I've been having issues with the Steam Overlay while playing The Witcher recently. I suspect that the issues are specific to the fact that the game was (somewhat sloppily) ported to Mac OS X with a quick Wineskin wrapper – a theory supported by this question. Specifically, the Overlay appears when I hit Shift-Tab (most of the time. Sometimes it's totally non-responsive until I restart the game), but it's completely non-interactive. The cursor remains as the games custom cursor, and I can still interact with the game behind the overlay. I cannot however, click on anything on the overlay.
Is there anything I can do to fix the overlay to make it usable?
Best Answer
The Witcher is simply put a horrible "port" that doesn't deserve the name "port".
You could try upgrading the version of Wine it runs on: http://www.insidemacgames.com/forum/index.php?showtopic=43407#entry409385
Now to get technical: The Steam Overlay for Mac is simply a slightly modified and recompiled version of the Windows Overlay. The Overlay tries to detect whether to use a DirectX hook or an OpenGL hook (since both coexist on Windows). The Overlay in this case chooses DirectX, will properly inject but then rely on Windows APIs which are obviously not available, leading to a malfunctioning overlay.
Since you can't tell the overlay what API to hook (Valves detection algorithm does that), this is an issue without a solution you can apply. Whoever ported the game, should take responsibility for this mess and clean it up.