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qrlogo.go
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qrlogo.go
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package qrlogo
import (
"bytes"
qr "github.com/skip2/go-qrcode"
"image"
"image/color"
"image/png"
)
// Encoder defines settings for QR/Overlay encoder.
type Encoder struct {
AlphaThreshold int
GreyThreshold int
QRLevel qr.RecoveryLevel
}
// DefaultEncoder is the encoder with default settings.
var DefaultEncoder = Encoder{
AlphaThreshold: 2000, // FIXME: don't remember where this came from
GreyThreshold: 30, // in percent
QRLevel: qr.Highest, // recommended, as logo steals some redundant space
}
// Encode encodes QR image, adds logo overlay and renders result as PNG.
func Encode(str string, logo image.Image, size int) (*bytes.Buffer, error) {
return DefaultEncoder.Encode(str, logo, size)
}
// Encode encodes QR image, adds logo overlay and renders result as PNG.
func (e Encoder) Encode(str string, logo image.Image, size int) (*bytes.Buffer, error) {
var buf bytes.Buffer
code, err := qr.New(str, e.QRLevel)
if err != nil {
return nil, err
}
img := code.Image(size)
e.overlayLogo(img, logo)
err = png.Encode(&buf, img)
if err != nil {
return nil, err
}
return &buf, nil
}
// overlayLogo blends logo to the center of the QR code,
// changing all colors to black.
func (e Encoder) overlayLogo(dst, src image.Image) {
grey := uint32(^uint16(0)) * uint32(e.GreyThreshold) / 100
alphaOffset := uint32(e.AlphaThreshold)
offset := dst.Bounds().Max.X/2 - src.Bounds().Max.X/2
for x := 0; x < src.Bounds().Max.X; x++ {
for y := 0; y < src.Bounds().Max.Y; y++ {
if r, g, b, alpha := src.At(x, y).RGBA(); alpha > alphaOffset {
col := color.Black
if r > grey && g > grey && b > grey {
col = color.White
}
dst.(*image.RGBA).Set(x+offset, y+offset, col)
}
}
}
}