Re: Font lookup ranges [was Re: Notes on Pango Xft backend]

[Owen Taylor <otaylor redhat com>]

Yao Zhang <yaoz vidar niaaa nih gov> writes:

> >From keithp keithp com Thu May 30 13:28:11 2002
> 
> > Around 12 o'clock on May 30, Yao Zhang wrote:
> 
> > > From your coverage map, it is easy to tell which category the font is in.
> > > But in my opinion, combining different Chinese fonts together to get
> > > a bigger coverage is generally not a good idea.
> 
> > It's good to know we can intuit the language tag from the Unicode coverage,
> > that will make using Type1 fonts (and others without OS/2 tables) easier.
> 
> I am still trying to understand what a language tag is.  If for a font,
> it means the font is designed for one region, then we can say category
> #1 and 2 is for zh_CN (mainland China) and probably zh_SG (Singapore), #3
> is for zh_TW (Taiwan), zh_HK (Hong Kong) and zh_MO (Macau). I am not sure
> about #4 and 5.  A font in category 4 or 5 could be for any of the above,
> and even ja_JP or ko_KR?

I think Keith's use of the term "language tag" to refer to how fonts
are tagged is a little bit confused.; a language tag identifies the language
for the _text_. This is then used to choose a font. The "language support"
identifiers for fonts don't have to be the same thing; you can easily
have:

 zh-tw => FC_LANG_SIMPLIFIED_CHINESE
 zh-hk =>  FC_LANG_SIMPLIFIED_CHINESE
 zh-cn => FC_LANG_SIMPLIFIED_CHINESE
 zh-sg =>  FC_LANG_SIMPLIFIED_CHINESE

Unfortunately, the common form of 'language-country' of a language
tag doesn't work perfectly for traditional vs. simplified Chinese,
since there isn't a one-to-one correspondence.

Pango doesn't enforce the language-country form on language tags;
so if some other identifiers become common for representing this
distinction, support for them can be easily added.

> > The question being discussed here is not combining multiple fonts ... 
> > Pango already does this; it's pretty much a requirement if you
> > want to be able display multilingual text. (The alternative is
> > that the document creator knows exactly what fonts the user
> > has on their system and specifies those fonts.)
> 
> > The question is how to combine multiple fonts in a way that avoids
> > the "mixed" appearance that you are seeing.
> 
z> What I am trying to say is that the current implementation goes to
> far to combine different Chinese fonts together or even different CJK
> fonts together.  In my opinion, that is bad.  They could be in different
> combined font, not in one combined font.
 
I don't understand this distinction; the idea is that you specify
a single alias (say "Sans-serif") to be used for an entire document;
and you want the system to "do the right thing". Being able to
do the right thing without user intervention.

 - The user may be viewing text in a mix of languages.
 - The software doesn't expose a font configuration mechanism.

What happens when the user specifies a particular font, say
a Japanese font "Mincho Gothic", and the text contains non-supported
characters is indeed not all that important; it's a pathalogical
case, and the results aren't expected to be pretty.

Regards,
                                        Owen