How to print a canvas element?

Question

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:

the button code:

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

'print_voucher()' function:

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

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();

But that didn't even start the printer.

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

**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.');
}

}

http://stackoverflow.com/questions/5217377/print-out-of-a-html5-canvas — Saturnix, Jun 09 '13 at 13:16
@Saturnix I tried it, but it still doesn't work - I don't see the image created. I edited my original post and included the code that creates the canvas and tries to create the image. — Igal, Jun 09 '13 at 13:43
you should also post any error you see in the javascript console - don't you see any? — Saturnix, Jun 09 '13 at 13:46

score 10 · Answer 1 · answered Jun 09 '13 at 15:08

This will convert the canvas to a .png image URL and open it in a new browser window

The Print Dialog is triggered to let the user print the page.

function print_voucher(){
    var win=window.open();
    win.document.write("<br><img src='"+canvas.toDataURL()+"'/>");
    win.print();
    win.location.reload();
}

Here is example code:

<style>
    body{ background-color: ivory; }
    canvas{border:1px solid red;}
</style>

<script>
$(function(){

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

    ctx.fillStyle="gold";
    ctx.strokeStyle="blue";
    ctx.lineWidth=5;
    ctx.rect(50,50,100,100);
    ctx.fill();
    ctx.stroke();

    function print_voucher(){
        var win=window.open();
        win.document.write("<br><img src='"+canvas.toDataURL()+"'/>");
        win.print();
        win.location.reload();
    }

    $("#printVoucher").click(function(){ print_voucher(); });


}); // end $(function(){});
</script>

</head>

<body>
    <canvas id="canvas" width=300 height=300></canvas><br>
    <button id="printVoucher">Print</button>
</body>
</html>

score 4 · Accepted Answer · answered Jun 09 '13 at 18:08

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

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

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';

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);
}

Now it worked!

How to print a canvas element?

2 Answers2

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