[Fontconfig] [PATCH] Make the cache filenames determinstic

[Keith Packard]

Akira TAGOH <akira at tagoh.org> writes:

> just reminds me that there should be some options to do this but
> wasn't too much if we keep compatibility in API and conditions not to
> modify application-side. given that we revert this change and are
> going to keep API compatibility and no changes in applications, what
> we can do is probably to let fontconfig know the directory mapping
> tables through a file and read it. though they need to re-generate it
> every time if the mappings is changed every time.

Ok, so what I've written today is an extension to the config file 'dir'
element which provides a mapping value back to the underlying system
font directory. flatpaks can then use this mechanism to locate the
correct cache files by adding a 'map' attribute like this:

        <dir map="/usr/share/fonts">/run/host/fonts</dir>

If the fontconfig version supplied in the flatpak supports this
mechanism, it will re-use the host font cache. Otherwise, it will
rebuild the font cache.

Older fontconfig versions ignore the new attribute, so flatpak
configuration can always include it.

-- 
-keith
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