Re: Font Problems

[Owen Taylor <otaylor redhat com>]

Eric Mader <mader jtcsv com> writes:

> At 11:53 AM 8/23/2002, Owen Taylor wrote:
> >You probably have a non-gzipped pcf version of clearlyu somewhere
> >in /usr/share/fonts or /etc/fonts/fonts.conf.
> >
> >Unfortunately, it's really hard to work around the problem of
> >fonts that have Arabic glyphs but no GSUB table, because fontconfig
> >works only by straight coverage, and it will have already said
> >"clearlyu has these glyphs, I don't need to add another font"
> >before Pango even gets involved at all.
> 
> It seems to me that passing the ClearlyU font to the arabic-xft shaper
> is just plain wrong. That shaper needs to be called with an OpenType
> font. We need to arrange things so that this shaper is never invoked
> with a non-OT font. Perhaps it should be given a chance to examine the
> font and say "no thanks. I can't use that font." so that another
> shaper can be invoked...

The thought of being able to do that is why shaper's have a 
get_coverage() function.

However, it doesn't do us any good for Xft, because fontconfig
pre-prunes the list of candidate fonts based on the coverage
information they report. If ClearlyU is the first arabic-supporting
font found, all other Arabic-supporting fonts will be pruned out of
the font list unless they support *additional* code points beyond
ClearlyU.

(And this is a very important performance optimization)

Regards,
                                        Owen