[RequireComponent(typeof(Camera))]
public class UECamera : MonoBehaviour
{
    bool draging;
    float fpsYaw;
    float fpsPitch;
    float yaw;
    Quaternion rotation = Quaternion.identity;

    const int MoveButton = 0;
    const int AngleButton = 1;
    const float ForwardScale = 15f;
    const float MoveScale = 5f;
    const float YawScale = 30f;
    const float FPYawScale = 50f;
    const float FPPitchScale = 50f;

    private void Awake()
    {
        fpsYaw = transform.localEulerAngles.y;
        fpsPitch = transform.localEulerAngles.x;
    }

    // 虚幻4风格相机控制
    // 鼠标左键左右拖动：左右旋转视角
    // 鼠标左键上下拖动：前后移动
    // 鼠标右键拖动：第一人称查看
    // 鼠标左右键拖动：上下左右平移
    private void LateUpdate()
    {
        if(GUIUtility.hotControl != 0 || (EventSystem.current != null && EventSystem.current.IsPointerOverGameObject()))
        {
            return;
        }

        if(!draging && (Input.GetMouseButton(MoveButton) || Input.GetMouseButton(AngleButton)))
        {
            draging = true;
            Cursor.visible = false;
            Cursor.lockState = CursorLockMode.Locked;
        }

        if(draging)
        {
            float x = Input.GetAxisRaw("Mouse X");
            float y = Input.GetAxisRaw("Mouse Y");

            if (Input.GetMouseButton(MoveButton))
            {
                if(Input.GetMouseButton(AngleButton))
                {
                    Vector3 right = rotation * Vector3.right;
                    transform.localPosition += right * x * Time.deltaTime * MoveScale;
                    transform.localPosition += Vector3.up * y * Time.deltaTime * MoveScale;
                }
                else
                {
                    yaw += x * Time.deltaTime * YawScale;
                    Quaternion yawRot = Quaternion.AngleAxis(yaw + fpsYaw, Vector3.up);
                    rotation = (yawRot * Quaternion.AngleAxis(fpsPitch, Vector3.right));
                    transform.localPosition += (yawRot * Vector3.forward) * y * Time.deltaTime * ForwardScale;
                }
            }
            else if(Input.GetMouseButton(AngleButton))
            {
                fpsYaw += x * Time.deltaTime * FPYawScale;
                fpsPitch -= y * Time.deltaTime * FPPitchScale;
                rotation = Quaternion.AngleAxis(fpsYaw + yaw, Vector3.up) * Quaternion.AngleAxis(fpsPitch, Vector3.right);
            }

            transform.localRotation = rotation;
        }

        if(draging && (Input.GetMouseButtonUp(MoveButton) || Input.GetMouseButtonUp(AngleButton)))
        {
            Cursor.visible = true;
            Cursor.lockState = CursorLockMode.None;
            draging = false;
        }
    }
}