Fonts in XFree86

                    Juliusz Chroboczek, <jch@xfree86.org>

                              17 November 2003

1.  Introduction

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

We assume some familiarity with digital fonts.  If anything is not clear to
you, please consult Appendix: Background (section 5., page 1) at the end of
this document for background information.

1.1  Two font systems

XFree86 includes two font systems: the core X11 fonts system, which is
present in all implementations of X11, and the Xft fonts system, which is not
currently distributed with implementations of X11 that are not based on
XFree86 but will hopefully be included by them in the future

The core X11 fonts system is directly derived from the fonts system included
with X11R1 in 1987, which could only use monochrome bitmap fonts.  Over the
years, it has been more or less happily coerced into dealing with scalable
fonts and rotated glyphs.

Xft was designed from the start to provide good support for scalable fonts,
and do so efficiently.  Unlike the core fonts system, it supports features
such as anti-aliasing and sub-pixel rasterisation.  Perhaps more importantly,
it gives applications full control over the way glyphs are rendered, making
fine typesetting and WYSIWIG display possible.  Finally, it allows applica-
tions to use fonts that are not installed system-wide for displaying docu-
ments with embedded fonts.

Xft is not compatible with the core fonts system: usage of Xft requires mak-
ing fairly extensive changes to toolkits (user-interface libraries).  While
XFree86 will continue to maintain the core fonts system, toolkit authors are
encouraged to switch to Xft as soon as possible.

2.  Installing fonts

This section explains how to configure both Xft and the core fonts system to
access newly-installed fonts.

2.1  Configuring Xft

Xft has no configuration mechanism itself, rather it relies upon the fontcon-
fig library to configure and customize fonts.  That library is not specific
to XFree86 or indeed on any particular font output mechanism.  This discus-
sion describes how fontconfig, rather than Xft, works.

2.1.1  Installing fonts in Xft

Fontconfig looks for fonts in a set of well-known directories that include
all of XFree86's standard font directories (`/usr/X11R6/lib/X11/lib/fonts/*')
by default) as well as a directory called `.fonts/' in the user's home direc-
tory.  Installing a font for use by Xft applications is as simple as copying
a font file into one of these directories.

     $ cp lucbr.ttf ~/.fonts/

Fontconfig will notice the new font at the next opportunity and rebuild its
list of fonts.  If you want to trigger this update from the command line (for
example in order to globally update the system-wide Fontconfig information),
you may run the command `fc-cache'.

     $ fc-cache

2.1.2  Fine-tuning Xft

Fontconfig's behaviour is controlled by a set of configuration files: a sys-
tem-wide configuration file, `/etc/fonts/fonts.conf', and a user-specific
file called `.fonts.conf' in the user's home directory (this can be overrid-
den with the `FONTCONFIG_FILE' environment variable).

Every Fontconfig configuration file must start with the following boiler-
plate:

     <?xml version="1.0"?>
     <!DOCTYPE fontconfig SYSTEM "fonts.dtd">
     <fontconfig>

In addition, every Fontconfig configuration file must end with the following
line:

     </fontconfig>

The default Fontconfig configuration file includes the directory `~/.fonts/'
in the list of directories searched for font files, and this is where user-
specific font files should be installed.  In the unlikely case that a new
font directory needs to be added, this can be done with the following syntax:

     <dir>/usr/local/share/fonts/</dir>

Another useful option is the ability to disable anti-aliasing (font smooth-
ing) for selected fonts.  This can be done with the following syntax:

     <match target="font">
         <test qual="any" name="family">
             <string>Lucida Console</string>
         </test>
         <edit name="antialias" mode="assign">
             <bool>false</bool>
         </edit>
     </match>

Anti-aliasing can be disabled for all fonts by the following incantation:

     <match target="font">
         <edit name="antialias" mode="assign">
             <bool>false</bool>
         </edit>
     </match>

Xft supports sub-pixel rasterisation on LCD displays.  XFree86 should auto-
matically enable this feature on laptops and when using an LCD monitor con-
nected with a DVI cable; you can check whether this was done by typing

     $ xdpyinfo -ext RENDER | grep sub-pixel

If this doesn't print anything, you will need to configure Render for your
particular LCD hardware manually; this is done with the following syntax:

     <match target="font">
         <edit name="rgba" mode="assign">
             <const>rgb</const>
         </edit>
     </match>

The string `rgb' within the `<const>'...`</const>' specifies the order of
pixel components on your display, and should be changed to match your hard-
ware; it can be one of `rgb (normal LCD screen), `bgr' (backwards LCD
screen), `vrgb' (LCD screen rotated clockwise) or `vbgr' (LCD screen rotated
counterclockwise).

2.1.3  Configuring applications

Because most current applications use the core fonts system by default, it is
necessary to explicitly configure them to use Xft.  How this is done depends
on the application.

XTerm can be set to use Xft by using the `-fa' command line option or by set-
ting the `XTerm*faceName' resource:

     XTerm*faceName: Courier

or

     $ xterm -fa "Courier"

For applications based on GTK+ 2.0 (including GNOME 2 applications), the
environment variable `GDK_USE_XFT' should be set to `1':

     $ export GDK_USE_XFT=1

GTK+ 2.2 uses Xft by default.

For KDE applications, you should select ``Anti-alias fonts'' in the ``Fonts''
panel of KDE's ``Control Center''.  Note that this option is misnamed: it
switches KDE to using Xft but doesn't enable anti-aliasing in case it was
disabled by your Xft configuration file.

(What about Mozilla?)

2.1.4  Troubleshooting

If some Xft-based applications don't seem to notice the changes you are mak-
ing to your configuration files, they may be linked against the XFree86 4.2
version of Xft.  In order to fix the problem, you should relink them against
a current version of Xft; on most systems, it is enough to install the cur-
rent version of the Xft and Fontconfig libraries.

If, for some reason, you cannot upgrade the shared libraries, please check
the Xft(3) manual page included with XFree86 4.2 for the configuration mecha-
nisms of the previous version of Xft.

2.2  Configuring the core X11 fonts system

Installing fonts in the core system 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.

2.2.1  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 will 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/
     $ mkfontdir /usr/local/share/fonts/bitmap/

All that remains is to tell the X server about the existence of the new font
directory; see Setting the server font path (section 2.2.4, page 1) below.

2.2.2  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 Installing CIDFonts (section 2.2.3, 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'.  While this can be done by hand, it is
best done by using the `mkfontscale' utility.

     $ mkfontscale /usr/local/share/fonts/Type1/
     $ mkfontdir /usr/local/share/fonts/Type1/

Under some circumstances, it may be necessary to modify the `fonts.scale'
file generated by mkfontscale; for more information, please see the mkfont-
dir(1) and mkfontscale(1) manual pages and Core fonts and internationalisa-
tion (section 4.1, page 1) later in this document.

2.2.3  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).

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 code 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 `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).  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.

2.2.4  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
of 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

2.2.4.1  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-'.  You may reset the font
path to its default value with `xset fp default'.

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

2.2.4.2  Permanent modification of the font path

The default font path (the one used just after server startup or after `xset
fp default') is specified in the X server's `XF86Config' file.  It is com-
puted 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.

2.2.5  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 (the X server usually runs as root, beware of NFS-
mounted font directories).  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, OpenType 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  "freetype": TrueType fonts (`*.ttf' and `*.ttc'), OpenType fonts
     (`*.otf' and `*.otc') and Type 1 fonts (`*.pfa' and `*.pfb');

   o  "type1": alternate Type 1 backend (`*.pfa' and `*.pfb') and CIDFont
     backend;

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

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

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 (SI) comes with a large number of bitmap
fonts, including the `fixed' family, and bitmap versions of Courier, Times,
Helvetica and some members of the Lucida family.  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 allows us to provide the stan-
dard 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-ISO8859-15.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-iso8859-15
     -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

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.

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 Troubleshooting (section 2.2.5, 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 XFree86.

4.  More about core fonts

This section describes XFree86-specific enhancements to the core X11 fonts
system.

4.1  Core fonts and internationalisation

The scalable font backends (Type 1, Speedo and TrueType) can automatically
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.

4.1.1  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 Using Symbol Fonts (section 4.1.5, page
1), as the intervening information does not apply to X-TT.  X-TT itself is
described in more detail in X-TrueType (section 4.2.2, 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.  Please see the mkfont-
dir(1) manual 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 Format of encodings
directory files (section 4.1.3, page 1) and Format of encoding files (section
4.1.4, page 1) later in this document.

4.1.2  Backend-specific notes about fontenc

4.1.2.1  The FreeType backend

For TrueType and OpenType fonts, the FreeType 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.

For Type 1 fonts, the FreeType 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 cov-
ers part of the Unicode code points that have been assigned names by Adobe.

Specifying an encoding value of adobe-fontspecific for a Type 1 font disables
the encoding mechanism.  This is useful with symbol and incorrectly encoded
fonts (see Incorrectly encoded fonts (section 4.1.6, page 1) below).

If a suitable mapping is not found, the FreeType backend defaults to
ISO 8859-1.

4.1.2.2  Type 1

The Type 1 backend behaves similarly to the FreeType backend with Type 1
fonts, except that it limits all encodings to 8-bit codes.

4.1.2.3  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.

4.1.3  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 either in the same directory
as the font file used or in a system-wide location
(`/usr/X11R6/lib/X11/fonts/encodings/' by default).

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 absolute.  Every encoding name
should agree with the encoding name defined in the encoding file.  For exam-
ple,

     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.

4.1.4  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

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.

4.1.5  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'.

4.1.6  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 on systems which are not easily extended
with new locale data.  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.

4.1.6.1  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.

4.1.6.2  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.

4.1.6.3  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 very
simple: it consists of a series of lines each mapping an alias name to a font
name.  A `fonts.alias' file might look as follows:

     "-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
more precisely described in the mkfontdir(1) manual page.

4.2  Additional notes about scalable core fonts

The FreeType (libfreetype-xtt2) backend (module `freetype', formerly known as
xfsft) is able to deal with both TrueType and Type 1 fonts.  This puts it in
conflict with the X-TT and Type 1 backends respectively.

If both the FreeType and the Type 1 backends are loaded, the FreeType backend
will be used for Type 1 fonts.  If both the FreeType and X-TT backends are
loaded, X-TT will be used for TrueType fonts.

4.2.1  About the FreeType backend

The FreeType (libfreetype-xtt2) backend (formerly xfsft) is a backend based
on version 2 of the FreeType library (see the FreeType web site
<URL:http://www.freetype.org/>) and has the X-TT functionalities for CJKV
support provided by the After X-TT Project (see the After X-TT Project web
site <URL:http://x-tt.sourceforge.jp/>).  The FreeType module has support for
the ``fontenc'' style of internationalisation (see The fontenc layer (section
4.1.1, page 1)).  This backend supports TrueType font files (`*.ttf'), Open-
Type font files (`*.otf'), TrueType Collections (`*.ttc'), OpenType Collec-
tions (`*.otc') and Type 1 font files (`*.pfa' and `*.pfb').

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 a pair of
colons, or by setting the 'fn' TTCap option.  For example,

     :1:mincho.ttc -misc-pmincho-medium-r-normal--0-0-0-0-p-0-jisx0208.1990-0

refers to face 1 in the `mincho.ttc' TrueType Collection file.

The new FreeType backend supports the extended `fonts.dir' syntax introduced
by X-TrueType with a number of options, collectively known as `TTCap'.  A
`TTCap' entry follows the general syntax

     option=value:

and should be specified before the filename.  The new FreeType almost per-
fectly supports TTCap options that are compatible with X-TT 1.4.  The Auto-
matic Italic (`ai'), Double Strike (`ds') and Bounding box Width (`bw')
options are indispensable in CJKV.  For example,

     mincho.ttc -misc-mincho-medium-r-normal--0-0-0-0-c-0-jisx0208.1990-0
     ds=y:mincho.ttc -misc-mincho-bold-r-normal--0-0-0-0-c-0-jisx0208.1990-0
     ai=0.2:mincho.ttc -misc-mincho-medium-i-normal--0-0-0-0-c-0-jisx0208.1990-0
     ds=y:ai=0.2:mincho.ttc -misc-mincho-bold-i-normal--0-0-0-0-c-0-jisx0208.1990-0
     bw=0.5:mincho.ttc -misc-mincho-medium-r-normal--0-0-0-0-c-0-jisx0201.1976-0
     bw=0.5:ds=y:mincho.ttc -misc-mincho-bold-r-normal--0-0-0-0-c-0-jisx0201.1976-0
     bw=0.5:ai=0.2:mincho.ttc -misc-mincho-medium-i-normal--0-0-0-0-c-0-jisx0201.1976-0
     bw=0.5:ds=y:ai=0.2:mincho.ttc -misc-mincho-bold-i-normal--0-0-0-0-c-0-jisx0201.1976-0

setup the complete combination of jisx0208 and jisx0201 using mincho.ttc
only.  More information on the TTCap syntax is found on the After X-TT
Project page <URL:http://x-tt.sourceforge.jp/>.

The FreeType backend uses the fontenc layer in order to support recoding of
fonts; this was described in The fontenc layer (section 4.1.1, page 1) and
especially FreeType-specific notes about fontenc (section 4.1.2.1, page 1)
earlier in this document.

4.2.2  About the X-TrueType TrueType backend

The `X-TrueType' backend is a backend based on version 1 of the FreeType
library.  X-TrueType doesn't use the `fontenc' layer for managing font encod-
ings, but instead uses its own database of encodings.

Since the functionalities for CJKV support introduced by X-TT have been
merged into the new FreeType backend, the X-TT backend will be removed from
XFree86's tree near the future.  Therefore, the use of FreeType backend is
preferred over the X-TT backend.

General information on X-TrueType may be found at the After X-TT Project page
<URL:http://x-tt.sourceforge.jp/>.

4.2.3  Delayed glyph rasterisation

When loading a proportional fonts which contain a huge number of glyphs, the
old FreeType delayed glyph rasterisation until the time at which the glyph
was first used.   The new FreeType (libfreetype-xtt2) has an improved `very
lazy' metric calculation method to speed up the process when loading TrueType
or OpenType fonts.   Although the X-TT module also has this method, the
"vl=y" TTCap option must be set if you want to use it.  This is the default
method for FreeType when it loads multi-byte fonts.   Even if you use a uni-
code font which has tens of thousands of glyphs, this delay will not be wor-
risome as long as you use the new FreeType backend -- its `very lazy' method
is super-fast.

The maximum error of bitmap position using `very lazy' method is 1 pixel, and
is the same as that of a character-cell spacing.  When the X-TT backend is
used with the `vl=y' option, a chipped bitmap is displayed with certain
fonts.  However, the new FreeType backend has minimal problem with this,
since it corrects left- and right-side bearings using `italicAngle' in the
TrueType/OpenType post table, and does automatic correction of bitmap posi-
tions when rasterisation so that chipped bitmaps are not displayed.  Never-
theless if you don't want to use the `very lazy' method when using multi-
bytes fonts, set `vl=n' in the TTCap option to disable it:

     vl=n:luxirr.ttf -b&h-Luxi Serif-medium-r-normal--0-0-0-0-p-0-iso10646-1

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

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

or

     fs=c:mincho.ttc -misc-mincho-medium-r-normal--0-0-0-0-p-0-jisx0208.1990-0

will not compute the metric for each glyph, but instead trust the font 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.  Appendix: background and terminology

5.1  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 sequence of two keystrokes <f><i> will typically cor-
respond a single glyph.  Similarly, if the system shapes Arabic glyphs in a
vaguely 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, from keystrokes to characters and
from characters to glyphs.  You may want to think of characters as the basic
unit of text 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 standardised 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 systems used 6 bit character sets, while 16 bit (or more) character
sets are necessary for ideographic writing systems.

5.2  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 the information nec-
essary 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), TrueType and Speedo.

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 core fonts system uses the data in a font file to generate font
instances, which are collections of glyphs at a given size indexed according
to a given encoding.

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

     -adobe-courier-medium-r-normal--12-120-75-75-m-70-iso8859-1

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

A scalable font is specified by an XLFD which contains zeroes instead of some
fields:

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

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 the server will not
start if font instances with these names cannot be opened.  These are
`fixed', which specifies the fallback 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 standard `fixed'
and `cursor' aliases are defined in

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

5.3  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, meaning that it
only defines 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 we
often use the terms Unicode and ISO 10646 interchangeably.

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

6.  References

XFree86 comes with extensive documentation in the form of manual pages and
typeset documents.  Before installing fonts, you really should read the font-
config(3) and mkfontdir(1) manual pages; other manual pages of interest
include X(7), Xserver(1), xset(1), Xft(3), 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 latest released version of the XFree86 documentation (including this doc-
ument and all manual pages) is available as current XFree86 documentation
<URL:http://www.xfree86.org/current/>.

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.

Xft and Fontconfig are described on Keith Packard's Fontconfig site
<URL:http://www.fontconfig.org>.

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 that it contains useful.  Joerg Pommnitz'
xfsft page <URL:http://www.joerg-pommnitz.de/TrueType/xfsft.html> is the
canonical source for the `ttmkfdir' utility, which is the ancestor of
mkfontscale.

The author's software pages <URL:http://www.pps.jussieu.fr/~jch/software/>
might or might not contain related scribbles and development versions of
software.

The documentation of X-TrueType is available from the After X-TT Project page
<URL:http://x-tt.sourceforge.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/>.

While the Unicode consortium site <URL:http://www.unicode.org> may be of
interest,  you are more likely to find what you need in Markus Kuhn's UTF-8
and Unicode 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; see
for example RFC 373.

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