[Fontconfig] Exposing match level

[Raimund Steger]

On 05/08/15 20:29, Behdad Esfahbod wrote:
> Hi all,
>
> I'm sure most of you who have been around know that it's been a very common
> request to want to know whether fontconfig found a match for a request or just
> fallbacks.  I've been thinking about this a lot recently, and like to make
> sure we fix it this time.

This sounds interesting. The recent discussion about LilyPond reminded 
me that while fontconfig does have FcFontList(3) and FcFontSetList(3) to 
query fonts without any scoring at all,

(1) this is normally not exposed by higher-level libraries;

(2) this doesn't sort regular variants near the top (obviously), so 
FcFontMatch(3) has to be called at some point anyway;

hence improving FcFontMatch(3) and FcFontSort(3) might indeed be worthwhile.

At the moment, whether a configuration rule uses prepend_first v. 
prepend v. append v. append_last might carry a meaning of 'approximate' 
v. 'fallback' when a human reader examines the config, but not to the 
matching engine where everything is only a position in the property 
list. The 'fallback' boundary somewhere in that list is one purely of 
convention.

As long as the original documented purpose of the binding value in terms 
of fonts-conf(5) (that 'lang' could overrule 'family' in the match if 
the user explicitly stated the former, i. e. one of prioritizing 
property A over property B) is kept unchanged I think yes, it is 
possible to factor that meaning into the value.
To state it more explicitly, it is probably not a good idea to introduce 
strong family bindings into a pattern that didn't originally have them, 
by means of alias rules, only because we now think of binding as "how 
close is family A to family B". Such alias rules, where they specify 
binding="same" now, could only specify something like "same-or-lower" in 
the future -- correct me if I'm wrong.

-Raimund



-- 
Worringer Str 31 Duesseldorf 40211 DE  home: <rs at mytum.de>
+49-179-2981632 icq 16845346           work: <rs at interface-ag.de>