Tuning Fontconfig

Overview of Fontconfig

If you only read text in English, and are happy with the common libre fonts listed on the next page, you may never need to worry about the details of how fontconfig works. But there are many things which can be altered if they do not suit your needs.

Although this page is long, it barely scratches the surface and you will be able to find many alternative views on the web (but please remember that some things have changed over the years, for example the autohinter is no longer the default). The aim here is to give you enough information to understand the changes you are making.

User Notes: http://wiki.linuxfromscratch.org/blfs/wiki/Fontconfig

The Xft Font Protocol

The Xft font protocol provides antialiased font rendering through freetype, and fonts are controlled from the client side using fontconfig (except for rxvt-unicode-9.22 which can use fonts listed in ~/.Xresources, and AbiWord-3.0.2 which only uses the specified font). The default search path is /usr/share/fonts and ~/.local/share/fonts although for the moment the old and deprecated location ~/.fonts still works. Fontconfig searches directories in its path recursively and maintains a cache of the font characteristics in each directory. If the cache appears to be out of date, it is ignored, and information is fetched from the fonts themselves (that can take a few seconds if you installed a lot of fonts).

If you've installed Xorg in any prefix other than /usr, any X fonts were not installed in a location known to Fontconfig. Symlinks were created from the OTF and TTF X font directories to /usr/share/fonts/X11-{OTF,TTF}. This allows Fontconfig to use the OpenType and TrueType fonts provided by X, although many people will prefer to use more modern fonts.

Fontconfig uses names to define fonts. Applications generally use generic font names such as "Monospace", "Sans" and "Serif". Fontconfig resolves these names to a font that has all characters that cover the orthography of the language indicated by the locale settings.

Useful Commands

The following commands may be helpful when working with fontconfig:

fc-list | less : show a list of all available fonts (/path/to/filename: Font Name:style). If you installed a font more than 30 seconds ago but it does not show, then it or one of its directories is not readable by your user.

fc-match 'Font Name' : will tell you which font will be used if the named font is requested. Typically you would use this to see what happens if a font you have not installed is requested, but you can also use it if the system is giving you a different font from what you expected (perhaps because fontconfig does not agree that the font supports your language).

fc-match -a 'Type' | less : will provide a list of all fonts which can be used for that type (Monospace, Sans, Serif). Note that in-extremis fontconfig will take a glyph from any available font, even if it is not of the specified type, and unless it knows about the font's type it will assume it is Sans.

If you wish to know which font will be used for a string of text (i.e. one or more glyphs, preceded by a space), paste the following command and replace the xyz by the text you care about:

FC_DEBUG=4 pango-view --font=monospace -t xyz | grep family : this requires Pango-1.40.14 and ImageMagick-7.0.7-11 - it will invoke display to show the text in a tiny window, and after closing that the last line of the output will show which font was chosen. This is particularly useful for CJK languages, and you can also pass a language, e.g. PANGO_LANGUAGE=en;ja (English, then assume Japanese) or just zh-cn (or other variants - 'zh' on its own is not valid).

The various files

The main files are in /etc/fonts.conf.d/. That was intended to be a directory populated by symlinks to some of the files in /usr/share/fontconfig/conf.avail/, but many people, and some packages, create the files directly. Each file name must be in the form of two digits, a dash, somename.conf and they are read in sequence.

By convention, the numbers are assigned as follows:

  • 00-09 extra font directories

  • 10-19 system rendering defaults (antialising etc)

  • 20-29 font rendering options

  • 30-39 family substitution

  • 40-49 map family to generic type

  • 50-59 load alternate config files

  • 60-69 generic aliases, map generic to family

  • 70-79 adjust which fonts are available

  • 80-89 match target scan (modify scanned patterns)

  • 90-99 font synthesis

You can also have a personal fonts.conf in $XDG_CONFIG_HOME which is ~/.config/fontconfig/.

The rules to choose a font

If the requested font is installed, and provided it contains the codepoints required for the current language (in the source, see the .orth files in the fc-lang/ directory), it will be used.

But if the document or page requested a font which is not installed (or, occasionally, does not contain all the required codepoints) the following rules come into play: First, 30-metric-aliases.conf is used to map aliases for some fonts with the same metrics (same size, etc). After that, an unknown font will be searched for in 45-latin.conf - if it is found it will be mapped as Serif or Monospace or Sans, otherwise it will be assumed to be Sans. Then 50-latin.conf provides ordered lists of the fallbacks - Dejavu fonts will be used if you installed them. Cyrillic and Greek appear to be treated in the same way. There are similar files with a 65- prefix for Persian and other non-latin writing systems. All of these files prefer commercial fonts if they are present, although modern libre fonts are often at least their equals.

Since fontconfig-2.12.5 there is also generic family matching for some emoji and math fonts, see {45,60}-generic.conf.

In the rare cases where a font does not contain all the expected codepoints, see 'Trial the First:' at I stared into the fontconfig for the long details.

Hinting and Anti-aliasing

It is possible to change how, or if, fonts are hinted. The following example file contains the default settings, but with comments. The settings are very much down to the user's preferences and to the choice of fonts, so a change which improves some pages may worsen others. The preferred location for this file is: ~/.config/fontconfig/fonts.conf

To try out different settings, you may need to exit from Xorg and then rerun startx so that all applications use the new settings. And if you use Gnome or KDE their desktops can override these changes. To explore the possibilities, create a file for your user:

mkdir -pv ~/.config/fontconfig &&
cat > ~/.config/fontconfig/fonts.conf << "EOF"
<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>

  <match target="font" >
    <!-- autohint was the old automatic hinter when hinting was patent
    protected, so turn it off to ensure any hinting information in the font
    itself is used, this is the default -->
    <edit mode="assign" name="autohint">  <bool>false</bool></edit>

    <!-- hinting is enabled by default -->
    <edit mode="assign" name="hinting">   <bool>true</bool></edit>
    
    <!-- for the lcdfilter see http://www.spasche.net/files/lcdfiltering/ -->
    <edit mode="assign" name="lcdfilter"> <const>lcddefault</const></edit>
    
    <!-- options for hintstyle:
    hintfull: is supposed to give a crisp font that aligns well to the
    character-cell grid but at the cost of its proper shape.

    hintmedium: poorly documented, maybe a synonym for hintfull.
    hintslight is the default: - supposed to be more fuzzy but retains shape.
    
    hintnone: seems to turn hinting off.
    The variations are marginal and results vary with different fonts -->
    <edit mode="assign" name="hintstyle"> <const>hintslight</const></edit>
    
    <!-- antialiasing is on by default and really helps for faint characters
    and also for 'xft:' fonts used in rxvt-unicode -->
    <edit mode="assign" name="antialias"> <bool>true</bool></edit>
    
    <!-- subpixels are usually rgb, see
    http://www.lagom.nl/lcd-test/subpixel.php -->
    <edit mode="assign" name="rgba">      <const>rgb</const></edit>
    
    <!-- thanks to the Arch wiki for the lcd and subpixel links -->
  </match>

</fontconfig>
EOF

You will now need to edit the file in your preferred editor.

For more examples see the blfs-support thread which started at /2016-September/078422, particularly 2016-September/078425, and the original poster's preferred solution at 2016-November/078658. There are other examples in Fontconfig in the Arch wiki and Fontconfig in the Gentoo wiki.

Disabling Bitmap Fonts

In previous versions of BLFS, the ugly old Xorg bitmap fonts were installed. Now, many people will not need to install any of them. But if for some reason you have installed one or more bitmap fonts, you can prevent them being used by fontconfig by creating the following file as the root user :

cat > /etc/fonts/conf.d/70-no-bitmaps.conf << "EOF"
<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
<!-- Reject bitmap fonts -->
 <selectfont>
  <rejectfont>
   <pattern>
     <patelt name="scalable"><bool>false</bool></patelt>
   </pattern>
  </rejectfont>
 </selectfont>
</fontconfig>
EOF

Adding extra font directories

Normally, system fonts and user fonts are installed in directories beneath the locations specified in The Xft Font Protocol and there is no obvious reason to put them elsewhere. However, a full BLFS install of texlive-20170524 puts many fonts in /opt/texlive/2017/texmf-dist/fonts/ in the opentype/ and truetype/ subdirectories. Although pulling in all of these files may appear useful (it allows you to use them in non TeX programs), there are several problems with such an approach:

  1. There are hundreds of files, which makes selecting the font hard.

  2. Some of the files do odd things, such as displaying semaphore flags instead of ASCII letters, or mapping cyrillic codepoints to character forms appropriate to Old Church Slavonic instead of the expected current shapes: fine if that is what you need, but painful for normal use.

  3. Several fonts have multiple sizes and impenetrable short names, which both make selecting the correct font even harder.

  4. When a font is added to CTAN, it is accompanied by TeX packages to use it in the old engines (xelatex does not normally need this), and then the version is often frozen whilst the font is separately maintained. Some of these fonts such as Dejavu fonts are probably already installed on your BLFS system in a newer version, and if you have multiple versions of a font it is unclear which one will be used by fontconfig.

However, it is sometimes useful to look at these fonts in non-TeX applications, if only to see whether you wish to install a current version. If you have installed all of texlive, the following example will make one of the Arkandis Open Type fonts available to other applications, and all three of the ParaType TrueType fonts. Adjust or repeat the lines as desired, to either make all the opentype/ or truetypefonts available, or to select different font directories. As the root user:

cat > /etc/fonts/conf.d/09-texlive.conf << "EOF"
<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
  <dir>/opt/texlive/2017/texmf-dist/fonts/opentype/arkandis/berenisadf</dir>
  <dir>/opt/texlive/2017/texmf-dist/fonts/truetype/paratype</dir>
</fontconfig>
EOF

If you do this, remember to change all instances of the year in that file when you upgrade texlive to a later release.

Preferring certain fonts

There are many reasons why people may wish to have pages which specify a particular font use a different font, or prefer specific fonts in Monospace or Sans or Serif. As you will expect, there a number of different ways of achieving this.

Fontconfig user docs

Fontconfig installs user documentation that includes an example 'User configuration file' which among other things prefers WenQuanYi ZenHei (a Sans font) if a Serif font is requested for Chinese (this part might be anachronistic unless you have non-free Chinese fonts, because in 65-nonlatin.conf this font is already among the preferred fonts when Serif is specified for Chinese) and to prefer the modern VL Gothic font if a Sans font is specified on a Japanese page (otherwise a couple of other fonts would be preferred if they have been installed).

If you have installed the current version, the user documentation is available in html, PDF and text versions at /usr/share/doc/fontconfig-2.12.6/ : change the version if you installed a different one.

Prefer a specific font

As an example, if for some reason you wished to use the Nimbus Roman No9 L font wherever Times New Roman is referenced (it is metrically similar, and preferred for Times Roman, but the Serif font from Liberation fonts will be preferred for the Times New Roman font if installed), as an individual user you could install the font and then create the following file:

mkdir -pv ~/.config/fontconfig/conf.d &&
cat >  ~/.config/fontconfig/conf.d/35-prefer-nimbus-for-timesnew.conf << "EOF"
<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
<!-- prefer Nimbus Roman No9 L for Times New Roman as well as for Times,
 without this Tinos and Liberation Serif take precedence for Times New Roman
 before fontconfig falls back to whatever matches Times -->
    <alias binding="same">
        <family>Times New Roman</family>
        <accept>
            <family>Nimbus Roman No9 L</family>
        </accept>
    </alias>
</fontconfig>
EOF

This is something you would normally do in an individual user's settings, but the file in this case has been prefixed '35-' so that it could, if desired, be used system-wide in /etc/fonts/conf.d/.

Prefer chosen CJK fonts

The following example of a local configuration (i.e. one that applies for all users of the machine) does several things:

  1. If a Serif font is specified, it will prefer the UMing variants, so that in the zh-cn, zh-hk and zh-tw languages things should look good (also zh-sg which actually uses the same settings as zh-cn) without affecting Japanese.

  2. It prefers the Japanese IPAex fonts if they have been installed (although VL Gothic will take precedence for (Japanese) Sans if it has also been installed.

  3. Because WenQuanYi ZenHei covers Korean Hangul glyphs and is also preferred for Serif in 65-nonlatin.conf, if installed it will be used by default for Korean Serif. To get a proper Serif font, the UnBatang font is specified here - change that line if you installed a different Serif font from the choice of Korean fonts.

  4. The Monospace fonts are forced to the preferred Sans fonts. If the text is in Korean then WenQuanYi ZenHei will be used.

In a non-CJK locale, the result is that suitable fonts will be used for all variants of Chinese, Japanese and Hangul Korean. All other languages should already work if a font is present. As the root user:

cat > /etc/fonts/local.conf << "EOF"
<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
    <alias>
        <family>serif</family>
        <prefer>
            <family>AR PL UMing</family>
            <family>IPAexMincho</family>
            <!-- WenQuanYi is preferred as Serif in 65-nonlatin.conf,
            override that so a real Korean font can be used for Serif -->
            <family>UnBatang</family>
        </prefer>
    </alias>
    <alias>
         <family>sans-serif</family>
         <prefer>
             <family>WenQuanYi Zen Hei</family>
             <family>VL Gothic</family>
             <family>IPAexGothic</family>
         </prefer>
    </alias>
    <alias>
         <family>monospace</family>
         <prefer>
             <family>VL Gothic</family>
             <family>IPAexGothic</family>
             <family>WenQuanYi Zen Hei</family>
         </prefer>
    </alias>
</fontconfig>
EOF

Editing Old-style conf files

Some fonts, particularly Chinese fonts, ship with conf files which can be installed in /etc/fonts/conf.d. However, if you do that and then use a terminal to run any command which uses fontconfig you may see error messages such as :

Fontconfig warning: "/etc/fonts/conf.d/69-odofonts.conf", line 14: Having multiple <family> in <alias> isn't supported and may not work as expected.

In practice, these old rules do not work. For non-CJK users, fontconfig will usually do a good job without these rules. Their origin dates back to when CJK users needed handcrafted bitmaps to be legible at small sizes, and those looked ugly next to antialiased Latin glyphs - they preferred to use the same CJK font for the Latin glyphs. There is a side-effect of doing this : the (Serif) font is often also used for Sans, and in such a situation the (English) text in Gtk menus will use this font - compared to system fonts, as well as being serif it is both faint and rather small. That can make it uncomfortable to read.

Nevertheless, these old conf files can be fixed if you wish to use them. The following example is the first part of 64-arphic-uming.conf from UMing - there are a lot more similar items which also need changing :


   <match target="pattern">
       <test qual="any" name="lang" compare="contains">
           <string>zh-cn</string>
           <string>zh-sg</string>
       </test>
       <test qual="any" name="family">
           <string>serif</string>
       </test>
       <edit name="family" mode="prepend" binding="strong">
           <string>AR PL UMing CN</string>
       </edit>
    </match>

The process to correct this is straightforward but tedious - for every item which produces an error message, using your editor (as the root user) edit the installed file to repeat the whole block as many times as there are multiple variables, then reduce each example to have only one of them. You may wish to work on one error at a time, save the file after each fix, and from a separate term run a command such as fc-list 2>&1 | less to see that the fix worked. For the block above, the fixed version will be :


   <match target="pattern">
       <test qual="any" name="lang" compare="contains">
           <string>zh-cn</string>
       </test>
       <test qual="any" name="family">
           <string>serif</string>
       </test>
       <edit name="family" mode="prepend" binding="strong">
           <string>AR PL UMing CN</string>
       </edit>
    </match>
   <match target="pattern">
       <test qual="any" name="lang" compare="contains">
           <string>zh-sg</string>
       </test>
       <test qual="any" name="family">
           <string>serif</string>
       </test>
       <edit name="family" mode="prepend" binding="strong">
           <string>AR PL UMing CN</string>
       </edit>
    </match>

See Also

I stared into the fontconfig ...

The blog entries by Eevee are particularly useful if fontconfig does not think your chosen font supports your language, and for preferring some non-MS Japanese fonts when an ugly MS font is already installed.

Fontconfig in the Arch wiki

Arch has a lot of information in its wiki at font_configuration.

Fontconfig in the Gentoo wiki

Gentoo has some information in its wiki at Fontconfig although a lot of the details (what to enable, and Infinality) are specific to Gentoo.

Last updated on 2017-11-06 20:26:32 -0600