hugo-heagren / qrencode-el

QRCode encoder for Emacs in pure elisp

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:

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 ImageMagick:

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

Installation

QREncode is available via MELPA and el-get.

Background

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 zbar.sf.net (Debian/Ubuntu package zbar-tools) to verify that generated QR Codes can be decoded. Unfortunately zbar doesn’t handle UTF-8 well, which prevents automated testing of Unicode. 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.