Upon initial startup, the default font is taken from the X11 resources as set in the system or user .Xdefaults file or on the command line.
Example:
gnuplot*font: lucidasans-bold-12
A new default font may be specified to the x11 driver from inside gnuplot using
`set term x11 font "<fontspec>"`
The driver first queries the X-server for a font of the exact name given. If this query fails, then it tries to interpret <fontspec> as "<font>,<size>,<slant>,<weight>" and to construct a full X11 font name of the form
-*-<font>-<weight>-<s>-*-*-<size>-*-*-*-*-*-<encoding>
<font> is the base name of the font (e.g. Times or Symbol) <size> is the point size (defaults to 12 if not specified) <s> is `i` if <slant>=="italic" `o` if <slant>=="oblique" `r` otherwise <weight> is `medium` or `bold` if explicitly requested, otherwise `*` <encoding> is set based on the current character set (see encoding).
So `set term x11 font "arial,15,italic"` will be translated to -*-arial-*-i-*-*-15-*-*-*-*-*-iso8859-1 (assuming default encoding). The <size>, <slant>, and <weight> specifications are all optional. If you do not specify <slant> or <weight> then you will get whatever font variant the font server offers first. You may set a default enconding via the corresponding X11 resource. E.g.
gnuplot*encoding: iso8859-15
The driver also recognizes some common PostScript font names and replaces them with possible X11 or TrueType equivalents. This same sequence is used to process font requests from `set label`.
If your gnuplot was built with configuration option –enable-x11-mbfonts, you can specify multi-byte fonts by using the prefix "mbfont:" on the font name. An additional font may be given, separated by a semicolon. Since multi-byte font encodings are interpreted according to the locale setting, you must make sure that the environmental variable LC_CTYPE is set to some appropriate locale value such as ja_JP.eucJP, ko_KR.EUC, or zh_CN.EUC.
Example:
set term x11 font 'mbfont:kana14;k14' # 'kana14' and 'k14' are Japanese X11 font aliases, and ';' # is the separator of font names. set term x11 font 'mbfont:fixed,16,r,medium' # <font>,<size>,<slant>,<weight> form is also usable. set title '(mb strings)' font 'mbfont:*-fixed-medium-r-normal--14-*'
The same syntax applies to the default font in Xresources settings, for example,
gnuplot*font: \\ mbfont:-misc-fixed-medium-r-normal--14-*-*-*-c-*-jisx0208.1983-0
If gnuplot is built with –enable-x11-mbfonts, you can use two special PostScript font names 'Ryumin-Light-*' and 'GothicBBB-Medium-*' (standard Japanese PS fonts) without the prefix "mbfont:".