(define-gboxed-variant-cstruct event "GdkEvent"
  (type event-type)
  (window (g:object window))
  (send-event (:boolean :int8))
  (:variant type
            ...
            ;; GdkEventPadAxis
            ((:pad-ring :pad-strip) event-pad-axis
             (time :uint32)
             (group :uint)
             (index :uint)
             (mode :uint)
             (value :double))
  ... ))