title: How can you use an ImageBrush to display a specified area of an image as the background of a rectangle?
body: <p>I'm trying to add a zoom feature for an image viewer control I'm creating.  When viewing the image, holding down the left mouse button brings up a rounded rectangle that is zoomed into the image.  I figure I can use An ImageBrush as the background but I can't figure out how to make it just display a specified area of the image. Can this even be done?</p>