Re: Font priorities

[Eric Mader <mader jtcsv com>]

At 08:14 PM 2/4/2003, Owen Taylor wrote:
> On Tue, 2003-02-04 at 22:27, Keith Packard wrote:
> > Around 21 o'clock on Feb 4, Owen Taylor wrote:
> >
> > > The thing is, fontconfig, when deciding between Raghindi and
> > > FreeSans for Hindi, says: FreeSans covers the current language,
> > > English, and Raghindi doesn't, lets' use FreeSans, even though
> > > Raghindi is part of the Sans alias, and FreeSans isn't.
> >
> > Fontconfig uses language to order font preferences; there's no other sane
> > way to choose between two otherwise similar fonts.  If Raghindi doesn't
> > support $LANG, then your application better let fontconfig know what
> > language you are interested in.
>
> Well, there are two problems:
>
>  Acute: fontconfig is picking fonts that don't have the right
>   OpenType tables.
>
>  Chronic: There is no reliable way for the user to specify
>   preferences as to what fallback fonts they prefer. Once
>   you get a fallback, you get the fallback that best matches
>   the current language tag, even if that font is the ugliest
>   font on the system.
>
> I think both need to be addressed.
>
> > > I've been somewhat unable to convince Keith there actually is
> > > a problem here, though I consider this a fairly major flaw
> > > of the fontconfig scheme.
> >
> > I think one issue here is only that pango wants OT tables and Fontconfig
> > doesn't provide a mechanism for selecting fonts based on that support.  We
> > could easily add that.
>
> Yeah ... I think for Pango's needs, a fontconfig key that was all
> the tables in the TrueType file would probably be sufficient.
> Generally, "Covers Hindi codepoints and has a GSUB table" is
> sufficient information. Unless for FreeFont they start adding
> the OpenType tables piecemeal, and have the tables for Arabic
> but not the tables for Hindi...

In the ICU LayoutEngine I go one step further: if the font has a GSUB 
table, I also check to see if the GSUB table contains an entry for the 
script. I can provide you with some sample code to do this; I suspect that 
most of it is already in FreeType...

Regards,
Eric