Hi Epic, hi all,
We are making an UE game that will likely have procedural animation and IK (it’s inspired by Bungie’s Oni, which sets quite a high bar for locomotion and animation). We’ve worked with the Mixamo rig until now (which hasn’t been long), and we want to start using the UE4 rig from now on, to take advantage of the work that has already gone into procedural animation and IK for it.
Anyway, I was tasked with making a character creation pipeline that would produce UE4-ready FBX files that would directly work with the UE4 rig, without any retargeting needed after import, so I took a look at the SK_Mannequin.FBX exported from UE4, intending to use it as a template. Apart from the unusual orientation of skeleton bone axes and the UE4-exclusive IK bones and “twist” controllers on the limbs, I noticed a weird asymmetry of the “twist” controllers on the arms (see the first image, “SK_Mannequin_twist.png”, and its annotation). My thoughts upon seeing this were, if I am going to import a character in a similar A-pose, with some vertices mapped to those “twist” regions to make the most of the UE4 rig, is this really what the rest position of the twist bones is supposed to be like?
It was also not clear to me why upperarm_twist_01_l and upperarm_twist_01_r start at the shoulder joints, whereas the other six “twist” bones start roughly in the middle of their respective limb section (lowerarm_twist_01_l and lowerarm_twist_01_r, thigh_twist_01_l and thigh_twist_01_r, calf_twist_01_l and calf_twist_01_r). See the attached “SK_Mannequin_twist2.jpg”.
So what I did is, I reimported that UE4-exported SK_Mannequin.FBX back into UE4. (Note that I didn’t save to FBX from Blender, so it’s essentially a roundtrip from UE to FBX and back. So you can reproduce the following on your side using UE4 and nothing else.) After animating the roundtripped Skeletal Mesh with one of the stock animations, here is what I get (“SK_Mannequin_Roundtrip_General.jpg”).
As you can see, the roundtrip is mostly OK, but something is going wrong with upperarm_twist_01_l (left shoulder) and with lowerarm_twist_01_r (right wrist). Both these groups end up translated in the direction of their respective limb section, for no clear reason, by about half the length of the limb section. See the closeup picture “SK_Mannequin_Roundtrip_Arms_Issues.jpg”
Another issue is with the feet (“SK_Mannequin_Roundtrip_Feet_Issues.jpg”). Somehow the toe sections are not aligned with the foot but end up slighlty lower. This is a comparatively minor issue, and at least it is symmetrical, so it can be worked around rather easily. The arm twist issue, though, is some asymmetrical bug that I’d rather not have to work around, if it can be fixed.
Can someone acknowledge this roundtrip issue, and confirm it as a bug of the FBX export and/or import from UE4? If it’s a bug, can it be adressed in some foreseeable future? Thanks.
I am exporting SK_Mannequin to FBX with all the default settings (filename SK_Mannequin_Roundtrip.FBX), then reimporting it into Mannequin/Characters/Mesh with all the default settings except the Skeleton (which I set to “None” because I want UE4 to import the supposedly UE4-consistent skeleton from the FBX). Finally I roundtrip an idle animation (exported as ThirdPersonIdleRoundtrip.FBX, then reimported into Mannequin/Animations (assigned to the roundtripped skeletal mesh SK_Mannequin_Roundtrip). If I roundtrip the animation and assign it to the base SK_Mannequin, it animates as expected, so as far as I can tell the animation roundtrips fine; it’s the Skeletal Mesh that isn’t self-consistent after roundtripping through FBX.
I am using UE 4.18.2, installed yesterday.
Thanks again for any response or assistance.