Barcodes

Two two-dimensional symbologies, each in its own package: QR Code and Data Matrix. Both draw the symbol as one vector rectangle per dark module over the graphics layer, so it stays crisp at every size and in every backend — there is no raster image anywhere in either.

\use{qrcode}
\use{datamatrix}

\qrcode{https://example.com}
\datamatrix{PARCEL-4471}

The data is read verbatim. A URL’s // is not a comment, and %, ~ and # reach the encoder as themselves. That is also the one restriction: a verbatim argument has to be written at the call, so the payload cannot arrive through another macro.

Which one

A QR code is what a phone camera expects and what a member of the public will recognise, and it carries a chosen level of error correction — up to about a third of the symbol can be damaged and it still reads. A Data Matrix packs the same payload into rather less area and needs a smaller quiet zone, which is why it is the symbology of shipping labels and of parts marked directly. Choose the QR code for something a person will scan, the Data Matrix for something a machine will.

Options

Both take one optional [key:value …] bracket, and every option has a document variable behind it that sets the default for every later call — so a document that wants all its symbols in one size sets it once.

\qrcode[ecc:h cell:4pt dark:navy]{HELLO}

\set qrcell {4pt}
\qrcode{one}  \qrcode{another}

The error-correction level is raised automatically to the strongest one the chosen symbol size still holds, so a short payload asking for ecc:l generally gets ecc:h at no cost in size.

How much fits

Both grow through the sizes their standards define, and pick the smallest that holds the payload. Digits are cheapest in either — a QR code packs three digits into ten bits, a Data Matrix two digits into one codeword — and upper-case letters and a few punctuation marks are cheaper than lower case in a QR code, because they have a mode of their own.

A payload too long to encode is reported on the diagnostic channel and nothing is drawn, rather than a truncated symbol being produced. The Data Matrix package builds the square symbols from 10×10 up to 48×48, which is 174 codewords; the rectangular symbols are not built.

Getting the value without drawing it

\qrmatrix and \dmxmatrix encode without drawing, leaving the symbol in qrmatrixvalue and dmxmatrixvalue as a sequence of rows, each a string of . and #. That is what the packages’ own tests read, and it is there for a document that wants to draw the modules some other way.

They are written in texish

Neither encoder is built into the engine. The mode selection, the Reed–Solomon check codewords over GF(256), the placement walks and — for the QR code — the eight-way mask search scored by four penalty rules are all \calc, \for and \put over sequences, in the document language. Both load a third package, barcode, which holds what they share: the payload as bytes, and the field arithmetic.

That is worth knowing for one practical reason. Encoding is real computation, and a large QR code is not instant — a version-4 symbol takes a few seconds in the command-line binary, where a small one takes about one. A document with a page of symbols will notice; a document with one will not. A Data Matrix is far quicker, since it has no mask search.