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.

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
+}