Using html2canvas to render a highcharts chart to pdf doesn't work on IE and Firefox

Question

We are using html2canvas.js and html2canvas.svg.js (version 0.5.0 beta1) and highcharts.js to download a donut chart into pdf.

This works as expected in Chrome, however in IE and Firefox this isnt working. In IE the chart is rendered incorrectly, and in Firefox it is not rendered at all.

Below are screenshots of the download in Chrome, IE and Firefox

Chrome

IE (Edge)

Firefox

The code i am using to do the html2canvas is as follows:

html2canvas($("#container"), {
    onrendered: function (canvas) {
      var imgData = canvas.toDataURL(
        'image/png');
      var doc = new jsPDF('p', 'mm');
      doc.addImage(imgData, 'PNG', 10, 10);
      doc.save('sample-file.pdf');
    }
  });

I have created a jsFiddle that demonstrates the issue here - http://jsfiddle.net/jko0rs5g/3/

Does anyone know what might be causing this issue, and how we can resolve it?

EDIT

Just to clarify why we are not using the built in Highcharts exporting, this for when we are adding additional html to the Highcarts, such as additional information above or below the chart, or a score inside the donut for example. I have updated the jsfiddle to reflect this.

Answer 1

Thanks to Pawel Fus for the nod in the right direction, we got this working using canvg.js, which temporarily replaces the svg with a canvas before calling html2canvas.

The final issue came when some of the html within the svg uses em's to size the font (which unfortunately a lot of our templates do). We got around this by updating the font size for anything using em's to the underlying pixel size before rendering the svg into a canvas (see Get computed font size for DOM element in JS for how we calculated the actual font size)

Below is the updated code for the download button click

$('#download').click(function() {
  var svgElements = $("#container").find('svg');

  //replace all svgs with a temp canvas
  svgElements.each(function() {
    var canvas, xml;

    // canvg doesn't cope very well with em font sizes so find the calculated size in pixels and replace it in the element.
    $.each($(this).find('[style*=em]'), function(index, el) {
      $(this).css('font-size', getStyle(el, 'font-size'));
    });

    canvas = document.createElement("canvas");
    canvas.className = "screenShotTempCanvas";
    //convert SVG into a XML string
    xml = (new XMLSerializer()).serializeToString(this);

    // Removing the name space as IE throws an error
    xml = xml.replace(/xmlns=\"http:\/\/www\.w3\.org\/2000\/svg\"/, '');

    //draw the SVG onto a canvas
    canvg(canvas, xml);
    $(canvas).insertAfter(this);
    //hide the SVG element
    $(this).attr('class', 'tempHide');
    $(this).hide();
  });


  html2canvas($("#container"), {
    onrendered: function(canvas) {
      var imgData = canvas.toDataURL(
        'image/png');
      var doc = new jsPDF('p', 'mm');
      doc.addImage(imgData, 'PNG', 10, 10);
      doc.save('sample-file.pdf');
    }
  });

  $("#container").find('.screenShotTempCanvas').remove();
  $("#container").find('.tempHide').show().removeClass('tempHide');
});

See an updated jsfiddle of it in action here - http://jsfiddle.net/zuvzcgvz/22/