Difference between revisions of "X Logical Font Description"
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Revision as of 12:10, 20 January 2013
Two different font systems are used by X11: the older or core X Logical Font Description, XLFD, and the newer X FreeType, Xft, systems. XLFD was originally designed for bitmap fonts and support for scalable fonts (Type1, TrueType and OpenType) was added later. XLFD does not support anti‑aliasing and sub‑pixel rasterization. Xft uses the FreeType and Fontconfig libraries and is more suitable when the smooth appearance of fonts is desired. A guide for using Fontconfig and Xft may be found at Font Configuration.
Font names are complex when using XLFD:
The name contains fourteen elements, with each element field preceded by a hyphen,
-. Not all elements are required to be present in a font name and a field may be empty. Names can be simplified for the user by the wildcards
?. On the command line, surround the font name with quotes to prevent the shell from interpreting the wildcards and to avoid backslashing whitespace.
$ xterm -fn "-*-fixed-medium-r-s*--12-87-*-*-*-*-iso10???-1" $ xterm -fn "-*-dejavu sans mono-medium-r-normal--*-80-*-*-*-*-iso10646-1"
Names can be simplified even more by using aliases:
$ xterm -fn 12x24
Two nearly indispensible utilities for working with XLFD names are xfontsel,, and xlsfonts, . Xfontsel uses dropdown menus for selecting parts of a font name and previews the font selected. Xlsfonts can list fonts by name, with selectable degrees of detail, and can show how wildcards and aliases will be interpreted by the XLFD system. If a fontname is not working, check for a match with xlsfonts.
$ xlsfonts -fn "*-fixed-medium-r-n*--13-120-75-*-iso1*-1" $ xlsfonts -ll -fn fixed
Font name elements
The following table provides a description of the font name fields. The elements are listed in the same order as they appear in a font name. The names used by xfontsel are listed below the longer uppercase names.
|The supplier of the font.
Specify this field when two different fonts share the same FAMILY_NAME, for example,
|The typeface name, defined by the foundry. Usually, fonts with the same family name are visually similar.|
|The degree of blackness of the glyphs, defined by the foundry. Common values are |
|Common values are |
Usually this needs to be specified.
|Values are set by the designer, examples are |
A value should be set, not wildcarded, when there are two or more possible values.
|Often an empty field, but values may be supplied by the foundry.
In xfontsel, an empty field is chosen by selecting
|The body size of a font for a particular POINT_SIZE and RESOLUTION_Y. Changes the height of a font independent of the point size for which the font was designed.
|The body heighth for which the font was designed. Values are expressed as tenths of a point (one point is nominally one seventy-secondth of an inch).
See Font sizes.
|The horizontal resolution as an integer-string for which the font was designed. The values are expressed as pixels or dpi.
For scalable fonts this may safely be set to zero or
|The vertical dpi for which the font was designed.
Similar to RESOLUTION_X, scalable fonts can have this value set to zero or
|Arithmetic mean of the widths of all glyphs. Zero is used for proportional fonts.
It is safe to wildcard this value with *.
|Always paired with the next field, this names the registration authority for the character encoding used. Examples are |
It's always safe to choose an available registry that is compatible with the user's locale settings.
|An identifier for the character set encoding.|
Font names are stored in the fonts.dir file in each font directory. For more information about these files, see The Font Search Path below. In a font name, the pixel and point sizes, and the x and y resolution values, may be changed and the changes will affect a font's displayed size and also the spacing between characters and between lines.
As a general rule, bitmap fonts have their best appearance at the sizes the designers specified. For these fonts, changing the size-related values from those stored in the font names may give unexpected or ugly distortions or an unmatchable font pattern.
Scalable fonts were designed to be resized. A scalable font name, as shown in the example below, has zeroes in the pixel and point size fields, the two resolution fields, and the average width field.
To specify a scalable font at a particular size you only need to provide a value for the POINT_SIZE field, the other size related values can remain at zero. As an example, the following line specifies Liberation Serif at 9 points.
The Font Search Path
Please see Fonts for a guide to installing font files and modifying the font path. For a font to be available to the X server, the directory containing the font file must be on the user's font path. You can check your current font path with:
$ xset q
When a font is requested, the X server searches the font directories in the order given in the font path. Each font directory will contain a file named fonts.dir that serves as an index connecting a font's XLFD name to the file containing the font. The search ends when the first matching font is found.
The first line in a fonts.dir file is the number of fonts listed in the file. The following lines then list the fonts in that directory: filename first, followed by a single space, and finally the font name. Below are the first four lines of an example fonts.dir:
1894 UTBI__10-ISO8859-1.pcf.gz -adobe-utopia-bold-i-normal--14-100-100-100-p-78-iso8859-1 UTBI__10-ISO8859-10.pcf.gz -adobe-utopia-bold-i-normal--14-100-100-100-p-78-iso8859-10 UTBI__10-ISO8859-13.pcf.gz -adobe-utopia-bold-i-normal--14-100-100-100-p-78-iso8859-13
mkfontscale and mkfontdir
To create a fonts.dir file, two programs are required,
mkfontdir. These programs were probably installed when you installed Xorg. Mkfontdir reads all the bitmap font files in a directory for the font names, and creates the fonts.dir file using the font and file names it has found. It also adds the entries from a file named fonts.scale.
Because mkfontdir cannot read scalable font files, the program mkfontscale is used to create the names for TrueType, OpenType and Type1 fonts. The font names and font filenames are stored in the file named fonts.scale. The structure of a fonts.scale file is identical to a fonts.dir file. The first line is the number of font names listed; the following lines contain the filename first, followed by a single space, and finally the font name.
Both fonts.scale and fonts.dir can be hand edited. However, every time mkfontscale or mkfontdir is run, any existing fonts.scale or fonts.dir is overwritten. Your edits are easily lost.
Any time mkfontdir is run, the font database should be updated, using the command:
$ xset fp rehash
Using aliases can greatly simplify the use of XLFD names. Aliases are stored in files named fonts.alias in the directories along the font path.
The packageprovides some common aliases that have become standard on X servers. This package provides a fonts.alias file for fonts in the directories 100dpi, 75dpi, cyrillic, and misc. Some applications depend on these standard aliases: the default font for xterm is coded to use the font matched by the alias "fixed". Changing these standardized aliases is not recommended, particularly for multi-user machines.
You can add aliases to your system by writing your own 'fonts.alias' file or by adding to an existing one. The format is simple. Comments are restricted to lines beginning with an exclamation point,
!. Blank lines are ignored. Each alias is defined on a single line. First is the alias name, followed by any amount of whitespace, and finally the font name or the alias name to be matched (an alias may refer to another alias). If an alias name or a font name includes spaces, that name must be enclosed within quotes. Here is a constructed example:
! This is a comment. djvsm9 "-misc-dejavu sans mono-medium-r-normal--0-90-0-0-m-0-iso10646-1" djvsm8 "-misc-dejavu sans mono-medium-r-normal--0-80-0-0-m-0-iso10646-1" "djvsm 8" djvsm8
The location of the fonts.alias file may be in any directory on the font path. The fonts referred to by the alias may also be in any directory along the font path; the fonts do not have to be in the same directory as the fonts.alias file.