Can't import or export Alembic with changing UVs #76132

New Issue

Niko Maisuradze · 2020-04-26T21:24:56+02:00

Niko Maisuradze commented

2020-04-26 21:24:56 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 432.00

Blender Version
Broken: version: 2.83 (sub 15), branch: master, commit date: 2020-04-23 21:07, hash: d712f1f83a
Worked: (newest version of Blender that worked as expected)

Short description of error
After exporting alembic of object with changing UVs, after importing, UVs either appear frozen on first frame, or in case of varying vertex count - they disappear after first frame.

Exact steps for others to reproduce the error

Open attached blend file. Export "sph_for_export" object to alembic. Import alembic. Assign material with texture on uv coordinates. UVs will be frozen to first frame.
Open attached blend file. Export "sph_varying_for_export" object to alembic. Import alembic. Assign material with texture on uv coordinates. UVs will desappear after first frame.

uv_test.blend

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 432.00 **Blender Version** Broken: version: 2.83 (sub 15), branch: master, commit date: 2020-04-23 21:07, hash: `d712f1f83a` Worked: (newest version of Blender that worked as expected) **Short description of error** After exporting alembic of object with changing UVs, after importing, UVs either appear frozen on first frame, or in case of varying vertex count - they disappear after first frame. **Exact steps for others to reproduce the error** 1. Open attached blend file. Export "sph_for_export" object to alembic. Import alembic. Assign material with texture on uv coordinates. UVs will be frozen to first frame. 2. Open attached blend file. Export "sph_varying_for_export" object to alembic. Import alembic. Assign material with texture on uv coordinates. UVs will desappear after first frame. [uv_test.blend](https://archive.blender.org/developer/F8496530/uv_test.blend)

Niko Maisuradze commented

2020-04-26 21:24:56 +02:00

Added subscriber: @NikoMaisuradze

Richard Antalik commented

2020-04-28 21:57:19 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Brecht Van Lommel commented

2020-05-01 18:01:25 +02:00

Added subscribers: @dr.sybren, @brecht

Brecht Van Lommel commented

2020-05-01 18:01:25 +02:00

@dr.sybren, not sure if this should be triaged as known limitation or bug.

Sybren A. Stüvel commented

2020-05-12 14:47:04 +02:00

This is a two-fold issue:

In the exporter, UVs are explictly only exported on the first frame (thanks to if (m_first_frame && m_settings.export_uvs) { … }).
In the importer, the animation of UVs and normals is overlooked; when the mesh geometry is not animated, the entire mesh is considered constant.

I consider the former as a bug, even though it looks like an explicit choice. When exporting an animated mesh the topology can change, and then the UV coordinates of the first frame are no longer valid. This issue is easy to fix by changing that if-statement to if (m_settings.export_uvs) { … }. The only downside to this is that Alembic files may become larger when a mesh is detected as "animated" while its UV map is not. Apart from the size of the exported file (and thus the speed of exporting & importing) I don't see any issue with this.

The latter I certainly also consider a bug. Fortunately, this is also very simple to fix by adding a few more checks to the appropriate has_animations() function.

This is a two-fold issue: - In the exporter, UVs are explictly only exported on the first frame (thanks to `if (m_first_frame && m_settings.export_uvs) { … }`). - In the importer, the animation of UVs and normals is overlooked; when the mesh geometry is not animated, the entire mesh is considered constant. I consider the former as a bug, even though it looks like an explicit choice. When exporting an animated mesh the topology can change, and then the UV coordinates of the first frame are no longer valid. This issue is easy to fix by changing that if-statement to `if (m_settings.export_uvs) { … }`. The only downside to this is that Alembic files may become larger when a mesh is detected as "animated" while its UV map is not. Apart from the size of the exported file (and thus the speed of exporting & importing) I don't see any issue with this. The latter I certainly also consider a bug. Fortunately, this is also very simple to fix by adding a few more checks to the appropriate `has_animations()` function.

Sybren A. Stüvel changed title from ~~Cant export Alembic with changing UVs~~ to Can't import or export Alembic with changing UVs

2020-05-12 14:47:45 +02:00

blender-admin commented

2020-05-12 14:48:18 +02:00

This issue was referenced by 65574463fa

This issue was referenced by 65574463fa2d31dc912cf886649c62a7d0ad2450

blender-admin commented

2020-05-12 15:06:29 +02:00

This issue was referenced by 94cbfb71bc

This issue was referenced by 94cbfb71bcf4f0499301f7c6f201124d8740cacf

Sybren A. Stüvel commented

2020-05-12 15:07:41 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Sybren A. Stüvel closed this issue

2020-05-12 15:07:41 +02:00

Sybren A. Stüvel self-assigned this 2020-05-12 15:07:41 +02:00

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Can't import or export Alembic with changing UVs #76132