Adding Grease Pencil Monkey Object crashes Blender if Link Material is set to Object in User Preferences #56220
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Reference: blender/blender#56220
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System Information
Windows 10, Quadro 4000
Blender Version
Broken: 2.8, Hash
3eab49dd36Worked: unknown
When you set the Material Link to Object in the User Preferences, and afterwards try to add the Grease Pencil Monkey Object, Blender crashes with an Access Violation.
Exact steps for others to reproduce the error
Load Factory Settings
Go to Edit -> User Preferences -> Editing
Set Link Materials To to Object
Use Shift + A -> Grease Pencil -> Monkey
Adding a Blank Grease Pencil object works, but misbehaves when drawing strokes. They disappear immediately after drawing.
Added subscriber: @RainerTrummer
Added subscriber: @s12a
I can confirm the crash with
e1a6861987and debug build under:Attaching console output and backtrace.
blender.crash.txt
console_output.txt
Added subscriber: @JoshuaLeung
@JoshuaLeung Could you take a look on this? You know better than me how works this and I'm not sure I understand the internal working of link material to object.
@JoshuaLeung Doing debug I have found the Material ***matar = give_matarar(ob); line returns NULL when is Object mode.
I know there is a copy between ob->mat and ob->data->mat but for some reason when the object is GPENCIL and mode is Object this copy is not working. Do you know where is this code?
Added subscriber: @mont29
@mont29 Could you give me any idea here? I don't know where look. It must be something I forgot, but I don't know what.
@antoniov Just seen from a user perspective, maybe it‘s not even needed to have the option Link To Object available for Grease Pencil objects. It makes a lot of sense for mesh objects, as it allows instances to receive different materials, but for Grease Pencil strokes this might be overkill. What do you think? Should Grease Pencil simply ignore that setting in the User Preferences?
Added subscriber: @brecht
I don't see a good reason to make an exception for grease pencil here, we should just fix the bug.
@antoniov, there is a synchronization between objects and data to ensure their material array size is the same. However the actual pointers to the material are not copied, so the material pointer in the object data material array can (and should) be
NULLin this case.I suggest to use
give_current_material()to retrieve the material in the loop where this crashes, so that it automatically gets you the material from the object or its data as needed, instead of usinggive_matarar().@brecht Thanks for the info, I going to try to fix it. And agree, why have an exception here?
@brecht Using give_current_material() fix the bug, but I have a new problem now, using BKE_object_material_slot_find_index(ob, ma) always returns 0, but when the material is at data level returns the right index. What I'm doing wrong?
I have checked and the materials are added to objects and the object materials mode is enabled.
Don't worry I have found the solution
Ok, I was just going to say
BKE_object_material_slot_find_indexseems to be only used by grease pencil, it should usegive_current_material()as well.This issue was referenced by
5c4fd52612Changed status from 'Open' to: 'Resolved'