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110 lines
2.4 KiB
Go
110 lines
2.4 KiB
Go
package qr
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import (
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"errors"
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"image"
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"image/color"
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"github.com/vitrun/qart/coding"
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)
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// A Level denotes a QR error correction level.
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// From least to most tolerant of errors, they are L, M, Q, H.
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type Level int
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const (
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L Level = iota // 20% redundant
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M // 38% redundant
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Q // 55% redundant
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H // 65% redundant
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)
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// Encode returns an encoding of text at the given error correction level.
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func Encode(text string, level Level) (*Code, error) {
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// Pick data encoding, smallest first.
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// We could split the string and use different encodings
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// but that seems like overkill for now.
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var enc coding.Encoding
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switch {
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case coding.Num(text).Check() == nil:
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enc = coding.Num(text)
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case coding.Alpha(text).Check() == nil:
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enc = coding.Alpha(text)
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default:
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enc = coding.String(text)
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}
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// Pick size.
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l := coding.Level(level)
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var v coding.Version
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for v = coding.MinVersion; ; v++ {
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if v > coding.MaxVersion {
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return nil, errors.New("text too long to encode as QR")
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}
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if enc.Bits(v) <= v.DataBytes(l)*8 {
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break
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}
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}
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// Build and execute plan.
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p, err := coding.NewPlan(v, l, 0)
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if err != nil {
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return nil, err
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}
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cc, err := p.Encode(enc)
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if err != nil {
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return nil, err
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}
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// TODO: Pick appropriate mask.
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return &Code{cc.Bitmap, cc.Size, cc.Stride, 8}, nil
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}
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// A Code is a square pixel grid.
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// It implements image.Image and direct PNG encoding.
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type Code struct {
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Bitmap []byte // 1 is black, 0 is white
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Size int // number of pixels on a side
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Stride int // number of bytes per row
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Scale int // number of image pixels per QR pixel
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}
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// Black returns true if the pixel at (x,y) is black.
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func (c *Code) Black(x, y int) bool {
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return 0 <= x && x < c.Size && 0 <= y && y < c.Size &&
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c.Bitmap[y*c.Stride+x/8]&(1<<uint(7-x&7)) != 0
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}
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// Image returns an Image displaying the code.
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func (c *Code) Image() image.Image {
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return &codeImage{c}
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}
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// codeImage implements image.Image
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type codeImage struct {
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*Code
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}
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var (
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whiteColor color.Color = color.Gray{0xFF}
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blackColor color.Color = color.Gray{0x00}
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)
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func (c *codeImage) Bounds() image.Rectangle {
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d := (c.Size + 8) * c.Scale
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return image.Rect(0, 0, d, d)
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}
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func (c *codeImage) At(x, y int) color.Color {
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if c.Black(x, y) {
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return blackColor
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}
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return whiteColor
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}
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func (c *codeImage) ColorModel() color.Model {
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return color.GrayModel
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}
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