Fontconfig

The fontconfig library is intended to provide uniform font selection and configuration amongst all GUI applications. Even though it is common for various desktop environments to provide their own font overrides and configuration, fontconfig is still the underlying library.

Generic
fontconfig uses XML files in the directory to generate its internal configuration. By default it parses (users should not edit this file!) which sets some sane defaults and usually contains code to also parse  content. In addition there is the directory that contains various possible configuration files that each cover some aspect of fontconfig. It's customary to symlink necessary files to. 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 specific
Gentoo ships an eselect module (eselect fontconfig) that does exactly what was described in generic way - it manages symlinks of files in by adding or removing them from the  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.

Enabling a file
Files can be enabled either by filename or by the number in brackets. These two do the same thing:

Disabling a file
Files can be disabled likewise:

Custom system wide configuration
To create a custom, system-wide fontconfig file, enable and create  (this is an XML file).

Per-user configuration
To create per-user fontconfig files, enable (which might be enabled by default), and have the end users use  (which has the same XML format as ).

Checking configuration
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.

Forcing hinting
The default fontconfig behavior regarding hinting is rather undocumented, but it can be made deterministically sub-optimal by making a system wide default.


 * 1) First enable
 * 2) Edit the  file to include full hinting by default

This snippet enables full hinting:

Using sub-pixel rendering
It's important to determine the sub-pixel layout of the LCD matrix. It's usually RGB 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 file.

It's strongly advised that lcdfilter, if available, is used with sub-pixel rendering. It comes in different varieties but the default should be appropriate for all common fonts.

Regarding autohinter
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.

Infinality
Infinality is a somewhat controversial set of patches for FreeType and accompanying fontconfig files. The goal of Infinality is to provide higher quality font rendering including emulation of other OS font rendering styles. It's at best of beta quality but newer FreeType ebuilds have a USE flag for enabling Infinality. It should be kept in mind that some fonts can be rendered worse than with vanilla FreeType and furthermore Infinality is known for making applications crash under certain conditions.

Enabling Infinality
Enable the 'infinality' USE flag by editing either manually or by using euse tool.

Next, rebuild the affected programs.

Unless messages shown after rebuild tell otherwise, enable.

Configuring Infinality
Infinality can be configured in various ways including custom configurations but easiest is to use pre-made profiles shipped in that along with eselect modules should have been installed as dependencies of the   USE flag.

Quick and reasonable config
It's also recommended to disable all fontconfig settings except for as they interfere with the rendering of infinality styles:

Certain fontconfig settings do not interfere with how the fonts are rendered, but rather determine the default fonts for font-types (such as Monospace, sans-serif, etc.). Such settings (for example the configurations) can be left enabled.

Explanation
Infinality provides FreeType environment variables that can be used to configure features introduced with its patches as well as fontconfig files to be used with these changes. Fontconfig file sets are administrated on Gentoo via eselect infinality while the FreeType behaviour is set using eselect lcdfilter.

These eselect modules function as usual:


 * Listing available fontconfig file sets.


 * Listing available FreeType variable sets.


 * Both sets should match of course except when there are multiple matches possible such as shown below.

Picking fonts
Choosing the right font can be trickier than deciding on the right hinting type. For one reason or another fonts will not be perfect but it's certainly doable to make that same fonts look better than, say, Windows 7 default font configuration. The following information is biased of course.

External resources

 * Arch Linux Wiki on this topic - an in-depth article on Linux font configuration and font selection
 * Official fontconfig documentation for users
 * Wikipedia article on font hinting