public void drawLevel( Graphics g ) {
        int x = 0, y = 0;
        for ( String[] row : field ) {
            for ( String cell_name : row ) {
                g.drawImage( images.get( cell_name ),
                             x, y, CELL_SIZE, CELL_SIZE, null);
                x += CELL_SIZE;
            }
            x = 0;
            y += CELL_SIZE;
        }
    }