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Linked Mesh Editing Doesn't Work As Expected When Using Data Transfer Modifier
Confirmed, NormalPublicKNOWN ISSUE

Description

System Information
Operating system: Windows-10-10.0.17763-SP0 64 Bits
Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.19

Blender Version
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-02-12 16:20, hash: rB77d23b0bd76f
Worked: 2.81 (sub 16), branch: master, commit date: 2019-12-04 11:32, hash: rBf1aa4d18d49d

Short description of error
Object instances doesn't work as in blender 2.81

Exact steps for others to reproduce the error

In blender 2.81, after entering the edit mode, all instances become active. You can see changes in real time.
Screen below:

In Blender 2.82 it work ok till some time. I couldn't determine at what moment it breaks...

Changes appears only after You enter to object mode.

Here is blend file to test

Event Timeline

Campbell Barton (campbellbarton) changed the task status from Needs Triage to Confirmed.Feb 17 2020, 3:30 AM
Campbell Barton (campbellbarton) changed the subtype of this task from "Report" to "Bug".

Confirmed, the strange thing about this behavior, is making a linked duplicate of Veg_Tree_Birch_A.002 does show in edit mode when any of the other objects are edited.

Hi. Its any chance to fix this issue and ad it to upcoming Blender 2.82a proposed revisions? For everyone who works in game industry this is a very annoying issue.

B282a is for crucial issues only (crashes, high prio etc). This might be an annoying issue for a small group of people, but if we let every annoyance become high prio than we will never be able to release anything. Better to keep to the proposed release schedule.

It is on my desk for b283.

After minimizing the scene it is clear that this related to the data transfer modifiers that are used. After removing the data transfer modifier it seems to work. Note that disabling the modifier isn't enough.

See here for the minimum example.

I will check if we can finetune this.

DRW_object_is_in_edit_mode ask the dependency graph if the object is changed. the depsgraph response that it is changed so the drawing assumes that it is a different mesh.

This is correct as the data transfer modifier adds data to the source mesh so the mesh is modified in the provided file. In the given example files both meshes are different. Only when selecting the original tree and enter edit mode result in that both meshes are in edit mode. The fact for this is that you always edit the base mesh.

In blender 2.82 we introduced the option to make edit mode modifier aware to overcome several issues.

  • editing objects in multiple windows at once.
  • don't show modifiers from other objects when editing a different object with the same base mesh

A solution to this specific problem is to not change the source mesh when the modifier is disabled in editmode or cage mode. Currently the object is already modified during building of the depsgraph. Which is really early on and might be a limitation of the current design. I will need to check with others as this is a bit outside of my knowledge.

Jeroen Bakker (jbakker) changed the subtype of this task from "Bug" to "Known Issue".EditedMar 31 2020, 9:03 AM
Jeroen Bakker (jbakker) edited projects, added Modifiers; removed Modeling.

The data transfer node changes the source object by adding some custom data masks
(MOD_datatransfer.c#130 -> DEG_add_customdata_mask(ctx->node, dtmd->ob_source, &cddata_masks);.
This makes the object modified as it will generates and store the custom data layers in the source object. This data will then be used during the transfer.

Removing the mentioned line will let the user edit both meshes, but of course would break the data transfer.
Blender 2.82 is more strict in the linked mesh edit, as the previous implementation could crash or render undesired results.

I will set this issue to known issue for now. as my impression the solution would need a redesign of the data transfer modifier. The linked mesh edit works as designed.

Related reports:

Jeroen Bakker (jbakker) renamed this task from Object instances doesn't work properly to Linked Mesh Editing Doesn't Work As Expected When Using Data Transfer Modifier.Mar 31 2020, 9:05 AM

Ok , I understand. So for solution we must wait a little longer than expected or its a higher possibility to have this situation work in blender 2.83?

@Kamil Makowski (kamilozo) Unfortunately not for 2.83.0. It's tagged as a Known Issue, so it won't be worked on for a while as this requires a lot of work and the developers are busy with other priorities.