Ancient notation: spacing, ligatures, bar lines: some ideas...

[Till Rettig]

Hi all, who are interested in Ancient notation.

I started now some trial how to improve the spacing of the notes. The 
goal is to have an even spacing where each note head regardless of their 
length takes up just the same space. Visible signs in the score as 
accidentals, clefs and lyrics should influence the spacing, though, as 
well as alignment of more than one system (even though this is quite 
rare in mensural music, it should be possible). To acchieve this I 
started removing the spaces that get added to a notehead according to 
its duration. I came up with those properties:

       \override SpacingSpanner #'spacing-increment = #0
       \override SpacingSpanner #'common-shortest-duration = 
#(ly:make-moment 1 1)
       \override SpacingSpanner #'base-shortest-duration = 
#(ly:make-moment 4 1)
       \override SpacingSpanner #'shortest-duration-space = #1
        
The first means, that longer notes than the smallest won't get more 
spacing around them (ie it gets increased by 0).
The next three properties, though, I was not so sure about what they do. 
As I understand I get quite close spacing when assigning the 
common-shortest-duration to a long note. But it seems a whole is the 
longes note it can handle, I don't see any changes in the layout when 
assigning it for instance to 4/1. The next property didn't seem to have 
much influence on spacing in this case -- can it just be ommitted, or 
did I understand this wrong?  
The last, I understand, sets the space the shortest note takes, to 1, 
that is to one notehead-width plus some amount left and right. I would 
understand that if my common-shortest-duration is a whole that this 
whole gets assigned the 1. But, as you can see from the attached file: 
The first semibreves (wholes) are much wider spaced than the smaller 
note values further on. When switching on the bar lines they reveal 
quite a lot of space they take up. This might be the reason why the 
semibreves get spaced so widely.
But there are also bigger and smaller gaps between notes of different 
duration. They show better in the example whith normal note heads, but 
are still present in the mensural examples as well. Yet they become more 
obvious when using a barline instead of the "empty barline". Is this 
some space added to each bar? Something about centering notes in bars? I 
don't understand where this space comes from.

Speaking of barlines: There are three ways avoiding bar lines, as I see it.
1. Remove the engraver. This is not a good solution, because sometimes 
there have to be inserted bar lines, for instance at the end of a piece.
2. Switch on Cadenza. There are two problems with this approach: First 
we don't have any breaks anymore. I thought of a funktion that enquires 
the last bar number of the engraved piece and sets then in regular 
spaces invisible bar lines, for instance repeating the pattern {\skip 
1*4 \bar " "} n/4 times, if the measures are a whole long. The other, 
bigger problem, are ligatures: they get really ugly squeezed when 
switching on Cadenza. What can we do there?
3. The approach from now. In addition the space bar lines take should be 
reduced. This again interferes with the cases when we actually need 
barlines. They should then get (automatically) added additional space.

Another problem are ligatures (and to some extent also ligature 
brackets). If I understand the underlying techniques right, ligatures 
get produced from legal note durations. Their duration is known to the 
spacing engine and they get accordingly space around them. But since 
ligatures are drawn as one graph of closely realted heads, the 
additional space that is counted to fit normallly between noteheads gets 
accumulated at the end of the ligature. In addition, the space which the 
barlines would normally take gets still added to the space (since 
ligatures are normally long notes, they use quite a lot of bars). So my 
naïve idea would be to count the amount of space of all ligature heads 
minus the real head-width and subtract this amount from the space of the 
ligature.
Unfortunately I know too few about programming to already provide some 
code here.

Well, another problem of the ligatures is their behaviour inside a 
Cadenza. They take up too few space so other notes start protruding 
them. This happens only, when the changed spacing values presented above 
are used. If used with the normal spacing engine, ligatures work out 
fine. But: when not using  "zero-spacing" the spacing is again too wide. 
This means that we cannot use Cadenza at the moment to display tightly 
spaced notes containing ligatures.

Actually, also the ligature brackets in the normal notation get badly 
cruched by the tight spacing: suddenly they appear in some cases to be 
too short and won't cover all the notes actually included in the 
ligature. Hopefully somebody has some hints at what I could look to make 
ligatures behave correctly. Juergen, do you have time reading the list?

If assuming that my ideas about the spacing engine are correct I thought 
to implement the tight spacing somehow into the MensuralStaff which 
automatically should call mensural voice -- there could be differently 
named staves and voices containing the different notation style that are 
available for ancient notation.

I hope you can bear my unprofessional approach, I am only learning how 
things work inside of lilypond.

Greetings
Till