File: groff.info,  Node: Font Positions,  Next: Using Symbols,  Prev: Font Families,  Up: Using Fonts

5.19.3 Font Positions
---------------------

To support typeface indirection through abstract styles, and for
compatibility with AT&T 'troff', the formatter maintains a list of font
"positions" at which fonts required by a document are "mounted".  An
output device's description file 'DESC' typically configures a set of
pre-mounted fonts; see *note Device and Font Description Files::.  A
font need not be explicitly mounted before it is selected; GNU 'troff'
will search 'GROFF_FONT_PATH' for it by name and mount it at the first
free mounting position on demand.

 -- Request: .fp pos id [font-description-file-name]
 -- Register: \n[.f]
 -- Register: \n[.fp]
     Mount a font under the name ID at mounting position POS, a
     non-negative integer.  When the formatter starts up, it reads the
     output device's description to mount an initial set of faces, and
     selects font position 1.  Position 0 is unused by default.  Unless
     the FONT-DESCRIPTION-FILE-NAME argument is given, ID should be the
     name of a font description file stored in a directory corresponding
     to the selected output device.  GNU 'troff' does not traverse
     directories to locate the font description file.

     The optional third argument enables font names to be aliased, which
     can be necessary in compatibility mode since AT&T 'troff' syntax
     affords no means of identifying fonts with names longer than two
     characters, like 'TBI' or 'ZCMI', in a font selection escape
     sequence.  *Note Compatibility Mode::.  You can also alias fonts on
     mounting for convenience or abstraction.  (See below regarding the
     '.fp' register.)

          .fp \n[.fp] SC ZCMI
          Send a \f(SChand-written\fP thank-you note.
          .fp \n[.fp] Emph TI
          .fp \n[.fp] Strong TB
          Are \f[Emph]these names\f[] \f[Strong]comfortable\f[]?

     'DESC', 'P', and non-negative integers are not usable as font
     identifiers.

     The position of the currently selected font (or abstract style) is
     available in the read-only register '.f'.  It is associated with
     the environment (*note Environments::).

     You can copy the value of '.f' to another register to save it for
     later use.

          .nr saved-font \n[.f]
          ... text involving many font changes ...
          .ft \n[saved-font]

     The index of the next (non-zero) free font position is available in
     the read-only register '.fp'.  Fonts not listed in the 'DESC' file
     are automatically mounted at position '\n[.fp]' when selected with
     the 'ft' request or '\f' escape sequence.  When mounting a font at
     a position explicitly with the 'fp' request, this same practice
     should be followed, although GNU 'troff' does not enforce this
     strictly.