Hi there, I replied to another topic with this information, but felt it better to start a new topic to hopefully bring it to other developers’ and Epic’s attention. Some context: for the project I work on, I’ve been fully documenting the character creation process in Unreal and finding lots of issues.
To illustrate the severity of the state of Unreal’s FBX importer: Due to the unit-conversion bug with Unreal’s FBX importer (below), I concluded it wasn’t possible to have a bug-free Blender-to-Unreal pipeline* (even with the official Unreal Blender add-on), so I made a new Blender add-on to circumvent the issue. This was then immediately followed by the release of UE5.5, which made the Interchange importer the new default, which introduced more bugs.
So, here are all the issues I know of with FBX importing in Unreal:
New bugs with the Interchange FBX Importer:
- If I import an animation FBX containing morph target animation, it will split it into 2 sequence files. This should be a toggle-able option, and it should not do this by default.
- When importing an FBX with a skeletal mesh and at least 1 animation, the skeletal mesh’s bind pose will be set to the first frame of the animation.
Existing bugs with the FBX Importer:
- In UE 5.4, the FBX importer appeared to fix unit-conversion issues (bones now appear the correct scale), but local bone transforms are still wrong. This means that Blender FBX exports (including those from Epic’s official addon) will import with incorrect local bone transforms. This causes Physics Assets to not generate correctly, and any Anim Graph logic working with local transforms will not compute correctly. More info here
- Morph Target normals are calculated incorrectly, as in the math is subtly wrong. I filed a bug about this forever ago but it didn’t get noticed. If memory serves, the code calculates an absolute normal direction but applies it as a delta, and it’s just luck that it kinda-sorta looks correct. More info here
- The FBX importer needs an option to toggle whether morph targets modify a model’s normals or not. This is something Unity supports, and is a key feature for NPR (non photo real) assets. Technically not a bug, but a critical oversight.
I want to brings these issues to Epic’s attention so that they can be fixed. The new Interchange importer is a disruption, but I’m hopeful it means better tools are on the horizon.
*The exception is if you use Auto Rig Pro, which has an export option to circumvent the unit conversion import bug. My add-on is a free alternative.