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  Argument
 
    page    Selects current active page
 
  Description
 
    For configurations with multiple screen pages, the _SetActivePage
    procedure specifies the video memory area where text and graphics
    output is written. The page argument selects the current active
    page. The default page number is 0.
 
    In contrast, the visual page is the area of video memory currently
    being displayed. If the active page is not the same as the visual
    page, the effect of text output and drawing routines will not be
    seen as they are executed, but will become visible when the visual
    page containing the output is selected.
 
    Screen animation can be done by alternating the pages displayed.
    Use _SetActivePage to select active pages and write to them using
    output routines. Use the _SetVisualPage procedure to display
    completed graphics pages alternately. One page can be displayed
    while another is being written.
 
    _SetActivePage can be used in all modes. To use these techniques
    in text modes, use the _OutText or _OutMem procedure rather than
    standard I/O functions.
 
    Note:  The CGA hardware has only 16K of RAM available to support
    multiple video pages, and only in text modes. EGA and VGA hardware
    may be equipped with up to 256K of RAM for multiple video pages in
    graphics modes. Use the _GetVideoConfig procedure to determine the
    number of video pages available on the current mode.
 
  _GrStatus Returns
 
    _GrInvalidParameter