Selecting "Remove unused slots" in Materials panel removes slots that are assigned to particle systems/hair #91691

New Issue

Nikhil Shringarpurey · 2021-09-24T21:02:10+02:00

2021-09-24 21:02:10 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.68

Blender Version
Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-09-24 14:03, hash: 95ec6e4dd3
Worked: never

Short description of error
In the Material panel in the Properties editor, there is a drop-down next to the material slots. Selecting "Remove unused slots" will remove materials that are assigned to particle systems/hair. So it seems unless material slots are assigned to at least one face, this function deletes their slots.

Exact steps for others to reproduce the error

Add 2 material slots to the default cube - Slot 1: skin and Slot 2: hair.
Ensure the skin material is applied to all faces of the cube
Add a hair particle system
Under the Particle System's Render tab, select the hair material slot.
Render to ensure materials are assigned correctly.
Return to the material tab in the properties editor and click the "Remove unused slots" option from the drop-down

Watch the hair material slot be deleted.

or

Open .blend file
Switch Viewport Shading to Material Preview

In material Properties: `Material Specials -> Remove Unused Slots`

Test File:
#91691.blend

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.68 **Blender Version** Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-09-24 14:03, hash: `95ec6e4dd3` Worked: never **Short description of error** In the Material panel in the Properties editor, there is a drop-down next to the material slots. Selecting "Remove unused slots" will remove materials that are assigned to particle systems/hair. So it seems unless material slots are assigned to at least one face, this function deletes their slots. **Exact steps for others to reproduce the error** - Add 2 material slots to the default cube - Slot 1: skin and Slot 2: hair. - Ensure the skin material is applied to all faces of the cube - Add a hair particle system - Under the Particle System's Render tab, select the hair material slot. - Render to ensure materials are assigned correctly. - Return to the material tab in the properties editor and click the "Remove unused slots" option from the drop-down # Watch the hair material slot be deleted. --- or - Open .blend file - Switch Viewport Shading to `Material Preview` # In material Properties: `Material Specials -> Remove Unused Slots` Test File: [#91691.blend](https://archive.blender.org/developer/F10585208/T91691.blend)

Nikhil Shringarpurey commented

2021-09-24 21:02:10 +02:00

Added subscriber: @Nikhil.Net

Nikhil Shringarpurey commented

2021-09-24 21:08:15 +02:00

This appears to be a shortcoming in the "bool BKE_object_material_slot_used(ID *id, short actcol)" function in material.c from what I can tell. I can work on a fix if others agree this behavior is not good.

Pratik Borhade commented

2021-09-25 12:52:22 +02:00

Added subscriber: @PratikPB2123

Pratik Borhade commented

2021-09-25 12:52:22 +02:00

Hi, thanks for the report. I think the option removes the materials which are not linked to any object.

Not quite sure if this is expected output. Will leave this for other triagers, developers to check.

Hi, thanks for the report. I think the option removes the materials which are not linked to any object. Not quite sure if this is expected output. Will leave this for other triagers, developers to check.

Nikhil Shringarpurey commented

2021-09-26 01:39:59 +02:00

In #91691#1225773, @PratikPB2123 wrote:
Hi, thanks for the report. I think the option removes the materials which are not linked to any object.

Not quite sure if this is expected output. Will leave this for other triagers, developers to check.

Thanks, Pratik. Yes, it currently only loops thru all MPoly's and all MFace's and checks if those have the material assigned. The real logic appears to exist in mesh.c at line 1447. The method is called "BKE_mesh_material_index_used(...)"

> In #91691#1225773, @PratikPB2123 wrote: > Hi, thanks for the report. I think the option removes the materials which are not linked to any object. > > Not quite sure if this is expected output. Will leave this for other triagers, developers to check. Thanks, Pratik. Yes, it currently only loops thru all MPoly's and all MFace's and checks if those have the material assigned. The real logic appears to exist in mesh.c at line 1447. The method is called "BKE_mesh_material_index_used(...)"

Germano Cavalcante commented

2021-09-27 15:19:02 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2021-09-27 15:19:02 +02:00

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

Germano Cavalcante commented

2021-09-27 15:19:02 +02:00

Apparently this operator only considers a material to be "used" if any face has the material assigned.
But the particles assigned to the object may be using the material, so it's technically being "used".
So I'm considering it as a bug, either because of the functionality or because of the Operator's description.

Apparently this operator only considers a material to be "used" if any face has the material assigned. But the particles assigned to the object may be using the material, so it's technically being "used". So I'm considering it as a bug, either because of the functionality or because of the Operator's description.

blender-admin commented

2021-09-27 18:07:01 +02:00

This issue was referenced by 6578db57cd

This issue was referenced by 6578db57cd878a94bdbdabe953c8819625c5a811

Bastien Montagne commented

2021-09-27 18:09:42 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Bastien Montagne closed this issue

2021-09-27 18:09:42 +02:00

Bastien Montagne self-assigned this 2021-09-27 18:09:42 +02:00

Thomas Dinges added this to the 3.0 milestone 2023-02-08 15:59:02 +01:00

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Selecting "Remove unused slots" in Materials panel removes slots that are assigned to particle systems/hair #91691

Watch the hair material slot be deleted.

In material Properties: Material Specials -> Remove Unused Slots

In material Properties: `Material Specials -> Remove Unused Slots`