Thanks for digging into this for me. Yes, both cases are necessary for typesetting shape note hymns, as illustrated by the attached scan. I believe the rule for this is that the notehead should be pointed up in the treble clef, and down in the bass clef.
>>> \partCombine #'(1 . 1)
>>> { \aikenHeads f'2 }
>>> { \aikenHeads f'2 }
>>
>> This is an interesting problem. LilyPond's Emmentaler font
>> contains two shapes of this glyph, namely `noteheads.d1fa` and
>> `noteheads.u1fa`, where the 'd' and 'u' stands for 'down' and 'up',
>> respectively (you can see the glyphs in Appendix A.8 of the
>> Notation Reference). It seems that the part combine engine uses
>> the 'down' version of the glyph if two voices fall together; AFAIK,
>> this is an arbitrary choice without a possibility to adjust.
>
> Looks like it’s not the part combiner, but the core note column
> merging logic. See note-collision.cc.
Indeed, thanks! There is the following code in function
`check_meshing_chords`:
```cpp
/* The solfa is a triangle, which is inverted depending on stem
direction. In case of a collision, one of them should be removed,
so the resulting note does not look like a block.
*/
SCM up_style = get_property (head_up, "style");
SCM down_style = get_property (head_down, "style");
if (merge_possible
&& (scm_is_eq (up_style, ly_symbol2scm ("fa"))
|| scm_is_eq (up_style, ly_symbol2scm ("faThin")))
&& (scm_is_eq (down_style, ly_symbol2scm ("fa"))
|| scm_is_eq (down_style, ly_symbol2scm ("faThin"))))
{
Offset att = Offset (0.0, -1.0);
set_property (head_up, "stem-attachment", to_scm (att));
set_property (head_up, "transparent", SCM_BOOL_T);
}
```
So the situation in question *is* handled, making the 'up' glyph
disappear. This can be easily changed to do the opposite.
Benjamin, do you have real-world examples that demonstrates such
mergings for Aiken note heads? Please provide scans if possible! In
particular it would be necessary to know whether the used note head
for merged notes is always the same.
Werner
glorybe.jpg