Once the Neutral Pose has been treated, before working on Expressions, it’s worthwhile to validate Skin Weights, and tweak them if necessary.
Skin Weights are the only part of the workflow that is LOD specific. Weight map tweaks will need to be repeated coherently across as many LODs as you plan to use in your assets.
When the character has human morphology, usually, only the eye region requires some attention. The further away from that morphology one moves, and the more likely it is that work on skin weights in other areas will benefit the model.
Skin weights are a large part of what makes vertices semantically significant. If you manipulate the vertex semantics, editing the skinning becomes necessary to re-establish vertex/joint correspondence that works with the new semantics of the vertices. Conversely, changes in vertex/joint coupling (what influences a vertex) change the vertex’ semantics, making it more/less suited to its placement.
In all cases, we recommend treating skinning as a technical exercise, not a creative one. To verify the work as it’s being performed we recommend the use of synthetic animation and poses that have a clear meaning and which are obviously correct or incorrect.
Step by Step
To edit skin weights, after having loaded the DNA with the Neutral Pose treatment, you can do the following:
Set Expression Editor to Skin Weights Editing mode.
Select as many LODs from the Expression Editor outliner as you intend to edit.
Assemble the selection into the scene (and confirm that you want a new scene to be created)You should now have a scene where the rig is available and connected to the mesh.
The rig in this scene acts as a preview rig, and doesn’t have morph targets, it relies entirely on skinning alone
(Optional but recommended) Load animation that controls the areas you wish to tweak, for example, a blink.
Lock joints in the Paint skin Weights tool, only leaving unlocked what you will be editing, including joints you want to subtract from; very frequently the head joint will be your main source to subtract from.
Proceed as you would normally when weight editing until the mesh looks correct in your test poses.
Repeat for as many meshes as necessary (matching eye meshes edits with head mesh).
Repeat for as many LODs as necessary.
Commit the changes to the DNA in memory by clicking Update From Scene Contents.
Save the work to a DNA file.
You can work on LODs and commit to DNA separately for each LOD. If you have 5 LODs you want to work on, you don’t have to work on them concurrently, you can work on them one at a time, commit to DNA in memory, then work on another.
Common Operations for the eyes
The eyes are by far the most common area where Skin Weights will be tweaked. The eye is the region with the most separate meshes contributing to its appearance. We recommend starting from the eyelids, then matching any changes to all other meshes.
It’s recommended to start by rotating FACIAL_[L|R]_EyelidUpperA joints (through the blink controls on the rig), look at whether the eyelids are being flattened (not preserving a sectional contour of the eyeball). When tweaking weights to close the eyelid seal, it’s recommended you keep an eye on the volume of the eyelid.
In fixing the eyes we recommend paying particular attention around FACIAL_[R|L]_EyeCornerOuter[1|2] and FACIAL_[R|L]_EyeCornerInner[1|2], the skin weights of those influences are best left alone as much as possible. Consider locking these influences and their weights before doing any work in the region.
In LOD 4 specifically, where some joints will have become excluded, there’s a specific trick you can use to help sealing the eyelid, but that should be used in small amounts:FACIAL_[L|R]_EyelidUpperA can be rotated slightly then translated down. This can help with the seal, but will also flatten the section of the eyelid. An excessive translation will likely result in the eyelid intersecting with the eyeball, so be mindful of that if you use it.
It’s not always possible to get perfectly to the look or correctness you need with just Skin Weight editing. For example, sometimes a small gap is acceptable and will have to be addressed in an Expression later.
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Eyelid closed before Skin Weight editing | Eyelid closed after Skin Weight editing |
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Expression Poses
Edit expression poses.