\version "2.19.80"

#(define-markup-command (qr-code layout props str size idn)(string? number? boolean?)
   "create QR-Code markup from <str> with width <size>. Use IDN for international domain names.
It needs qrencode, imagemagick convert, potrace and optionally idn commands installed in PATH."
  (let ((tmp (format "~A-~2A.eps" (strftime "%Y%m%d%H%M%S" (localtime (current-time))) (random 100)))
        (qr-stencil (interpret-markup layout props (markup #:with-color red #:filled-box (cons 0 size) (cons 0 size) 0.7)))
        (quali (chain-assoc-get 'qr-quality props "L")))
    (if (symbol? str)(let ((tmp (chain-assoc-get str props #f)))
                       (if tmp (set! str tmp))))
    (system (format (if idn
                        "echo \"~A\" | idn --quiet | qrencode -o - -m 0 -l ~A | convert PNG:- BMP:- | potrace -a -1 -o \"~A\""
                        "echo \"~A\" | qrencode -o - -m 0 -l ~A | convert PNG:- BMP:- | potrace -a -1 -o \"~A\"")
              str quali tmp))
    (set! qr-stencil (eps-file->stencil X size tmp))
    (system (format "rm -v \"~A\"" tmp))
    qr-stencil
    ))

\markup { \qr-code #"https://www.lilypond.org/" #50 ##f }