Cross Domain Canvas Images

By  on  

You can do some really awesome stuff with images when you push their data into canvas.  And of course, when you're done playing around with the image, you can export the canvas data to an IMG element and data URI.  What we sometimes don't remember, however, is that the cross-origin rules apply to those images, so if you try to convert an image from another host to canvas, you'll get an error.  You can use this snippet from HTML5 Boilerplate within the image host domain's .htaccess file to allow cross-origin data reading of images:

<IfModule mod_setenvif.c>
	<IfModule mod_headers.c>
		<FilesMatch "\.(cur|gif|ico|jpe?g|png|svgz?|webp)$">
			SetEnvIf Origin ":" IS_CORS
			Header set Access-Control-Allow-Origin "*" env=IS_CORS
		</FilesMatch>
	</IfModule>
</IfModule>

Allowing for CORS within .htaccess then allows you to pull image data when the image is on another domain. This is especially useful on CDNs! .htaccess is a life-saver sometimes!

Recent Features

  • By
    Write Simple, Elegant and Maintainable Media Queries with Sass

    I spent a few months experimenting with different approaches for writing simple, elegant and maintainable media queries with Sass. Each solution had something that I really liked, but I couldn't find one that covered everything I needed to do, so I ventured into creating my...

  • By
    CSS @supports

    Feature detection via JavaScript is a client side best practice and for all the right reasons, but unfortunately that same functionality hasn't been available within CSS.  What we end up doing is repeating the same properties multiple times with each browser prefix.  Yuck.  Another thing we...

Incredible Demos

  • By
    jQuery Chosen Plugin

    Without a doubt, my least favorite form element is the SELECT element.  The element is almost unstylable, looks different across platforms, has had inconsistent value access, and disaster that is the result of multiple=true is, well, a disaster.  Needless to say, whenever a developer goes...

  • By
    Digg-Style Dynamic Share Widget Using the Dojo Toolkit

    I've always seen Digg as a very progressive website. Digg uses experimental, ajaxified methods for comments and mission-critical functions. One nice touch Digg has added to their website is their hover share widget. Here's how to implement that functionality on your site...

Discussion

  1. I’m finding that I get CORS errors when I request from my own site and then convert them to base64 images using the “canvas technique” referred to here. Is that expected?

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!