Face instancing giving unexpected behaviour in combination with the mirror modifier and various deform modifiers #88708

New Issue

Mr Chocolate Bar · 2021-05-31T16:17:58+02:00

Mr Chocolate Bar commented

2021-05-31 16:17:58 +02:00

System Information
Operating system:
Win10
Graphics card:

Blender Version
Broken: 3.0.0 Alpha
Worked: -

Short description of error

Mirroring & using deform modifiers result in unpredictable results when using "face instancing".

As you can see in the screenshot, the "instanced" geometry (the children of the object using face instancing) wont mirror accordingly. Similar issues appear when using many of the deform modifiers,

Expected behaviour
Face instancing should be able to use in combination with modifiers, and the results should display appropriately.

Exact steps for others to reproduce the error
Create a new blend file, add a plane & enable face instancing, parent the default cube under it and move it so you can see the plane & cube separately.

Now add another mesh, move it to a location of choice & add a mirror modifier to our face instance plane & set the mirror object to this new mesh.

Rotate the default cube by some odd value, say 25 degrees on every angle and apply the rotation.

Now you should be able to clearly see how the cube doesnt mirror properly when instanced with the face instancing.

This can also be reproduced with most deform modifiers.

If you apply the modifiers of our face instanced plane, enable Viewport > Edit mode > Overlays > Developer > Indices you will see something like this:

and from here we can make a guess that likely, the face instancing algorithm uses face instances to determine the rotation of the face. Which gets broken by the mirror modifier (and several deform modifiers).

**System Information** Operating system: Win10 Graphics card: **Blender Version** Broken: 3.0.0 Alpha Worked: - **Short description of error** Mirroring & using deform modifiers result in unpredictable results when using "face instancing". As you can see in the screenshot, the "instanced" geometry (the children of the object using face instancing) wont mirror accordingly. Similar issues appear when using many of the deform modifiers, ![image.png](https://archive.blender.org/developer/F10150832/image.png) **Expected behaviour** Face instancing should be able to use in combination with modifiers, and the results should display appropriately. **Exact steps for others to reproduce the error** Create a new blend file, add a plane & enable face instancing, parent the default cube under it and move it so you can see the plane & cube separately. Now add another mesh, move it to a location of choice & add a mirror modifier to our face instance plane & set the mirror object to this new mesh. Rotate the default cube by some odd value, say 25 degrees on every angle and apply the rotation. Now you should be able to clearly see how the cube doesnt mirror properly when instanced with the face instancing. This can also be reproduced with most deform modifiers. If you apply the modifiers of our face instanced plane, enable Viewport > Edit mode > Overlays > Developer > Indices you will see something like this: ![image.png](https://archive.blender.org/developer/F10150849/image.png) and from here we can make a guess that likely, the face instancing algorithm uses face instances to determine the rotation of the face. Which gets broken by the mirror modifier (and several deform modifiers).

Mr Chocolate Bar commented

2021-05-31 16:17:58 +02:00

Added subscriber: @Olliver

Mr Chocolate Bar commented

2021-05-31 16:38:16 +02:00

Seems there is an abandoned branch for this already: https://developer.blender.org/D8445

Philipp Oeser commented

2021-06-01 14:05:18 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2021-06-01 14:05:18 +02:00

I think this is actually to be considered as a Known Limitation

https://docs.blender.org/manual/en/dev/scene_layout/object/properties/instancing/faces.html#limitations-considerations

But yeah, since we already have #77575 (collection instance rotates 90 degrees automatically when being instantiated by another object with mirror modifier) I think it makes sense to merge these reports.
And using geometry nodes might get the recommended way of doing this (even though the face method is a lot quicker to set up)

I think this is actually to be considered as a Known Limitation https://docs.blender.org/manual/en/dev/scene_layout/object/properties/instancing/faces.html#limitations-considerations But yeah, since we already have #77575 (collection instance rotates 90 degrees automatically when being instantiated by another object with mirror modifier) I think it makes sense to merge these reports. And using geometry nodes might get the recommended way of doing this (even though the face method is a lot quicker to set up)

Philipp Oeser commented

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

Closed as duplicate of #77575

Philipp Oeser closed this issue

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

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Face instancing giving unexpected behaviour in combination with the mirror modifier and various deform modifiers #88708