Animations Retargeting

Official Documentations

The Unreal Engine Documentation on Animation Retargeting can be a useful introduction for beginners.

Animation Retargeting is a feature that allows animations to be reused between characters that use the same Skeleton asset but may have vastly different proportions.

Character Lineup.
Showing the different proportions among Rabbit Heart characters

Before retargeting is applied, you can already use animations between any Skeletal Meshes that share the same Skeleton asset (check out UE5’s Compatible Skeletons feature).

That means you don’t have to do any retargeting to characters that have the exact same skeleton and same skeleton proportion (you can use Compatible Skeletons).

But for Rabbit Heart characters, they all have a different proportion from the UE4 and UE5 Mannequin, so retargeting is needed to convert the animation from one proportion to another proportion.

Retarget Before After

Retargeting in Unreal Engine 5

New Retargeting Video

Official Documentations

Unreal Engine Documentation on Retargeting Bipeds with IK Rig (Basic Overview)

Unreal Engine Documentation on IK Rig Retargeting (Detailed description of all the settings)

In UE5, you need to use IK Rig + IK Retargeter, the setup is a bit more involved, but it offers more robust retarget capabilities than UE4.

Process Summary

The process looks like this:

UE5 Retarget Process

1. Create/Prepare IK Rig for both source and target characters.
2. Create an IK Retargeter, select the two IK Rigs when prompted (UE5.2, for UE5.3 manually select them in the Details panels). Tweak settings and export animation from inside the IK Retargeter window (see the picture below).

IK Retargeter Window

Check out this video to see the retargeting process for Shenya in UE5 (this video should also applies to other Rabbit Heart characters).

Part 2 (An update to video above):

Create IK Rig

Option 1: Duplicate Existing IK Rig

Tips

Creating an IK Rig can be daunting because of many steps it involved, I find that I can just duplicate an existing IK Rig and change the Preview Skeletal Mesh inside and it * should * works the same (WARNING: I haven’t do test to confirm they are exactly the same, but things looks fine and also works fine when I just duplicate)

Get Stock IK Rig from Third Person Content Pack

Add Feature or Content Pack

The Third Person Content Pack contains the stock IK Rig for UE4 and UE5 Mannequins that we can duplicate and use. The IK Rigs for the UE4 and UE5 mannequins are located in their own Rigs folder.

Stock IK Rig Location

Since Rabbit Heart characters are using the same skeleton as UE4’s Mannequin, you can duplicate the UE4 IK Rig IK_UE4_Mannequin and just change the Preview Skeletal Mesh to one of my character.

Duplicate UE4 IK Rig

Option 2: Create IK Rig from Scratch

Tips: Create Keyboard Shortcuts

Tips: Create Keyboard Shortcuts

You can create keyboard shortcuts in Editor Preferences to speed up the process. For example, we can use hotkey C to create New Retarget Chain.

Create Keyboard Shortcuts for IK Rig

0. Right click in the Content Browser, select Animation > IK Rig > IK Rig

Create IK Rig with Menu

Give it a meaningful name and double click the asset to open up the IK Rig Window

IK Rig Asset Thumbnail

The Window is empty when first created, select your skeletal mesh in the details panel to load it.

Set Skeletal Mesh

1. Set Retarget Root on pelvis (first thing first!).

Set Retarget Root

2. Create Retarget Chains

These are a list of chains we need to create.

Joint Chain List

Double Check Naming

Make sure the name is the same across all your different IK Rigs so later on when we do chain-mapping (in the retargeter), the program will have no problem matching the same name.

Select the Left joint chains and Mirror them to create the Right side.

Mirror Chain

Double Check Start Bone & End Bone

Make sure the Start Bone and End Bone is set to the correct joint, as it can be hard to debug this later. Also check the “IK Rig Output Log” for any errors.

When mirroring the finger chains, UE5.2 didn’t mirror them correctly and I have to fix it.

IK Rig Output Log shows an error when we mirror the chains (UE5.2)

Create chains for the IK bones. There are 7 of them. These are optional since UE is not able to retarget IK bones properly. I haven’t have success with retargeting IK bones, please let me know if you have any solutions.

There’s a Free plugin that can retarget IK bones: Free Bone Snapper. (Video)

IK Chains to create

IK Naming Tips

• Look for the name while ignoring “ik_” (eg. ik_foot_root -> FootRoot)
• “Left” and “Right” is at the start of the name (eg. ik_foot_l -> LeftFoot )
• Replace “_l” with “Left” (eg. ik_foot_l -> LeftFoot )
• All the names ended in “IK” (eg. ik_foot_l -> LeftFootIK )

3. Setup IK Solver

Note

The setup below is a mimic of the setup from the stock UE4 Mannuquin IK Rig, so follow along if your character uses the same UE4 Mannequin skeleton.

Why create the IK Solver?

The solver that we are going to create is called the “Full Body IK” solver. Without it, we won’t be able to use IK when we are inside the IK Retargeter.

*This only applies to your Target IK Rig. For your Source IK Rig, I don’t think you need to create any solver for it though.

IK On VS OK Off

Setup IK Solver

Create Full Body IK solver and Set Root Bone on Selected Solver.

Create Full Body IK Solver

Set Root Bone on Solver

Create 4 IK Goals (on the hand_l, hand_r, foot_l, foot_r).

Tips: Hotkey Ctrl + N

Create IK Goals

Drag the foot goals to go under ball joints.

Drag foot_l goal to under ball_l

The foots got broken. Reset the foots goal Transforms to fix it.

Broken Foot

Reset Foot Goal’s Transforms in the Details panel

Create Bone Settings for the pelvis, spines, clavicles, thighs and calves.

Create Fullbody IK Bone Settings

Set Rotation Stiffness on Pelvis, all the Spines and Clavicles, with the following values:

Bone Name	Bone Rotation Stiffness
pelvis	1
spine_01	0.784
spine_02	0.928
spine_03	0.936
clavicle_l	1
clavicle_r	1

Set Rotation Stiffness

Set Preferred Angles on thighs and calfs, with the following values

Bone Name	Bone Preferrred Angles
thigh_l, thigh_r	(0, 0, -90)
calf_l, calf_r	(0, 0, 90)

Set Preferred Angles

4. Done

Final Check

Finally, last check on the chain’s naming and see if the chain point to the correct bones (eg. LeftRing: ring_01_l -> ring_03_l (correct), LeftRing: ring_01_l -> ring_*02*_l (incorrect)).

Check chain names and bones

Create IK Retargeter

After we got both IK Rigs for the source and target character, create an IK Retargeter. Right click in the Content Browser, select Animation > IK Rig > IK Retargeter

Set Preferred Angles

Naming Convention

I use the format of “RTG_{source}_to_{target}”, eg. RTG_UE4Mannequin_to_Shenya.

{source} is the character that we want to copy animations from, {target} is the character that wants to have the new animations.

Double click the IK Retargeter asset to open the IK Retargeter Window.

1. Select the source and target IK Rig in the Details panel.

IK Retargeter Window

2. Switch to Retarget Pose

Difference between UE5.2 VS UE5.3

Note that the interface is a bit different between UE5.2 and UE5.3. In UE 5.2, you want to press on the “Show Retarget Pose” green button ; In UE5.3, you click on the 3 vertical dots and select “Showing Retarget Pose”.

IK Retargeter Interface difference between UE5.2 & UE5.3

3. Import Pose Asset

Import Pose Asset

Select Pose Asset