* QREncode EL

  QR Code encoder written in pure Emacs Lisp.

  For example the self-link (https://github.com/ruediger/qrencode-el)
  below was generated using this code:

  [[file:qr-self.png]]

** Usage

  This package provides two user facing interactive functions, that
  will encode text into a QR Code and show it in a separate buffer.

  * =qrencode-region= :: Shows the current selection as a QR Code.
  * =qrencode-url-at-point= :: Encode URL at point as QR Code.

  Some customizations are provided using =M-x customize-group RET
  qrencode RET=.

  QR Codes are rendered as Unicode text, but there is an option to
  export them as bitmap (NetPBM format).  There are also some public
  elisp library functions to generate QR Codes for use in other elisp
  code.

*** Converting different bitmaps

  This package only supports exporting to NetPBM format due to the
  simplicity of the format.  If PNG or other bitmap formats are
  desired this can be achieved by using
  =qrencode-post-export-functions= to run a conversion after the
  export.  For example using =convert(1)= from [[https://www.imagemagick.org/script/convert.php][ImageMagick]]:

#+BEGIN_SRC emacs-lisp
  (add-hook 'qrencode-post-export-functions
          #'(lambda (filename)
              (call-process "convert" nil nil nil
                            filename
                            (file-name-with-extension filename "png"))))
#+END_SRC

** Installation

  [[https://melpa.org/#/qrencode][file:https://melpa.org/packages/qrencode-badge.svg]]
  [[https://stable.melpa.org/#/qrencode][file:https://stable.melpa.org/packages/qrencode-badge.svg]]

  QREncode is available via [[https://melpa.org/#/qrencode][MELPA]] and [[https://github.com/dimitri/el-get/blob/master/recipes/qrencode.rcp][el-get]].

** Background

   [[file:https://github.com/ruediger/qrencode-el/actions/workflows/test.yml/badge.svg]]

  The code is written in pure Emacs Lisp on GNU Emacs 27.  It should
  be backwards compatible to GNU Emacs 25.1 and potentially even
  earlier with =seq= and =cl-lib= compat libraries.

  There are unit tests and an integration test using [[https://zbar.sf.net][zbar.sf.net]]
  (Debian/Ubuntu package =zbar-tools=) to verify that generated QR
  Codes can be decoded.  https://qrlogo.kaarposoft.dk/qrdecode.html is
  another good way to test the generated codes, since the decoder
  supports debug output.

  The encoder is written for the ISO/IEC 18004:2015 standard.  It only
  supports regular QR Codes (Model 2) and byte encoding (#11).  I
  believe this is sufficient for use-cases in GNU Emacs.  The word "QR
  Code" is registered trademark of DENSO WAVE INCORPORATED in Japan
  and other countries.
