qr

README

Go QR encoder package.

go get [-u] github.com/unixdj/qr

Based on rsc.io/qr by Russ Cox. Drop in replacement for package qr. The API of package coding is incompatible.

Improvements to qr.Encode:

• Automatic mask selection
• Splitting text into segments to minimise encoded length
• Kanji mode segments
• Faster encoding

Added features in package qr:

• Splitting text into multiple QR codes (Structured Append)
• Printing QR codes as text
• Prepending an ECI mode segment to set character encoding
• Character encodings:
  • UTF-8 (default)
  • UTF-8 with byte mode segments encoded as ISO 8859-1
  • Shift JIS, Shift JISx0213 (Shift JIS-2004)
  • ASCII-compatible eight bit encodings

Packages coding and split:

• Adding segment encoders
• Adding input character encodings

Documentation

Overview

Package qr encodes QR codes.

Index

• Constants
• type Code
  • func Encode(text string, level Level) (*Code, error)
  • func EncodeData(data split.Data, level Level) (*Code, error)
  • func EncodeMulti(header, data split.Data, version coding.Version, level Level) ([]*Code, error)
  • func EncodeText(text string, c split.Charset, eci uint32, level Level) (*Code, error)
  • func EncodeTextMulti(text string, c split.Charset, eci uint32, version coding.Version, level Level) ([]*Code, error)
  • func (c *Code) Black(x, y int) bool
  • func (c *Code) Image() image.Image
  • func (c *Code) PNG() []byte
  • func (c *Code) Reverse() Reversed
  • func (c *Code) String() string
• type Level
• type Reversed
  • func (c Reversed) Black(x, y int) bool
  • func (c Reversed) Image() image.Image
  • func (c Reversed) PNG() []byte
  • func (c Reversed) String() string

Constants

const (
	UTF8         = split.UTF8         // UTF-8
	UTF8AsLatin1 = split.UTF8AsLatin1 // UTF-8, byte mode in ISO 8859-1
	ShiftJIS     = split.ShiftJIS     // Shift JIS
	ASCIICompat  = split.ASCIICompat  // ASCII-compatible 8 bit encodings
)

Predefined Charsets.

const (
	Latin1ECI   = split.Latin1ECI   // ISO 8859-1
	ShiftJISECI = split.ShiftJISECI // Shift JIS
	UTF8ECI     = split.UTF8ECI     // UTF-8
	BinaryECI   = split.BinaryECI   // 8-bit binary data
)

Extended Channel Interpretation assignment numbers.

Types

type Code

type Code struct {
	Bitmap []byte // 1 is black, 0 is white
	Size   int    // number of pixels on a side
	Stride int    // number of bytes per row
	Scale  int    // number of image pixels per QR pixel
}

A Code is a square pixel grid. It implements image.Image and direct PNG encoding.

func Encode

func Encode(text string, level Level) (*Code, error)

Encode returns an encoding of text at the given error correction level.

func EncodeData

func EncodeData(data split.Data, level Level) (*Code, error)

EncodeData returns an encoding of data at the given error correction level.

func EncodeMulti

func EncodeMulti(header, data split.Data, version coding.Version, level Level) ([]*Code, error)

EncodeMulti returns an encoding of data split across multiple QR codes with the given version and error correction level. If header is not nil, it is added at the beginning of each code.

func EncodeText

func EncodeText(text string, c split.Charset, eci uint32, level Level) (*Code, error)

EncodeText returns an encoding of text in the given Charset at the given error correction level. If the Charset is nil, it defaults to UTF8. If eci is not 0, the text is preceded by an ECI mode segment.

func EncodeTextMulti

func EncodeTextMulti(text string, c split.Charset, eci uint32, version coding.Version, level Level) ([]*Code, error)

EncodeTextMulti is a combination of EncodeText and EncodeMulti. The ECI mode segment is encoded in each code.

func (*Code) Black

func (c *Code) Black(x, y int) bool

Black returns true if the pixel at (x,y) is black.

func (*Code) Image

func (c *Code) Image() image.Image

Image returns an Image displaying the code.

func (*Code) PNG

func (c *Code) PNG() []byte

PNG returns a PNG image displaying the code.

PNG uses a custom encoder tailored to QR codes. Its compressed size is about 4x away from optimal, but it runs about 20x faster than calling png.Encode on c.Image().

func (*Code) Reverse

func (c *Code) Reverse() Reversed

Reverse returns a code with colors reversed.

func (*Code) String

func (c *Code) String() string

String returns a multiline string containing the code for printing on a dark background.

type Level

type Level int

A Level denotes a QR error correction level. From least to most tolerant of errors, they are L, M, Q, H.

const (
	L Level = iota // 20% redundant
	M              // 38% redundant
	Q              // 55% redundant
	H              // 65% redundant
)

type Reversed

type Reversed struct {
	*Code
}

Reversed is a Code with colors reversed.

func (Reversed) Black

func (c Reversed) Black(x, y int) bool

Black returns true if the original pixel at (x,y) is white.

func (Reversed) Image

func (c Reversed) Image() image.Image

Image returns an Image displaying the reversed code.

func (Reversed) PNG

func (c Reversed) PNG() []byte

PNG returns a PNG image displaying the reversed code.

func (Reversed) String

func (c Reversed) String() string

String returns a multiline string containing the code for printing on a light background.