Object material turns to Grease Pencil materials - Bug #71533

System Information
Operating system: Linux-4.15.0-66-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 435.21

Blender Version
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-08 22:59, hash: 0a0d735acd
Worked: (optional)

Short description of error
Material of mesh object turns to Grease Pencil material.

Exact steps for others to reproduce the error
I just created object and plug it to use in hair particle system and it's material turns to Grease Pencil material so I can not to change material properly anymore. It happens time to time.

Bug_Material.blend

Added subscriber: @viadvena

Blender convert mesh to Grease Pencil object. When I exit from material tab, duplicate this object and convert it to mesh - command works, but after this I go to material tab and mesh turns to grease pencil back and produce error when I try to convert it to mesh. I delete material and conversion works and object turns to a mesh but material lost forever.

Added subscriber: @lichtwerk

Having a hard time reproducing this:

could you try to come up with the steps from the default scene to reproduce this?
or do you have a file we can open and then do a couple of steps that lead to the problem?

I just created object and plug it to use in hair particle system and it's material turns to Grease Pencil material

cannot reproduce

And yes, I can see the problem in the file from the report (it is just that I cannot reproduce it from scratch or with the steps provided)

I picked blendfile before with corrupted object. Here I pick actual scene where all started.
test_MatBug.blend
Please look deeply in collections with suffix _S - it's origin meshes for instances in particle systems. As I see all meshes that was instanced turns their mats in gp mats.

Also I can assume that it's happens only with procedural materials without image textures. And used Annotation tool with draw mode above meshes. It's just happens and unfortunately I can not say more. At some moment I just noticed it.

Added subscriber: @antoniov

@lichtwerk I'm looking a t the bug too. Try to find where BKE_material_init_gpencil_settings() is called. If we found why this is called, we will catch the bug.

@viadvena While we found the solution to the bug, you can recover your material running these lines in console:

bpy.data.materials.remove_gpencil_data(ma)```

In #71533#810151, @antoniov wrote:
@viadvena While we found the solution to the bug, you can recover your material running these lines in console:
bpy.data.materials.remove_gpencil_data(ma)```

Thank you! I appreciate this!

I'm going to create an script to fix your file in one step.

This script fix the file:


for ob in bpy.data.objects:

if ob.type == 'MESH':
for slot in ob.material_slots:
bpy.data.materials.remove_gpencil_data(slot.material)```

In #71533#810159, @antoniov wrote:
This script fix the file:


for ob in bpy.data.objects:
    if ob.type == 'MESH':
        for slot in ob.material_slots:
            bpy.data.materials.remove_gpencil_data(slot.material)```

Thanks a lot! It works) Could you please to help me with another thing: how can I force recompile shaders? Sometimes materials completely won't to updates. I struggled with this few times and in this situations helps install new build of blender. But may be there is much more esthetic way.

@antoniov: great!

Think we confirm this then? (or do we wnat to merge with #63707?)

We could merge both, but I'm unable to reproduce it, so no idea how fix it.

In #71533#810175, @antoniov wrote:
We could merge both, but I'm unable to reproduce it, so no idea how fix it.

Ah, I was thinking you were squashing the bug already.

While we found the solution to the bug

Anyways, since both issues seems to stem from the same roots [Annotations in play...], will merge these reports.
@viadvena : lets continue discussion in #63707, and please keep us up to date if you have found a way to reproduce [thanx for providing test_MatBug.blend -- but the corruption has already taken place in that file as well, and I am still not able to reproduce... will try more though...]

Closed as duplicate of #63707

Added subscriber: @Yianni

This comment was removed by @Yianni

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Object material turns to Grease Pencil materials - Bug #71533