将mathml呈现为html5画布为png

我的最终目标是将呈现的呈现MathML保存为.PNG文件。只知道编程是危险的:-)可能有更好的方法来做到这一点...我在画布元素上绘制方程，然后试图将画布元素保存为.PNG。我开始与代码在这里找到 - https://developer.mozilla.org/en/HTML/Canvas/Drawing_DOM_objects_into_a_canvas - 并作如下修改：将mathml呈现为html5画布为png

<!DOCTYPE html> 
<html> 
<body> 
<canvas id="canvas" style="border:2px solid black;" width="200" height="200"> 
</canvas> 

<script> 
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/1998/Math/MathML'  style='fontsize:40px'>" + 
     "<math>" + 
     "<mtable>" + 
     "<mtr>" + 
     "<mtd columnalign='right'>" + 
      "<mn>2</mn>" + 
      "<mi>x</mi>" + 
      "<mo>+</mo>" + 
      "<mn>3</mn>" + 
      "<mo>&#8722;</mo>" + 
      "<mn>3</mn>" + 
     "</mtd>" + 
     "<mtd columnalign='center'> " +    
      "<mo>=</mo>" + 
     "</mtd>" + 
     "<mtd columnalign='left'> " +    
      "<mn>9</mn>" + 
      "<mo>&#8722;</mo>" + 
      "<mn>3</mn>" + 
     "</mtd>" + 
     "</mtr>" + 
     "</mtable>" + 
     "</math>" + 
     "</div>" + 
     "</foreignObject>" + 
     "</svg>"; 

var svg = new (self.BlobBuilder || self.MozBlobBuilder || self.WebKitBlobBuilder); 
var DOMURL = self.URL || self.webkitURL || self; 
var img = new Image(); 
svg.append(data); 
var url = DOMURL.createObjectURL(svg.getBlob("image/svg+xml;charset=utf-8")); 
img.onload = function() { 
    ctx.drawImage(img, 0, 0); 
    DOMURL.revokeObjectURL(url); 
}; 
img.src = url; 

window.open(canvas.toDataURL('image/png')); 

</script> 

</body> 
</html>

如果我注释掉window.open我可以看到MATHML在canvas元素，而是由toDataURL产生的.PNG是只是透明的（没有数学方程式）。我错过了什么？在此先感谢...

来源

2012-04-17 Sherri Warner

就在我看到的问题是，你推迟画布的渲染，直到图像加载，但你在代码中调用window.open而不确定它的加载。您需要执行以下操作

img.onload = function() { 
    ctx.drawImage(img, 0, 0); 
    DOMURL.revokeObjectURL(url); 
    // now the image has been drawn for sure *before* opening the window 
    window.open(canvas.toDataURL('image/png')); 
}; 
img.src = url;

来源

2012-04-17 19:17:11 Loktar

嗯，当我移动该语句时，出现“安全错误”。 – 2012-04-17 20:31:18

看起来像它发生在toDataURL ...也许画布是“脏”毕竟... – 2012-04-17 20:47:39

只是“安全错误” - 没有代码 – 2012-04-17 21:06:43

将mathml呈现为html5画布为png

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