private void OnTriggerExit(Collider other)
 {
     if (currentPiece != null && other.transform == currentPiece.transform)
     {
         LightOff();
         currentPiece.LightOff();
         currentPiece = null;
     }
 }
        private void OnTriggerEnter(Collider other)
        {
            BoxPuzzlePiece piece = other.GetComponent <BoxPuzzlePiece>();

            if (piece != null)
            {
                if (currentPiece != null && currentPiece.goalIndex == goalIndex)
                {
                    currentPiece.LightOff();
                }
                currentPiece = piece;
                if (piece.goalIndex == goalIndex)
                {
                    LightOn();
                    currentPiece.LightOn();
                }
            }
        }