static void Init()
    {
        SceneCameraTool window = (SceneCameraTool)EditorWindow.GetWindow(typeof(SceneCameraTool), false, "Cam Tool");

        window.Show();
        instance = window;
    }
    void OnEnable()
    {
        instance  = this;
        targetCam = Camera.main;

        UnityEditor.SceneView.beforeSceneGui -= OnPreSceneGUI;
        UnityEditor.SceneView.beforeSceneGui += OnPreSceneGUI;
    }