[Bug 151122] Need way to avoid selecting fonts which don't cover the relevant language Unicode range

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=151122

--- Comment #33 from Eyal Rozenberg <eyalroz1 at gmx.com> ---
(In reply to V Stuart Foote from comment #32)
> Then let users make active selection(s)

While that may be an additional, secondary, possibility for advanced users to
play with - we need a decent default mechanism, without the user having made
any changes. Remember most users aren't proficient enough to play with Unicode
ranges for definitions of what to filter.

To be honest, there is a fine point here I/we have not considered so far, which
is that range coverage is not a binary thing. For example, suppose a font
contains all the Hebrew letters, but no diacritics; it can still be used for
documents which don't use diacritics (and most, indeed, don't). Or - letters
and diacritics but no cantillation marks - that covers 99.9% of documents, but
still isn't full coverage. Or - coverage/non-coverage of digits - where the
fallback might be to the Western language group digits, or to some other
fallback font. And I understand (thanks Jonathan) that CJK fonts never cover
_everything_ possible - and there's even an OpenType limitation of 65Ki glyphs
per font, while there are more glyphs than that to cover if you include all
traditional forms and variants.

So, we may need some higher-level configuration of what to consider as
"covering" (e.g. "Require digits Y/N", "Require diacritics Y/N") - which might
even differ among some of the languages. Alternatively, we could have leeway
for partial-coverage, with some kind of small info widget opening a pop-up with
some coverage explanation. 

... but at the very least, there's the "easy" part, which is filtering (or
marking) fonts which clearly don't cover, e.g. are missing letters or common
ideograms.


> Extend the SCD framework to implement font filtering by Unicode block
> coverage? 

Would this really impact typeface selection combo-boxes? Or - are you
suggesting to "rewire" the combo-boxes that way? Hmm... are you sure that
doesn't introduce too much of a danger of messing things up?

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