[Bug 9917] New: Add X11 child window for client area

http://bugs.winehq.org/show_bug.cgi?id=9917

Summary: Add X11 child window for client area
           Product: Wine
           Version: 0.9.46.
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: wine-x11driver
        AssignedTo: [e-mail]
        ReportedBy: [e-mail]

The number of pixel formats which can be used in OpenGL is limited due to
constraints of the Wine X11 Driver. At Wine startup an X visual is selected
which is used for creating an X11 Window. This Window is in general reused for
OpenGL. In Windows OpenGL the pixel format is set when you want to use OpenGL.
(So in case of Wine we select a pixel format before actually setting up OpenGL;
second Windows OpenGL doesn't allow changing the pixel format).

Now thanks to the xcomposite/pixmap backends for child window rendering we can
enable multiple pixel formats. The use of those backends has performance
limitations, so far that reason only 1 pixel format is still offered.

We need to readd an X11 child window for the client area of the toplevel
window. This will help fullscreen OpenGL/D3D programs. For apps that use child
windows we use the xcomposite/pixmap backend.