as slide the pattern over the surface. This only seems to be an issue particularly with a subdivided mesh either via subdiv modifier or the subdivide nodes. **Exact steps for others to reproduce the error** Open a new file, add a plane and add a geo node tree. Add a Point Distribute node set to poisson disk and change the Seed value. [2021-04-05 18-02-00.mp4](https://archive.blender.org/developer/F9920735/2021-04-05_18-02-00.mp4) [PoissonSeedBug.blend](https://archive.blender.org/developer/F9920742/PoissonSeedBug.blend)

Erindale commented

2021-04-05 19:10:28 +02:00

Added subscriber: @Erindale

Victor-Louis De Gusseme commented

2021-04-05 21:31:40 +02:00

Added subscriber: @victorlouis

Victor-Louis De Gusseme commented

2021-04-05 21:31:40 +02:00

The problem is this line in sample_mesh_surface():

    const int looptri_seed = BLI_hash_int(looptri_index + seed);

Increasing seed by 1 thus effectively decreases the looptri indices that will receive a point by 1:

By multiplying with the seed instead of adding it, the behavior is more random for successive seeds:

I'm not sure how this change could be made without breaking backwards compatibility though.

The problem is this line in `sample_mesh_surface()`: ``` const int looptri_seed = BLI_hash_int(looptri_index + seed); ``` Increasing `seed` by 1 thus effectively decreases the looptri indices that will receive a point by 1: ![image.png](https://archive.blender.org/developer/F9920884/image.png) By multiplying with the seed instead of adding it, the behavior is more random for successive seeds: ![image.png](https://archive.blender.org/developer/F9920886/image.png) I'm not sure how this change could be made without breaking backwards compatibility though.

Victor-Louis De Gusseme commented

2021-04-05 21:52:37 +02:00

Another solution would be to create a single RandomNumberGenerator rng(seed); outside the loop over looptris, instead of creating a new rng for each looptri.

Also, this might be more correct than the proposal from my previous comment:

const int looptri_seed = BLI_hash_int(looptri_index + seed * amount_of_looptris);

Another solution would be to create a single `RandomNumberGenerator rng(seed);` outside the loop over looptris, instead of creating a new rng for each looptri. Also, this might be more correct than the proposal from my previous comment: ``` const int looptri_seed = BLI_hash_int(looptri_index + seed * amount_of_looptris); ```

Philipp Oeser commented

2021-04-06 10:26:25 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2021-04-06 10:26:25 +02:00

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

Philipp Oeser commented

2021-04-06 10:26:25 +02:00

Can sort of confirm, also thx @victorlouis for taking the time and investigate!

Dalai Felinto commented

2021-04-06 15:30:05 +02:00

Added subscriber: @dfelinto

Dalai Felinto commented

2021-04-06 15:30:05 +02:00

Confirmed bugs need to be tagged to one of the modules to show in the queries.

Dalai Felinto commented

2021-04-06 17:11:20 +02:00

I used the wrong option when setting Nodes & Physics projects. I didn't mean to remove BF Blender and the Geomtry Nodes projects.

Jacques Lucke commented

2021-04-07 11:55:50 +02:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2021-04-07 11:55:50 +02:00

Another solution would be to create a single RandomNumberGenerator rng(seed); outside the loop over looptris, instead of creating a new rng for each looptri.

The issue with that is that we loose all stability afaik.

Multiplying the seed with some large number seems to be the way to go here imo. Unfortunately, you are right and this changes the distribution pattern. I don't think there is a good way around that at this point, also not sure if it is worth it to make the code more complicate so that old patterns remain the same. One way to keep old distributions intact is to add a bool to the node storage that remembers whether the old or new behavior should be used.

> Another solution would be to create a single RandomNumberGenerator rng(seed); outside the loop over looptris, instead of creating a new rng for each looptri. The issue with that is that we loose all stability afaik. Multiplying the seed with some large number seems to be the way to go here imo. Unfortunately, you are right and this changes the distribution pattern. I don't think there is a good way around that at this point, also not sure if it is worth it to make the code more complicate so that old patterns remain the same. One way to keep old distributions intact is to add a bool to the node storage that remembers whether the old or new behavior should be used.

Victor-Louis De Gusseme commented

2021-04-07 21:11:05 +02:00

Ah yes indeed, forgot about that. Just tried it with the rng outside the loop and it causes the points to shift around while weight painting.

blender-admin commented

2021-04-16 11:43:16 +02:00

This issue was referenced by ca37d8485c

This issue was referenced by ca37d8485c73ebc050e49c6bce2f73756c7578e3

Jacques Lucke commented

2021-04-16 11:43:50 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Jacques Lucke closed this issue

2021-04-16 11:43:50 +02:00

Jacques Lucke self-assigned this 2021-04-16 11:43:50 +02:00

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Poisson Disk Seed Repeats distribution every 125 values #87217