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  Argument
 
    mode       Video mode to be set
 
  Returns
 
    Integer    Number of text rows if successful; otherwise 0
 
  Description
 
    The _SetVideoMode function selects a screen mode. If the mode
    selected is not supported by the current hardware configuration,
    the function returns 0. The mode argument can be any of the
    constants shown in the table below.
 
    Mode             Type    Size          Colors     Adapter
    ═════════════    ════    ══════════    ═══════    ══════════════════
    _TextBW40        BW/T    40 columns    32         CGA
    _TextC40         C/T     40 columns    32         CGA
    _TextBW80        BW/T    80 columns    32         CGA
    _TextC80         C/T     80 columns    32         CGA
    _MRes4Color      C/G     320x200       4          CGA
    _MResNoColor     BW/G    320x200       4          CGA
    _HResBW          BW/G    640x200       2          CGA
    _TextMono        M/T     80 columns    32         MDPA
    _HercMono        M/G     720x348       2          HGC
    _MRes16Color     C/G     320x200       16         EGA
    _HRes16Color     C/G     640x200       16         EGA
    _EResNoColor     M/G     640x350       2          EGA
    _EResColor       C/G     640x350       4/16       EGA
    _VRes2Color      C/G     640x480       2          VGA
    _VRes16Color     C/G     640x480       16         VGA
    _MRes256Color    C/G     320x200       256        VGA
    _OResColor       C/G     640x400       1 of 16    Olivetti graphics
 
    Type:      M   monochrome
               C   color output
               T   text
               G   graphics
               BW  black and white mode
 
    Size:      Characters (columns) for text modes
               Pixels (horizontal x vertical) for graphics modes
 
    Colors:    For monochrome displays, the number of colors is the
               number of gray shades, not necessarily unique.
 
    Adapters:  IBM (and compatible) Monochrome Display Printer
                   Adapter (MDPA),
               Color Graphics Adapter (CGA), Enhanced Graphics Adapter
               (EGA), Video Graphics Array (VGA), Hercules Graphics
               Card, (HGC), and Olivetti Graphics Adapters (OCGA,
               OEGA, OVGA)
 
    Note:  Descriptions for standard hardware also apply to display
    hardware 100% compatible with IBM, Hercules, or Olivetti hardware.
 
    In addition to the constants that specify particular modes, the
    following constants select modes depending on context:
 
      Constant         Mode Selection
      ═════════════    ═════════════════════════════════════════════════
      _DefaultMode     Mode on entry; use to restore original video mode
      _MaxResMode      Graphics mode with highest resolution
      _MaxColorMode    Graphics mode with most colors
 
    Note that _MaxResMode and _MaxColorMode vary depending on the
    hardware. For example with a CGA, _MaxResMode maps to _HResBW
    while _MaxColorMode maps to _MRes4Color. With a VGA, _MaxResMode
    maps to _VRes16Color while _MaxColorMode maps to _MRes256Color.
 
  Hercules Support
 
    The Hercules driver MSHERC.COM must be installed before running
    a program that uses _HercMono mode. Type MSHERC to load the driver.
    This can be put in your AUTOEXEC.BAT file.
 
    If both a Hercules monochrome card and a color video card are
    used, MSHERC.COM must be installed with the /H (/HALF) option.
    The /H option limits the driver to one video page instead of two.
    This prevents the two video cards from attempting to use the same
    memory. See Hercules hardware manual for more details on
    compatibility.
 
  _GrStatus Returns
 
    _GrError, _GrInvalidParameter, _GrModeNotSupported