NAME 
        GetScreenData -- Get copy of a screen data structure.

    SYNOPSIS 
        Success = GetScreenData( Buffer, Size, Type, screen )
        D0                       A0      D0    D1    A1

        bool getscreendata( aptr, uword, uword, struct screen * );

    FUNCTION 
        This function copies into the caller's buffer data from a screen
        structure.  Typically, this call will be used to find the size, title
        bar height, and other values for a standard screen, such as the
        Workbench screen.

        To get the data for the Workbench screen, one would call:
            GetScreenData(buff, sizeof(struct Screen), WBENCHSCREEN, NULL)

        NOTE: if the requested standard screen is not open, this function
        will have the effect of opening it.

        This function has been useful for two basic types of things:
        1) Determining information about the Workbench screen, in
           preparation for opening a window on it.
        2) Attempts at discerning the user's preferences in a working
           screen, for "cloning" the Workbench modes and dimensions
           when opening a similar custom screen.

        Providing compatibility with both of these goals has proven
        difficult, as we introduce new display modes and screen scrolling
        in V36.  read carefully the somewhat involved exceptions we
        elected to implement ...

        Changes as of V36:

        For V36 and later, the function lockpubscreen() is an improvement
        over this function, in that it doesn't copy the screen data
        but returns a pointer and a guarantee that the screen will not
        be closed.

        If the global public screen SHANGHAI mode is in effect (see
        setpubscreenmodes() ), this function will actually report on
        the default public screen, where "Workbench" windows will
        actually open.

        For V36 and later, this function does some "compatibility tricks"
        when you inquire about the WBENCHSCREEN.  To keep programs from
        "stumbling" into modes they don't understand, and because an NTSC
        machine may be running a PAL Workbench or PRODUCTIVITY, for example,
        the following "false" information is returned.

        The Screen.ViewPort.Modes field will either be HIRES or HIRES+LACE
        (with the SPRITES flag also set, as usual).  HIRES+LACE is
        used if the display mode selected for the Workbench screen
        is an interlaced screen of any type.

        The dimensions returned will be the *smaller* of the OSCAN_TEXT
        dimensions for the returned mode, and the actual dimensions
        of the Workbench screen.

        EXCEPTION: For specific compatibility considerations, if the
        Workbench is in one of the A2024 modes, the mode returned
        in Screen.ViewPort.Modes will be HIRES+LACE (with perhaps
        some "special" bits also set for future improvement), but
        with dimensions equal to the actual A2024-mode Workbench screen.
        This will favor programs which open windows on the A2024
        Workbench, but will cause some problems for programs which
        try to "clone" the Workbench screen using this function.

        If you want the real information about the modern Workbench
        screen, call LockPubScreen( "Workbench" ) and acquire its
        display mode ID by inquiring of the actual viewport (using
        graphics.library/getvpmodeid() ).

        You may then use the information you get to clone as many of
        the properties of the Workbench screen that you wish.

        In the long run, it's probably better to provide your user
        with a screen mode selection option, and skip all this.

    INPUTS 
        Buffer = pointer to a buffer into which data can be copied
        Size   = the size of the buffer provided, in bytes
        Type   = the screen type, as specified in openwindow() (wbenchscreen,
            CUSTOMSCREEN, ...)
        screen = ignored, unless type is customscreen, which results only in
            copying 'size' bytes from 'screen' to 'buffer'

    RESULT 
        TRUE if successful
        FALSE if standard screen of Type 'type' could not be opened.

    BUGS 
        You cannot support the new V36 display modes using this function.

    SEE ALSO 
        openwindow(), lockpubscreen(), graphics.library/getvpmodeid(),
        setpubscreenmodes(), openscreen()