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FBX Import Level node rotation bug under rare circumstances


When importing a fbx map will lights and some nodes that doesn't have attribute, I found out that a node that doesn't have an attribute, gets rotated around 90° yaw if the node before it was a light.

I had to debug the engine and found out that the potential issue is in the file "Engine\Source\Editor\UnrealEd\Private\Fbx\FbxMainImport.cpp" in functionFFbxImporter::TraverseHierarchyNodeRecursively. The issue is that ChildInfo.AttributeUniqueId is not initialized, causing it to get a value that was previously on the stack if the node doesn't have an attribute. For UE developers, the fix is to simply add ChildInfo.AttributeUniqueId = ChildInfo.UniqueId when the node doesn't have an attribute.

I have checked and the bug is still present on UE 4.13 preview.

Product Version: UE 4.12
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asked Aug 07 '16 at 07:14 PM in Bug Reports

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avatar image Tim Hobson ♦♦ STAFF Aug 08 '16 at 12:52 PM

Can you please provide detailed repro steps from your modeling program to UE4?

Also, is this any mesh or only Skeletal/Static that are affected? Does modeling program matter, or have you tested with multiple programs, or FBX versions (ie. 2013, 2014/2015, 2016)?

Thank you!


avatar image Ley0k Aug 09 '16 at 12:17 AM

Unfortunately, I generate FBX files through C++ code, I haven't found a way to reproduce this bug in 3ds max, I use FBX2016, so this affects other versions aswell. You can reproduce this through code by creating a light node and another node without setting to this one an attribute, adding the light first then the other node to the scene.

I have attached a FBX that reproduces this bug by using the Import Level feature in UE. The scene consists of one light, 2 nodes without an attribute and a node with a FbxNull attribute that is used avoid this bug.

When asking the question I didn't know about FbxNull, as it solved my issue since. However, people may encounter this rare bug if they use custom tools.

empty_level.zip (2.1 kB)
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1 answer: sort voted first

Thanks for the clarification. I've added a ticket for this issue.

You can track the status here: https://issues.unrealengine.com/issue/UE-34410

Thank you!


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answered Aug 09 '16 at 02:17 PM

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Tim Hobson ♦♦ STAFF
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avatar image Kakushi_52 Feb 12 '19 at 05:33 AM

Has this been fixed? With UE 4.21, whenever I try to import any FBX by "Import Into Level" with an option "Individual level Actors", all actors imported have been rotated 90 degrees in X.

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