qr

Make QR codes and barcodes as images, read them back from any image, and get a code's grid to draw it yourself.

std:qr makes QR codes and barcodes (Code 128, EAN-13, UPC-A and Code 39) and reads them back. A code is a plain *img.Image from img, so whatever takes an image takes a code: save it as a file, resize it, draw it into another image, or show it in a ui view.

Reach for it for sign-in links, tickets, labels and anything a phone camera should read.

A QR code#

qr.code(text) returns a result holding the image. It is 256 pixels square by default, black on white, with a blank border (the quiet zone) that scanners need:

import "std:qr"

auto code = qr.code("https://rotur.dev/link?code=AB12").unwrap()
log code.width() code.height()

Reading it back#

qr.read(image) finds a code in an image and returns its text. It reads codes qr.code made and ones in photos or screenshots at any angle, and it also reads barcodes. When there is no code, it fails with NotFoundError:

import "std:qr"
import "std:img"

auto code = qr.code("https://rotur.dev/link?code=AB12").unwrap()
log qr.read(code).unwrap()

*img.Image blank = img.new(50, 50, {fill: "white"})
log qr.read(blank).unwrapErr().kind

Options#

size is the image's width and height in pixels (it grows if needed to give each dot a whole pixel). margin is the border in modules, color and background are colours given as "#rrggbb", "#rrggbbaa" or {r, g, b, a}. level is how much of the code may be damaged and still read: "L", "M" (the default), "Q" or "H".

import "std:qr"

auto code = qr.code("hi", {
  size: 100,
  margin: 2,
  level: "H",
  color: "#000080",
  background: "#ffffff"
}).unwrap()
log code.width()
log code.pixel(1, 1)
log qr.read(code).unwrap()

log qr.code("x" * 5000).unwrapErr().kind

Text too long for a QR code fails with ValueError. A higher level makes a denser code that survives more damage, which suits a logo laid over the middle.

Saving and showing a code#

Because it is an image, a code saves like one, and a ui view shows it with an <image> tag:

import "std:qr"
import "std:img"
import "std:ui"
import "std:fs"

fs.remove("code.png", {force: true}).unwrap()

*img.Image code = qr.code("hello").unwrap()
code.save("code.png").unwrap()
log qr.read(img.decodeFile("code.png").unwrap()).unwrap()

def View() ui.node (
  return <column pad=10>
    <text>Scan me</text>
    <image src=${code} width=100 height=100/>
  </column>
)
log ui.html(View).contains("data:image/png")
fs.remove("code.png").unwrap()

Barcodes#

qr.barcode(text, options) makes a barcode. kind is "code128" (the default, any text), "ean13", "upca" or "code39" (upper-case letters, digits and - . $ / + % and space). height is in pixels. EAN-13 takes 12 or 13 digits, and UPC-A 11 or 12, adding or checking the last digit:

import "std:qr"

auto label = qr.barcode("HELLO-123", {kind: "code39", height: 40}).unwrap()
log label.height()
log qr.read(label).unwrap()

auto ean = qr.barcode("590123412345", {kind: "ean13"}).unwrap()
log qr.read(ean).unwrap()
log qr.checkDigit("590123412345").unwrap()

log qr.barcode("abc", {kind: "ean13"}).unwrapErr().kind

qr.checkDigit(digits) computes the final digit for the code without it. A barcode that doesn't fit its kind fails with ValueError.

Drawing a code yourself#

qr.modules(text) returns the code as a grid of booleans, true for dark, with no quiet zone. Use it to draw a code another way, such as with raylib rectangles or in a terminal:

import "std:qr"

auto grid = qr.modules("hi").unwrap()
log grid.len grid[1].len

for row in grid (
  string line = ""
  for dark in row (
    line = line ++ (if dark then "##" else "  ")
  )
  log line
)

Pass {kind: "code128"} or another barcode kind to get one row of bars instead.

import "std:qr"

auto code = qr.code("OSL").unwrap()
log code.width()

import "std:qr"

auto code = qr.code("OSL").unwrap()
log code.width()

OSL

API reference#