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spine.legacy

cartoon-friendly spline IK template module

Overview​

spine.legacy builds a flexible, cartoon-oriented spine rig based on a spline IK. It is designed to sit between the pelvis and upper body (shoulders) and to work with the other template modules (arms, legs, etc.) in a consistent way.

The module provides:

  • A spline-IK based deformation chain for smooth bending and stretching
  • FK/IK-style controllers along the spine curve
  • Optional automatic orientation helpers (pelvis, mid-spine, shoulders)
  • Several modes to control how deformation bones are distributed and how stretch is computed

Template Structure​

  • The root of the template defines the pelvis position.
  • The rest of the chain follows the spine up to the shoulders and neck.
  • The spline IK curve is created from these template joints and drives the deformation chain used for skinning.
  • You do not need to manually orient the template joints:
    • Base orientation is handled during rig build.
    • Additional automatic re-orientation can be enabled via the orient options.

The spine module is typically parented under a World template module and acts as the bridge between lower body (legs) and upper body (arms / neck / head).

Options​

Skin Bones & Distribution

  • bones (int, default: 6): Number of deformation bones generated along the spline IK for skinning.
  • bones_length (enum, default: equal): Controls how the skin joints are distributed along the spline:
    • parametric : Bones are distributed according to the curve parameter (even spacing in parameter space).
    • cvs : Bones are distributed relative to the positions of the FK controllers along the curve.
    • equal : Each bone has the same length along the deformation, giving evenly sized segments.

Orientation Helpers

Automatic orientation of key controllers and IK handles. When enabled, the module adjusts local axes based on their parent and the underlying spline.

  • orient_spine (bool, default: off) Automatically orients c_spine1 and c_spine2 along their primary axis.
  • orient_pelvis (bool, default: off) Automatically orients c_pelvis and pelvis_IK along their axis, relative to their parent.
  • orient_shoulders (bool, default: off) Automatically orients c_shoulders_IK along its axis, relative to its parent.

Pelvis Pivot

Defines where the pivot of c_pelvis_IK is placed. This affects how the hips rotate and how motion propagates into the spine.

  • pivots (enum, default: legacy)
    • legacy : Pivot is at the root (historical / backward-compatible behavior).
    • spine1 : Pivot is placed at the first FK spine controller.
    • centered : Pivot is placed between the two intermediate FK spine controllers.

Stretching

Controls stretch behavior for the spline IK spine.

  • default_stretch (bool, default: on) Enables spine stretching by default on rig build.
  • stretch_mode (enum, default: translate) Defines how stretch is computed and applied along the spline:
    • scale – Joints are scaled along the curve to achieve stretch.
    • translate – Joints are translated along the curve to follow the stretched length (preserves joint scales, useful in some pipelines).