The Twist Corrective node is a node that can drive curve values, such as Morph Targets, based on the twist of one bone relative to another. As an example, when the neck is twisted too far to the right or left you can apply a Morph Target to the neck in order to create a more natural look.
You can specify the Base Frame and Twist Frame using bone name and local axis, and a Twist Normal as the axis of the twist.
For example, if you'd like to check the twist to the right side along the Y axis, the normal would be (0, 1, 0). Or, if you'd like to check the twist to the left side along the Y axis, the normal would be (0, -1, 0). If you'd like to twist up/center along the Z axis, the normal would be (0, 0, 1). The Angle will be calculated between the plane and the twist frame.
Angle Delta of the range Max Angle in Degree will be mapped to Mapped Range Min and Mapped Range Max using a named curve.
You can add the Twist Corrective node in the AnimGraph of your Animation Blueprint.
The input pose to be transformed.
A float value in the range [0.0, 1.0] to use as the alpha value to determine the weighting of the Transform applied by the SkeletalControl. A value of 0.0 gives full weighting to the input pose, while a value of 1.0 gives full weighting to the control's computed Transform.
The final pose after the Transform has been applied.
Twist Corrective nodes are also affected by the LOD Threshold system introduced in 4.11. You can find the setting for this in the Details Panel for the Twist Corrective node.