using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class MouseLookTest : MonoBehaviour {

 //相機跟隨的目標物體，一般是一個空物體
 public Transform target;
 private int MouseWheelSensitivity = 1; //滾輪靈敏度設置
 private int MouseZoomMin = 1; //相機距離最小值
 private int MouseZoomMax = 20; //相機距離最大值

 private float moveSpeed = 10; //相機跟隨速度（中鍵平移時），采用平滑模式時起作用，越大則運動越平滑

 private float xSpeed = 250.0f; //旋轉視角時相機x軸轉速
 private float ySpeed = 120.0f; //旋轉視角時相機y軸轉速

 private int yMinLimit = -360;
 private int yMaxLimit = 360;

 private float x = 0.0f; //存儲相機的euler角
 private float y = 0.0f; //存儲相機的euler角

 private float Distance = 5; //相機和target之間的距離，因為相機的Z軸總是指向target，也就是相機z軸方向上的距離
 private Vector3 targetOnScreenPosition; //目標的屏幕坐標，第三個值為z軸距離
 private Quaternion storeRotation; //存儲相機的姿態(tài)四元數
 private Vector3 CameraTargetPosition; //target的位置
 private Vector3 initPosition; //平移時用于存儲平移的起點位置
 private Vector3 cameraX; //相機的x軸方向向量
 private Vector3 cameraY; //相機的y軸方向向量
 private Vector3 cameraZ; //相機的z軸方向向量

 private Vector3 initScreenPos; //中鍵剛按下時鼠標的屏幕坐標（第三個值其實沒什么用）
 private Vector3 curScreenPos; //當前鼠標的屏幕坐標（第三個值其實沒什么用）
 void Start () {
 //這里就是設置一下初始的相機視角以及一些其他變量，這里的x和y。。。是和下面getAxis的mouse x與mouse y對應
 var angles = transform.eulerAngles;
 x = angles.y;
 y = angles.x;
 CameraTargetPosition = target.position;
 storeRotation = Quaternion.Euler (y + 60, x, 0);
 transform.rotation = storeRotation; //設置相機姿態(tài)
 Vector3 position = storeRotation * new Vector3 (0.0F, 0.0F, -Distance) + CameraTargetPosition; //四元數表示一個旋轉，四元數乘以向量相當于把向量旋轉對應角度，然后加上目標物體的位置就是相機位置了
 transform.position = storeRotation * new Vector3 (0, 0, -Distance) + CameraTargetPosition; //設置相機位置

 // Debug.Log("Camera x: "+transform.right);
 // Debug.Log("Camera y: "+transform.up);
 // Debug.Log("Camera z: "+transform.forward);

 // //-------------TEST-----------------
 // testScreenToWorldPoint();

 }

 void Update () {
 //鼠標右鍵旋轉功能
 if (Input.GetMouseButton (1)) {
 x += Input.GetAxis ("Mouse X") * xSpeed * 0.02f;
 y -= Input.GetAxis ("Mouse Y") * ySpeed * 0.02f;

 y = ClampAngle (y, yMinLimit, yMaxLimit);

 storeRotation = Quaternion.Euler (y + 60, x, 0);
 var position = storeRotation * new Vector3 (0.0f, 0.0f, -Distance) + CameraTargetPosition;

 transform.rotation = storeRotation;
 transform.position = position;
 } else if (Input.GetAxis ("Mouse ScrollWheel") != 0) //鼠標滾輪縮放功能
 {
 if (Distance >= MouseZoomMin && Distance <= MouseZoomMax) {
 Distance -= Input.GetAxis ("Mouse ScrollWheel") * MouseWheelSensitivity;
 }
 if (Distance < MouseZoomMin) {
 Distance = MouseZoomMin;
 }
 if (Distance > MouseZoomMax) {
 Distance = MouseZoomMax;
 }
 var rotation = transform.rotation;

 transform.position = storeRotation * new Vector3 (0.0F, 0.0F, -Distance) + CameraTargetPosition;
 }

 //鼠標中鍵平移
 if (Input.GetMouseButtonDown (2)) {
 cameraX = transform.right;
 cameraY = transform.up;
 cameraZ = transform.forward;

 initScreenPos = new Vector3 (Input.mousePosition.x, Input.mousePosition.y, targetOnScreenPosition.z);
 Debug.Log ("downOnce");

 //targetOnScreenPosition.z為目標物體到相機xmidbuttonDownPositiony平面的法線距離
 targetOnScreenPosition = Camera.main.WorldToScreenPoint (CameraTargetPosition);
 initPosition = CameraTargetPosition;
 }

 if (Input.GetMouseButton (2)) {
 curScreenPos = new Vector3 (Input.mousePosition.x, Input.mousePosition.y, targetOnScreenPosition.z);
 //0.01這個系數是控制平移的速度，要根據相機和目標物體的distance來靈活選擇
 target.position = initPosition - 0.01f * ((curScreenPos.x - initScreenPos.x) * cameraX + (curScreenPos.y - initScreenPos.y) * cameraY);

 //重新計算位置
 Vector3 mPosition = storeRotation * new Vector3 (0.0F, 0.0F, -Distance) + target.position;
 transform.position = mPosition;

 // //用這個會讓相機的平移變得更平滑，但是可能在你buttonup時未使相機移動到應到的位置，導致再進行旋轉與縮放操作時出現短暫抖動
 //transform.position=Vector3.Lerp(transform.position,mPosition,Time.deltaTime*moveSpeed);

 }
 if (Input.GetMouseButtonUp (2)) {
 Debug.Log ("upOnce");
 //平移結束把cameraTargetPosition的位置更新一下，不然會影響縮放與旋轉功能
 CameraTargetPosition = target.position;
 }

 }

 //將angle限制在min~max之間
 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);
 }

 void testScreenToWorldPoint () {
 //第三個坐標指的是在相機z軸指向方向上的距離
 Vector3 screenPoint = Camera.main.WorldToScreenPoint (CameraTargetPosition);
 Debug.Log ("ScreenPoint: " + screenPoint);

 // var worldPosition = Camera.main.ScreenToWorldPoint(new Vector3(1,1,10));
 // Debug.Log("worldPosition: "+worldPosition);
 }
}