Expressions are stored and treated as differences from the Neutral Pose, this means it’s possible to go back to it without necessarily compromising successive work that had already happened; nonetheless getting the best possible Neutral Pose is always the first step, and shouldn’t be rushed. Ideally it’s a task that will be performed only once for a finalized design.
To inspect and/or modify the Neutral Pose you can enter the Neutral Pose editing mode, select an LOD, and assemble the scene.
We strongly recommend always working on LOD0, and letting the plugin take care of lower resolution LODs.
Technical Inspection
Whether you are satisfied with the likeness directly out of Mesh to MetaHuman, or need to treat the mesh to apply creative changes, there are a few things you always want to look at and correct for if they show up.
Lip Seal
In the neutral pose the lips should be completely sealed, without gaps and without intersections.
Eyelid Folds and Seal
Eyelids are by far the most intricate part of the mesh and the most likely to exhibit issues and require corrections.
The eyelid shell and folds shouldn’t intersect, nor be too thin. The eyelid shell shouldn’t intersect with the other EyeMeshes at all.
Mouth Pocket / Teeth
Teeth should be flush with the lips with no intersections; the pocket should have enough space to not intersect gums, teeth, or the outer shell.
Symmetry
The Neutral pose is supposed to be a relaxed, highly symmetrical pose. That’s not to say you can’t have characterized asymmetry in it, but it should not be asymmetry in expressions (for example, the talent that was scanned wasn’t fully relaxed and neutral.)
In the case of static asymmetry that looks like a pose (for example,. someone with a permanently pulled corner) it’s still better, if at all possible, to artificially symmetrize the Neutral Pose and reintroduce the detail as baseline animation.
Intersections
The most common intersections will be found in the eyes and mouth, but it’s still a good idea to inspect the ears and the fatty tissue spots around the chin and neck to make sure the head mesh isn’t self-intersecting there.
Mesh Correspondences
The eye is made of many meshes that need to be well aligned with the rest, for example, the eye film and the eyelashes. They should always be inspected and noted as needing fixing if they don’t line up with the head mesh and each other.
If there have been issues around the eyelids, they will almost certainly have carried over to other meshes. Even if you didn’t need any corrections to the eyelids, these details should still be inspected.
Shape Modeling
If you want to refine the results of a previous step, or that you have even larger creative needs like adding a characterization pass or a pseudo-human morphology, you’ll need to update the vertex positions accordingly in the DNA that’s in memory.
Depending on how close the mesh fitting and auto rigging pass got you to the desired results, you might not need this step at all.
LODs lower than 0 can be updated from the changes operated on LOD 0; unless you have very specific needs for one of the LODs you can rely on the automatic updates.
After operations that affect Multiple LODs automatically it’s recommended that you reload the DNA file. Multi-LOD operations that write to a file are performed separately from the in-memory image of DNA, which will then be out of sync.
To update the DNA in memory you need to assemble the LOD you want to change, modify its vertex positions to their target positions, then use Update Vertices in the Expression Editor toolbar in Neutral Pose editing mode.
The steps (with a loaded DNA) are as follows:
Set Expression Editor to Neutral Pose editing.
Select LOD 0.
Assemble LOD 0 into the scene.
Set Scene Meshes to desired vertex positions, this can be done two different ways:
By directly modifying the mesh in the scene.
- or -
By using reference meshes to copy their point positions.
Select first the assembled LOD0 mesh from the Expression Editor outliner, then the target (imported) mesh.
Click on “Transfer Vertices”.
Import the mesh(es) with the target vertices positions.
Repeat for all meshes that need changes.
Press “Update Vertices” in the Expression Editor toolbar, this will read from the meshes in the scene and write to the DNA in memory.
At this step, the surface joints and some volume joints are automatically placed tomatch the new volume.
If you decide to save at this point, and choose to automatically propagate changes to lower LODs, load the DNA before moving to following operations. Please note that saving isn’t strictly necessary here.
Joint Placement
There is only one skeleton working across all LODs. Joint placement should be performed in LOD0, where all the joints are visible and their effect can be inspected.
Once the Neutral Pose Geometry has been shaped, joint placement should be matched to the new volume.
If the Mesh comes from the Mesh to MetaHuman process with no reduction in the offset (using the Global Delta parameter in the Head controls), and/or the point positions were tweaked, you will almost certainly notice a gap between surface joints and the mesh. This, however, won’t be noticeable if you updated vertices, as those joints will have been automatically updated (see previous section.)
Surface joints should be left to automation and not tweaked manually. You can find an extensive list of joint categories and whether they are automatically placed or not in the Fundamental section, under Rig Operations.
There is no precise rule for volume joint placement, and some regions have a more obvious ideal placement than others. Some examples follow.
Eyes can simply be matched to the volume of the eyeball (taking care of not moving their children accidentally, which will be placed by surface positioning on the correct areas of the mesh.) In example for the left eye: FACIAL_L_EyelidUpperB, FACIAL_L_EyelidUpperA, FACIAL_L_EyelidLowerA, FACIAL_L_EyelidLowerB, FACIAL_L_Eye, FACIAL_L_EyeParallel would all be moved to the center of geometry of the eyeball mesh’s median loop.
The mouth is similar to the eye, but it has several joints that need to be treated in groups, and the positioning, while intuitive, needs to be eyeballed depending on the volume of the fleshy parts of the lips.
Next Up
Skin Weights
Validate and tweak skin weights.