Problem with parent_vertices attribute #96556

New Issue

Anys Bouchafra · 2022-03-17T12:28:40+01:00

Anys Bouchafra commented

2022-03-17 12:28:40 +01:00

System Information
Operating system: Microsoft Windows 10 Professionnel
Graphics card: Nvidia Gefroce RTX 2080 Super

Blender Version
Blender 3.0.0, hash: f1cca30557 , branch: master

Short description of the bug
The attributes parent_vertices is by default to [0,0,0] but it cause some problem :
When you select the 0th vertex of a mesh and parent an other object with the vertex_parent_set() function the list still be the same [0,0,0].
So when the parent mesh is deleted you cannot know if there were a parent before.
Maybe set the default list to [None, None, None] will avoid the problem.

**System Information** Operating system: Microsoft Windows 10 Professionnel Graphics card: Nvidia Gefroce RTX 2080 Super **Blender Version** Blender 3.0.0, hash: f1cca3055776 , branch: master **Short description of the bug** The attributes parent_vertices is by default to [0,0,0] but it cause some problem : When you select the 0th vertex of a mesh and parent an other object with the vertex_parent_set() function the list still be the same [0,0,0]. So when the parent mesh is deleted you cannot know if there were a parent before. Maybe set the default list to [None, None, None] will avoid the problem.

Anys Bouchafra commented

2022-03-17 12:28:40 +01:00

Added subscriber: @Anys-Bouchafra

Richard Antalik commented

2022-03-18 01:13:54 +01:00

Added subscriber: @iss

Richard Antalik commented

2022-03-18 01:13:54 +01:00

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

Richard Antalik commented

2022-03-18 01:13:54 +01:00

Can you provide sample .blend file with script to demonstrate this issue?

Anys Bouchafra commented

2022-03-18 12:19:36 +01:00

parent_vertices_problem.blend

Just run the first script, it will parent the sphere to the cube with vertex_parent_set() to the 0th vertex. Then go to object mode and run the second script. It will delete the cube and print the index of the vertex that was parent to the sphere. It will print 0, 0, 0 so we can't re-assign properly a cube in a scene just with this information. (It's not very problematic because I can use custom attributes to store informations but I think that default value to 0 is a bad idea when there are some 0th vertex)

[parent_vertices_problem.blend](https://archive.blender.org/developer/F12933200/parent_vertices_problem.blend) Just run the first script, it will parent the sphere to the cube with vertex_parent_set() to the 0th vertex. Then go to object mode and run the second script. It will delete the cube and print the index of the vertex that was parent to the sphere. It will print 0, 0, 0 so we can't re-assign properly a cube in a scene just with this information. (It's not very problematic because I can use custom attributes to store informations but I think that default value to 0 is a bad idea when there are some 0th vertex)

Richard Antalik commented

2022-03-19 00:41:28 +01:00

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

Richard Antalik commented

2022-03-19 00:41:29 +01:00

So if I understand correctly, the issue is that you don't know whether there was any relationship in first place? I am not sure if such information should be preserved after parent has been removed in first place however.

I would imagine normally you would do something like this:

if objects['Sphere'].parent_type == 'VERTEX':
  vert_index = objects["Sphere"].parent_vertices[0]
  ...

Will have to check on this with other devs.

So if I understand correctly, the issue is that you don't know whether there was any relationship in first place? I am not sure if such information should be preserved after parent has been removed in first place however. I would imagine normally you would do something like this: ``` if objects['Sphere'].parent_type == 'VERTEX': vert_index = objects["Sphere"].parent_vertices[0] ... ``` Will have to check on this with other devs.

Sergey Sharybin commented

2022-03-21 09:57:29 +01:00

Added subscriber: @Sergey

Sergey Sharybin commented

2022-03-21 09:57:29 +01:00

The parent_vertices requires some semantic treatment from the script writer:

The number of effective elements depends on the parent_type.
Reading the value without parent, or outside of effective number of elements is not well-defined.

For the scripts it is always better to build logic around properties visible to artists and script writers, than to rely on specific of internal memory representation.

Thanks for the report, but it is not really a bug.

The `parent_vertices` requires some semantic treatment from the script writer: - The number of effective elements depends on the `parent_type`. - Reading the value without parent, or outside of effective number of elements is not well-defined. For the scripts it is always better to build logic around properties visible to artists and script writers, than to rely on specific of internal memory representation. Thanks for the report, but it is not really a bug.

Philipp Oeser commented

2022-03-21 10:57:00 +01:00

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

Philipp Oeser removed the

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Problem with parent_vertices attribute #96556