Multi-voice half notes misaligned

Looking at this has proved interesting (to me anyhow). The issue stems (pun not intended but appreciated!) from the desire to align stems between staves. Half note heads are slightly wider than quarter note heads, so in order to make an upstem half note's stem align with a potential upstem quarter or shorter note in another staff, MuseScore is offsetting the upstem half note slightly to the left from where it might otherwise be. Thus, the stems align, but the left edge of the half note sticks out further than the left edge of the quarter note. This would be fine, but since there is a downstem half note here too, MuseScore is trying the same thing - aligning the stem of the downstem half note with a potential downstem quarter note in another staff. And now the half notes don't align with each other.

There are a couple of possible solutions to this. I think the best way for us will be to *not* try to align the half note stems with notes in other staves that or or may not actually be present, but instead to align the centers of the notes. This is what MuseScore already does for whole notes (try a whole note in voice one over a quarter in voice two to see what I mean). It's a one-line change to enable the same for half notes. It looks good to me to have half notes centered over quarter notes, and half notes would then align with each other perfectly, and it would actually be quite a bit more work too and thus come with more risk.

I don't imagine this will be noticed or cared about by most people, but I'm mentioning it here before submitting a PR in case someone wants to make a case for a different solution. LilyPond, for example, appears to always align left edges of notes. Even whole notes are left aligned with quarter notes, which I think looks odd, actually. But Sibelius does the same, and so does Finale. Elaine Gould in "Behind Bars" doesn't say anything specific about this that I can find. But we've got a pretty good history of centering our whole note (and larger) notes, so I'm not about to revisit that unless there is a *very* strong reason. I think it would be a more disruptive change than making half notes center.

Actually, if people really want the left-aligned notes, I think I can do it - the way I restructured the code a few months makes this simple, at least in theory. Initial testing seems to indicate things would still be fine otherwise, although it's still probably a bigger change to existing scores and comes with higher risk of screwing something else up than my proposal of adding half notes to the list of notes we center.

Here is how things would look if we went with always left aligning notes (and if you compare with LilyPond, Sibelius, or Finale, you'll see similar results):

And here is how it looks if I keep the centering of whole notes but now also center half notes:

Either way, we solve the alignment problem in the last chord of measure 4, which was the issue with the current algorithm. The difference between the approaches is most pronounced in the first measure. The bottom is how do we things currently with whole notes. The different in the third measure is probably to subtle for most people to ever notice. The fourth measures, again, come out identically either way.

I'm curious why we started centering whole notes since others don't seem to do it. Looking at published literature, I do see it done both ways, but left alignment is probably more common.

Can you show me examples of other scores with centered noteheads? To be clear, I am talking about centering a whole note above/below a quarter or half note as shown in the first two measures of the second example above. Or centering a half note above/below a quarter as shown in the same example, although the size difference is subtle so that is harder to see.

I'm trying to decide if we should back out the whole idea of centering notes heads at all. Or perhaps limit it to only breves and above. The fact that LilyPond, Sibelius, and Finale all do *not* center makes me think we shouldn't either, except I personally kind of *like* the effect, so I'm looking for an excuse to keep it :-) BTW, apparently this centering was added for 2.0 - it was not in 1.3.

Good, I like to see that. What publisher is this from? HL?

OK, here is a PR that centers half notes - preserving the centering for whole notes and breves too - and thereby fixing the alignment issue:

https://github.com/musescore/MuseScore/pull/1254

I also included comments showing which lines to change if we wish to left align as others do.