Custom tangents are destroyed upon FBX import and export #101303

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Festivity · 2022-09-23T16:24:30+02:00

Festivity commented

2022-09-23 16:24:30 +02:00

System Information
Operating system: Windows-10-10.0.22000-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3050 Laptop GPU/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 516.94

Blender Version
Broken: version: 3.3.0, branch: master, commit date: 2022-09-06 15:39, hash: 0759f671ce
Worked: As far as I know, never.

Short description of error
Meshes can have custom tangent data just as meshes can have custom normal data. With the in-built FBX I/O, I cannot bring meshes in and out of Blender without being able to keep data intact. Attached are images of what the custom tangents should look like in Unity. I know that Unity is Y-up and Blender is Z-up which could potentially cause these differences, but please read a bit further for my explanation.

Normals in Unity:

Custom tangents in Unity:

Normals in Blender:

Custom tangents in Blender:

The logic is this - if in Unity, the custom tangents (in this specific scenario) resemble the normals of the mesh, why does it look so vastly different from the normals in Blender? IF I were to take a guess, it might be Blender performing unnecessary calculations with the imported custom tangents. I hope I've gotten my point across.

Exact steps for others to reproduce the error

The problem can be seen when importing the mesh I will provide. Use the shader editor and the Geometry node outputting the Tangent to see the supposed custom tangents.

testmodel1.fbx

**System Information** Operating system: Windows-10-10.0.22000-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3050 Laptop GPU/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 516.94 **Blender Version** Broken: version: 3.3.0, branch: master, commit date: 2022-09-06 15:39, hash: `0759f671ce` Worked: As far as I know, never. **Short description of error** Meshes can have custom tangent data just as meshes can have custom normal data. With the in-built FBX I/O, I cannot bring meshes in and out of Blender without being able to keep data intact. Attached are images of what the custom tangents should look like in Unity. I know that Unity is Y-up and Blender is Z-up which could potentially cause these differences, but please read a bit further for my explanation. *Normals in Unity:* ![image.png](https://archive.blender.org/developer/F13560328/image.png) *Custom tangents in Unity:* ![image.png](https://archive.blender.org/developer/F13560312/image.png) *Normals in Blender:* ![image.png](https://archive.blender.org/developer/F13560330/image.png) *Custom tangents in Blender:* ![image.png](https://archive.blender.org/developer/F13560387/image.png) The logic is this - if in Unity, the custom tangents *(in this specific scenario)* resemble the normals of the mesh, why does it look so vastly different from the normals in Blender? IF I were to take a guess, it might be Blender performing unnecessary calculations with the imported custom tangents. I hope I've gotten my point across. **Exact steps for others to reproduce the error** 1. The problem can be seen when importing the mesh I will provide. Use the shader editor and the Geometry node outputting the Tangent to see the supposed custom tangents. [testmodel1.fbx](https://archive.blender.org/developer/F13560442/testmodel1.fbx)

Festivity commented

2022-09-23 16:24:30 +02:00

Added subscriber: @Festivity

Scurest commented

2022-09-23 16:33:48 +02:00

Added subscriber: @scurest

Scurest commented

2022-09-23 16:33:48 +02:00

Does Blender have custom tangents?

Festivity commented

2022-09-23 17:10:14 +02:00

In #101303#1421664, @scurest wrote:
Does Blender have custom tangents?

I am not sure what this means unfortunately. The meshes themselves have the custom tangents that are properly interpreted in Unity, Maya and 3DS Max.

> In #101303#1421664, @scurest wrote: > Does Blender have custom tangents? I am not sure what this means unfortunately. The meshes themselves have the custom tangents that are properly interpreted in Unity, Maya and 3DS Max.

Scurest commented

2022-09-23 17:37:24 +02:00

The FBX may have custom tangents, but if custom tangents are not a feature that exists in Blender they won't be imported. I'm asking does Blender even have custom tangents at all? AFAIK it doesn't. There are custom normals, but tangents are always computed as far as I can tell.

Festivity commented

2022-09-23 18:03:05 +02:00

In #101303#1421688, @scurest wrote:
The FBX may have custom tangents, but if custom tangents are not a feature that exists in Blender they won't be imported. I'm asking does Blender even have custom tangents at all? AFAIK it doesn't. There are custom normals, but tangents are always computed as far as I can tell.

They are imported albeit broken as I've said earlier. Tangents don't need to be computed. If a game developer wants to put custom information nothing related to tangents in the tangents then they can do it and access it in the shader. It seems that Blender doesn't allow us to choose between calculating the tangents or using the imported ones and so therefore, the custom tangents are always prioritized as far I know. These imported custom tangents are bugged however.

> In #101303#1421688, @scurest wrote: > The FBX may have custom tangents, but if custom tangents are not a feature that exists in Blender they won't be imported. I'm asking does Blender even have custom tangents at all? AFAIK it doesn't. There are custom normals, but tangents are always computed as far as I can tell. They are imported albeit broken as I've said earlier. Tangents don't need to be computed. If a game developer wants to put custom information nothing related to tangents in the tangents then they can do it and access it in the shader. It seems that Blender doesn't allow us to choose between calculating the tangents or using the imported ones and so therefore, the custom tangents are always prioritized as far I know. These imported custom tangents are bugged however.

Germano Cavalcante commented

2022-09-23 21:11:19 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2022-09-23 21:11:19 +02:00

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

Germano Cavalcante closed this issue

2022-09-23 21:11:19 +02:00

Germano Cavalcante commented

2022-09-23 21:11:19 +02:00

I don't know what you mean by "custom tangent data".
The tangents used for the normal maps are calculated from the UV map.
This is a convention of many 3D applications, otherwise a normal map would not work between applications.

And the image only shows a radially generated tangent in Blender. This is not informative.

This report does not contain all the requested information, which is required for us to investigate the issue.

Please submit a new report and carefully follow the instructions.

A guideline for making a good bug report can be found at https://wiki.blender.org/wiki/Process/Bug_Reports

I don't know what you mean by "custom tangent data". The tangents used for the normal maps are calculated from the UV map. This is a convention of many 3D applications, otherwise a normal map would not work between applications. And the image only shows a radially generated tangent in Blender. This is not informative. This report does not contain all the requested information, which is required for us to investigate the issue. Please submit a new report and carefully follow the instructions. A guideline for making a good bug report can be found at https://wiki.blender.org/wiki/Process/Bug_Reports

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Custom tangents are destroyed upon FBX import and export #101303