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linked duplicate objects - issues with selection in edit mode
Open, Needs Triage by DeveloperPublic


System Information
Operating system: Windows-10-10.0.16299 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.67

Blender Version
Broken: version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-12 18:00, hash: rB2404220e80a9

Short description of error

There are problems with selection when you edit two objects at the same time in edit mode: the original object and a linked duplicate. See the video:



Event Timeline

I see two things here:

  1. You want to edit the two linked objects at the same time, but you can only edit one the active one.

I don't think this rises to the level of a bug, but a feature request. Ideally you could select any element from the inactive object and it would instantly become the active object.
(It might also be nice to be able to work on any feature from both object, but I think the ability to perform operations such as rotate and scale on selections across multiple instances of the same mesh at the same time might introduce complexity.)

  1. The selection display falls out of sync between instances until you perform an operation.

I can confirm this. It happens either if you have one or multiple instances selected, all other instances enter edit mode then don't sync selections properly.

I really only meant that selections don't sync properly.

Ah, ok then. Yep that's a bug.

I can confirm this bug, but there are two scenarios:

  1. You are only editing one of the objects.

In this case I think we shouldn't draw the "edit mode engine" layer for the dupli objects. So the bug reported here won't even be a problem.

  1. You are editing both objects at the same time (multi-object editing):

In this case, in the ideal world, we should be able to select, snap, ... both of them, and be ready to some really unexpected effects when e.g. knife cutting across them both.
However since at the moment we iterate over "unique data" most of the time, I think it is no surprise this doesn't work well.

Any thoughts gentlemen? cc @Campbell Barton (campbellbarton) @Clément Foucault (fclem) @Brecht Van Lommel (brecht)

My short-term proposal is to disable drawing of the non-object mode engines for dupli objects. And in the future we can have (2) implemented.

Also note that the bug is real and it only happens for meshes - curves, lattice, armatures, they are all good.
That said I stick to what I said, despite what we had in 2.79 I think we should NOT draw edit data for the the dupli data of the other objects.

@Jeroen Bakker (jbakker) looked into a bug related to this, but I can't find it quickly now. Apparently it was not trivial to make it work well with modifiers.

I don't care too much about drawing the edit mode cage for other linked duplicates, it is somewhat confusing. It has just worked like that for a very long time.