The Spline IK control node constrains a chain of specified bones to a spline within an Animation Blueprint as Control Points.
Control Points can be driven by external values, with additional options for Roll and Twist (as well as Twist Blend options).
Below, we add the Spline IK node to our Animation Blueprint to control the character's spine.
See the table below for a full breakdown of the properties available for the Spline IK node.
| Property | Description |
|---|---|
| Parameters | |
| Start Bone | Name of the root bone from which the spline extends. |
| End Bone | Name of the bone at the end of the spline chain (bones after this will not be altered by the controller). |
| Bone Axis | Axis of the controlled bone (for example, the direction of the spline) to use as the direction for the curve. |
| Auto Calculate Spline | Whether the number of points in the spline should be automatically generated. |
| Point Count | The number of points in the spline if we are not auto-calculating. |
| (As Pin) Control Points | Transforms applied to spline points. |
| (As Pin) Roll | Overall roll of the spline, applied on top of other rotations along the direction of the spline. |
| (As Pin) Twist Start | The twist of the start bone. Twist is interpolated along the spline according to Twist Blend. |
| (As Pin) Twist End | The twist of the end bone. Twist is interpolated along the spline according to Twist Blend. |
| (As Pin) Stretch | The maximum stretch allowed when fitting bones to the spline. 0.0 means bones do not stretch their length while 1.0 means bones stretch to the length of the spline. |
| (As Pin) Offset | The distance along the spline from the start from which bones are constrained. |
| Twist Blend | |
| Blend Option | The type of Animation Blending Mode used. |
| Custom Curve | Enables you to specify a Custom Blend option where you specify the curve. |
| Blend Time | The duration of the blend. |
| Settings | |
| Alpha | Current strength of the skeletal control. |
| Alpha Scale Bias | Defines the minimum and maximum scale bias for the Alpha property. |
| Performance | |
| LOD Threshold | Max LOD that this node is allowed to run. |
The following table outlines the pins that are enabled by default on the Spline IK node.
| Pin | Description |
|---|---|
| Input Pins | |
| Component Pose | The incoming pose. |
| Alpha | The current strength of the control. |
Any of the properties denoted with (As pin) can be exposed on the node by checking their corresponding checkbox.