Fontsets

Fontsets

In X11R5 and X11R6, unlike previous releases of X, a string may contain characters from more than one codeset. There are several methods for determining which codeset a given character is in; which method is appropriate depends on the locale and the encoding used.

For information on installing and using fontsets with an application, refer to Chapter 5, "Working With Fonts."

Such multiple-codeset strings usually cannot be rendered using a single font. A fontset is a collection of fonts suitable for rendering all codesets represented in a locale's encoding. A fontset includes information to indicate which locale it was created in. Applications create fontsets for their own use; when a program creates a fontset, it is told which of the requested fonts are unavailable.

Example: EUC in Japanese

To render strings encoded in EUC in Japanese, an application would need fonts encoded in 8859-1, JIS X 208, and JIS X 201. The application doesn't need to know which characters in a string go with which font, since it doesn't deal with locale specifics. So it creates a fontset that is made from a list of user-specified fonts (under the assumption that the localizer has provided an appropriate list). Rendering is then done using that fontset. The locale-aware rendering system chooses the appropriate fonts for each character being rendered, from the supplied list. You can find additional information about EUC in "Asian Languages."

Specifying a Fontset

A fontset specification is just a string, enumerating XLFD names of fonts. (See X Logical Font Description Conventions, an MIT X Consortium standard, as well as "Font Names".) This string can include wild card characters. For example, a specification of 16-point "fixed" fonts might be as follows:

char *fontSetSpecString = "*fixed-medium-r-normal*150*";

Based on the fonts available, a particular server might expand this to a string such as:

-jis-fixed-medium-r-normal--16-150-75-75-c-160-jisx0208.1983-0
-sony-fixed-medium-r-normal--16-150-75-75-c-80-iso8859-1
-sony-fixed-medium-r-normal--16-150-75-75-c-80-jisx0201.1976-0

Specifying the fontset by simply enumerating the fonts is perfectly acceptable:

char *fontSetSpecString =
"-jis-fixed-medium-r-normal*150-75-75*jisx0208.1983-0,\
-sony-fixed-medium-r-normal*150-75-75*iso8859-1,\
-sony-fixed-medium-r-normal*150-75-75*jisx0201.1976-0";

A German locale would work with only the ISO font; a Japanese locale might use all three; a Chinese locale would have trouble with this fontset.

The developer should specify a default fontset suitable for the default locale. Furthermore, developers should ensure that the application accepts localized fontset specifications via resources (or message catalogs) or command line options. Localizers are responsible for providing default fontset specifications suitable for their locales.

Creating a Fontset

Creating fontsets in X is simply a matter of providing a string that names the fonts, as described above.

Example 6-6 : Creating a Fontset

XFontSet fontset;
char *base_name;  /* should get from resource */
char **missingCharsetList;
int missingCharsetCount;
char *defaultStringForMissingCharsets; 
base_name = "*fixed-medium-r*150*"; /* use resources! */ 
fontset = XCreateFontSet(display, base_name,
                       &missingCharsetList,
                       &missingCharsetCount,
                       &defaultStringForMissingCharsets);

The locale in effect at create time is bound to the fontset. Fontsets are freed with XFreeFontSet().

Using a Fontset

Fontsets are used when rendering text with X11R6 Xmb or Xwc text rendering routines. These routines are described in "Text Rendering Routines."