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[arabic] Do the joiner-flipping only for rlig feature 

See comment.
This commit is contained in:
Behdad Esfahbod 2018-09-26 18:42:37 -04:00
parent 7f30629cdd
commit 662f7d7e8b
1 changed files with 19 additions and 5 deletions
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24
src/hb-ot-shape-complex-arabic.cc
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@ -159,7 +159,7 @@ static const struct arabic_state_table_entry {
static void
nuke_joiners (const hb_ot_shape_plan_t *plan,
flip_joiners (const hb_ot_shape_plan_t *plan,
hb_font_t *font,
hb_buffer_t *buffer);
@ -200,7 +200,6 @@ collect_features_arabic (hb_ot_shape_planner_t *plan)
* work correctly. See https://github.com/harfbuzz/harfbuzz/issues/505
*/
map->add_gsub_pause (nuke_joiners);
map->enable_feature (HB_TAG('s','t','c','h'));
map->add_gsub_pause (record_stch);
@ -217,14 +216,29 @@ collect_features_arabic (hb_ot_shape_planner_t *plan)
map->add_gsub_pause (nullptr);
}
/* Normally, Unicode says a ZWNJ means "don't ligate". In Arabic script
* however, it says a ZWJ should also mean "don't ligate". So we convert
* a ZWJ to a ZWNJ for GSUB. We want to revert it back to ZWJ before
* GPOS processing though. So we just flip their roles, and flip back
* later. Note that this makes a ZWNJ into ZWJ for GSUB stage, which
* means it would *not* break ligatures. But since ligatures around
* ZWNJ are rare, we don't care.
*
* Since we don't currently have a way to apply a pause before GPOS
* starts, let's just do this dance around a few required GUSB features. */
map->add_gsub_pause (flip_joiners);
map->add_feature (HB_TAG('r','l','i','g'), F_GLOBAL | F_HAS_FALLBACK);
if (plan->props.script == HB_SCRIPT_ARABIC)
map->add_gsub_pause (arabic_fallback_shape);
/* No pause after rclt. See 98460779bae19e4d64d29461ff154b3527bf8420. */
map->enable_feature (HB_TAG('r','c','l','t'));
map->enable_feature (HB_TAG('c','a','l','t'));
map->add_gsub_pause (nullptr);
/* And undo here. */
map->add_gsub_pause (flip_joiners);
/* The spec includes 'cswh'. Earlier versions of Windows
* used to enable this by default, but testing suggests
@ -381,14 +395,14 @@ setup_masks_arabic (const hb_ot_shape_plan_t *plan,
static void
nuke_joiners (const hb_ot_shape_plan_t *plan HB_UNUSED,
flip_joiners (const hb_ot_shape_plan_t *plan HB_UNUSED,
hb_font_t *font HB_UNUSED,
hb_buffer_t *buffer)
{
unsigned int count = buffer->len;
hb_glyph_info_t *info = buffer->info;
for (unsigned int i = 0; i < count; i++)
if (_hb_glyph_info_is_zwj (&info[i]))
if (_hb_glyph_info_is_joiner (&info[i]))
_hb_glyph_info_flip_joiners (&info[i]);
}