[Devel] auto-hinter - separate "rules" from lib

[Vadim Plessky]

I know that David Turner was planning rewrite of FT2 auto-hinter module, but 
not aware of it's status.
Some ideas came to my mind rethinking once more hinting process and typical 
font usage (at least for languages I can speak/write)

What about to separate auto-hinter *rules* from FreeType lib/modules (and 
make it just another module or script in some pseudo-language)?
 Advantages:
* auto-hinter module can be updated more often than FreeType itself
* it's possible to make automatic web-based updates for rules (auto-hints), 
so it reduces TCO and provides way for faster, easy updates
* it's possible to modify rules without re-compilation of FT, which is 
clearly advantage for people who don't want (or can't) to compile FT on their 
own.

As it was already pointed out on FT mailing list, PostScript Type1 hints are 
in general more easy to understand than TrueType hints, and it's easier to 
hint PS T1 fonts than TT.
Speaking in terminology of programming languages, PS T1 hints are 
declarative, while TT is procedural.
(from other side, we can think of PS T1 as C language, while TT really 
reminds me pure assembler)
So, it makes sense IMO to make such external "rules" in pseudo-PostScript 
style.
hstem, vstem, hstem3, vstem3 PS hints look quite natural to me, we just need 
some mechanism to *measure* extremes (and, may be, to add character 
"semantics"  and map results like 
if ( condA ) 
 { apply hstem3  to ... }
else
 if (cond B)
   { apply hstem to p1, L1; and hstem to p2, L2  }

Probably, hstem3 and vstem3 hints are not very often used in latin-based 
fonts, but they are very common for many Cyrillic glyphs.
So I would like to improove auto-hinting for these characters/glyphs, writing 
specific routines in this pseudo-language.
After manual hinting of several fonts, I found that I am acting like 
computer, doing mechanical work. So, there is clearly a way to improove this 
part :-))

Any ideas, thoughts on auto-hinter "rules" and how (if) it can be implemented?
 Any feedback from you is highly appreciated. 
-- 

Vadim Plessky
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