drobban / qr_code

A library for generating QR code. https://hexdocs.pm/qr_code

QRCode

This library is useful for generating QR code to your projects.

Installation

def deps do
  [
    {:qr_code, "~> 3.0.0"}
  ]
end

Usage

If you want to create QR code, just use the function QRCode.create(your_string, level):

  iex> QRCode.create("Hello World")
  {:ok, %QRCode.QR{...}}

You can also change the error correction level according to your needs. There are four level of error corrections:

  | Error Correction Level    | Error Correction Capability    |
  |---------------------------|--------------------------------|
  | :low (default value)      | recovers 7% of data            |
  | :medium                   | recovers 15% of data           |
  | :quartile                 | recovers 25% of data           |
  | :high                     | recovers 30% of data           |

Be aware higher levels of error correction require more bytes, so the higher the error correction level, the larger the QR code will have to be.

We've just generated QR code and now we want to save it to some image file format with high quality. This library supports two image types: svg and png. So basic using is following:

  iex> "Hello World"
        |> QRCode.create(:high)
        |> QRCode.render()
        |> QRCode.save("/path/to/hello.svg")
  {:ok, "/path/to/hello.svg"}

where we used an error correction level :high. Note the function QRCode.render() has default render set up to :svg with default SvgSettings. Similarly, if you want to export to png just use QRCode.render(:png) with/without PngSettings. Calling by QRCode.save function you save QR code to file /path/to/file.type. Also instead of saving QR code to file, you can use a function QRCode.to_base64() to encode QR to base 64.

There are several options to change the appearance of svg or png:

Svg settings

| Option             | Type                   | Default value | Description                         |
|--------------------|------------------------|---------------|-------------------------------------|
| scale              | positive integer       | 10            | changes size of rendered QR code    |
| background_opacity | nil or 0.0 <= x <= 1.0 | nil           | sets background opacity of svg      |
| background_color   | string or {r, g, b}    | "#ffffff"     | sets background color of svg        |
| qrcode_color       | string or {r, g, b}    | "#000000"     | sets color of QR                    |
| image              | {string, size} or nil  | nil           | puts the image to the center of svg |
| structure          | :minify or :readable   | :minify       | minifies or makes readable svg file |

Notes:

• :image inserts image /path/to/image.type with size, this number must be positive integer. There are a few limitations:

  • The only image formats SVG software must support are JPEG, PNG, and other SVG files, see MDN.
  • Pay attention to the size of the embedded image, if you put it too large, it may not be readable by the QR reader.

• By :structure you can minify a final size of svg file or make it readable if you need. In the readable case, the file size can be slightly larger and the svg code is structured and thus more clearer.

Let's see an example with embedded image below:

  iex> alias QRCode.Render.SvgSettings
  iex> image = {"/docs/elixir.svg", 100}
  iex> qr_color = {17, 170, 136}
  iex> svg_settings = %SvgSettings{qrcode_color: qr_color, image: image, structure: :readable}
  %QRCode.Render.SvgSettings{
    background_color: "#ffffff",
    background_opacity: nil,
    image: {"/docs/elixir.svg", 100},
    qrcode_color: {17, 170, 136},
    scale: 10,
    structure: :readable
  }
  iex> "your_string"
        |> QRCode.create()
        |> QRCode.render(:svg, svg_settings)
        |> QRCode.save("/tmp/qr-with-image.svg")
  {:ok, "/tmp/qr-with-image.svg"}

Similarly, you can use png with/without PngSettings.

Png settings

| Option            | Type                   | Default value | Description                  |
|--------------------|------------------------|---------------|------------------------------|
| scale              | positive integer       | 10            | changes size of rendered QR  |
| background_color   | string or {r, g, b}    | "#ffffff"     | sets background color of png |
| qrcode_color       | string or {r, g, b}    | "#000000"     | sets color of QR             |

Limitations

The QR code is limited by characters that can contain. In our case this library was developed only for Byte and Alphanumeric mode. For example, the limits for 40 version are:

|                   |      Maximum number of characters      |
| Level             |   low   |  medium  | quartile |  high  |
|-------------------|---------|----------|----------|--------|
| Byte mode         |   2953  |   2331   |   1663   |  1273  |
| Alphanumeric mode |   4296  |   3391   |   2420   |  1852  |

For other versions and modes see Character Capacities in documentation.

If you get an {:error, "Input string can't be encoded"} it means that you overcame the limit for the given version and level (i.e. your string is too big).

If anyone needs the rest of encoding modes, please open new issue or push your code in this repository.

Notes

• You can also save the QR matrix to csv using by csvlixir:

  {:ok, qr} = QRCode.create("Hello World")
  save_csv(qr.matrix, "qr_matrix.csv")
  
  def save_csv(matrix, name_file) do
    name_file
    |> File.open([:write], fn file ->
      matrix
      |> CSVLixir.write()
      |> Enum.each(&IO.write(file, &1))
    end)
  end

References

• http://www.thonky.com/qr-code-tutorial/

License

QRCode source code is licensed under the BSD-4-Clause.

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Created: 2018-11-24Z