re-implement SVG version from scratch

This implementation is using the bit matrix returned by zxing,
and then we do our own SVG rendering.

The SIX-supplied Swiss Cross SVG version is now used for the overlay.

The resulting SVG has been successfully tested in a number of different SVG
rendering engines:

• Google Chrome 86
• Firefox 82
• Emacs 26
• GIMP
• Inkscape
• Mobile Safari

When rendering the SVG onto 1265x1265 px at 600 dpi,
the resulting image matches the PNG version exactly.

generate.go

@@ -14,4 +14,4 @@
 
 package qrbill
 
-//go:generate sh -c "go run third_party/goembed/goembed.go -package qrbill -var swisscross third_party/swiss-cross/CH-Kreuz_7mm/CH-Kreuz_7mm.png > GENERATED_swisscross.go && gofmt -w GENERATED_swisscross.go"
+//go:generate sh -c "go run third_party/goembed/goembed.go -package qrbill -var swisscross third_party/swiss-cross/CH-Kreuz_7mm/CH-Kreuz_7mm.png third_party/swiss-cross/CH-Kreuz_7mm/CH-Kreuz_7mm.svg > GENERATED_swisscross.go && gofmt -w GENERATED_swisscross.go"

go.mod

@@ -3,13 +3,10 @@ module github.com/stapelberg/qrbill
 go 1.14
 
 require (
-	github.com/aaronarduino/goqrsvg v0.0.0-20170617203649-603647895681
 	github.com/ajstarks/svgo v0.0.0-20200320125537-f189e35d30ca
-	github.com/boombuler/barcode v1.0.0
 	github.com/davecgh/go-spew v1.1.1
 	github.com/makiuchi-d/gozxing v0.0.0-20200903113411-25f730ed83da
 	github.com/mattn/go-isatty v0.0.12
-	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e
 	golang.org/x/text v0.3.4 // indirect
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
 )

go.sum

@@ -1,17 +1,11 @@
-github.com/aaronarduino/goqrsvg v0.0.0-20170617203649-603647895681 h1:eZrVcUgy0P6+B6Vu7SKPh3UZQS5nEuyjhbkFyfz7I2I=
-github.com/aaronarduino/goqrsvg v0.0.0-20170617203649-603647895681/go.mod h1:dytw+5qs+pdi61fO/S4OmXR7AuEq/HvNCuG03KxQHT4=
 github.com/ajstarks/svgo v0.0.0-20200320125537-f189e35d30ca h1:kWzLcty5V2rzOqJM7Tp/MfSX0RMSI1x4IOLApEefYxA=
 github.com/ajstarks/svgo v0.0.0-20200320125537-f189e35d30ca/go.mod h1:K08gAheRH3/J6wwsYMMT4xOr94bZjxIelGM0+d/wbFw=
-github.com/boombuler/barcode v1.0.0 h1:s1TvRnXwL2xJRaccrdcBQMZxq6X7DvsMogtmJeHDdrc=
-github.com/boombuler/barcode v1.0.0/go.mod h1:paBWMcWSl3LHKBqUq+rly7CNSldXjb2rDl3JlRe0mD8=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/makiuchi-d/gozxing v0.0.0-20200903113411-25f730ed83da h1:OgNu1PPD9EvZckyKDAc8DA4KymNXuc6vaCLsdOGyjOE=
 github.com/makiuchi-d/gozxing v0.0.0-20200903113411-25f730ed83da/go.mod h1:WoI7z45M7ZNA5BJxiJHaB+x7+k8S/3phW5Y13IR4yWY=
 github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHXY=
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
-github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e h1:MRM5ITcdelLK2j1vwZ3Je0FKVCfqOLp5zO6trqMLYs0=
-github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e/go.mod h1:XV66xRDqSt+GTGFMVlhk3ULuV0y9ZmzeVGR4mloJI3M=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42 h1:vEOn+mP2zCOVzKckCZy6YsCtDblrpj/w7B9nxGNELpg=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.4 h1:0YWbFKbhXG/wIiuHDSKpS0Iy7FSA+u45VtBMfQcFTTc=

qrbill.go

@@ -32,9 +32,8 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/aaronarduino/goqrsvg"
-	svg "github.com/ajstarks/svgo"
-	"github.com/boombuler/barcode/qr"
+	"github.com/makiuchi-d/gozxing/qrcode/decoder"
+	"github.com/makiuchi-d/gozxing/qrcode/encoder"
 
 	// We currently read the swiss cross PNG version.
 	_ "image/png"
@@ -265,37 +264,27 @@ type Bill struct {
 }
 
 func (b *Bill) EncodeToSVG() ([]byte, error) {
-	// as per https://www.paymentstandards.ch/dam/downloads/ig-qr-bill-en.pdf, section 5.1:
-	// Error correction level M (redundancy of around 15%)
-
-	// Section 4.2.1: Character set:
-	// UTF-8 should be used for encoding
-
-	code, err := qr.Encode(b.qrcontents, qr.M, qr.Unicode)
+	var err error
+	code, err := encoder.Encoder_encode(b.qrcontents, decoder.ErrorCorrectionLevel_M, qrEncodeHints())
 	if err != nil {
 		return nil, err
 	}
-	var buf bytes.Buffer
-	s := svg.New(&buf)
-	qrsvg := goqrsvg.NewQrSVG(code, 5)
-	qrsvg.StartQrSVG(s)
-	if err := qrsvg.WriteQrSVG(s); err != nil {
+
+	const quietzone = 4
+	qrCodeSVG, err := renderResultSVG(code, qrCodeEdgeSidePx, qrCodeEdgeSidePx, quietzone)
+	if err != nil {
 		return nil, err
 	}
 
-	// Overlay the swiss cross (not entirely scaled correctly, but should be
-	// good enough):
-	const px = 5
-	x := (30 - 4) * px
-	y := (30 - 4) * px
+	// overlay the swiss cross
+	cross := swisscross["third_party/swiss-cross/CH-Kreuz_7mm/CH-Kreuz_7mm.svg"]
+	// Remove XML document header, we embed the <svg> element:
+	cross = bytes.ReplaceAll(cross, []byte(`<?xml version="1.0" encoding="utf-8"?>`), nil)
+	// Overwrite position and size of the embedded <svg> element:
+	cross = bytes.ReplaceAll(cross, []byte(`x="0px" y="0px"`), []byte(`x="549" y="549" width="166" height="166"`))
 
-	s.Rect(x+0*px, y+0*px, 8*px, 8*px, "fill:#FFFFFF")
-	s.Rect(x+0*px+2, y+0*px+2, 8*px-4, 8*px-4, "fill:#000000")
-	s.Rect(x+3*px, y+1*px, 2*px, 6*px, "fill:#FFFFFF")
-	s.Rect(x+1*px, y+3*px, 6*px, 2*px, "fill:#FFFFFF")
-
-	s.End()
-	return buf.Bytes(), nil
+	// Inject the swiss cross into the <svg> document:
+	return bytes.ReplaceAll(qrCodeSVG, []byte(`</g>`), append(cross, []byte("</g>")...)), nil
 }
 
 func (b *Bill) EncodeToImage() (image.Image, error) {

qrcodegenerator.go

@@ -53,14 +53,25 @@ func generateSwissQrCode(payload string) (image.Image, error) {
 	return overlayWithSwissCross(qrCodeImage)
 }
 
-func generateQrCodeImage(payload string) (image.Image, error) {
-
-	w := qrcode.NewQRCodeWriter()
-	hints := map[gozxing.EncodeHintType]interface{}{
+func qrEncodeHints() map[gozxing.EncodeHintType]interface{} {
+	return map[gozxing.EncodeHintType]interface{}{
+		// as per https://www.paymentstandards.ch/dam/downloads/ig-qr-bill-en.pdf, section 5.1:
+		// Error correction level M (redundancy of around 15%)
 		gozxing.EncodeHintType_ERROR_CORRECTION: decoder.ErrorCorrectionLevel_M,
-		gozxing.EncodeHintType_CHARACTER_SET:    common.CharacterSetECI_UTF8,
+
+		// Section 4.2.1: Character set:
+		// UTF-8 should be used for encoding
+		gozxing.EncodeHintType_CHARACTER_SET: common.CharacterSetECI_UTF8,
 	}
-	matrix, err := w.Encode(payload, gozxing.BarcodeFormat_QR_CODE, qrCodeEdgeSidePx, qrCodeEdgeSidePx, hints)
+}
+
+func generateQrCodeImage(payload string) (image.Image, error) {
+	matrix, err := qrcode.NewQRCodeWriter().Encode(
+		payload,                       // contents
+		gozxing.BarcodeFormat_QR_CODE, // format
+		qrCodeEdgeSidePx,              // width
+		qrCodeEdgeSidePx,              // height
+		qrEncodeHints())               // hints
 	if err != nil {
 		return nil, err
 	}

qrcodegeneratorsvg.go

@@ -0,0 +1,76 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package qrbill
+
+import (
+	"bytes"
+
+	svg "github.com/ajstarks/svgo"
+	"github.com/makiuchi-d/gozxing"
+	"github.com/makiuchi-d/gozxing/qrcode/encoder"
+)
+
+// renderResultSVG is a copy of renderResult from
+// gozxing/qrcode/qrcode_writer.go, adapted to output to SVG.
+func renderResultSVG(code *encoder.QRCode, width, height, quietZone int) ([]byte, error) {
+	input := code.GetMatrix()
+	if input == nil {
+		return nil, gozxing.NewWriterException("IllegalStateException")
+	}
+	inputWidth := input.GetWidth()
+	inputHeight := input.GetHeight()
+	qrWidth := inputWidth + (quietZone * 2)
+	qrHeight := inputHeight + (quietZone * 2)
+	outputWidth := qrWidth
+	if outputWidth < width {
+		outputWidth = width
+	}
+	outputHeight := qrHeight
+	if outputHeight < height {
+		outputHeight = height
+	}
+
+	multiple := outputWidth / qrWidth
+	if h := outputHeight / qrHeight; multiple > h {
+		multiple = h
+	}
+	// Padding includes both the quiet zone and the extra white pixels to accommodate the requested
+	// dimensions. For example, if input is 25x25 the QR will be 33x33 including the quiet zone.
+	// If the requested size is 200x160, the multiple will be 4, for a QR of 132x132. These will
+	// handle all the padding from 100x100 (the actual QR) up to 200x160.
+	leftPadding := (outputWidth - (inputWidth * multiple)) / 2
+	topPadding := (outputHeight - (inputHeight * multiple)) / 2
+
+	var buf bytes.Buffer
+	s := svg.New(&buf)
+	s.Start(outputWidth, outputHeight)
+	s.Rect(0, 0, outputWidth, outputHeight, "fill:white;stroke:white")
+
+	s.Group(`shape-rendering="crispEdges"`)
+
+	for inputY, outputY := 0, topPadding; inputY < inputHeight; inputY, outputY = inputY+1, outputY+multiple {
+		// Write the contents of this row of the barcode
+		for inputX, outputX := 0, leftPadding; inputX < inputWidth; inputX, outputX = inputX+1, outputX+multiple {
+			if input.Get(inputX, inputY) == 1 {
+				s.Rect(outputX, outputY, multiple, multiple, "fill:black;stroke:none;")
+			}
+		}
+	}
+
+	s.Gend()
+
+	s.End()
+	return buf.Bytes(), nil
+}