unity3d 鼠标延各个方向拖拽物体

using UnityEngine;
using System.Collections;

//选择轴向
public enum directionEnum{

    x_dir,
    y_dir,
    z_dir,
}
public class DragObject : MonoBehaviour {

    // Use this for initialization

    public directionEnum myDirection;
    public Transform target;//需要拖拽的目标
    public bool isDrag;//表示当前是否可拖动
    public float MinDistance;
    public float MaxDistance;
    private Vector3 mousePos;
    /// </summary>
    void Start () {

        //下面是我用NGUI的事件添加的，也可以使用UGUI或者射线检测
        //UIEventListener.Get (this.gameObject).onDrag = DragTarget;
        //UIEventListener.Get (this.gameObject).onDragEnd = EndDrag;

    }

    // Update is called once per frame
    void Update () {

    }
    public void SetTarget(Transform go)
    {
        this.target = go;
        mousePos = Input.mousePosition;//初始化鼠标初始位置,或者放到Start函数里
    }

    public void DragTarget()
    {
        if (isDrag) {
            Vector3 ScreenSpace = Camera.main.WorldToScreenPoint(target.position); //目标世界坐标转屏幕，获取z值
            Vector3 curScreenSpace = new Vector3(Input.mousePosition.x,Input.mousePosition.y,ScreenSpace.z);//当前鼠标位置转世界
            Vector3 offset = target.position - Camera.main.ScreenToWorldPoint (new Vector3 (mousePos.x, mousePos.y, ScreenSpace.z));//鼠标上一帧的世界位置和目标点的位置差
            Vector3 CurPosition = Camera.main.ScreenToWorldPoint(curScreenSpace)+offset;//鼠标当前位置+位置差


            switch (myDirection) {
                case directionEnum.x_dir:

                    target.position = new Vector3 (Mathf.Clamp( CurPosition.x,MinDistance,MaxDistance), target.position.y, target.position.z); 

                    break;
                case directionEnum.y_dir:
                    target.position = new Vector3 (target.position.x,Mathf.Clamp( CurPosition.y,MinDistance,MaxDistance), target.position.z); 
                    break;
                case directionEnum.z_dir:
                    target.position = new Vector3 ( target.position.x, target.position.y, Mathf.Clamp( CurPosition.z,MinDistance,MaxDistance)); 
                    break;
                default:
                    break;
            }


            mousePos = Input.mousePosition;
        }

    }


}