[Fontconfig] Tutorial or guidance for using fontconfig

[Behdad Esfahbod]

Jesper L. Nielsen wrote:
> 
> Hi Behdad and list..

Hi,

> After poking around, using gprof and other things I found a reason for
> spending all the time in Fontconfig. I was calling
> pango_ft2_font_map_new() for every object I wanted to draw, and
> apparently this function can be reused throughout my application.
> 
> Now I'm looking at sharing the fontconfig-cache on NFS, and as each
> embedded devices share the same NFS mount, this should be simple however
> I have some questions for the format.
> 
> 1: Since the NFS mount is mounted as read/write, the first embedded
> system that boots will create the cache. Does the building of cache have
> a lock mechanism, or might this be a race condition?

It uses directory locks.  So, as long as mkdir is atomic on your NFS server
and clients, you should be fine.

> 2: It seems the fontcache leaves a file for every font used as it runs,
> and that the filenames have a hostname appended to them? If this is
> true, would it at all be possible to generate a fontconfig-cache on the
> NFS server, if the embedded system doesn't share the same hostname?
> Wouldn't this just generate a whole bunch of files for each embedded
> device?

Humm?  Got sample?  Which version?  Fontconfig creates one cache file per font
*directory*.  And only appends the architecture tag to the name.

> 3: Is the format of the cache files platform independent?

No, but the architecture tag is part of the cache file name, so it should all
work.

behdad

> Hope I can get some pointers now that I've regained my faith in
> FontConfig :)
> 
> All the best.
> Jesper
> 
> On Jan 9, 2009, at 11:06 AM, Jesper L. Nielsen wrote:
>>>
>>> Sure, building caches is slow.  The first question is why is it
>>> building the
>>> cache on each startup.
>>>
>>
>> Because it is on an embedded system and no place to save the caching
>> database after each reboot. However I can work past that using some
>> NFS trickery.
>>
>>>> I have been running sysprof and the majority of time spend while
>>>> rendering fonts seems to be in fontconfig.
>>>>
>>>> I don't know how to dump Sysprof output to text, so I've attached a
>>>> screendump.
>>>
>>> The screenshot shows nothing really.  The fontconfig functions you
>>> are showing
>>> in the shot are taking only 3% of the total time.
>>>
>>
>> True, I'll get some better numbers on the embedded system soon. But
>> the screenshot only shows a simple test program I produced to profile
>> the pango calls. So the times should be regarded as relativ, and
>> kernel time used disregarded.
>>>> So what I mean is that there a references to FcPattern, PangoFcFont and
>>>> other things defined in the Fontconfig specific source files. So taking
>>>> out just the Fontconfig part for the pangoft2.c would require some
>>>> work.
>>>
>>> pantoft2 subclasses pangofc.  So, you are pretty much talking about
>>> writing a
>>> new pango backend.  And then, the pango shapers also depend on
>>> pangofc.  So
>>> you have to modify those too.  Really, your fighting the wrong
>>> battle.  Just
>>> focus on getting fontconfig working for you.
>>>
>> I was mustering myself to write a whole new backend, but if the shaper
>> also uses FontConfig, I think I'll better give FontConfig another shot.
>>
>> Jesper
> 
>