collection instance rotates 90 degrees automatically when being instantiated by another object with mirror modifier #77575
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Reference: blender/blender#77575
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System Information
Operating system: mac os 10.14.6
Graphics card: Intel Iris Plus Graphics 655
Blender Version
Broken: version: 2.82a, 2.30.0 release, 2.90 (sub 3), branch: master, commit date: 2020-05-24 21:18, hash:
5db2d9c82b
Worked: Unsure.
Short description of error
as shown in the following screenshot, to use modifiers on a collection instance I parent the collection instance to a plane and change the instancing of the plane to faces, so that the collection instance will follow what modifiers will affect on the plane, but when using the mirror modifier with mirror object set to an empty at the center, the collection instance on the other side rotates 90 degrees on z axis automatically, which is not expected
Exact steps for others to reproduce the error
open the attached .blend file and you'll see the problem
collection instance problem.blend
Steps if you want to recreate from scratch:
Suzzane
.Suzzane
create a Suzzane (Monkey Head) then disable the collection in the outliner.Suzzane
by pressingShift+A -> Collection Instance -> Suzzane
. From now onwards, we will be working in this new collection.Suzzane
then the plane and parent theSuzzane
to the plane withCtrl+P -> Object
Suzzane
and hid it with the little eye icon.Object
tab selectInstancing -> Faces
.Suzzane
is rotated 90 degrees rather than mirrored.Added subscriber: @389150029
#88708 was marked as duplicate of this issue
Added subscriber: @Alaska
Changed status from 'Needs Triage' to: 'Needs User Info'
Are you able to upload the .blend file or provide the steps required to reproduce the issue?
I'm having difficultly trying to reproduce this issue in my own files.
sorry, I accidentally deleted the file when I edit the task and I didn't notice, the file is now uploaded
Changed status from 'Needs User Info' to: 'Confirmed'
Can confirm. Seems to also affect Blender 2.83 and 2.82.
Will add some steps to the original task just in case someone wants to recreate this from scratch.
Added subscriber: @Jamumamu
I encountered this same problem today and did a little investigation. It appears this is a side-effect of how face instancing works:
When calculating the basis for the instance it takes the Z axis to be the face normal and the X axis to point in the direction of the first edge of the polygon. Mirroring a polygon requires its vertex order to be reversed for the normal to be consistent, which means X will now point in the direction of the last edge. For a quad, this results in a 90 degree rotation.
Here's an illustration of the problem with a pentagon: only the two indicated vertices affect the orientation of the axis marker.
To solve this, Blender would need to either:
Hope this helps.
This comment was removed by @Jamumamu
Added subscriber: @tonpix
What's the status of this bug? Is there some ETA for fix? I had the same issue as well, parented Collection Instance to Plane that had Array + Curve + Mirror. Instances on mirrored side had incorrect rotations sadly. I've attached an simplified .blend if it helps anyone
arrayIssue.blend
Added subscriber: @SUNGHOON-JEONG
In my case, I was modeling an audio mixing console and found this problem.
With Faces Instancing, you only need to bind one object that array multiple planes to an armature.
It's very efficient because you only need one source mesh and one instance object.
A more complete modeling workflow would be possible if the opposite side flipped by the mirror modifier didn't rotate 90 degrees.
I created a potential fix for this some time ago but it never felt like the "right" solution. As far as I know this is (one of?) the only features in Blender that cares about vertex order. There aren't tools for viewing or reordering face vertices and based on the little bit of research I've done it seems that going down that path is discouraged (which I think I agree with).
In my opinion the real fix is improving the instancing toolset to provide some options for the instancing itself. This could better leverage features Blender already provides. For example:
I don't know whether this fits better with the roadmap for instancing in general, however.
Added subscribers: @Olliver, @lichtwerk
Added subscriber: @asdf-1
this seems to be still happening, does anybody know of a workaround?
I would suggest just using geometry nodes at this point since they give you a lot more control, at the expense of a more complex workflow.