[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.
diff --git a/src/hb-ot-layout-gsub-table.hh b/src/hb-ot-layout-gsub-table.hh
index 03244b5..a74f707 100644
--- a/src/hb-ot-layout-gsub-table.hh
+++ b/src/hb-ot-layout-gsub-table.hh
@@ -499,11 +499,20 @@
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 @@
{
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 ();
}
