svg 文本 渲染成canvas

https://developer.mozilla.org/zh-CN/docs/Web/API/Canvas_API/Drawing_DOM_objects_into_a_canvas

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');

var data = '<svg xmlns="http://www.w3.org/2000/svg" width="200" height="200">' +
           '<foreignObject width="100%" height="100%">' +
           '<div xmlns="http://www.w3.org/1999/xhtml" style="font-size:40px">' +
             '<em>I</em> like' + 
             '<span style="color:white; text-shadow:0 0 2px blue;">' +
             'cheese</span>' +
           '</div>' +
           '</foreignObject>' +
           '</svg>';

var DOMURL = window.URL || window.webkitURL || window;

var img = new Image();
var svg = new Blob([data], {type: 'image/svg+xml;charset=utf-8'});
var url = DOMURL.createObjectURL(svg);

img.onload = function () {
  ctx.drawImage(img, 0, 0);
  DOMURL.revokeObjectURL(url);
}

img.src = url;