NSMatrix with Shadowed buttons on sides
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I have an NSMatrix with a bunch of NSButtonCells as its content. I want to create an effect similar to the Xcode4 navigator area ([image from Apple website][1]), where the selected button has a recessed feel to it with a shadow on the left and right sides.

I have seen similar styles with larger icons in the preferences panel of many third party applications, and I am  wondering if there's an easy way to achieve this effect. Most likely, I don't know the right terminology for it.

I can of course draw these shadowed buttons myself and set it as alternate image of ButtonCell, I think the standard artwork that comes with apple is quite elegant and would like to use that instead.

Any help will be greatly appriciated


  [1]: http://developer.apple.com/library/ios/documentation/ToolsLanguages/Conceptual/Xcode4UserGuide/art/new_proj_struct_nav.png