Implement QR code display via unicode block characters.

Use `--draw` to use ANSImage instead which is less compatible with
legacy or remote terminals.

internal/bytes_to_unicode.go

@@ -0,0 +1,87 @@
+package internal
+
+import (
+	"io"
+	"strings"
+
+	"github.com/fatih/color"
+	"github.com/qpliu/qrencode-go/qrencode"
+)
+
+const (
+	Upper byte = 1 << iota
+	Lower
+)
+
+var (
+	// Got the information from https://de.wikipedia.org/wiki/Unicodeblock_Blockelemente
+	byteMapping = map[byte]rune{
+		0:             ' ',
+		Upper:         '\u2580', // UPPER HALF BLOCK
+		Lower:         '\u2584', // LOWER HALF BLOCK
+		Upper | Lower: '\u2588', // FULL BLOCK
+	}
+)
+
+func ConvertGridToUnicode(target io.Writer, source *qrencode.BitGrid) (err error) {
+	c := color.New(color.BgWhite)
+	c.Add(color.FgBlack)
+
+	writeSpaceLine := func() (n int, err error) {
+		n, err = c.Fprint(target, strings.Repeat(" ", source.Width()+2))
+		if err != nil {
+			return
+		}
+		m, err := target.Write([]byte{'\n'})
+		if err != nil {
+			return
+		}
+		n += m
+		return
+	}
+
+	if _, err = writeSpaceLine(); err != nil {
+		return
+	}
+
+	for y := 0; y < source.Height(); y += 2 {
+
+		// Go from left to right in both rows
+		line := " "
+		for x := 0; x < source.Width(); x++ {
+			var runeKey byte
+
+			// First row
+			if source.Get(x, y) {
+				runeKey |= Upper
+			}
+			if y+1 < source.Height() {
+				if source.Get(x, y+1) {
+					runeKey |= Lower
+				}
+			}
+
+			line += string(byteMapping[runeKey])
+		}
+
+		line += " "
+
+		_, err = c.Fprint(target, line)
+		if err != nil {
+			return
+		}
+
+		_, err = target.Write([]byte{'\n'})
+		if err != nil {
+			return
+		}
+	}
+
+	if err == io.EOF {
+		err = nil
+	}
+
+	_, err = writeSpaceLine()
+
+	return
+}

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"encoding/base32"
 	"errors"
 	"fmt"
@@ -48,6 +49,9 @@ var (
 var (
 	app = kingpin.New("pixelqr", "Generates QR code from any input and displays it in your ANSI true-color compatible terminal.")
 
+	flagANSImage = app.Flag("draw", "Use ANSI drawing code using ANSImage.").
+			Default("false").
+			Bool()
 	flagECLevel = app.Flag("ec", "Sets the error correction level for the generated code.").
 			Default(ECLevel_L).
 			Enum(ECLevel_L, ECLevel_M, ECLevel_Q, ECLevel_H)
@@ -115,7 +119,7 @@ func main() {
 		if err != nil {
 			return
 		}
-		generateCliQR(string(input))
+		err = generateCliQR(string(input))
 
 	case cmdOtp.FullCommand(): // otp -> qr
 		// https://github.com/google/google-authenticator/wiki/Key-Uri-Format
@@ -149,20 +153,36 @@ func main() {
 			RawQuery: query.Encode(),
 		}
 		log.Println("Generated URL:", url.String())
-		generateCliQR(url.String())
+		err = generateCliQR(url.String())
 
 	default: // other
 		err = ErrCommandNotFound
 	}
 }
 
-func generateCliQR(input string) {
+func generateCliQR(input string) (err error) {
 	grid, err := qrencode.Encode(input, ecLevelMapping[*flagECLevel])
 	if err != nil {
 		return
 	}
 
-	s, err := internal.ConvertGridToANSImage(grid)
+	var s string
+
+	if *flagANSImage {
+
+		s, err = internal.ConvertGridToANSImage(grid)
+		if err != nil {
+			return
+		}
+	} else {
+
+		w := new(bytes.Buffer)
+		err = internal.ConvertGridToUnicode(w, grid)
+		if err != nil {
+			return
+		}
+		s = string(w.Bytes())
+	}
 
 	fmt.Println(s)