jackpocket / 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, "~> 2.3.1"}
  ]
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. We can do that by using QRCode.Svg.save_as/3 function:

  iex> "Hello World"
        |> QRCode.create(:high)
        |> Result.and_then(&QRCode.Svg.save_as(&1,"/path/to/hello.svg"))
  {:ok, "/path/to/hello.svg"}

where we used an error correction level :high and our library Result. As you can see the svg file will be saved into /path/to/ directory.

Also there are a few settings for svg:

| Setting            | Type                   | Default value | Description               |
|--------------------|------------------------|---------------|---------------------------|
| scale              | positive integer       | 10            | scale for svg QR code     |
| background_opacity | nil or 0.0 <= x <= 1.0 | nil           | background opacity of svg |
| background_color   | string or {r, g, b}    | "#ffffff"     | background color of svg   |
| qrcode_color       | string or {r, g, b}    | "#000000"     | color of QR code          |
| format             | :none or :indent       | :none         | indentation of elements   |

By this option, you can set the size QR code, background color (and also opacity) of QR code or QR code colors. The format option is for removing indentation (of elements like is <rect.. />) in a svg file. It means that for value :none, the svg file contains only one "line of code" (no indentation), whereas for :indent svg file has a structure and svg code is more readable.

Let's see an example below:

  iex> settings = %QRCode.SvgSettings{qrcode_color: {17, 170, 136}}
  iex> "your_string"
        |> QRCode.create()
        |> Result.and_then(&QRCode.Svg.save_as(&1,"/tmp/your_name.svg", settings))
  {:ok, "/tmp/your_name.svg"}

Limitations

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

|           |      Maximum number of characters      |
| Level     |   low   |  medium  | quartile |  high  |
|-----------|---------|----------|----------|--------|
| Byte mode |   2953  |   2331   |   1663   |  1273  |

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

• If you need a png format instead of svg, you can use mogrify to convert it:

  import Mogrify
  
  "qr_code.svg"
    |> Mogrify.open()
    |> format("png")
    |> save(path: "qr_code.png")

• 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