直接挂载到模型上

using UnityEngine;
using System.Collections;public class OnDrag : MonoBehaviour
{//目标物体public Transform target;private int MouseWheelSensitivity = 1; //放大倍数的快慢private int MouseZoomMin = 1; //最小倍数private int MouseZoomMax = 5; //最大倍数//默认距离private float normalDistance = 3;private Vector3 normalized;//拖拽的移动速度private float xSpeed = 250.0f;private float ySpeed = 120.0f;//拖拽的高度限制private int yMinLimit = -20;private int yMaxLimit = 80;//角度private float x = 0.0f;private float y = 0.0f;//记录目标物体的坐标private Vector3 screenPoint;private Vector3 offset;//围绕x旋转30°private Quaternion rotation = Quaternion.Euler(new Vector3(30f, 0f, 0f));//目标的3D坐标private Vector3 CameraTarget;//打印欧拉角:绕各个轴旋转的角度，顺时针为正方向public void Awake(){target = transform;print(transform.eulerAngles.x);print(transform.eulerAngles.y);print(transform.eulerAngles.z);}void Start(){//找到目标飞机的3d坐标CameraTarget = target.position;//目标飞机的z-3，距离摄像机更近了float z = target.transform.position.z - normalDistance;//给当前相机给定位，现在的3D坐标乘以30°transform.position = rotation * new Vector3(transform.position.x, transform.position.y, z);//将视角转向物体transform.LookAt(target);//记录各个轴偏离的角度var angles = transform.eulerAngles;x = angles.y;y = angles.x;}void OnGUI(){GUI.Label(new Rect(10, 10, 300, 30), "左击:旋转；滚轮：缩放；中击：拖拽");}void Update(){//如果左击了，旋转if (Input.GetMouseButton(0)){x += Input.GetAxis("Mouse X") * xSpeed * 0.02f;y -= Input.GetAxis("Mouse Y") * ySpeed * 0.02f;y = ClampAngle(y, yMinLimit, yMaxLimit);var rotation = Quaternion.Euler(y, x, 0);var position = rotation * new Vector3(0.0f, 0.0f, -normalDistance) + CameraTarget;transform.rotation = rotation;transform.position = position;}//滚轮缩放else if (Input.GetAxis("Mouse ScrollWheel") != 0){//摄像机3d坐标-物体的3d坐标normalized = (transform.position - CameraTarget).normalized;if (normalDistance >= MouseZoomMin && normalDistance <= MouseZoomMax){normalDistance -= Input.GetAxis("Mouse ScrollWheel") * MouseWheelSensitivity;}if (normalDistance < MouseZoomMin){normalDistance = MouseZoomMin;}if (normalDistance > MouseZoomMax){normalDistance = MouseZoomMax;}//改变摄像机的远近transform.position = normalized * normalDistance;}//案件按下 记录鼠标的else if (Input.GetMouseButtonDown(2)){//将目标物体的坐标转化成平面坐标screenPoint = Camera.main.WorldToScreenPoint(target.transform.position);//计算鼠标的3维坐标跟物体的3维坐标的差值offset = target.transform.position - Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z));}//中键拖拽，改变飞机的坐标，每帧调用if (Input.GetMouseButton(2)){//鼠标的平面坐标Vector3 curScreenPoint = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z);//鼠标转移的3d空间坐标值Vector3 curPosition = Camera.main.ScreenToWorldPoint(curScreenPoint) + offset;//改变鼠标的3D空间坐标target.transform.position = curPosition;}//朝向，每动一帧都要改变朝向transform.LookAt(CameraTarget);}//控制旋转的角度，如果旋转的角度大于360或者小于360都要加上或者减去对应的角度static float ClampAngle(float angle, float min, float max){if (angle < -360)angle += 360;if (angle > 360)angle -= 360;return Mathf.Clamp(angle, min, max);}
}