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FBX Exporter: vertices exported in incorrect position causing mesh deformation
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Description

System Information
Operating system: Windows 10 x64
Graphics card: RTX 2070

Blender Version
Broken: 2.79, 2.8

Short description of error
When skinned meshes are exported with FBX 7.4 binary the position of vertices does not export correctly.
As a result meshes are deformed (visible but not extreme in most cases) after export.

Note that external tools/software may be required to compare the meshes as the bug may be invisible upon re-import to blender.
A good way to see the differences is to use the mesh wireframe in iso view in blender versus unity for example.

Comparison of before and after in sample case (Click to load gif)

Exact steps for others to reproduce the error

  1. Load the attached blend file.

  1. Export to FBX using 7.4 binary
  2. Compare the position of vertices before and after export.

Details

Type
Bug

Event Timeline

Tsuna Hiiragi (Tsuna) updated the task description. (Show Details)
Tsuna Hiiragi (Tsuna) updated the task description. (Show Details)
Tsuna Hiiragi (Tsuna) updated the task description. (Show Details)
Tsuna Hiiragi (Tsuna) updated the task description. (Show Details)
Sebastian Parborg (zeddb) lowered the priority of this task from Needs Triage by Developer to Needs Information from User.Mar 7 2019, 12:58 PM

I can't reproduce this on re-import into blender.

If blender imports the generated file, that means that at least to blender, the positions does not change.
There is not much we can do with simply "it doesn't import correctly in other program".

Tsuna Hiiragi (Tsuna) added a comment.EditedMar 9 2019, 9:35 PM

It may be difficult to see in blender on its own but this is a significant issue as you can not trust blenders export.
This means that the model is deformed in unity, unreal etc when it has been exported from blender (and only from blender).

It's a big deal when any kind of precision is needed.

Sebastian Parborg (zeddb) raised the priority of this task from Needs Information from User to Needs Triage by Developer.Mar 11 2019, 11:47 AM

@Bastien Montagne (mont29) can you reproduce this?

Bastien Montagne (mont29) lowered the priority of this task from Needs Triage by Developer to Normal.Mar 12 2019, 10:25 AM

No, cannot reproduce, but I don’t have access to Unity or UE currently.

Re-importing into Blender works as expected, so geometry itself is definitively not altered, issue likely comes from the rigging (binding matrices and all that). Although I would still find it odd that this shows in some other app but not in Blender. FBX works in mysterious ways… :(

Tsuna Hiiragi (Tsuna) added a comment.EditedAug 6 2019, 2:52 PM

{F7651610}So I found a semi viable workaround which is to set pose to rest position until the issue was small enough. This can take anywhere between 1 to 30 attempts. However due to some changes in 2.8 this is not possible anymore.
The mesh always exports in the exact same state. However the incorrect positioning of the verts is more major in 2.8

See attached a testcase for 2.8