[Fontconfig] Request for implementing font substitution for CJK fonts

[BlissSam]

Sorry for the delay of this mail. For I am busy these couple of days.

So let us provide a tool to generate fallback rules instead of making user write XML conf on their own from scratch.
Also it can generate some other things useful (e.g. preference, anti-alias and so on).

And I think the current syntax of fallback rules is so complicated that I cannot understand--Mapping specific to generic, and map generic to specific, and other stuff. I don't know if what I said right, but I want this mechanism to be simpler.
Simply allow a method of `bind' some font families together and tell fontconfig that these fonts are `compatible', so fontconfig will choose other fonts if one is missing.

And the font substitution can be more smart, user can specify whether only to fallback when a font is missing, or to replace whenever that font is installed; also, some users may want to substitute only on screen or when printing.

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> Date: Tue, 5 Jun 2012 09:25:39 +0200
> Subject: Re: [Fontconfig] Request for implementing font substitution for CJK fonts
> From: nicolas.mailhot at laposte.net
> To: m13253 at hotmail.com
> CC: akira at tagoh.org; fontconfig at lists.freedesktop.org
>
> Hi,
>
> What we do in Fedora is shipping fallback rules with the font themselves in
> the same package so if font foo is installed the package also declares to
> fontconfig it's an acceptable substitute for bar, but if the user didn't
> install foo the system does not waste time processing rules for fonts which
> are not available.
>
> And BTW it's very dangerous to declare a substitution rule for a popular font,
> because your substitution font will then be used in lots of contexts and if
> it's not as good (design or coverage-wise) as the original font users won't be
> happy at all.
>
> --
> Nicolas Mailhot
>