##

    Emulated Display
    Both the standard video controller as well as the extended bitmap option are emulated.
    However, only the Pro's 1024 x 240 mode is implemented.  This doesn't appear to be an
    issue with P/OS or Venix, as they don't seem to use the lower-resolution modes.

    The Pro's screen is displayed through X-windows, either in windowed mode or full-
    screen.  The latter is implemented using DGA extensions, and is only available with
    XFree86 X-servers.  The "screen" variable in the configuration file controls which
    mode the emulator starts up in.  While the emulator is running, it is also possible
    to switch back and forth between the two modes, using the emulator control menu.

    To start the emulator in windowed mode, the following should be set in the
    configuration file:

      screen = window

    And, to start the emulator in full-screen mode, set the following:

      screen = full

    Full-screen mode requires root privileges.  See the "Building Xhomer" section for
    more details.

    The Pro's display will likely need vertical stretching to look reasonable.
    Vertical scale factors are set independently for windowed and full-screen modes,
    using the "window_scale" and "full_scale" variables in the configuration file.
    Following are the defaults, if nothing is specified:

      window_scale = 2

      full_scale = 3

    Additionally, full-screen mode requires a special display mode to be defined in
    the XFree86 configuration file (not the emulator configuration file).  This mode
    must be for a displayable resolution of 1024 x (240*full_scale).  For example, if
    "full_scale" is set to 3, then a 1024 x 720 display mode must be defined.  If the
    emulator is unable to find the appropriate mode when switching to full-screen mode,
    it will print an error message.  Following is an example mode definition that works
    with an SGI 1600SW flatpanel monitor with a #9 graphics card, when "full_scale" is
    set to 3:

      Modeline "1024x720_SGI" 103.125 1024 1312 1366 1664 720 872 877 1030 HSkew 5 +Hsync +Vsync

    And, the following mode definition is for more conventional monitors:

      Modeline "1024x720" 65 1024 1048 1184 1328 720 771 777 806

    Full-screen mode is able to utilize anywhere from one to three frame buffers of
    display memory in the graphics card.  Having two frame buffers allows accelerated
    text scrolling.  Having three frame buffers, additionally, allows for smooth glitch-
    free transitions when turning the simulator control menu on and off.  The default
    is to auto-detect the number of available frame buffers.  However, this number may
    also be forced (to a number less than or equal to the maximum number of available
    frame buffers) through the "framebuffers" variable in the configuration file.  The
    emulator will print an error message when attempting to switch into full-screen
    mode if the requested number of frame buffers is greater than what is available.

    Please note that support for DGA full-screen mode is considered experimental at
    this point.  Please see the "Known Problems" section for more information.

    It is also possible to adjust the display gamma correction function through the
    emulator configuration file.  This is done with the "screen_gamma" variable.  An
    integer value equal to 10 times the desired gamma value should be specified.  For
    most monitors, a value of 10 (corresponding to a gamma of 1.0) should be used.  If
    the color monitor from a real Pro is connected to a PC, it seems to need a value in
    the neighborhood of 22.  (A value greater than 10 will make the display brighter,
    and a value less than 10 will make it dimmer)