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Spline IK Constraint

The Spline IK constraint aligns a chain of bones along a curve. By leveraging the ease and flexibility of achieving aesthetically pleasing shapes offered by curves and the predictability and well-integrated control offered by bones, Spline IK is an invaluable tool in the riggers' toolbox. It is particularly well suited for rigging flexible body parts such as tails, tentacles, and spines, as well as inorganic items such as ropes.

To set up Spline IK, it is necessary to have a chain of connected bones and a curve to constrain these bones to.

  1. With the last bone in the chain selected, add a Spline IK constraint from the Bone Constraints tab in the Properties Editor.
  2. Set the 'Chain Length' setting to the number of bones in the chain (starting from and including the selected bone) that should be influenced by the curve.
  3. Finally, set Target to the curve that should control the curve.

Options

Spline IK panel
Target
The target curve
Spline Fitting
Chain Length
How many bones are included in the chain
Even Division
Ignore the relative length of the bones when fitting to the curve
Chain Offset
Offset the entire chain relative to the root joint
Chain Scaling
Y stretch
Stretch the Y axis of the bones to fit the curve
XZ Scale Mode
None
Don't scale the X and X axes (default)
Bone Original
Use the original scaling of the bones
Volume Preservation
Scale of the X and Z axes is the inverse of the Y scale
Use Curve Radius
Average radius of the endpoints is used to tweak the X and Z scaling of the bones, on top of the X and Z scale mode

See also

This subject is seen in depth in the Rigging/Posing section.