as3跨域加载外部图片

跨域加载外部图片除需要设置crossdomain外，还需要在loader.load()方法添加context参数，文档显示context参数为LoaderContext 类：

load(request:URLRequest, context:LoaderContext = null):void

When loading images (JPEG, GIF, or PNG) instead of SWF files, there is no need to specify a SecurityDomain or an application domain, because those concepts are meaningful only for SWF files. Instead, you have only one decision to make: do you need programmatic access to the pixels of the loaded image? If so, see the checkPolicyFile property.
所以，跨域加载正确的写法为：

import flash.system.LoaderContext;

var lc:LoaderContext = new LoaderContext(true);
var loader:Loader = new Loader();
var request:URLRequest = new URLRequest(url);
loader.load(request, lc);

否则，flash player安全沙箱会报“checkPolicyFile ”错误。

这个疏忽出现在了Papervision3D中。使用BitmapFileMaterial时，如果使用的是跨域图片进行贴图，尽管设置了crossdomain.xml，仍然会报沙箱错误，解决方法是修改loadNextBitmap方法：

// ___________________________________________________________________ LOAD NEXT BITMAP

  private function loadNextBitmap():void
  {
    // Retrieve next filename in queue
    var file:String = _waitingBitmaps[0];

    var request:URLRequest = new URLRequest( file );
    var lc:LoaderContext = new LoaderContext(true);
    var bitmapLoader:Loader = new Loader();

    bitmapLoader.contentLoaderInfo.addEventListener( Event.COMPLETE, loadBitmapCompleteHandler );

    try
    {
      // Load bitmap
      bitmapLoader.load( request, lc );

      // Save original url
      _loaderUrls[ bitmapLoader ] = file;

      // Busy loading
      _loadingIdle = false;

      Papervision3D.log( "BitmapFileMaterial: Loading bitmap from " + file );
    }
    catch( error:Error )
    {
      // Remove from queue
      _waitingBitmaps.shift();

      // Loading finished
      _loadingIdle = true;

      Papervision3D.log( "[ERROR] BitmapFileMaterial: Unable to load file " + error.message );
    }
  }