first commit

pigo/internal/remotecontrol/qr.go

@@ -0,0 +1,51 @@
+package remotecontrol
+
+import (
+	"strings"
+
+	qrcode "github.com/skip2/go-qrcode"
+)
+
+// Render encodes url as a QR code drawn with Unicode half-block characters,
+// suitable for scanning off a terminal by a phone camera. Two matrix rows are
+// packed into each text line (▀ ▄ █ and space), halving the printed height.
+//
+// The rendering assumes a dark-background terminal: light QR modules are drawn
+// as bright block glyphs and dark modules as the terminal background. go-qrcode
+// includes the mandatory quiet-zone border in its bitmap.
+//
+// On any encoding error Render returns ("", err); callers should degrade
+// gracefully by printing the URL alone (the QR is a convenience, not required).
+func Render(url string) (string, error) {
+	q, err := qrcode.New(url, qrcode.Medium)
+	if err != nil {
+		return "", err
+	}
+	bm := q.Bitmap() // true = dark module; includes quiet-zone border.
+
+	var b strings.Builder
+	for y := 0; y < len(bm); y += 2 {
+		row := bm[y]
+		for x := 0; x < len(row); x++ {
+			// A "light" pixel is drawn as a block; a "dark" pixel is left as
+			// background. Rows beyond the matrix are treated as light (quiet).
+			topLight := !bm[y][x]
+			botLight := true
+			if y+1 < len(bm) {
+				botLight = !bm[y+1][x]
+			}
+			switch {
+			case topLight && botLight:
+				b.WriteRune('█')
+			case topLight && !botLight:
+				b.WriteRune('▀')
+			case !topLight && botLight:
+				b.WriteRune('▄')
+			default:
+				b.WriteByte(' ')
+			}
+		}
+		b.WriteByte('\n')
+	}
+	return b.String(), nil
+}