When matching lookups, be smart about default-ignorable characters.
In particular:
Do nothing specific about ZWNJ, but for the other default-ignorables:
If the lookup in question uses the ignorable character in a sequence,
then match it as we used to do. However, if the sequence match will
fail because the default-ignorable blocked it, try skipping the
ignorable character and continue.
The most immediate thing it means is that if Lam-Alef forms a ligature,
then Lam-ZWJ-Alef will do to. Finally!
One exception: when matching for GPOS, or for backtrack/lookahead of
GSUB, we ignore ZWNJ too. That's the right thing to do.
It certainly is possible to build fonts that this feature will result
in undesirable glyphs, but it's hard to think of a real-world case
that that would happen.
This *does* break Indic shaping right now, since Indic Unicode has
specific rules for what ZWJ/ZWNJ mean, and skipping ZWJ is breaking
those rules. That will be fixed in upcoming commits.
API additions:
hb_segment_properties_t
HB_SEGMENT_PROPERTIES_DEFAULT
hb_segment_properties_equal()
hb_segment_properties_hash()
hb_buffer_set_segment_properties()
hb_buffer_get_segment_properties()
hb_ot_layout_glyph_class_t
hb_shape_plan_t
hb_shape_plan_create()
hb_shape_plan_create_cached()
hb_shape_plan_get_empty()
hb_shape_plan_reference()
hb_shape_plan_destroy()
hb_shape_plan_set_user_data()
hb_shape_plan_get_user_data()
hb_shape_plan_execute()
hb_ot_shape_plan_collect_lookups()
API changes:
Rename hb_ot_layout_feature_get_lookup_indexes() to
hb_ot_layout_feature_get_lookups().
New header file:
hb-shape-plan.h
And a bunch of prototyped but not implemented stuff. Coming soon.
(Tests fail because of the prototypes right now.)
That's really the logic desired. Except that MONGOLIAN VOWEL SEPARATOR
is not default_ignorable but it really should be. Reported to Unicode.
Based on suggestion from Konstantin Ritt.
Also remove shaper_options argument to hb_shape_full(). That was
unused and for "future". Let it go.
More shaper API coming in preparation for plan/planned API.
As reported by Khaled on the list:
"After the introduction of canonical reordering of combining marks
(commit 34c22f8), I'm no longer able to do mark/mark substitution or
positioning for mark sequences that involve shadda as a first mark (or
most interesting sequences at least).
"After some digging, it turned out that shadda have a ccc=33 while most
Arabic marks that combine with it have a lower ccc value, which results
in the shadda being reordered after the other mark which,
unsurprisingly, breaks my contextual substitution and mkmk anchors."
See:
http://unicode.org/faq/normalization.html#8http://unicode.org/faq/normalization.html#9
Nothing functional in there yet.
So far, we're parsing IndicSyllabicCategory.txt and IndicMatraCategory.txt
fils from Unicode Character Database and store them in an array to be used
by the shaper. Also hooked up the shaper, but it does not do anything
right now.
Behdad Esfahbod