protected void OnKeyRelease(object sender, KeyReleaseEventArgs args)
        {
            GtkKey key = (GtkKey)Keyval.ToLower((uint)args.Event.Key);

            _pressedKeys.Remove(key);
        }
        protected void OnKeyPress(object sender, KeyPressEventArgs args)
        {
            GtkKey key = (GtkKey)Keyval.ToLower((uint)args.Event.Key);

            _pressedKeys.Add(key);
        }