How to use Fabric.js to save a canvas as an image

Question

I have a Fabric.js prototype where people can load photos, text, and maps into the canvas. When they're done, I want them to be able to save the canvas as an image. I've tried using the standard:

canvasURL = canvas.toDataURL();
var image = new Image();
image.src = canvas.toDataURL("image/png");
$('#canvasContainer').replaceWith(image);

but it says that the canvas is tainted - I think because of the images (the method above works when it's just text). The error is:

Uncaught SecurityError: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported. 

I can use Fabric's built-in method to save as SVG:

var canvasSVG = canvas.toSVG();
$('#canvasContainer').replaceWith(canvasSVG);

But I'd rather have a PNG/JPG. Any ideas?

Here's the Fabric.js documentation on serialization of the canvas.

http://fabricjs.com/fabric-intro-part-3/#serialization

Answer 1

The following must be true:

1. Your cross-domain <img> elements must contain a crossorigin attribute.
2. The server hosting the images must return an Access-Control-Allow-Origin header in the response with either a wildcard, or your specific domain as the value.
3. The browser must support CORS on HTMLMediaElements, specifically HTMLImageElements. This is only currently possible in Chrome, Firefox, and Opera 15+

Answer 2

This works well for me

function convertToImagen() {
  canvas.deactivateAll().renderAll();  
  window.open(canvas.toDataURL('png')); 
}

Answer 3

As a side note, remember that if you're developing on your local computer rather on a server, you will probably see this security error message.

Answer 4

I faced the same issue, solved it by first passing the image url in an ajax call to a php file that would convert the image and return a data url

<?php
$content=file_get_contents($_POST['imageurl']);
echo "data:image/png;base64,". base64_encode($content);
?>

make sure to set the async:false for the ajax call

you can use the returned data to create your image object and load it on canvas.