Re: Improves horizontal spacing of axis groups that SpanBar grobs traverse. (issue 4917046)

[Mike Solomon]

On Sep 9, 2011, at 7:09 PM, address@hidden wrote:

> Hi Mike
> I found a visual difference with one of my scores.  I finally tracked
> this down to a dependence on the stem direction.  Try this:
> 
> SopranoMusic = \relative g' {
> b2 b
> \once \override Staff . BarLine #'allow-span-bar = ##f
> b2 b
> }
> 
> TenorMusic = \relative a' {
> b2 b |
> b2 b |
> }
> 
> \score {
> \new GrandStaff <<
>   \new Staff {
>     \new Voice = "Soprano" {
>       \stemDown
>       \SopranoMusic
>     }
>   }
>   \new Lyrics \lyricsto "Soprano" {
>     a b long-syllable a
>   }
>   \new Staff {
>     \new Voice = "Tenor" {
>       \TenorMusic
>     }
>   }
>>> 
> }
> 
> \score {
> \new GrandStaff <<
>   \new Staff {
>     \new Voice = "Soprano" {
>       \stemUp
>       \SopranoMusic
>     }
>   }
>   \new Lyrics \lyricsto "Soprano" {
>     a b long-syllable a
>   }
>   \new Staff {
>     \new Voice = "Tenor" {
>       \TenorMusic
>     }
>   }
>>> 
> }

Good catch!
The problem comes not from this patch but from the calculation of the 
horizontal skylines for NonMusicalPaperColumns.  Try adding:

\override Score . NonMusicalPaperColumn #'stencil = #ly:separation-item::print

To the beginning of SopranoMusic and then running LilyPond with 
-ddebug-skylines.  You'll see that in the first example, the downward stem 
pushes the lyrics under the end point of the NonMusicalPaperColumn, whereas 
this does not happen in the second example.

Thus, the dependency is not stems (drop the soprano an octave and you'll see 
that) but NonMusicalPaperColumn grobs.

I'd recommend fixing this in a separate patch.  I also think it should be put 
on the tracker, although I don't feel comfortable reporting it because I'm not 
sure how to describe this bug (my gut reaction would be to say that 
NonMusicalPaperColumn horizontal skylines are sometimes incorrect, but I'm not 
sure if these overshoots are in fact incorrect or if they need to be there to 
prevent other problems from happening, in which case the description would be 
more like "Over-extended NonMusicalPaper columns must be present for X but 
interfere with lyric spacing in certain cases").

So, as it has passed a countdown and I've gotten no responses saying that the 
SpanBars look different with the patch applied, I'll push the SpanBarStub patch 
w/in the next 24ish hours.

Cheers,
MS