private void PanelOnMouseDown(object sender, MouseEventArgs e)
        {
            if (_game.Board.SelectedPiece == null)
            {
                ChessPiece piece = _game.Board.GetPiece(e.Location, _ratio);
                if (piece != null)
                {
                    _game.Board.SelectedPiece = piece;
                }
            }
            else
            {
                Point p = _game.Board.GetGridLocation(e.Location, _ratio);
                if (p != Point.Empty)
                {
                    _game.MovePiece(_game.Board.SelectedPiece, p);
                }
            }
        }