Regression: Instanced NURBs or CURVES on mesh vertices are not visible in 3.2+ #100706

System Information
Operating system: Linux-5.19.2-arch1-1-x86_64-with-glibc2.36 64 Bits
Graphics card: AMD CEDAR (DRM 2.50.0 / 5.19.2-arch1-1, LLVM 14.0.6) X.Org 4.3 (Core Profile) Mesa 22.1.6

Blender Version
Broken: version: 3.2, 3.3, 3.4.0
Worked: 3.1

NURBS issue caused by edcbf741df
Same for curves if they have geometry, that is broken b9febb54a4

Short description of error

When instancing surfaces like NURB sphere on mesh vertices through parenting, the surfaces are not visible.

instancedNURBS.blend

In 3.1:

In 3.2+:

Added subscriber: @OmarEmaraDev

blender/blender-addons#100566 was marked as duplicate of this issue

blender/blender-addons#100553 was marked as duplicate of this issue

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

Added subscriber: @Zhaoxu-Li

Added subscriber: @fzm

Added subscriber: @lichtwerk

Same for curves if they have geometry (actually think this has been reported before and was ruled a Known Issue, let me dig that up)

works with Geometry Nodes:
instancedNURBS_GN.blend

Added subscriber: @HooglyBoogly

Caused by edcbf741df

Reading the commit message it is not totally clear if this was expected, will raise prio here to get an answer shortterm.
Would assume this ends up as a Known Issue though.

CC @HooglyBoogly

related: #93159 (Particle don't emit curves/text in 3.0 beta )
The same thing for curves is broken since b9febb54a4 btw.

Added subscriber: @Blendphys

Dear all:

I can confirm this bug because it quite strongly affects the [Atomic Blender add-on ]] (NURB balls are used to represent the atoms and are inside an [ https:*docs.blender.org/manual/en/dev/addons/import_export/mesh_atomic.html#the-instancing-vertex-structure | instancing vertex structure , with the vertices being the atom positions). With version 3.1.2 it works but starting with version 3.2.x it started to not work. It is not working with the current exp. version 3.4.0.
Note that there is no such an issue with Mesh balls ... .

Operating system: Ubuntu 22.04, 64Bit

I'll try to look into this one tomorrow. Can't say for sure how fixable it is yet though.

Added subscriber: @brecht

It turns out the instances are being created properly, but the dependency graph iterator skips them because of deg_object_hide_original.
I don't really understand that function. I guess it's hiding instances when the instance of type OB_DUPLIVERTS | OB_DUPLIFACES but the parent object did have one of those types turned on?

That said, the comment doesn't make much sense to me: Automatic hiding if this object is being instanced on verts/faces/frames by its parent.
"Being instanced on verts" seems like a typical situation, I'm not sure why it has special attention here.

@brecht, do you remember adding that function in D4109? I'm curious if the issue it's working around is related to missing depsgraph relations or just plain visibility handling.

This is logic has existed forever, but was lost in the new depsgraph and then restored again in D4109. The idea is that if you instance an object on vertices/faces, you automatically hide the original object. We don't want to hide the instances, only the original.

The logic is a bit more complicated for the case where you instance a collection containing a setup like this. In that case the instance of the original object that comes in through the collection should be hidden, but the instances from the vertices/faces should be visible.

The easiest way to keep backwards compatibility may be to set dob->type to the same value it would have had if there were was no geometry set. I also see some code in OBJECT_OT_duplicates_make_real checking dob->type, for that case it may also be better if geometry sets didn't change it.

This issue was referenced by e508de0417

Changed status from 'Confirmed' to: 'Resolved'

Dear Hans, thanks for your kind support!

I tried out the instancing, and see what I get (2 example files). It seems that the instancing only works for 2 vertices so far? ;-) Or is it me who is doing something wrong? Thanks for some comments ... . Cle.

System: 64Bit Ubuntu, Blender Info see last image

Example_cube.blend

Example_KBr_crystal.blend

Thanks for testing @blendphys. It looks like that was broken by a follow-up fix to this fix.
Now I committed another fix for that, your file works for me now: 0e6d893d07

Yep, now it works, thanks a lot, @HooglyBoogly !

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Regression: Instanced NURBs or CURVES on mesh vertices are not visible in 3.2+ #100706