Re: Manipulating instrument names and staff group names

[Lukas-Fabian Moser]

> > Nice! This definitely solves the basic problem nicely.
> >
> > Lukas sent me [off-list] a totally different solution that was also 
> > excellent.
> >
> > Maybe we can/should discuss the pros and cons of each approach — and 
> > others, if they’re offered — with an eye to eventually submitting a 
> > patch…?
>
> I don't know what Lukas proposed. For a new feature
> added to LilyPond proper, I don't see a way around
> the good old methods: define two new grobs and an
> engraver to create them.

Well, the code I sent Kieren off-list was more-or-less equivalent to 
what Harm provided: We both had the same cruel idea of hijacking the 
Y-offset calculation using a procedure that changes the stencil as a 
side-effect. (Probably we were both inspired by the fact that the 
necessary computations of the StaffGroup's total Y extent are contained 
in system-start-text::calc-y-offset, the standard callback for 
InstrumentName.Y-offset.)
We also both did not bother try to do the horizontal alignment the right 
way.

Here are some thoughts on the subject:

- I'm not sure if "staff-group names with brackets" should be done as a 
new Layout object / by a new engraver, or if this should be added to the 
functionality of InstrumentName and the Instrument_name_engraver.
Conceptually, I was never really happy with the staff group names being 
called InstrumentName's, but I have to admit it's convenient, and for 
reasons of backwards compatibility, it should probably stay that way.

- The ability to deal with the needs of multi-staff groups specifically 
might make it reasonable to create a dedicated engraver 
(Group_name_engraver?) that mimicks and extends the 
Instrument_name_engraver. The context definitions of StaffGroups etc. 
then could be changed such that only Staff (and TabStaff etc.) contexts 
\consist the standard Instrument_name_engraver, whereas the grouping 
contexts should have the Group_name_engraver.

- Grouping staves visually by a bracketed instrument name means that it 
might be reasonable not to have SystemStartBracket's etc. for the same 
group. I think this is a good opportunity to add something I've wanted 
for a long time, namely a staff grouping context that provides _only_ 
logical grouping and has no hardwired visual grouping elements (SpanBar, 
SystemStartBracket etc.), and from which StaffGroup and all the other 
contexts should be derived. Maybe StaffCollection would be a suitable name?

- Vertical ("rotated") printing of the Group Name should be available as 
a boolean option, not depend on manual markup rotation.

- The hard part seems to be horizontal spacing. Two layout options come 
to mind which should both be supported: Staff names on the inside ("on 
the right"), group name with bracket on the outside ("on the left"); and 
vice versa: group name with bracket on the inside ("on the right"), and 
single staff names on the outside ("on the left"). These pose different 
layout problems: For the first option, the machinery creating the 
GroupName has to know the extents of all the single-staff 
InstrumentNames. For the second option, the GroupName machinery has to 
increase the padding for the single staff names. I'm not clear yet if 
this requires a separate implementation of the two options.

- The first option wished for by Adam (horizontal alignment of all the 
brackets) is very easy to implement; this is just a matter of fixed 
paddings.

As Harm already stated that he won't have time to work on this for now, 
I'd be happy to try my hands on this a bit.

Lukas