metaClient/Assets/Plugins/RootMotion/FinalIK/_DEMOS/FBBIK/Scripts/TwoHandedProp.cs

using UnityEngine;
using System.Collections;
using RootMotion.FinalIK;

namespace RootMotion.Demos {

	// Targeting hands to 2-handed props with the FullBodyBipedIK component. It is not good to parent IK targets directly to the bones that use IK (circular dependency).
	// The bones are moved in the solving process, but it will not update the IK targets parented to the bones. All IK target positions/rotations need to be set before the solver updates.
	public class TwoHandedProp : MonoBehaviour {

		[Tooltip("The left hand target parented to the right hand.")] public Transform leftHandTarget;

		private FullBodyBipedIK ik;
		private Vector3 targetPosRelativeToRight;
		private Quaternion targetRotRelativeToRight;

		void Start() {
			ik = GetComponent<FullBodyBipedIK>();

			// Get a call from FBBIK each time it has finished updating
			ik.solver.OnPostUpdate += AfterFBBIK;

			// Weight in the effectors
			ik.solver.leftHandEffector.positionWeight = 1f;
			ik.solver.rightHandEffector.positionWeight = 1f;

			if (ik.solver.rightHandEffector.target == null) Debug.LogError("Right Hand Effector needs a Target in this demo.");
		}

		void LateUpdate() {
			// Get the position/rotation of the left hand target relative to the right hand.
			targetPosRelativeToRight = ik.references.rightHand.InverseTransformPoint(leftHandTarget.position);
			targetRotRelativeToRight = Quaternion.Inverse(ik.references.rightHand.rotation) * leftHandTarget.rotation;

			// Set the position/rotation of the left hand target relative to the right hand effector target.
			ik.solver.leftHandEffector.position = ik.solver.rightHandEffector.target.position + ik.solver.rightHandEffector.target.rotation * targetPosRelativeToRight;
			ik.solver.leftHandEffector.rotation = ik.solver.rightHandEffector.target.rotation * targetRotRelativeToRight;
		}

		// Called by FBBIK after it updates
		void AfterFBBIK() {
			// Rotate the hand bones to effector.rotation directly instead of using effector.rotationWeight that might fail to get the limb bending right under some circumstances
			ik.solver.leftHandEffector.bone.rotation = ik.solver.leftHandEffector.rotation;
			ik.solver.rightHandEffector.bone.rotation = ik.solver.rightHandEffector.rotation;
		}

		// Clean up the delegate
		void OnDestroy() {
			if (ik != null) ik.solver.OnPostUpdate -= AfterFBBIK;
		}
	}
}