I’m so going to blog this!

So one of the most annoying things I’ve ever come across in Flash/ActionScript development is dealing with dynamically loaded images from other domains and accessing their inner BitmapData. In enterprise apps, it’s almost never the case that all of your images are coming from the same domain.

Recently, I had a project come up that asked me once again to deal with this issue. The goal was to get JPGs to smoothly zoom slowly something like the Ken Burns effect. The problem was that the images were all hosted in a completely different domain. In my ignorance, I threw my hands up and said, “Nope, sorry it’s going to be a crappy effect. You can never get that sort of thing to work without getting at the BitmapData. Which is impossible because it’s coming from another site.”

At which point Arpit pointed out that in AS3 we now have this absolutely beautiful LoaderContext class. I know I’m late to the game on this one, but I wanted to blog it because I hate when this stuff isn’t easily found on the web and the more we blog, the easier it is to find.

The solution couldn’t be easier. Here’s how you get around it:

1. Make sure the domain which is serving out the images has a crossdomain.xml file at its root.
   1. If you’re unfamiliar with crossdomain policy files or the security sandbox in general, check out this security white paper from Adobe.
2. Add the SmoothImage component by Ben Longoria from the Adobe Flex cookbook beta.
3. Add the SmoothImage component to your project.
   ...
<foo:SmoothImage id="imageDisplayer">
width="308" height="274"
complete="onImageChangeComplete(event);"
/>
...
4. Add a LoaderContext with a checkPolicy property set to true. See the docs for more info.
   ...
<foo:SmoothImage id="imageDisplayer">
width="308" height="274"
loaderContext=”{new LoaderContext(true)}”
complete=”onImageChangeComplete(event);”
/>
…
5. Sigh your relief that you will never again have to deal with the hell that is cross domain image manipulation.

Links in this blog:

• Ken Burns Effect: http://en.wikipedia.org/wiki/Ken_Burns_Effect
• LoaderContext: http://livedocs.adobe.com/flex/201/langref/flash/system/LoaderContext.html
• Adobe security white paper: http://www.adobe.com/devnet/flashplayer/articles/flash_player_9_security.pdf
• Ben Longoria’s SmoothImage component: http://www.adobe.com/cfusion/communityengine/index.cfm?event=showdetails&productId=2&postId=4001
• Also see the Image component live docs and how it deals with loaderContext:
  http://livedocs.adobe.com/flex/201/langref/mx/controls/Image.html
  http://livedocs.adobe.com/flex/201/langref/mx/controls/SWFLoader.html#loaderContext