ArtQRCode cross-platform

[HannibalZA]

Here's a 'tweak' - or at least a start to handle rounded, dot-style rendering using the SvgQRCode option for linux based implementations where System.Drawing becomes a problem.

Play nice, have fun...

    public IActionResult GetQRCode()
    {
        string url = $"https://www.example.com/qr/code/12345";

        var generator = new QRCodeGenerator();
        var data = generator.CreateQrCode(url, QRCodeGenerator.ECCLevel.Q);

        var svgQr = new SvgQRCode(data);

        string svg = svgQr.GetGraphic(10); // pixels per module = 10, tweak as needed

        svg = SvgToDots(svg); //style it

        return Content(svg, "image/svg+xml");
    }


    public static string SvgToDots(string svg)
    {
        const string black = "#000000"; // to identify workable elements to style

        var pattern = @"<rect x=""(\d+)"" y=""(\d+)"" width=""(\d+)"" height=""(\d+)"" fill=""(#[A-Fa-f0-9]{6})""\s*/>";
        var regex = new Regex(pattern, RegexOptions.Compiled);

        var rects = new List<(int x, int y, int width, int height, string fill)>();
        int moduleSize = int.MaxValue;
        int maxX = 0, maxY = 0;

        foreach (Match match in regex.Matches(svg))
        {
            int x = int.Parse(match.Groups[1].Value);
            int y = int.Parse(match.Groups[2].Value);
            int width = int.Parse(match.Groups[3].Value);
            int height = int.Parse(match.Groups[4].Value);
            string fill = match.Groups[5].Value.ToLowerInvariant();

            rects.Add((x, y, width, height, fill));

            if (fill == black && width > 0 && width < moduleSize) moduleSize = Math.Min(moduleSize, width);
            if (fill == black && height > 0 && height < moduleSize) moduleSize = Math.Min(moduleSize, height);

            maxX = Math.Max(maxX, x + width);
            maxY = Math.Max(maxY, y + height);
        }
        int dotspace = 11; // v|h space occupied by finder
        int finderSize = moduleSize * dotspace;

        bool IsInFinderZone(int x, int y, int width, int height, int moduleSize, int fullWidth, int fullHeight)
        {
            return
                (x < moduleSize * dotspace && y < moduleSize * dotspace) ||                   // Top-left
                (x + width > fullWidth - finderSize && y < finderSize) ||                     // Top-right
                (x < finderSize && y + height > fullHeight - finderSize);                     // Bottom-left
        }

        var builder = new StringBuilder();
        builder.AppendLine($@"<svg xmlns=""http://www.w3.org/2000/svg"" version=""1.1"" viewBox=""0 0 {maxX} {maxY}"" preserveAspectRatio=""xMidYMid meet"">");

        foreach (var (x, y, width, height, fill) in rects)
        {
            if (fill != black)
                continue; // skip whitespace and non-black fills

            // fill = "#FF0000"; // Uncomment to change fill color as needed

            if (IsInFinderZone(x, y, width, height, moduleSize, maxX, maxY)) //we don't want to style the finders - for now
            {
                // Keep original rect for finder zone
                builder.AppendLine($"<rect x=\"{x}\" y=\"{y}\" width=\"{width}\" height=\"{height}\" fill=\"{fill}\" />");
                continue;
            }

            int cols = width / moduleSize;
            int rows = height / moduleSize;
            int r = moduleSize / 2;

            for (int row = 0; row < rows; row++)
            {
                for (int col = 0; col < cols; col++)
                {
                    int cx = x + (col * moduleSize) + r;
                    int cy = y + (row * moduleSize) + r;
                    builder.AppendLine($"<circle cx=\"{cx}\" cy=\"{cy}\" r=\"{r}\" fill=\"{fill}\" />");
                }
            }
        }

        builder.AppendLine("</svg>");
        return builder.ToString();
    }