Unity 拖动3d物体跟随鼠标（手指）移动

demo下载地址 demo下载

代码

 if (Input.GetMouseButtonDown(0))  
        {
            Ray ray = mainCamera.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;
            if (Physics.Raycast(ray, out hit))
            {
                Debug.Log(hit.collider.gameObject.tag);
                if (hit.collider.gameObject.CompareTag("sheep"))
                {
                    // currentObj 可以直接外部赋值，不用射线检测 
                    currentObj = hit.collider.transform;
                    sheep = currentObj.GetComponent();
                    sheep.StartDrag();
                    objScreenPos = mainCamera.WorldToScreenPoint(currentObj.position);

                    Vector3 mousePos = new Vector3(Input.mousePosition.x, Input.mousePosition.y, objScreenPos.z);
                    mousePos = mainCamera.ScreenToWorldPoint(mousePos);
                    offest = currentObj.position - mousePos;
                }
            }
        }
        if (Input.GetMouseButton(0))
        {
            if (currentObj != null)
            {
                Vector3 curMousePos = new Vector3(Input.mousePosition.x, Input.mousePosition.y, objScreenPos.z);
                curMousePos = mainCamera.ScreenToWorldPoint(curMousePos);
                Vector3 newPos = curMousePos + offest;
                currentObj.transform.position = new Vector3(newPos.x, currentObj.position.y, newPos.z);
                yield return new WaitForFixedUpdate();
            }
        }