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This is a feature request to have more flexibility around vertex attributes and skinning. When blend weights and/or blend indices are present in the vertex streams Unity enforces a strict layout. This enforced layout firstly, enforces the division of attributes in certain streams. Secondly, it enforces specific format and dimension. For normals this means 3 components in float32. For tangents this is 4 components in float32. This is described in part here (https://docs.unity3d.com/2023.2/Documentation/ScriptReference/Rendering.VertexAttributeDescriptor.html). I have added a ticket to the backlog to update documentation in order to call out the latter detail more explicitly. In this case it is observed that the issue does not reproduce when “FBX Import Settings > Rig > Animation Type” is set to None. This is because when the option is set to None blend weights and indices are not added to the vertex stream. As a result the layout for skinning is not enforced.
Reproduction steps:
1. Open the “MeshAttribs” project
2. In Project Browser expand the “unit_orc“ asset
3. Select the “unit_orc (Mesh)” subasset
4. In Inspector observe the Normal and Tangent values
Expected result: Both are “Float16 x 4 (8 bytes)”
Actual result: Normal is “Float32 x 3 (12 bytes)“, Tangent is “Float32 x 4 (16 bytes)“
Reproduced in: 2021.3.27f1, 2022.3.2f1, 2023.1.0f1, 2023.2.0a20
Reproduced using: Windows 10, macOS 13.4 (Intel)
Note: The reporter is trying to optimize the mesh vertex buffer formats by using “Float16 x 4” for normals and tangents. They do so with SetVertexBufferParams in an AssetPostprocessor using OnPostprocessModel. This works as expected for non-skinned meshes. But when importing a skinned mesh, the normal format gets reset to “Float32 x 3” and the tangent format to “Float32 x 4”. Not reproduced when “FBX Import Settings > Rig > Animation Type” is set to None. Calling UploadMeshData after SetVertexBufferParams also resets the format. Calling GetVertexAttributes after UploadMeshData shows the reset Normal and Tangent format
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