Re: grob-object information

[Marc Hohl]

Am 11.09.2012 21:54, schrieb address@hidden:
> On 11 sept. 2012, at 22:29, Marc Hohl <address@hidden> wrote:
>
> > > Are you certain that every vertical axis group will always contain the same 
> > > number of bar lines?  If not, it's possible that the matrix you're talking 
> > > about may not have complete rows, in which case it's difficult to know how to 
> > > break it.
> > I am not 100% sure – there could be corner cases where a staff line stops 
> > before the
> > volta bracket is closed, but this could lead to an error when compiling the .ly 
> > file.
> What about pieces with different simultaneous time signatures?  They'd have 
> different numbers of bars for a given section.
>
> > > One way to check it is to look at the left or right of the spanned_rank_interval of the 
> > > grobs (the values will be the same as you're dealing with items which only ever 
> > > "span" one column).  Once it goes backwards, you know that you've skipped to 
> > > the next row.
> > What kind of values does spanned_rank_interval return?
> The column number of a grob's left and right bound. Columns are linearly 
> ordered from the beginning of a score to the end, so you can use it to know 
> when a new staff is beginning in your array.  For bar lines, the grob only 
> spans one column so the left and right values of the returned will be the same 
> - you can use either one.
Ok, so I defined

LY_DEFINE (ly_grob_spanned_rank_interval, "ly:grob-spanned-rank-interval",
           2, 0, 0, (SCM grob, SCM dir),
           "Get the spanned rank interval of grob @var{grob}; @var{dir}"
           " may be @code{LEFT} or @code{RIGHT}.")
{
  Grob *gr = unsmob_grob (grob);

  LY_ASSERT_SMOB (Grob, grob, 1);
  LY_ASSERT_TYPE (scm_is_number, dir, 2);

  return scm_from_int (gr->Grob::spanned_rank_interval ()[to_dir (dir)]);
}

in lily/grob-scheme.cc.

Calling this function as (ly:grob-spanned-rank-interval grob dir)
returns -1 if dir = LEFT and 0 if dir = RIGHT
for *every* BarLine grob regardless of the grob's position in the
array.

Probably I made a mistake somewhere, but I don't know where.

Any hints are highly appreciated!

Regards,

Marc