使用 jQuery 选择画布内的图像
我有以下 JavaScript 代码：
var canvas = document.getElementsByTagName('canvas')[0];
var ctx = canvas.getContext('2d');
var img = new Image;
var x;
img.onload = function(){ ctx.drawImage(img,0,0); };
img.src='img.svg';
执行上述代码后，我想使用 jQuery 选择 SVG 图像。为此，我编写了以下代码 $('svg')，但这不起作用。
有人可以帮助我选择图像吗？
非常感谢您的帮助！
I have following JavaScript code:
var canvas = document.getElementsByTagName('canvas')[0];
var ctx = canvas.getContext('2d');
var img = new Image;
var x;
img.onload = function(){ ctx.drawImage(img,0,0); };
img.src='img.svg';
After execution of the above code I would like to select the SVG-image with jQuery. To do this I wrote following code $('svg'), but this doesn't work.
Can somebody help me so that I can select the image?
Thank you very much for your help!
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图像本身在 DOM 中不可用，您只是临时创建它以将其绘制到画布中。所以画布保存了图像的内容，图像本身并不在 DOM 中。尽管如此，您可以使用
$(img)来获取图像，但对此元素的任何操作都不会显示在任何地方。The image itself is not available in the DOM, you just created it temporarily to draw it into the canvas. So the canvas holds the content of the image, the image itself is not in the DOM. Nevertheless you can get a hold on the image using
$(img), but any manipulation of this element will not show anywhere.画布只是一个包含图像数据的位图，没有内置的诸如对象之类的抽象概念。您可以做的就是在画布上写入和读取。也就是说，只要没有不安全的（即来自其他域的）写入画布即可。不幸的是，当在画布上写入/绘制 SVG 时，它会被错误地视为不安全内容，并且您将无法再读取位图。
The canvas is just a bitmap containing image data, there are no built-in abstract concepts such as objects. What you can do is write to and read from the canvas. That is, as long as no unsecure (i.e. from other domains) are written to the canvas. Unfortunately when writing/drawing SVG to the canvas it's faulty considered to be unsecure content and you will no longer be able to read the bitmap.