private:
bool _trackview_only; ///< true if pointer y value should always be relative to the top of the trackview group
bool _move_threshold_passed; ///< true if the move threshold has been passed, otherwise false
+ bool _starting_point_passed; ///< true if we called move () with first_move flag, otherwise false
bool _was_double_click; ///< true if drag initiated by a double click event
double _grab_x; ///< trackview x of the grab start position
double _grab_y; ///< y of the grab start position, possibly adjusted if _trackview_only is true