[Bug 39440] embedded (XEMBED) windows are blank

https://bugs.winehq.org/show_bug.cgi?id=39440

--- Comment #18 from Stan  ---
I'll continue to test various things.

This code works for Pipelight but not for a shared Linux library (in a daw
host) communicating with a Wine based server.

Linux shared library code

child is __wine_x11_whole_window (from the Wine servers hwnd) sent to the Linux
shared library from the Wine server, parent is the daw host plugin window.

display = XOpenDisplay(0);
        XReparentWindow(display, child, parent, 0, 0);
    sendXembedMessage(display, child, XEMBED_EMBEDDED_NOTIFY, 0, parent, 0);
        XMapWindow(display, child);
        XSync(display, false);
        XFlush(display);
        XCloseDisplay(display);

Wine server code

then a message is sent to the Wine server to run ShowWindow(hwnd) and
UpdateWindow(hwnd)

If a 1/2 second delay is placed before calling the Wine server code, then it's
sort of ok but even that can be hit/miss on different Linux setups.