Re: InstrumentName misalignment in incipit snippets

[Joe Neeman]

On Tue, 2009-08-11 at 21:57 +0100, Neil Puttock wrote:
> Hi Joe,
> 
> While fixing the last bug with the new instrument name code, I noticed
> that the instrument name positioning for both inicipit snippets
> (Documentation/snippets/incipit.ly and input/regression/incipit.ly)
> has changed for the worse.  By a process of elimination, I've traced
> the change to your commit which removed all the overrides for
> minimum-Y-extent in engraver-init.ly.  I've played around with the new
> spacing overrides, but the only thing that seems to correct the
> misalignment is to add a manual override for
> MensuralStaff.VerticalAxisGroup #'Y-extent.  Can you suggest an
> alternative to this?

I think the problem is the Y-offset callback in the snippet, which says
"place the top of my extent 4 staff-spaces above the center line of the
staff." If top of the incipit's extent is anything other than 4
staff-spaces above its own center staff line, it won't work.

IWBN if it were possible to extract the staff-refpoints of a marked up
system in a grob callback (in which case we could write a less fragile
Y-offset callback), but I'm not sure if it is. In the meantime, I'd
suggest changing the snippet to include the Y-extent override (note that
it will still break if the incipit has a note far above the staff). I'll
put extracting staff refpoints from score markups on my TODO list, after
the remaining spacing bugs.

Cheers,
Joe