Rewind time (or problems with arrays)

Question

Hi all,

I'm implementing a mechanic where when triggered, target objects would rewind to their initial positions/rotations/etc. The problematic part of this currently looks something like:

     ArrayList Movements = new ArrayList();
     ArrayList Rotations = new ArrayList();
     public GameObject[] targets;
 
 (in update when not rewinding:)
 
             for (int i = targets.Length-1; i >= 0 ; i--)
             {
                 Movements.Add(targets[i].transform.position);
                 Rotations.Add(targets[i].transform.rotation);
             }
 
 (coroutine to rewind when trigerred:)
 
             for(int i = 0; i<targets.Length; i++)
             {
                 targets[i].transform.position = (Vector3)Movements[MovementIndex];
                 Movements.RemoveAt(MovementIndex);
                 targets[i].transform.rotation = (Quaternion)Rotations[MovementIndex];
                 Rotations.RemoveAt(MovementIndex);
             }
             yield return new WaitForSeconds(0f);

I think I've pasted in all the relevant parts for solving what's wrong. Basically, it worked well for just one target, e.g. player, but I want to implement an open array defined in the editor (GameObject[] targets) so I can apply the rewind to any object I want. So when I went and tried it with a player and the camera, it, for some reason (possibly my lack of understand how these arrays are called), it looks like the camera jumps around as if it's using all of the positions and rotations recorded, not just the ones captured from the camera transform. I played around with order of execution in the "for" functions but to no avail..

Any ideas?

Additionally, if anyone has a suggestion on how to implement the captured parameters in a single multi-dimensional array, please share, I couldn't wrap my head around that either. Something like [(player.position1, player.rotation1),(cam.pos1, cam.rot1),....] but that'd be there just to make it neat so is not as important.

ALSO, optimization related advice would be most welcome as well. I.e. storing all of these states will be expensive if a player takes a while going through a level and I can't really delete any of the stored data as I want everything to come back to the point when the level started. I guess storing every other frame would do, but then how would I smoothly transition across two states without it looking like glitchy teleportation?

Answer 1

@erikiene OMG This was a lot of fun trying to figure this out.

I made 2 scripts, it sort of allows you allocate which objects you want to have rewind via AddComponent, this lets each object have their own position and rotation list so you don't have some gigantic multidimensional array to worry about. Clears the list after a rewind occurs. This example will allocate which objects will be able to rewind during Start(), but it's pretty easy to implement dynamically during gameplay too.

First Script (placed on an empty object in the scene, just used for allocating which objects get to rewind, you retain a reference to each object in this Object's targets List)

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.UI;
 
 
 public class TimeController : MonoBehaviour {
 
 
     public List<Vector3> targetPos = new List<Vector3>();
     public List<Quaternion> targetRotate = new List<Quaternion>();
     public GameObject[] targets;
 
 
     void Start()
     {
         targets = GameObject.FindGameObjectsWithTag ("Target");
 
         foreach(GameObject target in targets)
         {
             target.AddComponent<Rewinder> ();
         }
 
     } 
 
 
 }

Second Script (This one gives the Rewind class to the object, I made RigidBody a required component, may or may not want to implement that depending on your game)

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.UI;
 
 [RequireComponent(typeof(Rigidbody))]
 public class Rewinder : MonoBehaviour {
 
 
     public List<Vector3> targetPos = new List<Vector3>();
     public List<Quaternion> targetRotate = new List<Quaternion>();
     public bool record;
     
 
     void Start()
     {
         record = true;
 
     } 
 
 
     void Update()
     {
 
         if(record)
         {
             targetPos.Add (transform.position);
             targetRotate.Add (transform.rotation);
 
         }
 
 
         if (Input.GetKeyDown (KeyCode.Space) && record == true)
         {
             StartCoroutine ("Rewind");
         }
             
 
     }
 
     IEnumerator Rewind()
     {
         record = false;
         GetComponent<Rigidbody> ().isKinematic = true;
         for(int i = targetPos.Count - 1; i > -1; i--)
         {
             transform.position = targetPos [i];
             transform.rotation = targetRotate [i];
 
             yield return null;
         }
 
         GetComponent<Rigidbody> ().isKinematic = false;
         targetPos.Clear ();
         targetRotate.Clear ();
         record = true;
         yield return new WaitForSeconds(0);
     }
 
 
 
 }

I put yield return null in the for loop of the coroutine as it makes rewind playback frame by frame the same as it was recorded. If you are rewinding to a state in which you were airborne at the start you need kinematic set to true, then revert it when it is finished or else the acceleration of gravity whilst you're airborne is still in effect and it makes the object fall faster when rewind finishes.

Rewind time (or problems with arrays)

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