Sorry, I don’t. I mean, you could of course identify the unobscured area of the window and paint over it pretty quickly, but if you wanted to draw what’s behind that I don’t know of a way to do that efficiently.
Really neat project, by the way: I love seeing technically elegant solutions to these kinds of singular problems! Did you run into any Mac App Store sandboxing restrictions with respect to capturing the screen?
Dunno if I should be impressed or going “what the hell?” Seems kind of absurd that they enforce the sandbox pretty heavily in the MAS just to let things like that get by pretty easily. Apple confuses me.