collection instance rotates 90 degrees automatically when being instantiated by another object with mirror modifier #77575

New Issue

zyc17 · 2020-06-07T19:43:10+02:00

zyc17 commented

2020-06-07 19:43:10 +02:00

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:

Create a new collection, I will call it Suzzane.
In the collection Suzzane create a Suzzane (Monkey Head) then disable the collection in the outliner.
In the new collection, create an instance of the collection Suzzane by pressing Shift+A -> Collection Instance -> Suzzane. From now onwards, we will be working in this new collection.
Create a plane. Select the instanced Suzzane then the plane and parent the Suzzane to the plane with Ctrl+P -> Object
In the outliner, select the instanced Suzzane and hid it with the little eye icon.
Select the plane and in the properties editor in the Object tab select Instancing -> Faces.
Give the plane a mirror modifier and notice how to newly instanced Suzzane is rotated 90 degrees rather than mirrored.

**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 ![屏幕快照 2020-06-08 上午1.30.46.png](https://archive.blender.org/developer/F8589456/屏幕快照_2020-06-08_上午1.30.46.png) **Exact steps for others to reproduce the error** open the attached .blend file and you'll see the problem [collection instance problem.blend](https://archive.blender.org/developer/F8597871/collection_instance_problem.blend) Steps if you want to recreate from scratch: 1. Create a new collection, I will call it `Suzzane`. 2. In the collection `Suzzane` create a Suzzane (Monkey Head) then disable the collection in the outliner. 3. In the new collection, create an instance of the collection `Suzzane` by pressing `Shift+A -> Collection Instance -> Suzzane`. From now onwards, we will be working in this new collection. 4. Create a plane. Select the instanced `Suzzane` then the plane and parent the `Suzzane` to the plane with `Ctrl+P -> Object` 5. In the outliner, select the instanced `Suzzane` and hid it with the little eye icon. 6. Select the plane and in the properties editor in the `Object` tab select `Instancing -> Faces`. 7. Give the plane a mirror modifier and notice how to newly instanced `Suzzane` is rotated 90 degrees rather than mirrored.

zyc17 commented

2020-06-07 19:43:10 +02:00

Added subscriber: @389150029

blender-admin commented

2020-06-07 19:43:10 +02:00

#88708 was marked as duplicate of this issue

Alaska commented

2020-06-08 06:43:22 +02:00

Added subscriber: @Alaska

Alaska commented

2020-06-08 06:43:22 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Alaska commented

2020-06-08 06:43:22 +02:00

open the attached .blend file and you'll see the problem

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.

> open the attached .blend file and you'll see the problem 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.

zyc17 commented

2020-06-08 07:13:14 +02:00

In #77575#948123, @Alaska wrote:

open the attached .blend file and you'll see the problem

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

> In #77575#948123, @Alaska wrote: >> open the attached .blend file and you'll see the problem > 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

Alaska commented

2020-06-08 07:25:18 +02:00

Changed status from 'Needs User Info' to: 'Confirmed'

Alaska commented

2020-06-08 07:25:18 +02:00

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.

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.

David Swift commented

2020-08-02 03:22:32 +02:00

Added subscriber: @Jamumamu

David Swift commented

2020-08-02 03:22:33 +02:00

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:

rotate the vertices by one spot any time it reverses the vertex order; i.e. [0,1,2,3] would become [1,0,3,2] (instead of [0,3,2,1]), or
change how the coordinate space is calculated (and probably offer options to select how to decide the X axis)

Hope this helps.

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. ![image.png](https://archive.blender.org/developer/F8737095/image.png) To solve this, Blender would need to either: - rotate the vertices by one spot any time it reverses the vertex order; i.e. [0,1,2,3] would become [1,0,3,2] (instead of [0,3,2,1]), or - change how the coordinate space is calculated (and probably offer options to select how to decide the X axis) Hope this helps.

David Swift commented

2020-08-02 19:04:17 +02:00

This comment was removed by @Jamumamu

*This comment was removed by @Jamumamu*

nameless commented

2020-10-05 21:38:08 +02:00

Added subscriber: @tonpix

nameless commented

2020-10-05 21:38:08 +02:00

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

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](https://archive.blender.org/developer/F8958783/arrayIssue.blend) ![image.png](https://archive.blender.org/developer/F8958761/image.png)

SHnJ commented

2020-11-25 09:51:46 +01:00

Added subscriber: @SUNGHOON-JEONG

SHnJ commented

2020-11-25 09:51:46 +01:00

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.

![img.png](https://archive.blender.org/developer/F9371002/img.png) 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.

David Swift commented

2020-12-06 23:51:48 +01:00

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:

Texture coordinates:
- Use the tangent space of the UV map to define the local x/y space
- z is calculated to be perpendicular (same as current behaviour)
- Mirroring geometry will produce predicable results
- UV tools can be used to adjust instancing

I don't know whether this fits better with the roadmap for instancing in general, however.

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: - Texture coordinates: - Use the tangent space of the UV map to define the local x/y space - z is calculated to be perpendicular (same as current behaviour) - Mirroring geometry will produce predicable results - UV tools can be used to adjust instancing I don't know whether this fits better with the roadmap for instancing in general, however.

Philipp Oeser commented

2021-06-01 14:05:26 +02:00

Added subscribers: @Olliver, @lichtwerk

G commented

2023-01-17 13:09:13 +01:00

Added subscriber: @asdf-1

G commented

2023-01-17 13:09:13 +01:00

this seems to be still happening, does anybody know of a workaround?

David Swift commented

2023-01-17 17:04:04 +01:00

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.

Philipp Oeser removed the

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collection instance rotates 90 degrees automatically when being instantiated by another object with mirror modifier #77575