The old hb-ot-tag.cc functions, `hb_ot_tags_from_script` and
`hb_ot_tag_from_language`, are now wrappers around a new function:
`hb_ot_tags`. It converts a script and a language to arrays of script
tags and language tags. This will make it easier to add new script tags
to scripts, like 'dev3'. It also allows for language fallback chains;
nothing produces more than one language yet though.
Where the old functions return the default tags 'DFLT' and 'dflt',
`hb_ot_tags` returns an empty array. The caller is responsible for
using the default tag in that case.
The new function also adds a new private use subtag syntax for script
overrides: "x-hbscabcd" requests a script tag of 'abcd'.
The old hb-ot-layout.cc functions,`hb_ot_layout_table_choose_script` and
`hb_ot_layout_script_find_language` are now wrappers around the new
functions `hb_ot_layout_table_select_script` and
`hb_ot_layout_script_select_language`. They are essentially the same as
the old ones plus a tag count parameter.
Closes#495.
`hb_language_from_string` accepts not only ISO 639 but also BCP 47. Not
all ISO 639 codes are valid BCP 47 tags but the function does not accept
overlong language subtags anyway.
Tested using Kannada MN:
$ HB_OPTIONS=aat ./hb-shape Kannada\ MN.ttc -u 0C95,0CCd,C95,CCD
[kn_ka.virama=0+1299|kn_ka.vattu=0+115|_blank=0@-115,0+385]
$ HB_OPTIONS=aat ./hb-shape Kannada\ MN.ttc -u 0C95,0CCd,C95,CCD --features=-kern
[kn_ka.virama=0+1799|kn_ka.vattu=0+230|_blank=0+0]
I don't see the GPOS table in the font do the same. ¯\_(ツ)_/¯
Tested that Format0 works with Kannada MN font:
$ make -j5 lib -s && HB_OPTIONS=aat ./hb-shape Kannada\ MN.ttc -u 0C95,0CC2
[kn_ka=0+1000|kn_matra_uu=0@-30,0+1345]
$ make -j5 lib -s && HB_OPTIONS=aat ./hb-shape Kannada\ MN.ttc -u 0C95,0CC2 --features=-kern
[kn_ka=0+1030|kn_matra_uu=0+1375]
Note that GPOS does the same with 'dist' feature, and applies the whole difference to the
same glyph:
$ make -j5 lib -s && ./hb-shape Kannada\ MN.ttc -u 0C95,0CC2
[kn_ka=0+970|kn_matra_uu=0+1375]
$ make -j5 lib -s && ./hb-shape Kannada\ MN.ttc -u 0C95,0CC2 --features=-dist
[kn_ka=0+1030|kn_matra_uu=0+1375]
David Corbett
Behdad Esfahbod