[Fontconfig] Regularizing contains operator semantics

[Ambrose Li]

On Fri, Jul 11, 2003 at 01:54:56PM -0700, Keith Packard wrote:

> The font supports all of the langs requested by the
> application.  I think this means that the font 'contains'
> all of the langs requested by the application (remember,
> we're talking about LISTING here).  Now, the tricky part of
> defining what 'support' means for a specific lang entry.  When
> the application provides a language/territory pair, then the
> font must either provide a matching language/territory pair,
> or a bare language entry.  When the application provides
> a bare language, the font must either provide a matching
> bare language entry or a language/territory pair with *any*
> territory:
> 
> 	application	font		"supports"
> 	-----------	----		----------
> 	zh		zh_cn		YES
> 	zh_tw		zh_cn		NO

This is theoretically sound. However, for practical purposes it
is wrong; fonts having incomplete coverages are generally still
useful (not in general but for particular tasks like typesetting
short pieces or even longer pieces of text). Especially with the
scarcity of free CJK fonts, it is almost a must to, for example,
use zh_CN or even ja/ko fonts for zh_TW in certain cases. (The
reverse is also true; i.e., a zh_TW and/or zh_CN font will be
useful for setting Japanese in a limited way.) In fact, there
are even commercial zh_TW fonts that cover less than half of the
Big5 code space (e.g., only the "frequently used characters"
space, i.e., 4501 code points out of the complete Big5 coverage
of 17552; because of the structure of Big5, just having 4501
of the "most frequently used" characters should at least already
make the font "support zh_TW").

With the current version of fontconfig (and gtk2), it is getting
difficult to get X applications to let me use, for example, a
Japanese font for traditional Chinese, even if the font is
perfectly fine for the task I do, because the application will
believe the fontconfig notion of "support" for my locale, and
filter out all the "unsupported" fonts.  I think it
counter-productive to put so much trust in the mechanical notion
of "complete code space coverage".


Regards,
-- 
Ambrose LI Cheuk-Wing  <a.c.li at ieee.org>

http://ada.dhs.org/~acli/