Object-linked material slot not working correctly with generated geometry in geometry nodes #88455

New Issue

Simon Thommes · 2021-05-21T11:01:36+02:00

Simon Thommes commented

2021-05-21 11:01:36 +02:00

System Information
Operating system: Linux-5.8.0-7630-generic-x86_64-with-glibc2.32 64 Bits
Graphics card: Quadro RTX 6000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.32.03

Blender Version
Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-05-21 07:43, hash: c154b078b5
Worked: last week (no specific hash, sorry)

Short description of error
An object-linked material slot does not properly assign a material to generated geometry. This worked previously and adding an Assign Material node seems to fix it, even though nothing is filled in. I guess this has to do with the evaluated material slot list not behaving as it should.
object_material_bug.mp4

Exact steps for others to reproduce the error
See this file:
material_assing_object.blend

**System Information** Operating system: Linux-5.8.0-7630-generic-x86_64-with-glibc2.32 64 Bits Graphics card: Quadro RTX 6000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.32.03 **Blender Version** Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-05-21 07:43, hash: `c154b078b5` Worked: last week (no specific hash, sorry) **Short description of error** An object-linked material slot does not properly assign a material to generated geometry. This worked previously and adding an `Assign Material` node seems to fix it, even though nothing is filled in. I guess this has to do with the evaluated material slot list not behaving as it should. [object_material_bug.mp4](https://archive.blender.org/developer/F10133507/object_material_bug.mp4) **Exact steps for others to reproduce the error** See this file: [material_assing_object.blend](https://archive.blender.org/developer/F10133505/material_assing_object.blend)

Simon Thommes commented

2021-05-21 11:01:36 +02:00

Added subscriber: @SimonThommes

blender-admin commented

2021-05-21 11:01:36 +02:00

#88446 was marked as duplicate of this issue

Jacques Lucke commented

2021-05-21 11:16:49 +02:00

Added subscribers: @HooglyBoogly, @JacquesLucke

Jacques Lucke commented

2021-05-21 11:16:49 +02:00

The issue here is that the number of materials on the geometry is the ground truth (this was mentioned in 1a81d268a1). In your example, the generated cylinder has no materials and therefore no material can't be overwritten by the object.
The Material Assign node currently does add a material slot to the mesh, even though it is empty. Because it exists, it can be overwritten by the object.

The proper solution might be to create one empty material slot in the mesh primitive nodes. This material slot is referenced by all faces anyway, because their material_index is 0.
@HooglyBoogly What do you think?

The issue here is that the number of materials on the geometry is the ground truth (this was mentioned in 1a81d268a1). In your example, the generated cylinder has no materials and therefore no material can't be overwritten by the object. The Material Assign node currently does add a material slot to the mesh, even though it is empty. Because it exists, it can be overwritten by the object. The proper solution might be to create one empty material slot in the mesh primitive nodes. This material slot is referenced by all faces anyway, because their `material_index` is 0. @HooglyBoogly What do you think?

Philipp Oeser commented

2021-05-21 14:18:04 +02:00

Added subscriber: @LloydAlmeida

Philipp Oeser commented

2021-05-21 14:18:22 +02:00

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

Hans Goudey commented

2021-05-21 22:19:46 +02:00

Adding a material slot to newly created meshes is a bit hacky, but it's also simple, and not user-visible, so it seems like a fine solution. We would have to take care to do this for all new meshes, not just the mesh primitives. It's also inconsistent with regular mesh primitive objects.

It would definitely be more complicated, but another solution would be refactoring code so that the information of the number of materials in the object is always available when rendering meshes.
The situation we're in currently where we retrieve materials from the object with a callback except for the length of the material array is a little odd IMO. I don't have a strong opinion about which approach is the best though.

Adding a material slot to newly created meshes is a bit hacky, but it's also simple, and not user-visible, so it seems like a fine solution. We would have to take care to do this for all new meshes, not just the mesh primitives. It's also inconsistent with regular mesh primitive objects. It would definitely be more complicated, but another solution would be refactoring code so that the information of the number of materials in the object is always available when rendering meshes. The situation we're in currently where we retrieve materials from the object with a callback except for the length of the material array is a little odd IMO. I don't have a strong opinion about which approach is the best though.

Jacques Lucke commented

2021-05-21 22:25:59 +02:00

Maybe we could change eevee so that it can read the number of materials from the object, not sure how much needs to be changed for that. Could be simple but might also be a more complex refactor.
Note that this refactor should not only be done for meshes, but for the other types as well.

Maybe we could change eevee so that it can read the number of materials from the object, not sure how much needs to be changed for that. Could be simple but might also be a more complex refactor. Note that this refactor should not only be done for meshes, but for the other types as well.

Jacques Lucke self-assigned this 2021-05-31 16:31:20 +02:00

blender-admin commented

2021-06-01 15:24:29 +02:00

This issue was referenced by 6583fb67c6

This issue was referenced by 6583fb67c6e1e5d714d723a09312e9dd25e02152

Jacques Lucke commented

2021-06-01 15:28:25 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Jacques Lucke closed this issue

2021-06-01 15:28:25 +02:00

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Object-linked material slot not working correctly with generated geometry in geometry nodes #88455