Procedure EnableVScreen(VideoSystem:VideoCardTypes)

    This  procedure  sets  up  the  character   lengths  for  the  smooth
    scrolling procedures and installs DisableVScreen on ExitProc.

    VideoSystem  should  be  any  of  the  video  types,  however, if you
    specify SVGA you must be using a Super VGA mode.  If a Super VGA card
    is being used for a  standard  (80x25)  VGA  screen mode, VGA must be
    specified.

    When setting up the screen, the  following  procedures  must be used,
    in this order:

    VideoCard[Card].CardType:= <Card>;
    TextMode(<Mode Numbers>);
    EnableVScreen(<Card>);
    VideoCard[Card].ScrollMethod:=ScrollMethod2;  {If <Card> = SVGA}
    SetVirtualScreen(<Size>);
    Mouse.Init(True);                             {If a Mouse is}
    InstallVScreenMouse;                          {to be used}

    Note that if a VGA mode (80x25) is  used,  you  must not set the card
    type to SVGA.