rig.rechain

Builds a virtual Forward Kinematics (FK) hierarchy over disconnected or constrained nodes.

This modifier solves the classic "Necklace Problem" in rigging. Imagine a chain of armor plates or necklace links: you want each link to stick to the deforming body (via rig.rivet), but you also want the animator to rotate the top link and have all subsequent links follow it naturally like an FK chain.

Because each link is already constrained to a rivet, you cannot physically parent them to one another in the Outliner without breaking the rivet or creating a dependency cycle. rig.rechain solves this by mathematically extracting the local matrix rotations of your controllers and cascading them virtually down the chain.

Parameters

Parameter	Type	Default	Description
ctrls	list[node]		The driver controllers representing the FK chain (the nodes the animator will rotate).
nodes	list[node]		The driven transform nodes (usually the root offset groups of the subsequent joints). Must be exactly the same length as ctrls.
roots	list[node]		Optional. The local reference spaces for each controller. Only necessary if your ctrls do not have zeroed-out local matrices.
weight	bool	off	Automatically generates an animatable weight attribute to blend the virtual hierarchy on or off.
name	str		Base name used to register the generated IDs.

Target Proper Nodes

When using default.bones templates, ensure the nodes list targets the root offset groups (e.g., joint::roots.0), NOT the joints or controllers themselves. The modifier needs a clean transform matrix to inject the virtual hierarchy.

Output

Animatable Attributes

If weight: on a @weight attribute (ranging from 0.0 to 1.0) is automatically added to each driven node in the nodes list. This allows the rig to dynamically disable the FK chain cascade on a per-link basis.

Examples

Virtual Hierarchy Between Riveted Joints

In this example, we have 3 joints pinned to a surface. We want chain::skin.0 to act as the parent of chain::roots.1, and chain::skin.1 to act as the parent of chain::roots.2. By feeding the controllers into ctrls and the roots into nodes, Mikan cascades the offsets.

rig.rechain:
  ctrls:
    - chain::skin.0
    - chain::skin.1
  nodes:
    - chain::roots.1
    - chain::roots.2

Demo Scene

To see this setup in action, download the mod_rechain_rivet.ma demo scene from our Google Drive folder.

Subchains Driven by a Main Chain

A more advanced setup: animating multiple subchains using a main structural chain.

First, you break the original physical hierarchy so the subchains can be constrained to the main chain hooks (acting as dynamic rivets). Then, you use rig.rechain to rebuild the lost FK behavior virtually, allowing the animator to pose the subchain controllers directly.

# 1. Disconnect subchain controllers and parent them to the main chain hooks
#> n: [0, 1, 2, 3, 4]
parent: side.L::roots.<n> main::hooks.<n>

# 2. Rebuild the FK behavior virtually
rig.rechain:
  roots:
    - side.L::roots.0
    - side.L::roots.1
    - side.L::roots.2
    - side.L::roots.3
  ctrls:
    - side.L::skin.0
    - side.L::skin.1
    - side.L::skin.2
    - side.L::skin.3
  nodes:
    - side.L::roots.1
    - side.L::roots.2
    - side.L::roots.3
    - side.L::roots.4

Demo Scene

To see this setup in action, download the mod_rechain.ma demo scene from our Google Drive folder.