Two Bone IK

The Two Bone IK control applies an Inverse Kinematic (IK) solver to a 3-joint chain, such as the limbs of a character.

node_twobone.png

Below, a series of Two Bone IK controllers are used, along with Hand IK Retargeting to control how the character holds a weapon.

Variables are used to drive the Join Target Location properties on the controller for the hand_l and hand_r bones of our character. By adjusting these values we can determine how the character holds the weapon without having to hand-animate different poses based on different characters.

Property Description

IK

IK Bone Name of the bone to apply the IK solver to. This should be the bone at the end of the bone chain, i.e. the ankle or wrist bone.

Stretch Limits

X The ratio of the Max Limb Length, which is used to determine when to scale the bones.
Y The maximum allowable amount of scaling of the translation component.
Allow Stretching If true, allows the bones to be stretched.

End Effector

Effector Space Bone Name The name of the bone to use as the effector location when Effector Location Space is set to BCS_BoneSpace.
Take Rotation from Effector Space If enabled, the Rotation of the effector (component, parent, or bone) is applied to the IK Bone.
Maintain Effector Rel Rot If enabled, the IK Bone will maintain its Rotation relative to the effector.

This is overridden when Take Rotation from Effector Space is enabled.

Effector Location Space The reference frame for the Effector Location.
Value Effect
Translation The XYZ component of translation on the target bone.
Rotation The XYZ component of rotation on the target bone.
Scale The XYZ component of scale on the target bone.

Join Target

Joint Target Location Space The reference frame for the Joint Target Location.
Value Effect
Translation The XYZ component of translation on the target bone.
Rotation The XYZ component of rotation on the target bone.
Scale The XYZ component of scale on the target bone.
Joint Target Space Bone Name The name of the bone to use as the joint target location when Joint Target Location Space is set to BCS_BoneSpace.
Pin Description

Input Pins

Effector Location A Vector specifying the location effector in the Effector Location Space.
Joint Target Location A Vector specifying the location joint target in the Joint Target Location Space.

Two Bone IK 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 Two Bone IK node.

perf.png

Property Description
LOD Threshold This is the max Level of Detail (LOD) that this node is permitted to run on. For example: if you have LOD Threshold set to 2, it will run until LOD 2, but disable itself once the component's LOD becomes 3.