Bitmap rounded area transparency

Question

I need to slide an image over another image. The bottom image is a picture. The top image is a ring with a thick solid border. I want to move the ring over the image like a magnifying glass. My problem is how do I make the ring have a transparent circular area so when it moves it shows the image below?
I was planning to use bitmap threshold() but it the sourceRect (e.g. the area for transparency) parameter is rectangular. Does anyone know if this will work with a rounded rectangle? Or is there some other trick I should look at.
Thanks
public function threshold(sourceBitmapData:BitmapData, sourceRect:Rectangle, destPoint:Point, operation:String, threshold:uint, color:uint = 0, mask:uint = 0xFFFFFFFF, copySource:Boolean = false):uint

Answer 1

I believe transparency is unsupported, although not specifically listed:
http://office.microsoft.com/en-us/sharepoint-server-help/differences-between-using-a-workbook-in-excel-and-excel-services-HA010105457.aspx#BMviewing_a_workbook
Trevor Seward
Follow or contact me at...
&nbsp&nbsp
This post is my own opinion and does not necessarily reflect the opinion or view of Microsoft, its employees, or other MVPs.