在画布上绘制背景图像

我想将dom对象绘制到画布上，如下所示。在画布上绘制背景图像

https://developer.mozilla.org/en-US/docs/HTML/Canvas/Drawing_DOM_objects_into_a_canvas

我有下面的代码，它看起来好像背景图片不工作？我在这里做错了什么？或者有没有办法解决它？

<canvas id="canvas" style="border:2px solid black;" width="400" height="300"></canvas> 
    <div style='background-color:red' class='test'><h1>Hello World</h1></div> 
    <div style='background-image:url(http://lorempixel.com/400/100/transport/)' class='test'><h1>Hello World</h1></div> 


    <script> 
    var canvas = document.getElementById("canvas"); 
    var ctx = canvas.getContext("2d"); 
    var data = "<svg xmlns='http://www.w3.org/2000/svg' width='500' height='500'>" + 
       "<foreignObject width='100%' height='100%'>" + 
        "<div xmlns='http://www.w3.org/1999/xhtml' style='font-size:40px'>" + 
     "<div style='background-color:red' class='test'><p>Hello World</p></div>" + 
     "<div style='background-image:url(http://lorempixel.com/500/500/transport/)' class='test'><p>Hello World</p></div>" + 
        "</div>" + 
       "</foreignObject>" + 
       "</svg>"; 
    var DOMURL = self.URL || self.webkitURL || self; 
    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; 
    </script>

来源

2013-03-04 ak85