The systray/notification area code has to do that: http://source.winehq.org/source/dlls/winex11.drv/systray.c#L620
I don't think it can be done without modifying winex11.drv.
- Embedding a HWND window into an X11 window Alexandre Bique
- Re: Embedding a HWND window into an X11 window Vincent Povirk
- Re: Embedding a HWND window into an X11 window Erich E. Hoover
- Re: Embedding a HWND window into an X11 wind... André Hentschel
- Re: Embedding a HWND window into an X11 ... Erich E. Hoover
- Re: Embedding a HWND window into an X11 wind... Alexandre Bique
- Re: Embedding a HWND window into an X11 ... Vincent Povirk
- Re: Embedding a HWND window into an... Alexandre Bique
