Can't use shape key properties in driver when modifiers generate a new mesh #65148

New Issue

Jose Conseco · 2019-05-26T15:17:22+02:00

Jose Conseco commented

2019-05-26 15:17:22 +02:00

System Information
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 660/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 416.94

Blender Version
Broken: version: 2.80 (sub 72), branch: blender2.7, commit date: 2019-05-23 20:37, hash: b3f96da2e6
Worked: 2.79

Short description of error
I have simple setup: two objects with shape keys. Lets say obj1 called 'Parent' (not really parented) with shape key that drives shape key 2 on child object. Works ok.
But when we add modifier to 'Parent' obj, and use 'Update dependencies' of child driver properties, error is displayded: 'Invalid python expression'. This works ok in blender 2.79

Exact steps for others to reproduce the error
In attached blend file:

Change shapekey value on 'Parent' object. Child is updated. Works ok
Add subsurf od 'Parent' obj, and press 'update dependencies'. It won't work now even though it worked in 2.79
Blend file:
Shape_modifier_bug.blend
And video with steps:
Shape_modifer_bug.mp4

And for reference same file for blender 2.79b - it works ok:
Shape_modifier_works279.blend

**System Information** Operating system: Windows-10-10.0.17134 64 Bits Graphics card: GeForce GTX 660/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 416.94 **Blender Version** Broken: version: 2.80 (sub 72), branch: blender2.7, commit date: 2019-05-23 20:37, hash: `b3f96da2e6` Worked: 2.79 **Short description of error** I have simple setup: two objects with shape keys. Lets say obj1 called 'Parent' (not really parented) with shape key that drives shape key 2 on child object. Works ok. But when we add modifier to 'Parent' obj, and use 'Update dependencies' of child driver properties, error is displayded: 'Invalid python expression'. This works ok in blender 2.79 **Exact steps for others to reproduce the error** In attached blend file: 1. Change shapekey value on 'Parent' object. Child is updated. Works ok 2. Add subsurf od 'Parent' obj, and press 'update dependencies'. It won't work now even though it worked in 2.79 Blend file: [Shape_modifier_bug.blend](https://archive.blender.org/developer/F7070375/Shape_modifier_bug.blend) And video with steps: [Shape_modifer_bug.mp4](https://archive.blender.org/developer/F7070379/Shape_modifer_bug.mp4) And for reference same file for blender 2.79b - it works ok: [Shape_modifier_works279.blend](https://archive.blender.org/developer/F8307299/Shape_modifier_works279.blend)

Jose Conseco commented

2019-05-26 15:17:22 +02:00

Added subscriber: @JoseConseco

blender-admin commented

2019-05-26 15:17:22 +02:00

#74207 was marked as duplicate of this issue

Jacques Lucke commented

2019-05-27 14:39:07 +02:00

Added subscribers: @Sergey, @JacquesLucke

Jacques Lucke commented

2019-05-27 14:39:07 +02:00

I guess the issue is that the shape keys do not exist on the mesh anymore after modifiers are applied. So the data path does not exist on the parent, when the driver is evaluated.
I don't really see how that could be fixed in a good way...

@Sergey Any ideas? Should this work currently?

I guess the issue is that the shape keys do not exist on the mesh anymore after modifiers are applied. So the data path does not exist on the parent, when the driver is evaluated. I don't really see how that could be fixed in a good way... @Sergey Any ideas? Should this work currently?

Sergey Sharybin self-assigned this 2019-05-27 14:50:27 +02:00

Sergey Sharybin commented

2019-05-27 14:50:27 +02:00

@JacquesLucke, confusing part here is that path might or might not depending on the order of updates. There is definitely something to be sanitized here.

Sergey Sharybin was unassigned by Dalai Felinto

2019-12-23 16:34:15 +01:00

Bastien Montagne commented

2020-02-26 18:40:27 +01:00

Added subscribers: @Jun-Takahashi, @mont29, @lichtwerk

Sybren A. Stüvel self-assigned this 2020-02-28 10:47:41 +01:00

Bastien Montagne commented

2020-02-28 10:51:21 +01:00

(Copy-pasting my comment from #74207):

The issue here is that the drivers gets evaluated by the depsgraph, using evaluated datablocks. And evaluated objects have evaluated obdata (like mesh) from modifier stack, which obviously have no shapekeys anymore (since those shapekey data would be completely invalid for the mesh generated by the modifiers most of the time).

Am not sure how to fix that best tbh, @Sergey Sharybin (sergey) might have ideas here?

(Copy-pasting my comment from #74207): The issue here is that the drivers gets evaluated by the depsgraph, using evaluated datablocks. And evaluated objects have evaluated obdata (like mesh) from modifier stack, which obviously have no shapekeys anymore (since those shapekey data would be completely invalid for the mesh generated by the modifiers most of the time). Am not sure how to fix that best tbh, @Sergey Sharybin (sergey) might have ideas here?

Sybren A. Stüvel commented

2020-02-28 11:02:49 +01:00

@mont29 To me that sounds like this is not a bug in Blender but a known limitation. There is quite a simple workaround: add a few custom properties and use those to drive the shapekeys on both objects. Here is a demo:

workaround.blend

@mont29 To me that sounds like this is not a bug in Blender but a known limitation. There is quite a simple workaround: add a few custom properties and use those to drive the shapekeys on both objects. Here is a demo: [workaround.blend](https://archive.blender.org/developer/F8377600/workaround.blend)

Bastien Montagne commented

2020-02-28 11:09:18 +01:00

@dr.sybren wouldn't mind having some depsgraph expertise on this topic first. If (as I suspect) this is not easily solvable, then yes, think we can consider it a known limitation. But if some relatively simple solution exists, then I think the issue is important enough to be considered a bug. :)

Sybren A. Stüvel removed their assignment 2020-02-28 11:12:17 +01:00

Sybren A. Stüvel commented

2020-02-28 11:12:17 +01:00

Added subscriber: @dr.sybren

Sergey Sharybin commented

2020-02-28 14:27:41 +01:00

@dr.sybren, this used to work before dependency graph changes done in 2.80, so is something to be fixed in one way or another than to be called a limitation. "New" dependency graph is to allow having more comprehensive setups, not to introduce limitations.

@mont29, simple idea: allow evaluated mesh to reference shapekeys with mesh it was crated for, Will keep RNA paths valid, and should not cause issues: sine evaluated mesh is not meant to be re-evaluated, so shapekeys will be ignored.

@dr.sybren, this used to work before dependency graph changes done in 2.80, so is something to be fixed in one way or another than to be called a limitation. "New" dependency graph is to allow having more comprehensive setups, not to introduce limitations. @mont29, simple idea: allow evaluated mesh to reference shapekeys with mesh it was crated for, Will keep RNA paths valid, and should not cause issues: sine evaluated mesh is not meant to be re-evaluated, so shapekeys will be ignored.

Sybren A. Stüvel changed title from ~~Cant drive ob1 shape key, by obj2 shape key, if modifier is added to obj2~~ to Can't use shape key properties in driver when modifiers generate a new mesh

2020-05-19 12:08:20 +02:00

Sybren A. Stüvel self-assigned this 2020-05-19 12:08:20 +02:00

blender-admin commented

2020-08-13 12:53:21 +02:00

This issue was referenced by cb2565195e

This issue was referenced by cb2565195e72ee4dc5c0b53b7cd5037b2169d55f

Sybren A. Stüvel commented

2020-08-13 14:01:21 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Sybren A. Stüvel closed this issue

2020-08-13 14:01:21 +02:00

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Can't use shape key properties in driver when modifiers generate a new mesh #65148