Change in distribution seed for some faces when the source mesh is moved #100214
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Reference: blender/blender#100214
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System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.59
Blender Version
Broken: version: 3.3.0 Beta, branch: master, commit date: 2022-07-29 15:54, hash:
cfd16c04f8Short description of error
My emitter object got its distribution seed corrupted on one island of the mesh. i did not do any specific edit mode manipulation.
Note that the scatter is done on a global (relative) space
it is very strange because only this specific island is corrupted, even when duplicated
Exact steps for others to reproduce the error
BUG un-stable global distribution.blend
Added subscriber: @BD3D
Added subscriber: @OmarEmaraDev
Changed status from 'Needs Triage' to: 'Needs User Info'
I feel like this is naturally caused by the transformation applied on the geometry when using Relative mode in the Object Info node. Small imprecision can cause that seed difference.
So ideally you would apply the transformation after distribution, like this.
Does that make sense?
>Does that make sense?It Depends on the user context, users might want to distribute in global space, let say he is using a collection of emitter surface for example> Small imprecision can cause that seed difference.
What kind of imprecision? Commonly, rotation/location changes do not recalculate the seed of the distribution in relative space
In the case of this precise example, all of a sudden the seed of one island of the mesh became unreliable
I'm not sure what kind of characteristics this island have over the others
Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'
By imprecision, I mean slight variations in properties like areas which are used by the node. There is also probably triangulation happening which can make this worse.
But I don't want to speculate further, so I will tag the module and see what they think.
Corrupted distribution seed with geometry nodeto Change in distribution seed for some faces when the source mesh is movedAdded subscriber: @mod_moder
This task has a high degree of transformation of the initial data. Each new point raises the seed to a power. Because of this, the more points, the greater the difference even for the most similar seeds. This is like an N-object problem. It cannot be solved like an algorithm. Private methods only, like snapping islands to a grid... . Or the user simply has to reduce the impact of the transformations to distribution.
>There is also probably triangulation happening which can make this worse.
Aha, indeed, the error is linked with triangulation,
if I enter edit mode and triangulate the problematic emitting face, the seed is stable again!
It is strange because the problematic island is just a copy/paste of the other islands but somehow the triangulation of this face became corrupted along the way
I will try to investigate what cause this instability, as I said, initially everything was stable, i did some tests in the node tree then it became unstable
Added subscriber: @JacquesLucke
Changed status from 'Needs Developer To Reproduce' to: 'Archived'
Generally, the Distribute Points on Faces node does not guarantee stability when the input mesh topology or deformation changes. Therefore, this is not a bug.