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Synopsis:
    #include <graph.h>
    short _FAR _setactivepage( short pagenum );

Description:
    The _setactivepage function selects the page (in memory) to which
    graphics output is written.  The page to be selected is given by the
    pagenum argument.

    Only some combinations of video modes and hardware allow multiple pages
    of graphics to exist.  When multiple pages are supported, the active
    page may differ from the visual page.  The graphics information in the
    visual page determines what is displayed upon the screen.  Animation may
    be accomplished by alternating the visual page.  A graphics page can be
    constructed without affecting the screen by setting the active page to
    be different than the visual page.

    The number of available video pages can be determined by using the
     _getvideoconfig function.  The default video page is 0.

Returns:
    The _setactivepage function returns the number of the previous page when
    the active page is set successfully; otherwise, a negative number is
    returned.

Example:
    #include <conio.h>
    #include <graph.h>

    main()
    {
        int old_apage;
        int old_vpage;

        _setvideomode( _HRES16COLOR );
        old_apage = _getactivepage();
        old_vpage = _getvisualpage();
        /* draw an ellipse on page 0 */
        _setactivepage( 0 );
        _setvisualpage( 0 );
        _ellipse( _GFILLINTERIOR, 100, 50, 540, 150 );
        /* draw a rectangle on page 1 */
        _setactivepage( 1 );
        _rectangle( _GFILLINTERIOR, 100, 50, 540, 150 );
        getch();
        /* display page 1 */
        _setvisualpage( 1 );
        getch();
        _setactivepage( old_apage );
        _setvisualpage( old_vpage );
        _setvideomode( _DEFAULTMODE );
    }

Classification:
    PC Graphics

Systems:
    DOS, QNX

See Also:
    _getactivepage, _setvisualpage, _getvisualpage, _getvideoconfig