DragAndDropbehaviour.cs

using UnityEngine;
using System.Collections;

public class DragAndDropBehaviour : MonoBehaviour {

    private bool _mouseState;
    private GameObject target;
    private GameObject lastTarget;
    private Vector3 lastPos;

    public Vector3 screenSpace;
    public Vector3 offset;
    public float level = 0;

    // Update is called once per frame
    public void Update ()
    {
        #region MouseDown
        if (Input.GetMouseButtonDown (1))
        {
            RaycastHit hitInfo;
            target = GetClickedObject (out hitInfo);
            Debug.Log (target);
            if( target == null)
            {
                return;//target = null;
            }

            if (target != null && target.GetComponent<DraggableObject>().isDraggable == true)
            {
                /*if(target.GetComponent<Pontoon>() != null)
                {
                    target.GetComponent<Pontoon>().deadlock = false;
                }*/
                _mouseState = true;
                screenSpace = Camera.main.WorldToScreenPoint (target.transform.position);
                offset = (target.transform.position - Camera.main.ScreenToWorldPoint (new Vector3 (Input.mousePosition.x, Input.mousePosition.y, screenSpace.z))) * Time.deltaTime * 10;
            }
        }
        #endregion

        #region MouseUp
        if (Input.GetMouseButtonUp (1)) {
            /*if(target.GetComponent<Pontoon>() != null)
            {
                target.GetComponent<Pontoon>().deadlock = true;
            }*/
            _mouseState = false;
            level = 0;
        }
        #endregion

        #region Movement And Boundary Setting
        if (_mouseState) {
            if(target.transform.GetComponent<PlaceableObject>())
            {
                level = target.transform.GetComponent<PlaceableObject>().level;
                Debug.Log ("A New Level: " + level);
            }
            //keep track of the mouse position
            var curScreenSpace = new Vector3 (Input.mousePosition.x, Input.mousePosition.y, screenSpace.z);

            //convert the screen mouse position to world point and adjust with offset
            var curPosition = Camera.main.ScreenToWorldPoint (curScreenSpace) + offset;

            //setting boundaries
            if(curPosition.x < 1)
            {
                curPosition.x = 1;
            }
            if(curPosition.z < 1)
            {
                curPosition.z = 1;
            }
            if(curPosition.x > 59)
            {
                curPosition.x = 59;
            }
            if(curPosition.z > 59)
            {
                curPosition.z = 59;
            }

            //update the position of the object in the world
            curScreenSpace = new Vector3(Mathf.Round(curPosition.x), 0F + this.level, Mathf.Round(curPosition.z));
            target.transform.position = curScreenSpace;
        }
        #endregion
    }

    public GameObject GetClickedObject(out RaycastHit hit)
    {
        GameObject target = null;
        Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
        if (Physics.Raycast (ray.origin, ray.direction * 10, out hit)) {

            target = hit.collider.gameObject;
        }
        return target;
    }
}