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[GSUB] Don't set new lig_id on mark ligatures 

If two marks form a ligature, retain their previous lig_id, such that
the mark ligature can attach to ligature components...

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=676343

In fact, I noticed that we should not let ligatures form between glyphs
coming from different components of a previous ligature.  For example,
if the sequence is: LAM,SHADDA,LAM,FATHA,HEH, the LAM,LAM,HEH form a
ligature, putting SHADDA and FATHA next to eachother.  However, it would
be wrong to ligate them.  Uniscribe has this bug also.
This commit is contained in:
Behdad Esfahbod 2012-07-29 20:37:38 -04:00
parent 97a201becf
commit cb3d340631
1 changed files with 14 additions and 4 deletions
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18
src/hb-ot-layout-gsub-table.hh
View File

@ -499,11 +499,20 @@ struct Ligature
if (likely (c->buffer->info[skippy_iter.idx].codepoint != component[i])) return TRACE_RETURN (false);
}
unsigned int klass = first_was_mark && found_non_mark ? HB_OT_LAYOUT_GLYPH_CLASS_LIGATURE : 0;
bool is_a_mark_ligature = first_was_mark && !found_non_mark;
unsigned int klass = is_a_mark_ligature ? 0 : HB_OT_LAYOUT_GLYPH_CLASS_LIGATURE;
/* If it's a mark ligature, we should leave the lig_id / lig_comp alone such that
* the resulting mark ligature has the opportunity to attach to ligature components
* of it's base later on. See for example:
* https://bugzilla.gnome.org/show_bug.cgi?id=676343
*/
/* Allocate new ligature id */
unsigned int lig_id = allocate_lig_id (c->buffer);
set_lig_props (c->buffer->cur(), lig_id, 0);
unsigned int lig_id = is_a_mark_ligature ? 0 : allocate_lig_id (c->buffer);
if (!is_a_mark_ligature)
set_lig_props (c->buffer->cur(), lig_id, 0);
if (skippy_iter.idx < c->buffer->idx + count) /* No input glyphs skipped */
{
@ -526,7 +535,8 @@ struct Ligature
{
while (c->should_mark_skip_current_glyph ())
{
set_lig_props (c->buffer->cur(), lig_id, i);
if (!is_a_mark_ligature)
set_lig_props (c->buffer->cur(), lig_id, i);
c->buffer->next_glyph ();
}