Sunday, August 22, 2021

ERC Morphs and FACS

Enhanced Remote Control (ERC) consists of a number of methods for remotely controlling various channels in DAZ Studio. It can be viewed as generalized morphs, which in practice come in three types:

  1. Shapekeys that change the mesh.
  2. Bone translations, rotations and scale transformations that affect the meshes.
  3. Changes to the bones' pivot point without affecting the meshes.

The first type corresponds to driven shapekeys in Blender, and the second to drivers for the bones' location, rotation and scale channels. However, the third type has no counterpart in Blender. It would correspond to morphs that modify the head and tail of bones in edit mode, but in Blender this is impossible. 

Old-fashioned morphs for Genesis 3 and 8 consist mainly of bone poses of the second type, accompanied by additional shapekeys, and they work well in Blender. (Even more old-fashioned morphs for Genesis 1 and 2 are pure shapekeys.) However, the FACS morphs for Genesis 8.1 mostly consist of shapekeys together with changes in the pivot points, i.e. a combination of type 1 and 3, although some morphs rotate bones where rotation is necessary (eyes, eyelids, jaw and tongue). This can lead to problems in some cases, in particular with tongue morphs.

To the left we have the FACS Tongue Out morph. A shapekey moves the tongue mesh out of the mouth, but the tongue bones do not follow. In DAZ Studio the bones are also moved without affecting the mesh further. That would correspond to the change in edit mode to the right. However, these changes are ignored by the plugin, since it is impossible to drive the rest pose location in Blender.
This problem does not affect the mesh as long as we only combine this morph with other morphs that also work with shapekeys. However, if we combine it with morphs that rotate the bones, we may have problems.
Here we have such a case, where Tongue Out is combined with Tongue Right and Tongue Tip Bend. The two latter morphs rotate the tongue, and their influence it too big because the pivot points remain too far back. Note that the FACS morphs have non-zero final values, to the right, even though the sliders are zero. This is because another morph drives the FACS morphs.
We can compensate by increasing the Tongue Tip Bend slider. That increases the final value of this morph (i.e. it decreases the magnitude of the final value), and the tongue no longer intersects the skin.