Convert an SVG to PNG using Javascript/jQuery and C# for download

Question

I have an svg image on a page. A user then clicks a link and this is called to get the toDataUrl():

            console.log('Processing svg for NOT Internet Explorer');
            var svgText = $("#div-surrounding-svg-element").html();
            var d3Canvas = document.getElementById("d3-canvas");
            d3Canvas.width = 2000;
            d3Canvas.height = 300;
            var ctxt = d3Canvas.getContext("2d");
            // make canvas background
            ctxt.fillStyle = "#fff";
            ctxt.fillRect(0, 0, d3Canvas.width, d3Canvas.height);

            var svg = new Blob([svgText], { type: "image/svg+xml;charset=utf-8" });
            var domURL = self.URL || self.webkitURL || self;
            var url = domURL.createObjectURL(svg);
            var img = new Image();

            img.onload = function ()
            {
                ctxt.drawImage(this, 0, 0);
                domURL.revokeObjectURL(url);
                var dataUrl = d3Canvas.toDataURL();
                // $('#download-chart-dataUrl').val(dataUrl);
                // var downloadExcelForm = $('#download-chart-form');
                // downloadExcelForm.submit();

                // $('#download-chart-form').submit();
                DownloadPNG(dataUrl);
            };

            img.src = url;
        }

DownloadPNG does a POST to the server and C# does this:

        var base64Data = Regex.Match(dataUrl, @"data:image/(?<type>.+?),(?<data>.+)").Groups["data"].Value;
        var binData = Convert.FromBase64String(base64Data);

        using (var stream = new MemoryStream(binData))
        {
            var tempFolder = ConfigurationManager.AppSettings["tempFilesDirectory"];
            var bitmap = new Bitmap(stream);

            var folder = Server.MapPath(tempFolder);
            var imagePath = folder + $"/{Guid.NewGuid().ToString()}.png";
            bitmap.Save(imagePath);

            //return File(imagePath, "image/png", "Chart.png");
            Response.Clear();
            Response.AddHeader("Content-Disposition", "attachment;filename=Chart.png");
            Response.WriteFile(imagePath);
            Response.End();
        }

I am getting a plain white png instead of the image I want. What am I missing? Thanks.

Answer 1

You don't need any server-side for download png)))Please see an example P.S. Using jquery for a dom manipulation is a "bad taste" in 2k18, please use dom api))

Update: I have added querySelector to the SVG child of SVG, and SVG serializing code.

downloadPng=function(){
   var img = new Image();
   img.onload = function (){
	var canvas = document.createElement("canvas");
	canvas.width = img.naturalWidth;
	canvas.height = img.naturalHeight;
	var ctxt = canvas.getContext("2d");
	ctxt.fillStyle = "#fff";
	ctxt.fillRect(0, 0, canvas.width, canvas.height);
        ctxt.drawImage(img, 0, 0);
	var a = document.createElement("a");
	a.href = canvas.toDataURL("image/png");
	a.download = "image.png"
	document.body.appendChild(a);
	a.click();
	document.body.removeChild(a);
   };
   var innerSvg = document.querySelector("#div-surrounding-svg-element svg svg");
   var svgText = (new XMLSerializer()).serializeToString(innerSvg);
   img.src = "data:image/svg+xml;utf8," + encodeURIComponent(svgText);
}

<div id="div-surrounding-svg-element">
  <svg id="inner-svg" height="100" width="500" xmlns="http://www.w3.org/2000/svg">
    <svg height="100" width="500" xmlns="http://www.w3.org/2000/svg">
      <ellipse cx="240" cy="50" rx="220" ry="30" style="fill:green" />
    </svg>
    <ellipse cx="240" cy="50" rx="220" ry="30" style="fill:yellow" />
  </svg>
</div>
<button onclick="downloadPng()">download</button>