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When rendering text in an X Windows
TM client, at least two aspects are sensitive
to internationalization: Obtaining the
localized text itself Selecting the one or more fonts that contain all
the glyphs needed to render the characters in the localized text.
“Extracting
Localized Text”
describes how to choose the correct fonts to render localized text. Matching Fonts to Character
Sets | |
A font contains a set of glyphs
used to render the characters of a locale. However, you may also want to
do the following for a given locale: Determine the fonts
needed Specify the necessary fonts Determine the charset of a font in a resource file Choose multiple fonts per locale
The last two fields of a font XFLD identify which glyphs are contained in a font
and which value is used to obtain a specific glyph from the set.
These last two fields identify the encoding of the glyphs contained
in the font. For example: -adobe-courier-medium-r-normal24-240-75-75-m-150-iso8859-1 |
The last two fields of this
XLFD name are iso8859
and 1. These
fields specify that the ISO8859-1 standard glyphs are contained
in the font. Further, it specifies that the character code values of the
ISO8859-1 standard are used to index the corresponding glyph for
each character. The font charset used by the application to render data depends
on the locale you select. Because the font charset of the data changes
is based on the choice of locale, the font specification must not
be hardcoded by the application. Instead, it should be placed in
an app-defaults
file, allowing localized versions of the
app-defaults
file to be created. Further, the font should be specified as a fontset. A fontset
is an Xlib concept in which an XLFD is used to specify the fonts.
The font charset fields of the XLFD are specified by the Xlib code
that creates the fontset and fills in these fields based on the
locale that the user has specified. For many languages (such as Japanese, Chinese, and Korean),
multiple font charsets are combined to support single encoding.
In these cases, multiple fonts must be opened to render the character
data. Further, the data must be parsed into segments that correspond
to each font, and in some cases, these segments must be transformed
to convert the character values into glyphs indexes. The XFontset,
which is a collection of all fonts necessary to render character
data in a given locale, also deals with this set of problems. Further,
a set of rendering and metric routines are provided that internally
take care of breaking strings into character-set-consistent segments
and transforming values into glyph indexes. These routines relieve
the burden of the application developer, who needs only the user
fontsets and the Xlib rendering and metric application program interfaces
(APIs). For more information on matching fonts to character sets,
refer to DtStdInterfaceFontNames(1,5). Also note
that if your CDE provides the set of Standard Application Font Names,
you can use a locale-independent resource. Font Objects | |
This section describes the following font objects: Generally, all internationalized programs expecting to draw
localized text using Xlib are required to use an XmFontSet
for specifying the locale- dependent fonts. Specific fonts within
a font set should be specified using XLFD naming conventions without
the charset field specified. The resource name for an XFontset
is *fontSet.
Refer to “Localized
Resources”
for a list of font resources. Applications directly using Xlib to render text (as opposed
to using XmString
functions or widgets) may take advantage of the string-to-fontSet
converter provided by Xt. For example, the following code fragment
shows how to obtain a fontset when using Xt and when not using Xt: /* pardon the double negative... means "If using Xt..." */
#ifndef NO_XT
typedef struct {
XFontSet fontset;
char *foo;
} ApplicationData, *ApplicationDataPtr;
static XtResource my_resources[] = {
{ XtNfontSet, XtCFontSet, XtRFontSet, sizeof (XFontSet),
XtOffset (ApplicationDataPtr, fontset), XtRString,
"*-18-*"}}
#endif /* NO_XT */
...
#ifdef NO_XT
fontset = XCreateFontSet (dpy, "*-18-*", &missing_charsets,
&num_missing_charsets. &default_string);
if (num_missing_charsets > 0) {
(void) fprintf(stderr, "&s: missing charsets.\n",
program_name);
XFreeStringList(missing_charsets);
}
#else
XtGetApplicationResources(toplevel, &data, my_resources,
XtNumber(my_resources), NULL, 0);
fontset = data.fontset;
#endif /* NO_XT */ |
Internationalized programs should avoid
using fonts directly, that is, XFontStruct,
unless they are being used for a specific charset and a specific
character set. Use of XFontStruct
may be limiting if the server you are connecting to does not support
the specific charsets needed by a locale. The resource name for
an XFontStruct
is *font. For information on render tables, refer to Motif
Programmer's Guide. Font Set and Render Table Syntax | |
Table 2-1 “Font Set and Render
Table Syntax” shows
the syntax for a font set and render table. Table 2-1 Font Set and Render
Table Syntax Resource Type | XLFD Separator | Terminator | FontEntry
Separator |
|---|
*fontSet:
(Xlib) | comma | None | None | *renderTable:
(Motif) | semicolon | colon | comma |
Here are some examples of font resource specifications: app_foo*renderTable: -adobe-courier-medium-r-normal24-240-75-75-m-\
150-*: |
The preceding renderTable specifies a fontset, consisting
of one or more 24-point Adobe Courier fonts, as appropriate for
the user's locale. app_foo*renderTable: -adobe-courier-medium-r-normal18-*; *-gothic-\
*-18-*: |
This renderTable specifies a fontset consisting of an 18-point
Courier font (if available) for some characters in the users data,
and an 18-point Gothic font for the others. Font
and Render Table Functions | |
The following Xlib font management API functions are available: XBaseFontNameListOfFontSet()
The following Motif Render Table API functions are available: XmRenderTableAddRenditions() XmRenderTableCvtFromProp() XmRenderTableGetRendition() XmRenderTableGetRenditions() XmRenderTableRemoveRenditions()
Font Charsets | |
To improve basic interchange,
fonts are organized according to the standard X- Consortium font
charsets. Default
Font Set Per Language Group | |
Selecting base font names of a font set associated with a
developer's language is usually easy because the developer is familiar
with the language and the set of fonts needed. Yet, when selecting the base font names of a font set for
various locales, this task can be difficult because an XLFD font
specification consists of 15 fields. For localized usage, the following
fields are critical for selecting font sets: This simplifies the number of fields, yet the possible values
for each of these fields may vary per locale. The actual point size
(POINT_SIZE) may vary across platforms. Throughout this documentation, the following convention should
be used when specifying localized fonts: -dt-%F- %W-%S-normal- %A-*-*-*-%SP-* |
The following describes the minimum
set of recommended values for each field to be used within the desktop
for the critical fields when specifying font sets in resource (app-defaults)
files. The same values defined for ISO8859-1 are recommended. CNS Traditional Chinese FontGB Simplified Chinese Font |
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