Shape keys missing from bpy.data.meshes.new_from_object() even when the mesh Object is not evaluated #109313

New Issue

Thomas Barlow · 2023-06-23T23:24:28+02:00

Thomas Barlow commented

2023-06-23 23:24:28 +02:00

System Information
Operating system: Windows-10-10.0.19045-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 531.41

Blender Version
Broken: version: 4.0.0 Alpha, branch: main, commit date: 2023-06-19 17:26, hash: cedec09d0594
Worked: 2.79 (sort of, the API was a bit different due to the depsgraph not existing)

Short description of error
Creating a new Mesh from a mesh Object with bpy.data.meshes.new_from_object removes the shape keys (or simply does not copy the them in the first place), even when the Object is not evaluated.

The API in 2.79 is a little different to 2.80+, since there is no depsgraph; you choose with the function arguments whether or not to apply modifiers:
When using apply_modifiers=True, the new mesh has no shape keys as expected. Providing an evaluated Object to the function in 2.80+ is equivalent to this.
When using apply_modifiers=False, the new mesh retains its shape keys as expected. In my opinion, providing a non-evaluated Object to the function in 2.80+ should be equivalent to this.

2.79 API docs: https://docs.blender.org/api/2.79/bpy.types.BlendDataMeshes.html#bpy.types.BlendDataMeshes.new_from_object
Current API docs: https://docs.blender.org/api/current/bpy.types.BlendDataMeshes.html#bpy.types.BlendDataMeshes.new_from_object

Since the API changed between 2.79 and 2.80, it's not clear whether this is a bug or intended behaviour.
Object.to_mesh() and BlendDataMeshes.new_from_object() appear to have identical behaviour in 2.79, though this is again a bit different in 2.80+ because Object.to_mesh() now creates a temporary mesh owned by the Object that is not added to bpy.data.meshes.

Exact steps for others to reproduce the error

Create a mesh Object
Add a shape key (other than the 'Basis')
Enter Edit Mode
Modify the shape key so that it noticeably moves the mesh
Exit Edit Mode
Change the value of the shape key to 1.0
Run in the Python Console:
1. new_mesh = D.meshes.new_from_object(C.object, preserve_all_data_layers=True, depsgraph=C.evaluated_depsgraph_get())
2. C.object.data = new_mesh
Observe that the new mesh has no shape keys (and is not evaluated as expected)

Attached are some .blend files created in different Blender versions that have a script and three Objects that go over different cases (has modifiers/no modifiers/has modifiers but they're disabled) of creating meshes with both BlendDataMeshes.new_from_object and Object.to_mesh as well as making a copy of an evaluated mesh with Object.copy in 2.80+.

The 2.79 version is a bit different due to the different API, but the 2.80+ version in 4.0.0a results in this:
(the .to_mesh().copy() behaviour of evaluated Objects has been reported separately as #109327)

**System Information** Operating system: Windows-10-10.0.19045-SP0 64 Bits Graphics card: NVIDIA GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 531.41 **Blender Version** Broken: version: 4.0.0 Alpha, branch: main, commit date: 2023-06-19 17:26, hash: `cedec09d0594` Worked: 2.79 (sort of, the API was a bit different due to the depsgraph not existing) **Short description of error** Creating a new Mesh from a mesh Object with `bpy.data.meshes.new_from_object` removes the shape keys (or simply does not copy the them in the first place), even when the Object is not evaluated. The API in 2.79 is a little different to 2.80+, since there is no depsgraph; you choose with the function arguments whether or not to apply modifiers: When using `apply_modifiers=True`, the new mesh has no shape keys as expected. Providing an evaluated Object to the function in 2.80+ is equivalent to this. When using `apply_modifiers=False`, the new mesh retains its shape keys as expected. In my opinion, providing a non-evaluated Object to the function in 2.80+ should be equivalent to this. 2.79 API docs: https://docs.blender.org/api/2.79/bpy.types.BlendDataMeshes.html#bpy.types.BlendDataMeshes.new_from_object Current API docs: https://docs.blender.org/api/current/bpy.types.BlendDataMeshes.html#bpy.types.BlendDataMeshes.new_from_object Since the API changed between 2.79 and 2.80, it's not clear whether this is a bug or intended behaviour. `Object.to_mesh()` and `BlendDataMeshes.new_from_object()` appear to have identical behaviour in 2.79, though this is again a bit different in 2.80+ because `Object.to_mesh()` now creates a temporary mesh owned by the Object that is not added to `bpy.data.meshes`. **Exact steps for others to reproduce the error** 1. Create a mesh Object 1. Add a shape key (other than the 'Basis') 1. Enter Edit Mode 1. Modify the shape key so that it noticeably moves the mesh 1. Exit Edit Mode 1. Change the value of the shape key to 1.0 1. Run in the Python Console: 1. `new_mesh = D.meshes.new_from_object(C.object, preserve_all_data_layers=True, depsgraph=C.evaluated_depsgraph_get())` 1. `C.object.data = new_mesh` 1. Observe that the new mesh has no shape keys (and is not evaluated as expected) Attached are some .blend files created in different Blender versions that have a script and three Objects that go over different cases (has modifiers/no modifiers/has modifiers but they're disabled) of creating meshes with both `BlendDataMeshes.new_from_object` and `Object.to_mesh` as well as making a copy of an evaluated mesh with `Object.copy` in 2.80+. The 2.79 version is a bit different due to the different API, but the 2.80+ version in 4.0.0a results in this: (the .to_mesh().copy() behaviour of evaluated Objects has been reported separately as https://projects.blender.org/blender/blender/issues/109327) ![image](/attachments/ed5d740a-37b9-48b9-9881-87c64774f8ac)

(2.80)to_mesh_and_new_from_object_tests.blend

119 KiB

image.png

504 KiB

(2.79)to_mesh_and_new_from_object_tests.blend

87 KiB

Thomas Barlow added the

labels 2023-06-23 23:24:29 +02:00

Thomas Barlow referenced this issue from blender/blender-addons

2023-06-23 23:49:44 +02:00

Missing shape keys in FBX export when using Triangulate Faces #104714

YimingWu commented

2023-06-24 04:46:22 +02:00

Can confirm the behaviour.

From what I can see, new_from_object and to_mesh().copy() both respect the evaluation status if they do things this way:

new_from_object gives "original mesh without anything" when called on unevaluated object, and gives "completely applied result" when called on evaluated objects.
to_mesh() applies modifier if there is any, but when applying modifier it will have to apply shape keys (? because it's not applying modifiers to every single shape keys since that would lead to topology changes?)

So I think the problem is that if we want to make things consistent, we need to make sure that:

new_from_object to give mesh with shape keys
to_mesh() to always apply shape keys (?)

Can confirm the behaviour. From what I can see, `new_from_object` and `to_mesh().copy()` both respect the evaluation status if they do things this way: - `new_from_object` gives "original mesh without anything" when called on unevaluated object, and gives "completely applied result" when called on evaluated objects. - `to_mesh()` applies modifier if there is any, but when applying modifier it will have to apply shape keys (? because it's not applying modifiers to every single shape keys since that would lead to topology changes?) So I think the problem is that if we want to make things consistent, we need to make sure that: - `new_from_object` to give mesh _with_ shape keys - `to_mesh()` to always apply shape keys (?)

YimingWu added

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Shape keys missing from bpy.data.meshes.new_from_object() even when the mesh Object is not evaluated #109313

Shape keys missing from `bpy.data.meshes.new_from_object()` even when the mesh Object is not evaluated #109313