如何打印canvas元素？ [英] How to print a canvas element?

问题描述

我的页面上有一个canvas元素。我在它上面绘制一个图像和用户输入的一些数据。在按下按钮我想把画布发送到打印机，打印在纸上。我尝试使用此插件： jQuery.printElement ，像这样：

I have a canvas element on my page. I draw an image over it and some data that the user entered. On a press of a button I want to send the canvas to printer, to print it on paper. I tried to use this plug-in: jQuery.printElement, like that:

按钮代码：

<a href="javascript:print_voucher()">PRINT</a>

'print_voucher（）'函数：

'print_voucher()' function:

function print_voucher()
{
    $("#canvas_voucher").printElement();
}

canvas_voucher是我的画布元素的ID。它打印了页面，但没有打印画布。我试图像这样使用它：

canvas_voucher is the ID of my canvas element. It printed the page, but didn't print the canvas. I tried to use it like that as well:

$("#canvas_voucher img").printElement();

但是这还没有启动打印机。

But that didn't even start the printer.

那么我该怎么办呢？如何打印画布的内容？

So how can I do that? How can I print the content of the canvas?

** EDIT **
这里是代码创建我的画布，并尝试用它创建一个图像：

**EDIT** Here's the code that creates my canvas and tries to create an image with it:

function create_voucher(visitor_name, visitor_identity_num, unique_number)
{
var canvas = $("#canvas_voucher")[0];
if (canvas.getContext)
{
    var ctx = canvas.getContext('2d');

    // Draw image
    var img = new Image();
    img.src = 'https://someurl.com/image.jpg';

    img.onload = function(){
        ctx.drawImage(img,0,0);
        ctx.fillStyle="#CCC";
        ctx.font="bold 20px Arial";
        ctx.fillText(visitor_name, 750, 270);
        ctx.fillText(visitor_identity_num, 750, 295);

        ctx.font="bold 25px Arial";
        ctx.fillText(unique_number, 620, 325);
    }
    var voucher = canvas.toDataURL("image/png");
    $("#voucher_img").attr("src", voucher);
} else {
    alert('You need Safari or Firefox 1.5+ to see this.');
}

}

推荐答案

找到问题并修复它。
显然这是一行的安全问题：

Found the problem and fixed it. Apparently it was a security issue at this line:

img.src = 'https://someurl.com/image.jpg';

一旦指向服务器，就被认为是潜在的安全威胁。所以我把它改成：

Once it was pointing out to a server, it was considered as a potential security threat. So I changed it to:

img.src = 'images/image.jpg';

之后，我创建了一个函数来从canvas创建一个图像，并在'img中调用它。 onload'部分：

After that I created a function to make an image from the canvas and called it within the 'img.onload' part:

...
img.onload = function(){
    ctx.drawImage(img,0,0);
    ctx.fillStyle="#CCC";
    ctx.font="bold 20px Arial";
    ctx.fillText(visitor_name, 750, 270);
    ctx.fillText(visitor_identity_num, 750, 295);
    ctx.font="bold 25px Arial";
    ctx.fillText(unique_number, 620, 325);
    draw_voucher_img();
...

function draw_voucher_img()
{
   var canvas = $("#canvas_voucher")[0];
   var voucher = canvas.toDataURL();
   $("#voucher_img").attr("src", voucher);
}

现在工作了！

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