The fontconfig library (media-libs/fontconfig) is intended to provide uniform font selection and configuration amongst all GUI applications. Although it is common for a desktop environment to provide its own font overrides and configuration utilities, fontconfig is still the underlying library.
fontconfig doesn't know many USE flags.
USE flags for media-libs/fontconfig A library for configuring and customizing font access
||Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally|
||Add Native Language Support (using gettext - GNU locale utilities)|
||Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)|
Changes to fontconfig files will reflect only in applications started after the change!
fontconfig uses XML files in the /etc/fonts/ directory to generate its internal configuration. By default it parses /etc/fonts/fonts.conf (users should not edit this file!) which sets some sane defaults and usually contains code to also parse /etc/fonts/conf.d/ content. In addition there is the /etc/fonts/conf.avail/ directory that contains various possible configuration files that each cover some aspect of fontconfig. It's customary to symlink necessary files to /etc/fonts/conf.d/. These files are executed in order they are named; for this reason their names start with a two digit number with the first digit (tens) indicating what the file affects (called the class).
Gentoo ships an eselect module (eselect fontconfig) that does exactly what was described in generic way - it manages symlinks of files in /etc/fonts/conf.avail/ by adding or removing them from the /etc/fonts/conf.d/ directory. For obvious reasons changing system wide configuration requires appropriate permissions.
The following subsections explain how to deal with the fontconfig eselect module.
Listing available files
The list command shows the available fontconfig files, and marks the enabled ones with an asterisk (
eselect fontconfig list
Available fontconfig .conf files (* is enabled):  10-autohint.conf *  10-no-sub-pixel.conf  10-sub-pixel-bgr.conf  10-sub-pixel-rgb.conf  10-sub-pixel-vbgr.conf  10-sub-pixel-vrgb.conf  10-unhinted.conf  11-lcdfilter-default.conf  11-lcdfilter-legacy.conf ...
Different systems have different files in fonts.avail so the output will be different. Never blindly use a list number from another source (such as blog posts or wiki articles).
Enabling a file
Files can be enabled either by filename or by the number in brackets. These two do the same thing:
eselect fontconfig enable 10-sub-pixel-rgb.conf
eselect fontconfig enable 4
Disabling a file
Files can be disabled likewise:
eselect fontconfig disable 10-sub-pixel-rgb.conf
eselect fontconfig disable 4
Custom system wide configuration
To create a custom, system-wide fontconfig file, enable 51-local.conf and create /etc/fonts/local.conf (this is an XML file).
<?xml version="1.0"?> <!DOCTYPE fontconfig SYSTEM "fonts.dtd"> <fontconfig> <alias> <family>sans-serif</family> <prefer> <family>Ubuntu</family> <family>TakaoPGothic</family> <family>Droid Sans</family> </prefer> <default><family>DejaVu Sans</family></default> </alias> </fontconfig>
To be clear, this says that when it comes to sans-serif fonts, we prefer using Ubuntu, TakaoPGothic, and Droid Sans fonts (in that order) over DejaVu Sans (which can be used as a default choice only when necessary). Obviously, different choices can be made here.
To create per-user fontconfig files, enable 50-user.conf (which might be enabled by default), and have the end users use the ~/.config/fontconfig/fonts.conf file. This file has the same XML format as local.conf.
This is one way how a desktop environment might try to affect font rendering. It might be prudent to disable this to be sure that what's being shown is actually system wide configuration when customizing it. Disabling it also makes font rendering more uniform across user accounts.
The previously used ~/.fonts.conf is now deprecated in favor of the $XDG_CONFIG_HOME based location. This variable by defaults points to ~/.config.
Check the default font replacement, for example for Arial, by typing:
Anti-aliasing, hinting, and sub-pixel rendering
Rendering aspects can be tuned as well. In the following sections the Anti-aliasing, Hinting and Sub-pixel rendering features are tuned.
|Anti-aliasing||is enabled by default and makes fonts less blocky.|
|Hinting||is an attempt to cope with the low pixel count per unit of area of current displays. Correct hinting makes characters more crisp but since font metrics aren't changed (and arguably should not change) affects how overall the rendered text looks like.|
|Sub-pixel rendering||uses the fact that LCD matrix has three primaries to effectively triple the resolution of text but can make characters appear not entirely black. To combat that lcdfilter is to be used with sub-pixel rendering (available for newer fontconfig) but it can blur the characters too much. In the end this entirely depends on person how they like their text.|
The default fontconfig behavior regarding hinting is rather undocumented, but it can be made deterministically sub-optimal by making a system wide default.
- First enable /etc/fonts/local.conf
- Edit the local.conf file to include full hinting by default
This local.conf snippet enables full hinting:
<match target="font"> <edit mode="assign" name="hintstyle"> <const>hintfull</const> </edit> </match>
Most fonts look best with full hinting but others need slight or more rarely some other hinting option. Some fonts for one reason or another will always be ugly.
Using sub-pixel rendering
It's important to determine the sub-pixel layout of the LCD matrix. It's usually RGB (10-sub-pixel-rgb.conf) but the only way to be sure is to either consult display specification or use this sub-pixel layout test to determine it.
Once determined, enable the appropriate 10-sub-pixel-<matrix type>.conf file.
eselect fontconfig enable 10-sub-pixel-rgb.conf
It's strongly advised that lcdfilter, if available, is used with sub-pixel rendering. It comes in different varieties but the default (11-lcdfilter-default.conf) should be appropriate for all common fonts.
eselect fontconfig enable 11-lcdfilter-default.conf
Autohinter attempts to do automatic hinting disregarding any existing hinting information. Until recently it was the default because TrueType2 was covered by patents but now that they have expired there's very little reason to use it. From technical point of view it does better than broken or no hinting information but it will be strongly sub-optimal for fonts with good hinting information. Generally system fonts are of the second kind so autohinter should not be used.
Autohinter is not compatible with sub-pixel rendering, do not use the two together!
Choosing the right font can be trickier than deciding on the right hinting type. For one reason or another, some fonts will never be perfect — but it's certainly possible to make them look better than, say, the Windows 7 default font configuration.
Many fonts don't provide glyphs for every assigned Unicode codepoint, due to the size of Unicode. If a font doesn't provide a glyph for a given codepoint, the character might be represented by a substitute character (such as a rectangle containing the hexadecimal value of the code point), or by a glyph from a different font (the "fallback font"), depending on the application.
Here are some recommendations regarding well known fonts in Gentoo:
|Red Hat's fonts, which are metric-compatible with MS TrueType corefonts, have a decent, modern look. This is the Gentoo Fonts team recommendation for default Latin fonts. Covers about 2,600 code points.||Latin, Greek, Cyrillic, and Hebrew only. A few glyphs may have hinting trouble.|
|Very similar to Liberation, covering about 2,700 code points. Linux Libertine itself is proportional serif only, but the package contains less extensive sans and mono fonts, as well. Can be used as a fallback for some glyphs not in Liberation.||Latin, Greek, Cyrillic, and Hebrew only. Sans and mono fonts are limited.|
|Google's font family that aims to support all the world's languages (so, well over 60,000 code points). It goes well with Liberation or Droid. Adobe's Source Han Sans fonts are included for CJK. Recommended as a fallback for many glyphs not covered by Liberation.||Big download.|
|Many styles and covers a lot of code points (about 6,100 for sans).||Exceptionally wide — even condensed is wider than same-height monospace. Overall second to Verdana (an MS font) in width. Sans-serif font is only average.|
|Covers a lot of code points and scripts.||Very dry, wide yet thin glyphs. Clearly designed with handheld devices and their small screens in mind.|
|Fairly distinctive; might appeal to people who like narrow fonts.||Serif only. As with other SIL fonts, the hinting is questionable.|
|Used in Ubuntu (obviously). A distinctive font family with a style which might not appeal to everyone. Overall looks good and covers a fair number of code points.||Only the sans-serif font is truly polished; narrow and monospaced versions are unfinished. No known serif font that would accompany it well.|
|Metric compatible with popular Adobe fonts (among others?).||Seem to require slight hinting.|
|MS TrueType corefonts
|Includes most fonts used in documents and on the web.||MS does not distribute them nowadays, so the available fonts are from many years ago and do not reflect their current state (not to mention the state of the art). Obviously, lacks fonts introduced more recently. Require full hinting.|
|Covers a lot of code points.||In addition to being ugly as sin, it also fails some basic requirements to be considered a typeface. Is it sans-serif? Is it serif? Please never use this.|