Attribute Compare node is writing vertex-groups with no weight. #87102

New Issue

DorianB · 2021-04-01T01:14:53+02:00

DorianB commented

2021-04-01 01:14:53 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.71

Blender Version
Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-03-31 07:46, hash: 645fc0c767

Short description of error
If we are using geometry node to do some vertex-group manipulation,
using attr compare will write a vertex-group with no weight.

In the blend file below, you will see an example of this behavior, the spreadsheet show weight, but none of the values are transferred to the vertex group

attrcomparevg.blend

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.71 **Blender Version** Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-03-31 07:46, hash: `645fc0c767` **Short description of error** If we are using geometry node to do some vertex-group manipulation, using attr compare will write a vertex-group with no weight. ![Capture d’écran 2021-04-01 011142.png](https://archive.blender.org/developer/F9916352/Capture_d_écran_2021-04-01_011142.png) In the blend file below, you will see an example of this behavior, the spreadsheet show weight, but none of the values are transferred to the vertex group [attrcomparevg.blend](https://archive.blender.org/developer/F9916354/attrcomparevg.blend)

DorianB commented

2021-04-01 01:14:53 +02:00

Added subscriber: @dodododorian

Germano Cavalcante commented

2021-04-02 16:41:50 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2021-04-02 16:41:50 +02:00

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

Germano Cavalcante commented

2021-04-02 16:41:50 +02:00

I'm not sure exactly how it works, but attribute B is actually being overwritten. So it looks like a bug to me.

Wannes Malfait commented

2021-04-06 13:16:22 +02:00

Added subscriber: @wannes.malfait

Wannes Malfait commented

2021-04-06 13:16:22 +02:00

It seems that this is caused by the return type of the compare node being a boolean attribute, while the vertex group is a float attribute. Since the types don't match, a new Span is created (with the same name), instead of overwriting the vertex group using an implicit conversion. From then on, the attribute B refers to that Span and not the vertex group. There are multiple ways around this, but I'm not sure if this should be considered intended behaviour.

Alternative 1:
Use the Attribute Math node instead (return float attribute so this overwrites)

Alternative 2:
Use a temporary attribute, and then overwrite with the attribute convert node.

It seems that this is caused by the return type of the compare node being a `boolean` attribute, while the vertex group is a `float` attribute. Since the types don't match, a new `Span` is created (with the same name), instead of overwriting the vertex group using an implicit conversion. From then on, the attribute `B` refers to that `Span` and not the vertex group. There are multiple ways around this, but I'm not sure if this should be considered intended behaviour. Alternative 1: Use the `Attribute Math` node instead (return `float` attribute so this overwrites) ![image.png](https://archive.blender.org/developer/F9921720/image.png) Alternative 2: Use a temporary attribute, and then overwrite with the attribute convert node. ![image.png](https://archive.blender.org/developer/F9921728/image.png)

DorianB commented

2021-04-06 13:19:35 +02:00

In #87102#1141479, @wannes.malfait wrote:
It seems that this is caused by the return type of the compare node being a boolean attribute, while the vertex group is a float attribute. Since the types don't match, a

Why is the attr convert node not working then?

> In #87102#1141479, @wannes.malfait wrote: > It seems that this is caused by the return type of the compare node being a `boolean` attribute, while the vertex group is a `float` attribute. Since the types don't match, a Why is the attr convert node not working then?

Wannes Malfait commented

2021-04-06 13:31:30 +02:00

Why is the attr convert node not working then?

After the Attribute Compare Node the attribute B refers to a new boolean attribute that has nothing to do with the vertex group B. The Attribute Convert node only modifies this new attribute, and not the vertex group. Due to the fact that they have the same name (B) the vertex group is no longer accessible in the node tree, as any use of the the name B will refer to the boolean attribute instead.

Like I said, this is not very intuitive, and should probably be changed.

> Why is the attr convert node not working then? After the `Attribute Compare Node` the attribute `B` refers to a **new** `boolean` attribute that has nothing to do with the vertex group `B`. The `Attribute Convert` node only modifies this new attribute, and not the vertex group. Due to the fact that they have the same name (`B`) the vertex group is no longer accessible in the node tree, as any use of the the name `B` will refer to the `boolean` attribute instead. Like I said, this is not very intuitive, and should probably be changed.

Jacques Lucke commented

2021-04-16 12:06:46 +02:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2021-04-16 12:06:46 +02:00

Changed status from 'Confirmed' to: 'Archived'

Jacques Lucke closed this issue

2021-04-16 12:06:46 +02:00

Jacques Lucke commented

2021-04-16 12:06:46 +02:00

This is actually working as expected. There can't be two attributes with the same name and different types. We could change the output type of the attribute compare node, but I'm not sure we should. Either way, this is not a bug, so I'm closing this report. The alternative of using a separate attribute for intermediate computations makes sense to me.

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Attribute Compare node is writing vertex-groups with no weight. #87102