nodemcu-firmware/docs/modules/qrcodegen.md

QR Code Generator Module

Since	Origin / Contributor	Maintainer	Source
2018-10-20	https://github.com/nayuki/QR-Code-generator.git integrated by Tom Sutcliffe	Tom Sutcliffe	qrcodegen.c

This module wraps the QR Code Generator API written in C by https://github.com/nayuki/QR-Code-generator.git for producing a QR Code.

qrcodegen.encodeText()

Generates a QR Code from a text string. In the most optimistic case, a QR Code at version 40 with low ECC can hold any UTF-8 string up to 2953 bytes, or any alphanumeric string up to 4296 characters, or any digit string up to 7089 characters.

Syntax

qrcodegen.encodeText(text, [options])

Parameters

• text The text or URL to encode. Should be UTF-8 or ASCII.
• options An optional table, containing any of:
  • minver the minimum version according to the QR Code Model 2 standard. If not specified, defaults to 1.
  • maxver the maximum version according to the QR Code Model 2 standard. If not specified, defaults to 40. Specifying a lower maximum version reduces the amount of temporary memory the function requires, so it can be worthwhile to specify a smaller value if you know the text will fit in a lower-version QR Code.
  • ecl the error correction level in a QR Code symbol. Higher error correction produces a larger QR Code. One of:
    • qrcodegen.LOW (default if not specified)
    • qrcodegen.MEDIUM
    • qrcodegen.QUARTILE
    • qrcodegen.HIGH
  • mask the mask pattern used in a QR Code symbol. An integer 0-7, or qrcodegen.AUTO (the default).
  • boostecl defaults to false.

Returns

The QR Code, encoded as a string. Use qrcodegen.getSize() and qrcodegen.getPixel() to extract data from the result. If the text cannot be represented within the given version range (for example it is too long) then nil is returned.

Example

qrcode = qrcodegen.encodeText("https://nodemcu.readthedocs.io/", {minver=1, maxver=4})
print("Size:", qrcodegen.getSize(qrcode))

qrcodegen.getSize()

Syntax

qrcodegen.getSize(qrcode)

Parameters

• qrcode a QR Code string, as returned by qrcodegen.encodeText().

Returns

Returns the side length in pixels of the given QR Code. The result is in the range [21, 177].

qrcodegen.getPixel(qrcode, x, y)

Get the color of the pixel at the given coordinates of the QR Code. x and y must be between 0 and the value returned by qrcodegen.getSize().

Syntax

qrcodegen.getPixel(qrcode, x, y)

Parameters

• qrcode a QR Code string, as returned by qrcodegen.encodeText().
• x
• y

Returns

true if the given pixel is black, false if it is white.

Example

qrcode = qrcodegen.encodeText("https://nodemcu.readthedocs.io/", {maxver=4})
size = qrcodegen.getSize(qrcode)
for y = 0, size-1 do
    local row = {}
    for x = 0, size-1 do
        row[x + 1] = qrcodegen.getPixel(x, y) and "*" or " "
    end
    print(table.concat(row))
end