InteractableObjectGrabHook.cs

using System;
using UnityEngine;
using VRTK;

[RequireComponent(typeof(VRTK_InteractGrab))]
public class InteractableObjectGrabHook : MonoBehaviour
{
    [Tooltip("How long a complete move of the interactable object should take (in either direction).")]
    public float Duration;

    private enum GrabState
    {
        None,
        Grabbed,
        Ungrabbed
    }

    private VRTK_InteractGrab grabScript;
    private GrabState grabState = GrabState.None;
    private Rigidbody grabbedRigidbody;
    private Rigidbody grabbingRigidbody;
    private Vector3 grabStartPosition;
    private float grabStartTime;

    private void OnEnable()
    {
        grabScript = GetComponent<VRTK_InteractGrab>();
        grabScript.ControllerGrabInteractableObject += OnControllerGrabInteractableObject;
        grabScript.ControllerUngrabInteractableObject += OnControllerUngrabInteractableObject;
    }

    private void OnDisable()
    {
        grabScript.ControllerGrabInteractableObject -= OnControllerGrabInteractableObject;
        grabScript.ControllerUngrabInteractableObject -= OnControllerUngrabInteractableObject;
        grabScript = null;
        grabState = GrabState.None;
        grabbedRigidbody = null;
        grabbingRigidbody = null;
        grabStartTime = Time.time;
    }

    private void FixedUpdate()
    {
        switch (grabState)
        {
            case GrabState.Grabbed:
                if (Vector3.Distance(grabbedRigidbody.position, grabbingRigidbody.position) < float.Epsilon)
                {
                    grabState = GrabState.None;
                    return;
                }

                var timeSinceGrabStart = Time.time - grabStartTime;
                var grabMovementPercentageComplete = timeSinceGrabStart / Duration;

                grabbedRigidbody.MovePosition(
                    Vector3.Lerp(
                        grabStartPosition,
                        grabbingRigidbody.position,
                        grabMovementPercentageComplete
                    )
                );
                break;
            case GrabState.Ungrabbed:
                if (Vector3.Distance(grabbedRigidbody.position, grabStartPosition) < float.Epsilon)
                {
                    grabState = GrabState.None;
                    return;
                }

                var timeSinceUngrabStart = Time.time - grabStartTime;
                var ungrabMovementPercentageComplete = timeSinceUngrabStart / Duration;

                grabbedRigidbody.MovePosition(
                    Vector3.Lerp(
                        grabbingRigidbody.position,
                        grabStartPosition,
                        ungrabMovementPercentageComplete
                    )
                );
                break;
            case GrabState.None:
                break;
            default:
                throw new ArgumentOutOfRangeException();
        }
    }

    private void OnControllerGrabInteractableObject(object sender, ObjectInteractEventArgs objectInteractEventArgs)
    {
        grabState = GrabState.Grabbed;
        grabbedRigidbody = objectInteractEventArgs.target.GetComponent<Rigidbody>();
        grabbingRigidbody = VRTK_DeviceFinder.GetControllerByIndex(objectInteractEventArgs.controllerIndex, false)
                                             .gameObject.GetComponent<Rigidbody>();
        grabStartPosition = grabbedRigidbody.position;
        grabStartTime = Time.time;
    }

    private void OnControllerUngrabInteractableObject(object sender, ObjectInteractEventArgs objectInteractEventArgs)
    {
        grabState = GrabState.Ungrabbed;
        grabStartTime = Time.time;
    }
}