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(emacs)MS-DOS Display

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Display on MS-DOS
=================

   Display on MS-DOS cannot use font variants, like bold or italic, but
it does support multiple faces, each of which can specify a foreground
and a background color.  Therefore, you can get the full functionality
of Emacs packages that use fonts (such as `font-lock', Enriched Text
mode, and others) by defining the relevant faces to use different
colors.  Use the `list-colors-display' command (Note: Frame
Parameters) and the `list-faces-display' command (Note: Faces) to
see what colors and faces are available and what they look like.

   Note: MS-DOS and MULE, later in this chapter, for information on
how Emacs displays glyphs and characters that aren't supported by the
native font built into the DOS display.

   When Emacs starts, it changes the cursor shape to a solid box.  This
is for compatibility with other systems, where the box cursor is the
default in Emacs.  This default shape can be changed to a bar by
specifying the `cursor-type' parameter in the variable
`default-frame-alist' (Note: Creating Frames).  The MS-DOS terminal
doesn't support a vertical-bar cursor, so the bar cursor is horizontal,
and the `WIDTH' parameter, if specified by the frame parameters,
actually determines its height.  As an extension, the bar cursor
specification can include the starting scan line of the cursor as well
as its width, like this:

      '(cursor-type bar WIDTH . START)

In addition, if the WIDTH parameter is negative, the cursor bar begins
at the top of the character cell.

   The MS-DOS terminal can only display a single frame at a time.  The
Emacs frame facilities work on MS-DOS much as they do on text-only
terminals (Note: Frames).  When you run Emacs from a DOS window on
MS-Windows, you can make the visible frame smaller than the full
screen, but Emacs still cannot display more than a single frame at a
time.

   The `mode4350' command switches the display to 43 or 50 lines,
depending on your hardware; the `mode25' command switches to the
default 80x25 screen size.

   By default, Emacs only knows how to set screen sizes of 80 columns by
25, 28, 35, 40, 43 or 50 rows.  However, if your video adapter has
special video modes that will switch the display to other sizes, you can
have Emacs support those too.  When you ask Emacs to switch the frame to
N rows by M columns dimensions, it checks if there is a variable called
`screen-dimensions-NxM', and if so, uses its value (which must be an
integer) as the video mode to switch to.  (Emacs switches to that video
mode by calling the BIOS `Set Video Mode' function with the value of
`screen-dimensions-NxM' in the `AL' register.)  For example, suppose
your adapter will switch to 66x80 dimensions when put into video mode
85.  Then you can make Emacs support this screen size by putting the
following into your `_emacs' file:

     (setq screen-dimensions-66x80 85)

   Since Emacs on MS-DOS can only set the frame size to specific
supported dimensions, it cannot honor every possible frame resizing
request.  When an unsupported size is requested, Emacs chooses the next
larger supported size beyond the specified size.  For example, if you
ask for 36x80 frame, you will get 40x80 instead.

   The variables `screen-dimensions-NxM' are used only when they
exactly match the specified size; the search for the next larger
supported size ignores them.  In the above example, even if your VGA
supports 38x80 dimensions and you define a variable
`screen-dimensions-38x80' with a suitable value, you will still get
40x80 screen when you ask for a 36x80 frame.  If you want to get the
38x80 size in this case, you can do it by setting the variable named
`screen-dimensions-36x80' with the same video mode value as
`screen-dimensions-38x80'.

   Changing frame dimensions on MS-DOS has the effect of changing all
the other frames to the new dimensions.