                              Fonts in XFree86

                    Juliusz Chroboczek, <jch@xfree86.org>

                              26 November 2001

1.  Introduction

This document describes the support for fonts in XFree86.  Section Installing
fonts (section 2., page 1) is aimed at the casual user wishing to install
fonts in the X server; the rest of the document describes the font support in
more detail.

We only describe font support within the core X protocol.  Issues relating to
fonts within the RENDER extension, the GLX (OpenGL) extension or the PEX
extension are outside the scope of this document.

We assume some familiarity with digital fonts.  If anything is not clear to
you, please consult Appendix Background (section 6., page 1) at the end of
this document for background information.

2.  Installing fonts

Installing fonts in XFree86 is a two step process.  First, you need to create
a font directory that contains all the relevant font files as well as some
index files.  You then need to inform the X server of the existence of this
new directory by including it in the font path.

2.1  Installing bitmap fonts

The XFree86 server can use bitmap fonts in both the cross-platform BDF format
and the somewhat more efficient binary PCF format.  (XFree86 also supports
the obsolete SNF format.)

Bitmap fonts are normally distributed in the BDF format.  Before installing
such fonts, it is desirable (but not absolutely necessary) to convert the
font files to the PCF format.  This is done by using the command `bdftopcf',
e.g.

     $ bdftopcf courier12.bdf

You may then want to compress the resulting PCF font files:

     $ gzip courier12.pcf

After the fonts have been converted, you should copy all the font files that
you wish to make available into a arbitrary directory, say
`/usr/local/share/fonts/bitmap/'.  You should then create the index file
`fonts.dir' by running the command `mkfontdir' (please see the mkfontdir(1)
manual page for more information):

     $ mkdir /usr/local/share/fonts/bitmap
     $ cp *.pcf.gz /usr/local/share/fonts/bitmap
     $ cd /usr/local/share/fonts/bitmap
     $ mkfontdir

All that remains is to tell the X server about the existence of the new font
directory; see Section Setting the server font path (section 2.4, page 1).

2.2  Installing scalable fonts

The XFree86 server supports scalable fonts in four formats: Type 1, Speedo,
TrueType and CIDFont.  This section only applies to the former three; for
information on CIDFonts, please see Section Installing CIDFonts (section 2.3,
page 1) later in this document.

Installing scalable fonts is very similar to installing bitmap fonts: you
create a directory with the font files, and run `mkfontdir' to create an
index file called `fonts.dir'.

There is, however, a big difference: `mkfontdir' cannot automatically recog-
nise scalable font files.  For that reason, you must first index all the font
files in a file called `fonts.scale'.  This file has the same format as a
`fonts.dir' file, and typically looks as follows:

     4
     cour.pfa -adobe-courier-medium-r-normal-0-0-0-0-p-0-iso8859-1
     cour.pfa -adobe-courier-medium-r-normal-0-0-0-0-p-0-iso8859-2
     couri.pfa -adobe-courier-medium-i-normal-0-0-0-0-p-0-iso8859-1
     couri.pfa -adobe-courier-medium-i-normal-0-0-0-0-p-0-iso8859-2

The first line indicates the number of entries in the file.  Each line after
the first consists of two fields separated by a space; the first field is the
name of the font file, and the second one is the name under which the font
will appear to the server.  This name should obey the X Logical Font Descrip-
tion conventions (see Section The X Logical Font Description (section 6.2,
page 1)).  The format of this file is fully described in the mkfontdir(1)
manual page.

Note that multiple lines may point at the same font file.  This is most com-
monly done in order to make a single font available under multiple encodings;
please see Section Fonts and internationalisation (section 4., page 1).

While it is possible to create the `fonts.scale' file by hand, it is simpler
and more convenient to have it generated automatically.  Utilities to perform
this task are available, but are not currently included with XFree86. For
Type 1 fonts, you may use a utility called `type1inst' which is available
from standard Free Software repositories <URL:http://www.ibib-
lio.org/pub/Linux/X11/xutils/> throughout the world.

For TrueType fonts, you may use `ttmkfdir', available from Joerg Pommnitz's
xfsft page <URL:http://www.joerg-pommnitz.de/TrueType/xfsft.html>.

After the `fonts.scale' is created, you may run `mkfontdir' as above; this
time, however, you need to create an index of encoding files called `encod-
ings.dir' in addition to the `fonts.dir' file.  This is done by using
`mkfontdir' with the `-e' flag:

     $ cd /usr/local/share/fonts/Type1
     $ mkfontdir -e /usr/X11R6/lib/font/encodings

For more information, please see the mkfontdir(1) manual page and Section
Fonts and internationalisation (section 4., page 1) later in this document.

2.3  Installing CID-keyed fonts

The CID-keyed font format was designed by Adobe Systems for fonts with large
character sets.  A CID-keyed font, or CIDFont for short, contains a collec-
tion of glyphs indexed by character ID (CID).

Adobe make some sample CIDFonts and a complete set of CMaps available from
O'Reilly's FTP site <URL:ftp://ftp.oreilly.com/pub/examples/nut-
shell/cjkv/adobe/>.

In order to map such glyphs to meaningful indices, Adobe provide a set of
CMap files.  The PostScript name of a font generated from a CIDFont consists
of the name of the CIDFont and the name of the CMap separated by two dashes.
For example, the font generated from the CIDFont `Munhwa-Regular' using the
CMap `UniKS-UCS2-H' is called

     Munhwa-Regular--UniKS-UCS2-H

The CIDFont support in XFree86 requires a very rigid directory structure.
The main directory must be called `CID' (its location defaults to
`/usr/X11R6/lib/X11/fonts/CID' but it may be located anywhere), and it should
contain a subdirectory for every CID collection.  Every subdirectory must
contain subdirectories called CIDFont (containing the actual CIDFont files),
CMap (containing all the needed CMaps), AFM (containing the font metric
files) and CFM (initially empty).  For example, in the case of the font
Munhwa-Regular that uses the CID collection Adobe-Korea1-0, the directory
structure should be as follows:

     CID/Adobe-Korea1/CIDFont/Munhwa-Regular
     CID/Adobe-Korea1/CMap/UniKS-UCS2-H
     CID/Adobe-Korea1/AFM/Munhwa-Regular.afm
     CID/Adobe-Korea1/CFM/
     CID/fonts.dir
     CID/fonts.scale

After creating this directory structure and copying the relevant files, you
should create a <`tt/fonts.scale/' file.  This file has the same format as in
the case of (non-CID) scalable fonts, except that its first column contains
PostScript font names with the extension `.cid' appended rather than actual
filenames:

     1
     Adobe-Korea1/Munhwa-Regular--UniKS-UCS2-H.cid \
       -adobe-munhwa-medium-r-normal--0-0-0-0-p-0-iso10646-1

(both names on the same line).  As above, running `mkfontdir' creates the
`fonts.dir' file:

     $ cd /usr/local/share/fonts/CID
     $ mkfontdir

Finally, you should create the font metrics summary files in the directory
`CFM' by running the command `mkcfm':

     $ mkcfm /usr/local/share/fonts/CID

If no CFM files are available, the server will still be able to use the CID
fonts but querying them will take a long time.  You should run `mkcfm' again
whenever a change is made to any of the CID-keyed fonts, or when the CID-
keyed fonts are copied to a machine with a different architecture.

2.4  Setting the server's font path

The list of directories where the server looks for fonts is known as the font
path.  Informing the server of the existence of a new font directory consists
in putting it on the font path.

The font path is an ordered list; if a client's request matches multiple
fonts, the first one in the font path is the one that gets used.  When match-
ing fonts, the server makes two passes over the font path: during the first
pass, it searches for an exact match; during the second, it searches for
fonts suitable for scaling.

For best results, scalable fonts should appear in the font path before the
bitmap fonts; this way, the server will prefer bitmap fonts to scalable fonts
when an exact match is possible, but will avoid scaling bitmap fonts when a
scalable font can be used.  (The `:unscaled' hack, while still supported,
should no longer be necessary in XFree86 4.0 and later.)

You may check the font path of the running server by typing the command

     $ xset q

2.4.1  Temporary modification of the font path

The `xset' utility may be used to modify the font path for the current ses-
sion.  The font path is set with the command xset fp; a new element is added
to the front with xset +fp, and added to the end with xset fp+.  For example,

     $ xset +fp /usr/local/fonts/Type1
     $ xset fp+ /usr/local/fonts/bitmap

Conversely, an element may be removed from the front of the font path with
`xset -fp', and removed from the end with `xset fp-'.

For more information, please consult the xset(1) manual page.

2.4.2  Permanent modification of the font path

The default font path (the one used just after server startup) is specified
in the X server's `XF86Config' file.  It is computed by appending all the
directories mentioned in the `FontPath' entries of the `Files' section in the
order in which they appear.

     FontPath "/usr/local/fonts/Type1"
     ...
     FontPath "/usr/local/fonts/bitmap"

For more information, please consult the `XF86Config'(5) manual page.

2.5  Troubleshooting

If you seem to be unable to use some of the fonts you have installed, the
first thing to check is that the `fonts.dir' files are correct and that they
are readable by the server.  If this doesn't help, it is quite possible that
you are trying to use a font in a format that is not supported by your
server.

XFree86 supports the BDF, PCF, SNF, Type 1, Speedo, TrueType and CIDFont font
formats.  However, not all XFree86 servers come with all the font backends
configured in.

On most platforms, the XFree86 servers are modular: the font backends are
included in modules that are loaded at runtime.  The modules to be loaded are
specified in the `XF86Config' file using the `Load' directive:

     Load "type1"

If you have trouble installing fonts in a specific format, you may want to
check the server's log file in order to see whether the relevant modules are
properly loaded.  The list of font modules distributed with XFree86 is as
follows:

   o  "bitmap": bitmap fonts (`*.bdf', `*.pcf' and `*.snf');

   o  "type1": Type 1 fonts (`*.pfa' and `*.pfb') and CIDFonts;

   o  "speedo": Bitstream Speedo fonts (`*.spd');

   o  "freetype": TrueType fonts (`*.ttf' and `*.ttc');

   o  "xtt": alternate TrueType backend (`*.ttf' and `*.ttc').

Please note that the argument of the `Load' directive is case-sensitive.

3.  Fonts included with XFree86

3.1  Standard bitmap fonts

The Sample Implementation of X11 comes with a large number of bitmap fonts,
including the `fixed' family, and bitmap versions of Courier, Times and Hel-
vetica.  In the SI, these fonts are provided in the ISO 8859-1 encoding (ISO
Latin Western-European).

In XFree86, a number of these fonts are provided in Unicode-encoded font
files instead.  At build time, these fonts are split into font files encoded
according to legacy encodings, a process which enables us to provide the
standard fonts in a number of regional encodings with no duplication of work.

For example, the font file

     /usr/X11R6/lib/X11/fonts/misc/6x13.bdf

with XLFD

     -misc-fixed-medium-r-semicondensed--13-120-75-75-c-60-iso10646-1

is a Unicode-encoded version of the standard `fixed' font with added support
for the Latin, Greek, Cyrillic, Georgian, Armenian, IPA and other scripts
plus numerous technical symbols. It contains over 2800 glyphs, covering all
characters of ISO 8859 parts 1-5, 7-10, 13-15, as well as all European IBM
and Microsoft code pages, KOI8, WGL4, and the repertoires of many other char-
acter sets.

This font is used at build time for generating the font files

     6x13-ISO8859-1.bdf
     6x13-ISO8859-2.bdf
     6x13-ISO8859-3.bdf
     6x13-ISO8859-4.bdf
     6x13-ISO8859-5.bdf
     6x13-ISO8859-7.bdf
     6x13-ISO8859-8.bdf
     6x13-ISO8859-9.bdf
     6x13-ISO8859-10.bdf
     6x13-ISO8859-13.bdf
     6x13-ISO8859-15.bdf
     6x13-KOI8-R.bdf

with respective XLFDs

     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-1
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-2
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-3
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-4
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-5
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-7
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-8
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-9
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-10
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-13
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-15
     -misc-fixed-medium-r-normal--13-120-75-75-c-60-koi8-r

The standard short name `fixed' is normally an alias for

     -misc-fixed-medium-r-normal--13-120-75-75-c-60-iso8859-1

(The conversion of the standard fonts to Unicode was mainly performed by
Markus Kuhn.  Markus is a man of taste, which makes his use of Perl in the
conversion process somewhat surprising.)

3.2  The ClearlyU Unicode font family

The ClearlyU family of fonts provides a set of 12 pt, 100 dpi proportional
fonts with many of the glyphs needed for Unicode text.  Together, the fonts
contain approximately 7500 glyphs.

The main ClearlyU font has the XLFD

     -mutt-clearlyu-medium-r-normal--17-120-100-100-p-101-iso10646-1

and resides in the font file

     /usr/X11R6/lib/X11/fonts/misc/cu12.pcf.gz

Additional ClearlyU fonts include

     -mutt-clearlyu alternate glyphs-medium-r-normal--17-120-100-100-p-91-iso10646-1
     -mutt-clearlyu pua-medium-r-normal--17-120-100-100-p-111-iso10646-1
     -mutt-clearlyu arabic extra-medium-r-normal--17-120-100-100-p-103-fontspecific-0
     -mutt-clearlyu ligature-medium-r-normal--17-120-100-100-p-141-fontspecific-0

The Alternate Glyphs font contains additional glyph shapes that are needed
for certain languages.  A second alternate glyph font will be provided later
for cases where a character has more than one commonly used alternate shape
(e.g. the Urdu heh).

The PUA font contains extra glyphs that are useful for certain rendering pur-
poses.

The Arabic Extra font contains the glyphs necessary for characters that don't
have all of their possible shapes encoded in ISO 10646.  The glyphs are
roughly ordered according to the order of the characters in the ISO 10646
standard.

The Ligature font contains ligatures for various scripts that may be useful
for improved presentation of text.

(The ClearlyU family was designed by Mark Leisher.  Mark's usage of the
foundry name mutt predates the mailer of the same name, but he won't say
more.)

3.3  Standard scalable fonts

XFree86 includes all the scalable fonts distributed with X11R6.

3.3.1  Standard Type 1 fonts

The IBM Courier set of fonts cover ISO 8859-1 and ISO 8859-2 as well as Adobe
Standard Encoding.  These fonts have XLFD

     -adobe-courier-medium-*-*--0-0-0-0-m-0-*-*

and reside in the font files

     /usr/X11R6/lib/X11/fonts/Type1/cour*.pfa

The Adobe Utopia set of fonts only cover ISO 8859-1 as well as Adobe Standard
Encoding.  These fonts have XLFD

     -adobe-utopia-*-*-normal--0-0-0-0-p-0-iso8859-1

and reside in the font files

     /usr/X11R6/lib/X11/fonts/Type1/UT*.pfa

Finally, XFree86 also comes with Type 1 versions of Bitstream Courier and
Charter.  These fonts have XLFD

     -bitstream-courier-*-*-normal--0-0-0-0-m-0-iso8859-1
     -bitstream-charter-*-*-normal--0-0-0-0-p-0-iso8859-1

and reside in the font files

     /usr/X11R6/lib/X11/fonts/Type1/c*bt_.pfb

3.3.2  Standard Speedo fonts

XFree86 includes Speedo versions of the Bitstream Courier and Charter fonts.
In order to use these fonts, you should ensure that your X server is loading
the `Speedo' font backend; see Section Troubleshooting (section 2.5, page 1).

These fonts cover all of ISO 8859-1 and almost all of ISO 8859-2.  They have
XLFD name

     -bitstream-courier-*-*-normal--0-0-0-0-m-0-*-*
     -bitstream-charter-*-*-normal--0-0-0-0-p-0-*-*

and reside in the font files

     /usr/X11R6/lib/X11/fonts/Speedo/font*.spd

3.4  The Bigelow & Holmes Luxi family

XFree86 includes the Luxi family of scalable fonts, in both TrueType and
Type 1 format.  This family consists of the fonts Luxi Serif, with XLFD

     -b&h-luxi serif-medium-*-normal--*-*-*-*-p-*-*-*

Luxi Sans, with XLFD

     -b&h-luxi sans-medium-*-normal--*-*-*-*-p-*-*-*

and Luxi Mono, with XLFD

     -b&h-luxi mono-medium-*-normal--*-*-*-*-m-*-*-*

Each of these fonts comes Roman, oblique, bold and bold oblique variants The
TrueType version have glyphs covering the basic ASCII Unicode range, the
Latin 1 range, as well as the Extended Latin range and some additional punc-
tuation characters.  In particular, these fonts include all the glyphs needed
for ISO 8859 parts 1, 2, 3, 4, 9, 13 and 15, as well as all the glyphs in the
Adobe Standard encoding and the Windows 3.1  character set.

The glyph coverage of the Type 1 versions is somewhat reduced, and only cov-
ers ISO 8859 parts 1, 2 and 15 as well as the Adobe Standard encoding.

The Luxi fonts are original designs by Kris Holmes and Charles Bigelow. Luxi
fonts include seriffed, sans serif, and monospaced styles, in roman and
oblique, and normal and bold weights. The fonts share stem weight, x-height,
capital height, ascent and descent, for graphical harmony.

The character width metrics of Luxi roman and bold fonts match those of core
fonts bundled with popular operating and window systems.

The license terms for the Luxi fonts are included in the file `COPYRIGHT.BH',
as well as in the License document.

Charles Bigelow and Kris Holmes from Bigelow and Holmes Inc.  developed the
Luxi typeface designs in Ikarus digital format.

URW++ Design and Development GmbH converted the Ikarus format fonts to True-
Type and Type1 font programs and implemented the grid-fitting "hints" and
kerning tables in the Luxi fonts.

For more information, please contact <design@bigelowandholmes.com> or
<info@urwpp.de>, or consult the URW++ web site <URL:http://www.urwpp.de>.

An earlier version of the Luxi fonts was made available under the name
Lucidux.  This name should no longer be used due to trademark uncertainties,
and all traces of the Lucidux name have been removed from this version of
XFree86.

4.  Fonts and internationalisation

The scalable font backends (Type 1, Speedo and TrueType) can now automati-
cally re-encode fonts to the encoding specified in the XLFD in fonts.dir.
For example, a fonts.dir file can contain entries for the Type 1 Courier font
such as

     cour.pfa -adobe-courier-medium-r-normal--0-0-0-0-m-0-iso8859-1
     cour.pfa -adobe-courier-medium-r-normal--0-0-0-0-m-0-iso8859-2

which will lead to the font being recoded to ISO 8859-1 and ISO 8859-2
respectively.

4.1  The fontenc layer

Three of the scalable backends (Type 1, Speedo, and the FreeType TrueType
backend) use a common fontenc layer for font re-encoding.  This allows these
backends to share their encoding data, and allows simple configuration of new
locales independently of font type.

Please note: the X-TrueType (X-TT) backend does not use the fontenc layer,
but instead uses its own method for font reencoding.  If you are only inter-
ested in X-TT you may want to skip to Section Using Symbol Fonts (section
4.5, page 1), as the intervening information does not apply to X-TT.  X-TT
itself is described in more detail in Section X-TrueType (section 5.2, page
1).

In the fontenc layer, an encoding is defined by a name (such as iso8859-1),
possibly a number of aliases (alternate names), and an ordered collection of
mappings.  A mapping defines the way the encoding can be mapped into one of
the target encodings known to fontenc; currently, these consist of Unicode,
Adobe glyph names, and arbitrary TrueType ``cmap''s.

A number of encodings are hardwired into fontenc, and are therefore always
available; the hardcoded encodings cannot easily be redefined.  These
include:

   o  iso10646-1: Unicode;

   o  iso8859-1: ISO Latin-1 (Western Europe);

   o  iso8859-2: ISO Latin-2 (Eastern Europe);

   o  iso8859-3: ISO Latin-3 (Southern Europe);

   o  iso8859-4: ISO Latin-4 (Northern Europe);

   o  iso8859-5: ISO Cyrillic;

   o  iso8859-6: ISO Arabic;

   o  iso8859-7: ISO Greek;

   o  iso8859-8: ISO Hebrew;

   o  iso8859-9: ISO Latin-5 (Turkish);

   o  iso8859-10: ISO Latin-6 (Nordic);

   o  iso8859-15: ISO Latin-9, or Latin-0 (Revised Western-European);

   o  koi8-r: KOI8 Russian;

   o  koi8-u: KOI8 Ukrainian (see RFC 2319);

   o  koi8-ru: KOI8 Russian/Ukrainian

   o  koi8-uni: KOI8 ``Unified'' (Russian, Ukrainian, and Byelorussian);

   o  koi8-e: KOI8 ``European,'' ISO-IR-111, or ECMA-Cyrillic;

   o  microsoft-symbol and apple-roman: these are only likely to be useful
     with TrueType symbol fonts.

Additional encodings can be added by defining encoding files.  When a font
encoding is requested that the fontenc layer doesn't know about, the backend
checks the directory in which the font file resides (not necessarily the
directory with fonts.dir!) for a file named `encodings.dir'.  If found, this
file is scanned for the requested encoding, and the relevant encoding defini-
tion file is read in.  The `mkfontdir' utility, when invoked with the `-e'
option followed by the name of a directory containing encoding files, can be
used to automatically build `encodings.dir' files.  See the mkfontdir(1) man-
ual page for more details.

A number of encoding files for common encodings are included with XFree86.
Information on writing new encoding files can be found in Section Format of
encodings directory files (section 4.3, page 1) and Format of encoding files
(section 4.4, page 1) later in this document.

4.2  Backend-specific notes about fontenc

4.2.1  Type 1

The Type 1 backend first searches for a mapping with a target of PostScript.
If one is found, it is used.  Otherwise, the backend searches for a mapping
with target Unicode, which is then composed with a built-in table mapping
codes to glyph names.  Note that this table only covers part of the Unicode
code points that have been assigned names by Adobe.

If neither a PostScript or Unicode mapping is found, the backend defaults to
ISO 8859-1.

Specifying an encoding value of adobe-fontspecific disables the encoding
mechanism.  This is useful with symbol and incorrectly encoded fonts (see
Section Incorrectly encoded fonts (section 4.6, page 1) below).

The Type 1 backend currently limits all encodings to 8-bit codes.

4.2.2  Speedo

The Speedo backend searches for a mapping with a target of Unicode, and uses
it if found.  If none is found, the backend defaults to ISO 8859-1.

The Speedo backend limits all encodings to 8-bit codes.

4.2.3  The FreeType TrueType backend

The TrueType backend scans the mappings in order.  Mappings with a target of
PostScript are ignored; mappings with a TrueType or Unicode target are
checked against all the cmaps in the file.  The first applicable mapping is
used.

If you are writing an encoding file to be used with the TrueType backend, you
should ensure that mappings are mentioned in decreasing order of preference.

4.3  Format of encoding directory files

In order to use a font in an encoding that the font backend does not know
about, you need to have an `encodings.dir' file in the same directory as the
font file used.  The `encodings.dir' file has a similar format to
`fonts.dir'.  Its first line specifies the number of encodings, while every
successive line has two columns, the name of the encoding, and the name of
the encoding file; this can be relative to the current directory, or abso-
lute.  Every encoding name should agree with the encoding name defined in the
encoding file.  For example,

     3
     mulearabic-0 /usr/X11R6/lib/X11/fonts/encodings/mulearabic-0.enc
     mulearabic-1 /usr/X11R6/lib/X11/fonts/encodings/mulearabic-1.enc
     mulearabic-2 /usr/X11R6/lib/X11/fonts/encodings/mulearabic-2.enc

The name of an encoding must be specified in the encoding file's `STARTENCOD-
ING' or `ALIAS' line.  It is not enough to create an `encodings.dir' entry.

If your platform supports it (it probably does), encoding files may be com-
pressed or gzipped.

The `encoding.dir' files are best maintained by the `mkfontdir' utility.
Please see the mkfontdir(1) manual page for more information.

4.4  Format of encoding files

The encoding files are ``free form,'' i.e. any string of whitespace is equiv-
alent to a single space.  Keywords are parsed in a non-case-sensitive manner,
meaning that `size', `SIZE', and `SiZE' all parse as the same keyword; on the
other hand, case is significant in glyph names.

Numbers can be written in decimal, as in `256', in hexadecimal, as in
`0x100', or in octal, as in `0400'.

Comments are introduced by a hash sign `#'.  A `#' may appear at any point in
a line, and all characters following the `#' are ignored, up to the end of
the line.

The encoding file starts with the definition of the name of the encoding, and
possibly its alternate names (aliases):

     STARTENCODING mulearabic-0
     ALIAS arabic-0
     ALIAS something-else

The name of the encoding and its aliases should be suitable for use in an
XLFD font name, and therefore contain exactly one dash `-'.

The encoding file may then optionally declare the size of the encoding.  For
a linear encoding (such as ISO 8859-1), the SIZE line specifies the maximum
code plus one:

     SIZE 0x2B

For a matrix encoding, it should specify two numbers.  The first is the num-
ber of the last row plus one, the other, the highest column number plus one.
In the case of `jisx0208.1990-0' (JIS X 0208(1990), double-byte encoding,
high bit clear), it should be

     SIZE 0x75 0x80

In the case of a matrix encoding, a `FIRSTINDEX' line may be included to
specify the minimum glyph index in an encoding.  The keyword `FIRSTINDEX' is
followed by two integers, the minimum row number followed by the minimum col-
umn number:

     FIRSTINDEX 0x20 0x20

In the case of a linear encoding, a `FIRSTINDEX' line is not very useful.  If
for some reason however you chose to include on, it should be followed by a
single integer.

Note that in most font backends inclusion of a `FIRSTINDEX' line has the side
effect of disabling default glyph generation, and this keyword should there-
fore be avoided unless absolutely necessary.

Codes outside the region defined by the `SIZE' and `FIRSTINDEX' lines are
understood to be undefined.  Encodings default to linear encoding with a size
of 256 (0x100).  This means that you must declare the size of all 16 bit
encodings.

What follows is one or more mapping sections.  A mapping section starts with
a `STARTMAPPING' line stating the target of the mapping.  The target may be
one of:

   o Unicode (ISO 10646):

          STARTMAPPING unicode

   o a given TrueType ``cmap'':

          STARTMAPPING cmap 3 1

   o PostScript glyph names:

          STARTMAPPING postscript

Every line in a mapping section maps one from the encoding being defined to
the target of the mapping.  In mappings with a Unicode or TrueType mapping,
codes are mapped to codes:

     0x21 0x0660
     0x22 0x0661
     ...

As an abbreviation, it is possible to map a contiguous range of codes in a
single line.  A line consisting of three integers

     <it/start/ <it/end/ <it/target/

is an abbreviation for the range of lines

     start     target

     start+1   target+1

     ...

     end       target+end-start

For example, the line

     0x2121 0x215F 0x8140

is an abbreviation for

     0x2121 0x8140
     0x2122 0x8141
     ...
     0x215F 0x817E

Codes not listed are assumed to map through the identity (i.e. to the same
numerical value).  In order to override this default mapping, you may specify
a range of codes to be undefined by using an `UNDEFINE' line:

     UNDEFINE 0x00 0x2A

or, for a single code,

     UNDEFINE 0x1234

PostScript mappings are different.  Every line in a PostScript mapping maps a
code to a glyph name

     0x41 A
     0x42 B
     ...

and codes not explicitly listed are undefined.

A mapping section ends with an ENDMAPPING line

     ENDMAPPING

After all the mappings have been defined, the file ends with an ENDENCODING
line

     ENDENCODING

In order to make future extensions to the format possible, lines starting
with an unknown keyword are silently ignored, as are mapping sections with an
unknown target.

4.5  Using symbol fonts

Type 1 symbol fonts should be installed using the adobe-fontspecific encod-
ing.

In an ideal world, all TrueType symbol fonts would be installed using one of
the microsoft-symbol and apple-roman encodings. A number of symbol fonts,
however, are not marked as such; such fonts should be installed using
microsoft-cp1252, or, for older fonts, microsoft-win3.1.

In order to guarantee consistent results (especially between Type 1 and True-
Type versions of the same font), it is possible to define a special encoding
for a given font. This has already been done for the ZapfDingbats font; see
the file encodings/adobe-dingbats.enc.

4.6  Hints about using badly encoded fonts

A number of text fonts are incorrectly encoded. Incorrect encoding is some-
times done by design, in order to make a font for an exotic script appear
like an ordinary Western text font.  It is often the result of the font
designer's laziness or incompetence; for some reason, most people seem to
find it easier to invent idiosyncratic glyph names rather than follow the
Adobe glyph list.

There are two ways of dealing with such fonts: using them with the encoding
they were designed for, and creating an ad hoc encoding file.

4.6.1  Using fonts with the designer's encoding

In the case of Type 1 fonts, the font designer can specify a default encod-
ing; this encoding is requested by using the `adobe-fontspecific' encoding in
the XLFD name. Sometimes, the font designer omitted to specify a reasonable
default encoding, in which case you should experiment with `adobe-standard',
`iso8859-1', `microsoft-cp1252', and `microsoft-win3.1'. (The encoding
`microsoft-symbol' doesn't make sense for Type 1 fonts).

TrueType fonts do not have a default encoding.  However, most TrueType fonts
are designed with either Microsoft or Apple platforms in mind, so one of
`microsoft-symbol', `microsoft-cp1252', `microsoft-win3.1', or `apple-roman'
should yield reasonable results.

4.6.2  Specifying an ad hoc encoding file

It is always possible to define an encoding file to put the glyphs in a font
in any desired order. Again, see the `encodings/adobe-dingbats.enc' file to
see how this is done.

4.6.3  Specifying font aliases

By following the directions above, you will find yourself with a number of
fonts with unusual names --- with encodings such as `adobe-fontspecific',
`microsoft-win3.1' etc.  In order to use these fonts with standard applica-
tions, it may be useful to remap them to their proper names.

This is done by writing a `fonts.alias' file. The format of this file is sim-
ilar to the format of the `fonts.dir' file, except that it maps XLFD names to
XLFD names. A `fonts.alias' file might look as follows:

     1
     "-ogonki-alamakota-medium-r-normal--0-0-0-0-p-0-iso8859-2" \
       "-ogonki-alamakota-medium-r-normal--0-0-0-0-p-0-adobe-fontspecific"

(both XLFD names on a single line).  The syntax of the `fonts.alias' file is
precisely described in the mkfontdir(1) manual page.

5.  Additional notes about TrueType support

This version of XFree86 comes with two TrueType backends, FreeType (module
`freetype', formerly known as xfsft) and X-TrueType (module `xtt').  These
two backends are not compatible: only one of them can be used at any one
time.

In order to use the FreeType backend, please check that the `Module' section
of your `XF86Config' file contains a line that reads

     Load "freetype"

In order to use the X-TrueType backend, replace the line in your XF86Config
file that loads the freetype module with a line that reads

         Load "xtt"

Both TrueType backends delay glyph rasterisation up to the time at which a
glyph is first used.  For this reason, they only provide an approximate value
for the ``average width'' font property.

Both backends also support an optimisation for character-cell fonts (fonts
with all glyph metrics equal, or terminal fonts).  A font with an XLFD speci-
fying a character-cell spacing `c', as in

     -misc-mincho-medium-r-normal--0-0-0-0-c-0-jisx0208.1990-0

will not rasterise glyphs at metrics computation time, but instead trust the
font really to be a character-cell font.  You are encouraged to make use of
this optimisation when useful, but be warned that not all monospaced fonts
are character-cell fonts.

5.1  The FreeType TrueType backend

The FreeType backend (formerly xfsft) is a backend based on the FreeType
library (see the FreeType web site <URL:http://www.freetype.org/>) and has
support for the ``fontenc'' style of internationalisation (see Section The
fontenc layer (section 4.1, page 1)).  This backend supports TrueType Font
files (`*.ttf') and TrueType Collections (`*.ttc').

In order to access the faces in a TrueType Collection file, the face number
must be specified in the fonts.dir file before the filename within colons.
For example,

     :2:mincho.ttc -misc-mincho-medium-r-normal--0-0-0-0-c-0-jisx0208.1990-0

refers to face 2 in the `mincho.ttc' TrueType Collection file.

The FreeType backend uses the fontenc layer in order to support recoding of
fonts; this was described in Section The fontenc layer (section 4.1, page 1)
and especially Section FreeType-specific notes about fontenc (section 4.2.3,
page 1) earlier in this document.

5.2  The X-TrueType TrueType backend

The `X-TrueType' backend is another backend based on the FreeType library.
X-TrueType doesn't use the `fontenc' layer for managing font encodings, but
instead uses its own database of encodings.  However, X-TrueType includes a
large number of encodings, and any encoding you need is likely to be present
in X-TrueType.

X-TrueType extends the `fonts.dir' syntax with a number of options, known as
`TTCap'.  A `TTCap' entry follows the general syntax

     :option=value:

and should be specified before the filename.

The most useful TTCap option is used to specify the face number to use with
TTCs; this is the `fn' TTCap option.  For example, face 2 of font file `min-
cho.ttc' is specified using:

     :fn=2:mincho.ttc -misc-mincho-medium-r-normal--0-0-0-0-c-0-jisx0208.1990-0

More information on the TTCap syntax, and on X-TrueType in general, may be
found on the X-TrueType home page <URL:http://x-tt.dsl.gr.jp/>.

6.  Appendix: background and terminology

6.1  Characters and glyphs

A computer text-processing system inputs keystrokes and outputs glyphs, small
pictures that are assembled on paper or on a computer screen.  Keystrokes and
glyphs do not, in general, coincide: for example, if the system does generate
ligatures, then to the two keystrokes <f><i> will typically correspond a sin-
gle glyph.  Similarly, if the system shapes Arabic glyphs in a reasonable
manner, then multiple different glyphs may correspond to a single keystroke.

The complex transformation rules from keystrokes to glyphs are usually fac-
tored into two simpler transformations, going through the intermediary of
characters.  You may want to think of characters as the basic unit of data
that is stored e.g. in the buffer of your text editor.  While the definition
of a character is intrinsically application-specific, a number of standard-
ised collections of characters have been defined.

A coded character set is a set of characters together with a mapping from
integer codes --- known as codepoints --- to characters.  Examples of coded
character sets include US-ASCII, ISO 8859-1, KOI8-R, and JIS X 0208(1990).

A coded character set need not use 8 bit integers to index characters. Many
early mainframes used 6 bit character sets, while 16 bit (or more) character
sets are necessary for ideographic writing systems.

6.2  Font files, fonts, and XLFD

Traditionally, typographers speak about typefaces and founts.  A typeface is
a particular style or design, such as Times Italic, while a fount is a
molten-lead incarnation of a given typeface at a given size.

Digital fonts come in font files.  A font file contains all the information
necessary for generating glyphs of a given typeface, and applications using
font files may access glyph information in an arbitrary order.

Digital fonts may consist of bitmap data, in which case they are said to be
bitmap fonts.  They may also consist of a mathematical description of glyph
shapes, in which case they are said to be scalable fonts.  Common formats for
scalable font files are Type 1 (sometimes incorrectly called ATM fonts or
PostScript fonts), Speedo and TrueType.

The glyph data in a digital font needs to be indexed somehow.  How this is
done depends on the font file format.  In the case of Type 1 fonts, glyphs
are identified by glyph names.  In the case of TrueType fonts, glyphs are
indexed by integers corresponding to one of a number of indexing schemes
(usually Unicode --- see below).

The X11 system uses the data in font file to generate font instances, which
are collections of glyphs at a given size indexed according to a given encod-
ing.

X11 font instances are usually specified using a notation known as the X Log-
ical Font Description (XLFD).  An XLFD starts with a dash `-', and consists
of fourteen fields separated by dashes, for example

     -adobe-courier-medium-r-normal--0-0-0-0-m-0-iso8859-1

Or particular interest are the last two fields `iso8859-1', which specify the
font instance's encoding.

X11 font instances may also be specified by short name.  Unlike an XLFD, a
short name has no structure and is simply a conventional name for a font
instance.  Two short names are of particular interest, as they are handled
specially by the server, and the server will not start if font instances with
these names cannot be opened.  These are `fixed', which specifies the fall-
back font to use when the requested font cannot be opened, and `cursor',
which specifies the set of glyphs to be used by the mouse pointer.

Short names are usually implemented as aliases to XLFDs; the `fixed' and
`cursor' aliases are defined in

     /usr/X11R6/lib/X11/font/misc/fonts.alias

6.3  Unicode

Unicode (<URL:http://www.unicode.org>) is a coded character set with the goal
of uniquely identifying all characters for all scripts, current and histori-
cal.  While Unicode was explicitly not designed as a glyph encoding scheme,
it is often possible to use it as such.

Unicode is an open character set, meaning that codepoint assignments may be
added to Unicode at any time (once specified, though, an assignment can never
be changed).  For this reason, a Unicode font will be sparse, and only define
glyphs for a subset of the character registry of Unicode.

The Unicode standard is defined in parallel with the international standard
ISO 10646.  Assignments in the two standards are always equivalent, and this
document uses the terms Unicode and ISO 10646 interchangeably.

When used in X11, Unicode-encoded fonts should have the last two fields of
their XLFD set to `iso10646-1'.

7.  References

XFree86 comes with extensive documentation in the form of manual pages and
typeset documents.  Before installing fonts, you really should read the
mkfontdir(1) manual page; other manual pages of interest include X(1),
Xserver(1), xset(1), xlsfonts(1) and showfont(1).  In addition, you may want
to read the X Logical Font Description document, by Jim Flowers, which is
provided in the file `xc/doc/xlfd.PS.Z'.

The comp.fonts FAQ <URL:http://www.netmeg.net/faq/computers/fonts/>, which is
unfortunately no longer being maintained, contains a wealth of information
about digital fonts.

The xfsft home page <URL:http://www.dcs.ed.ac.uk/home/jec/programs/xfsft/>
has been superseded by this document, and is now obsolete; you may however
still find some of the information it contains useful.  Joerg Pommnitz' xfsft
page <URL:http://www.joerg-pommnitz.de/TrueType/xfsft.html> is the canonical
source for the `ttmkfdir' utility.

The documentation of X-TrueType is available from the X-TrueType home page
<URL:http://x-tt.dsl.gr.jp/>.

A number of East-Asian CIDFonts are available from O'Reilly's FTP site
<URL:ftp://ftp.oreilly.com/pub/examples/nutshell/cjkv/adobe/>.

The Unicode consortium site <URL:http://www.unicode.org> may be of interest.
But you are more likely to find what you need on Markus Kuhn's UTF-8 and Uni-
code FAQ <URL:http://www.cl.cam.ac.uk/~mgk25/unicode.html>.

The IANA RFC documents, available from a number of sites throughout the
world, often provide interesting information about character set issues; my
favourite is RFC 373.

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$XFree86: $
