先看演示效果

实现方案

1.创建几个用于演示的Cube

2.创建一个脚本

3.编写脚本的内容

附上代码片段

  float distance;

  // Update is called once per frame
  void Update()
  {
      var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
      RaycastHit hit;
      if (Input.GetMouseButtonDown(0))
      {
          if (Physics.Raycast(ray, out hit))
          {
              distance = Vector3.Distance(hit.transform.position, Camera.main.transform.position);
          }
      }
      if (Input.GetMouseButton(0))
      {

          if (Physics.Raycast(ray, out hit))
          {
              if (hit.collider != null)
              {
                  var mousePoint = Input.mousePosition;
                  mousePoint.z = distance;
                  hit.collider.gameObject.transform.position = Camera.main.ScreenToWorldPoint(mousePoint);
              }
          }
      }
  }

4.挂载脚本

5.点击运行就可以看到效果啦