The base_font_name_list argument is a list of base font names that Xlib uses to load the fonts needed for the locale. The base font names are a comma-separated list. The string is null-terminated and is assumed to be in the Host Portable Character Encoding; otherwise, the result is implementation-dependent. White space immediately on either side of a separating comma is ignored.
Use of XLFD font names permits Xlib to obtain the fonts needed for a variety of locales from a single locale-independent base font name. The single base font name should name a family of fonts whose members are encoded in the various charsets needed by the locales of interest.
An XLFD base font name can explicitly name a charset needed for the locale. This allows the user to specify an exact font for use with a charset required by a locale, fully controlling the font selection.
If a base font name is not an XLFD name, Xlib will attempt to obtain an XLFD name from the font properties for the font. If this action is successful in obtaining an XLFD name, the XBaseFontNameListOfFontSet function will return this XLFD name instead of the client-supplied name.
Xlib uses the following algorithm to select the fonts that will be used to display text with the XFontSet.
For each font charset required by the locale, the base font name list is searched for the first appearance of one of the following cases that names a set of fonts that exist at the server:
For example, assume that a locale required the charsets:
ISO8859-1 JISX0208.1983 JISX0201.1976 GB2312-1980.0
The user could supply a base_font_name_list that explicitly specifies the charsets, ensuring that specific fonts are used if they exist. For example:
"-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-240-JISX0208.1983-0,\ -JIS-Fixed-Medium-R-Normal--26-180-100-100-C-120-JISX0201.1976-0,\ -GB-Fixed-Medium-R-Normal--26-180-100-100-C-240-GB2312-1980.0,\ -Adobe-Courier-Bold-R-Normal--25-180-75-75-M-150-ISO8859-1"
Alternatively, the user could supply a base_font_name_list that omits the charsets, letting Xlib select font charsets required for the locale. For example:
"-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-240,\ -JIS-Fixed-Medium-R-Normal--26-180-100-100-C-120,\ -GB-Fixed-Medium-R-Normal--26-180-100-100-C-240,\ -Adobe-Courier-Bold-R-Normal--25-180-100-100-M-150"
Alternatively, the user could simply supply a single base font name that allows Xlib to select from all available fonts that meet certain minimum XLFD property requirements. For example:
If XCreateFontSet is unable to create the font set, either because there is insufficient memory or because the current locale is not supported, XCreateFontSet returns NULL, missing_charset_list_return is set to NULL, and missing_charset_count_return is set to zero. If fonts exist for all of the charsets required by the current locale, XCreateFontSet returns a valid XFontSet, missing_charset_list_return is set to NULL, and missing_charset_count_return is set to zero.
If no font exists for one or more of the required charsets, XCreateFontSet sets missing_charset_list_return to a list of one or more null-terminated charset names for which no font exists and sets missing_charset_count_return to the number of missing fonts. The charsets are from the list of the required charsets for the encoding of the locale and do not include any charsets to which Xlib may be able to remap a required charset.
If no font exists for any of the required charsets or if the locale definition in Xlib requires that a font exist for a particular charset and a font is not found for that charset, XCreateFontSet returns NULL. Otherwise, XCreateFontSet returns a valid XFontSet to font_set.
When an Xmb/wc drawing or measuring function is called with an XFontSet that has missing charsets, some characters in the locale will not be drawable. If def_string_return is non-NULL, XCreateFontSet returns a pointer to a string that represents the glyphs that are drawn with this XFontSet when the charsets of the available fonts do not include all font glyphs required to draw a codepoint. The string does not necessarily consist of valid characters in the current locale and is not necessarily drawn with the fonts loaded for the font set, but the client can draw and measure the default glyphs by including this string in a string being drawn or measured with the XFontSet.
If the string returned to def_string_return is the empty string (""), no glyphs are drawn, and the escapement is zero. The returned string is null-terminated. It is owned by Xlib and should not be modified or freed by the client. It will be freed by a call to XFreeFontSet with the associated XFontSet. Until freed, its contents will not be modified by Xlib.
The client is responsible for constructing an error message from the missing charset and default string information and may choose to continue operation in the case that some fonts did not exist.
The returned XFontSet and missing charset list should be freed with XFreeFontSet and XFreeStringList, respectively. The client-supplied base_font_name_list may be freed by the client after calling XCreateFontSet.