Firefox error rendering an SVG image to HTML5 canvas with drawImage

Question

I am trying to convert an external svg icon to a base64 png using a canvas. It is working in all browsers except Firefox, which throws an error "NS_ERROR_NOT_AVAILABLE".

var img = new Image();
img.src = "icon.svg";

img.onload = function() {
    var canvas = document.createElement("canvas");              
    canvas.width = this.width;
    canvas.height = this.height;
    var ctx = canvas.getContext("2d");
    ctx.drawImage(this, 0, 0);
    var dataURL = canvas.toDataURL("image/png");
    return dataURL;
};

Can anyone help me on this please? Thanks in advance.

Answer 1

Firefox does not support drawing SVG images to canvas unless the svg file has width/height attributes on the root <svg> element and those width/height attributes are not percentages. This is a longstanding bug.

You will need to edit the icon.svg file so it meets the above criteria.

Answer 2

As mentioned, this is an open bug caused by limitations on what Firefox accepts as specification for SVG sizes when drawing to a canvas. There is a workaround.

Firefox requires explicit width and height attributes in the SVG itself. We can add these by getting the SVG as XML and modifying it.

var img = new Image();
var src = "icon.svg";

// request the XML of your svg file
var request = new XMLHttpRequest();
request.open('GET', src, true)

request.onload = function() {
    // once the request returns, parse the response and get the SVG
    var parser = new DOMParser();
    var result = parser.parseFromString(request.responseText, 'text/xml');
    var inlineSVG = result.getElementsByTagName("svg")[0];
    
    // add the attributes Firefox needs. These should be absolute values, not relative
    inlineSVG.setAttribute('width', '48px');
    inlineSVG.setAttribute('height', '48px');
    
    // convert the SVG to a data uri
    var svg64 = btoa(new XMLSerializer().serializeToString(inlineSVG));
    var image64 = 'data:image/svg+xml;base64,' + svg64;
    
    // set that as your image source
    img.src = img64;

    // do your canvas work
    img.onload = function() {
        var canvas = document.createElement("canvas");              
        canvas.width = this.width;
        canvas.height = this.height;
        var ctx = canvas.getContext("2d");
        ctx.drawImage(this, 0, 0);
        var dataURL = canvas.toDataURL("image/png");
        return dataURL;
    };
}
// send the request
request.send();

This is the most basic version of this solution, and includes no handling for errors when retrieving the XML. Better error handling is demonstrated in this inline-svg handler (circa line 110) from which I derived part of this method.