Background:
The shot below is of Mail.app in OS X Lion. When the source list gets too long, a nice shadowy line appears just above the buttons at the bottom of the source list. When you scroll, the source list moves under that shadowy line. When you expand the window so that everything in the source list fits without scrolling, the shadowy line disappears.
The question:
How can I draw this shadowy line using Cocoa? I'm aware of NSShadow and such, but it seems to me there's more going on here than just a shadow. There's a line that subtly fades to points (as if you applied a gradient mask to each end in Photoshop.) Likewise, the shadow is oval and tapers off as you approach the end of the lines. So it's not just a regular NSShadow, is it? (It's definitely not an image, as it scales nicely when you expand the width of the source view.)
Any tips on how to approach drawing this shape would be greatly appreciated.
And for the sticklers out there, no, this does not violate the NDA, as Mail.app has been shown publicly by Apple.