AFAIK, there is no API to retrieve a ligature information (if a glyph is a ligature). hb_ot_layout_get_ligature_carets() only works when a OT font supports the information. If there is an API that can retrieve, - If the glyph is a ligature, - How many caret positions it may have, that would be handy. For now, those need to be retrieved with a conjunction of other line breaking components.
Hi Hak, What do you exactly need to do? Some of that information is returned as part of shaping result in the cluster field. hb_ot_layout_get_glyph_class() is also close. But as you noted, again, this depends on what the font developer decided to set for glyph class and has no meaning outside the font.
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