get metahumans working

[AchimTuran]

Within this issue I will try to get a MetaHuman working for ALS with the help of TTToolbox v0.4. I will not create a detailed step by step guide here, only create some notes for myself. I'm planning to create a proper video for it soon.

We can tweak the hand locations slightly with offsets

And with a custom pose (scaled the preview a little bit to match the rotations better)

[AchimTuran]

1. Introduce unweighted bones
   make sure to set the correct preview mesh in the skeleton asset
   
   add unweighted bones to the skeleton asset (otherwise the preview mesh might not have enabled ik bones)
   

NOTE!
Check that the output log does not show any error messages (scripts will force the recompression of all anim sequences to constraint virtual bones)

[AchimTuran]

2. Introduce sockets
   

[AchimTuran]

3. Introduce virtual bones
   

[AchimTuran]

So we should see the sockets and virtual bones (hand vbs are not shown in the screenshot) after closing and reopening the skeleton asset of the MetaHuman

[AchimTuran]

4. ik rig creation
   It seems to be that the easiest way is to duplicate the existing ik rig from the metahuman
   

Then we delete the *Metacarpal (otherwise we will see very weird finger distortions) bone chains.

Again we set our correct preview meshm which makes it easier to see if everything works as expected.

If some ik bone chains exist we delete them as well. We will use the constraint solver from TTToolbox to retarget them properly.

Constraint bone chains are added to the solver settings.

((ConstraintBone="root",ModifiedBone="ik_foot_root"),(ConstraintBone="foot_l",ModifiedBone="ik_foot_l"),(ConstraintBone="foot_r",ModifiedBone="ik_foot_r"),(ConstraintBone="root",ModifiedBone="ik_hand_root"),(ConstraintBone="hand_r",ModifiedBone="ik_hand_gun"),(ConstraintBone="hand_r",ModifiedBone="ik_hand_r"),(ConstraintBone="hand_l",ModifiedBone="ik_hand_l"),(ConstraintBone="ik_foot_l",ModifiedBone="VB ik_foot_l_Offset"),(ConstraintBone="ik_foot_r",ModifiedBone="VB ik_foot_r_Offset"),(ConstraintBone="ik_hand_gun",ModifiedBone="VB RHS_ik_hand_gun"),(ConstraintBone="ik_hand_gun",ModifiedBone="VB LHS_ik_hand_gun"),(ConstraintBone="Hand_L",ModifiedBone="VB RHS_ik_hand_l"),(ConstraintBone="hand_r",ModifiedBone="VB LHS_ik_hand_r"),(ConstraintBone="calf_l",ModifiedBone="VB ik_knee_target_l"),(ConstraintBone="calf_r",ModifiedBone="VB ik_knee_target_r"),(ConstraintBone="root",ModifiedBone="VB Curves"),(ConstraintBone="ik_foot_l",ModifiedBone="VB foot_target_l"),(ConstraintBone="ik_foot_r",ModifiedBone="VB foot_target_r"))

Then we should see white bone names, which shows us that the solver is correctly setup.

In case the ik bones do not follow the ik goal. Reopen the ik rig.

[AchimTuran]

5. Skeleton Retargeting Options
   https://docs.metahuman.unrealengine.com/en-US/MetahumansUnrealEngine/MetaHumanRetargetAnimations/
   Everything set to skeleton and unweighted bones + root + pelivs to animation
   

[AchimTuran]

6. ik retargeter setup
   Duplicate the RTG_UE4Manny_UE5Manny and set the IK_metahuman_legacy and the preview mesh.
   
   

Introduce a custom pose (scaled the preview a little bit to match the rotations better)

We can tweak the hand locations slightly with offsets

To use root motion we need to set Globally Scaled on the root bone