Spline IK Constraint

The Spline IK constraint fits a chain of bones to the shape of a Curve. It’s particularly well suited for rigging flexible body parts such as tails, tentacles, and spines, as well as inorganic objects such as ropes.

Note

The IK constraints are special in that they modify multiple bones. For this reason, they ignore their position in the stack and always run after all other constraints on the affected bones. To apply constraints after IK, it is necessary to first copy the final transformation to a new bone chain, e.g. using Copy Transforms.

Options

Spline IK constraint.

Target

The Curve whose shape to match.

Influence

How strongly the constraint affects the bone chain.

Fitting

Chain Length

The number of bones affected by the constraint, starting with the owner bone and walking up its chain of ancestors. A value of 1 will only fit the bone itself, a value of 2 will fit the bone and its parent, and so on.

Even Divisions

When disabled, each bone will cover a distance along the curve relative to its rest length. When enabled, each bone will cover the same distance regardless of its rest length.

Chain Offset

When disabled, the bone chain will move to match the position of the curve. When enabled, the bone chain will stay at its original starting location and mimic the shape of the curve from there.

Chain Scaling

Use Curve Radius

Whether to use the radii of the curve control points as additional X and Z scaling factors for the bones.

Y Scale Mode

How to stretch the bones along the length of the curve.

None:

Reset the bones to their rest length.

Fit Curve:

Stretch the bones to cover the entire length of the curve.

Bone Original:

Keep the bones’ original length (including their Pose Mode scale).

XZ Scale Mode

How to scale the bones along the normals of the curve (or in other words, how to determine the thickness of the bones).

None:

Reset the bones’ X and Z scales to 1.

Bone Original:

Keep the bones’ original X and Z scales from Pose Mode.

Inverse Scale:

Set the X and Z scales to the inverse of the Y scale.

Volume Preservation:

Similar to the Stretch To constraint.

Use Original Scale

Apply Inverse Scale or Volume Preservation on top of the Pose Mode bone scales, like in the Stretch To constraint.

See also

This subject is seen in-depth in the Armature Posing section.

Example