91 lines
2.3 KiB
Go
91 lines
2.3 KiB
Go
package qrbill
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import (
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"image"
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"image/draw"
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"os"
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"github.com/boombuler/barcode"
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"github.com/boombuler/barcode/qr"
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)
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// This is a port of the Java 1.7 reference example from paymentstandards.ch:
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// https://www.paymentstandards.ch/dam/downloads/qrcodegenerator.java
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//
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// The priority was to write idiomatic Go code first, and match the reference
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// example as good as possible second.
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const (
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swissCrossEdgeSidePx = 166
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swissCrossEdgeSideMm = 7
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// The edge length of the qrcode inclusive its white border.
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qrCodeEdgeSideMm = 42 + 13
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qrCodeEdgeSidePx = swissCrossEdgeSidePx / swissCrossEdgeSideMm * qrCodeEdgeSideMm
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)
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func generateSwissQrCode(payload string) (image.Image, error) {
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// generate the qr code from the payload
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qrCodeImage, err := generateQrCodeImage(payload)
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if err != nil {
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return nil, err
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}
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// overlay the qr code with a Swiss Cross
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return overlayWithSwissCross(qrCodeImage)
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}
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func generateQrCodeImage(payload string) (image.Image, error) {
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code, err := qr.Encode(payload, qr.M, qr.Unicode)
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if err != nil {
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return nil, err
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}
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qrcode, err := barcode.Scale(code, qrCodeEdgeSidePx, qrCodeEdgeSidePx)
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if err != nil {
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return nil, err
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}
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return qrcode, nil
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}
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func overlayWithSwissCross(qrCodeImage image.Image) (image.Image, error) {
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// TODO: bundle the swiss cross image instead of reading it
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const swissCrossPath = "/home/michael/go/src/github.com/stapelberg/qrbill/third_party/swiss-cross/CH-Kreuz_7mm/CH-Kreuz_7mm.png"
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f, err := os.Open(swissCrossPath)
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if err != nil {
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return nil, err
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}
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defer f.Close()
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swissCrossImage, _, err := image.Decode(f)
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if err != nil {
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return nil, err
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}
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combinedQrCodeImage := image.NewRGBA(qrCodeImage.Bounds())
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{
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sr := qrCodeImage.Bounds() // source rect
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destRect := image.Rectangle{image.Point{0, 0}, sr.Size()}
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draw.Draw(combinedQrCodeImage, destRect, qrCodeImage, sr.Min, draw.Src)
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}
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{
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sr := swissCrossImage.Bounds() // source rect
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const swissCrossPosition = (qrCodeEdgeSidePx / 2) - (swissCrossEdgeSidePx / 2)
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destPoint := image.Point{
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X: swissCrossPosition,
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Y: swissCrossPosition,
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}
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// Convert the source image bounds into the destination image’s coordinate
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// space:
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destRect := image.Rectangle{
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destPoint,
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destPoint.Add(sr.Size()),
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}
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draw.Draw(combinedQrCodeImage, destRect, swissCrossImage, sr.Min, draw.Src)
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}
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return combinedQrCodeImage, nil
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}
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