Re: [frogs] Re: New frog in an empty pond?

[Pavel Roskin <proski@xxxxxxx>]

Hi, Janek!

Quoting Janek Warchol <janek.lilypond@xxxxxxxxx>:

> Hi Pavel,
>
> unfortunately this list is quite dead right now (time for a change?).

It's the second reply, I got, so maybe the list is not as dead as I feared.

> It's great to see you working on LilyPond!
>
> Cross-staff stems would indeed be a valuable addition.  I would begin by
> reading code that creates brackets and cross-system barlines (and perhaps
> grid lines).

I actually wanted to make a stopgap solution in Scheme.  I wrote some  
code that looks for other stems and sets the stem length so it would  
touch the stem above (attached).  But the code is unreliable.  Some  
stems are not calculated yet.  So I need a different approach to do my  
calculations at a later time.  That's where an advice of an  
experienced developer could save a lot of time.

I'm going to see the C++ code, that's for sure.  It may help me to  
understand some missing details.  But the main missing detail at this  
point is using the appropriate interface in Scheme.

I don't think I can write C++ code for cross-staff stems at this  
point.  The may reason is that I won't be able to meet the quality  
standards of the Lilypond core code.

> It would be good indeed if you have a mentor; unfortunately, i don't think
> you'll find one here, on frogs.  It's hard to find a mentor in general...
> I'm not much Lily-knowledgeable, so i don't think i would be a good mentor
> for you, but if you have any problems with git, our development cycle or
> other general issues, feel free to ask me privately.

Mike has agreed to be my mentor.

--
Regards,
Pavel Roskin

\version "2.14.2"

#(define (grobParentByInterface grob intf axis)
   (if (memq intf (ly:grob-interfaces grob))
       grob
       (grobParentByInterface (ly:grob-parent grob axis) intf axis)))

#(define ((connectableStem? xref yref stemone dir below?) stemtwo)
   (cond
    ((not (memq 'stem-interface (ly:grob-interfaces stemtwo))) #f)
    ((equal? stemone stemtwo) #f)
    ((inf? (car (ly:grob-extent stemtwo xref X))) #f)
    ((not (equal? (ly:grob-extent stemone xref X) (ly:grob-extent stemtwo xref X))) #f)
    ((not (equal? dir (ly:grob-property stemtwo 'direction))) #f)
    ((below? (car (ly:grob-extent stemtwo yref Y)) (car (ly:grob-extent stemone yref Y))) #f)
    (else #t)))

#(define ((lowerStem? ref below?) lower upper)
   (below? (car (ly:grob-extent lower ref Y)) (car (ly:grob-extent upper ref Y))))

#(define (crossStaffLength grob)
   (let* ((papercolumn (grobParentByInterface grob 'paper-column-interface X))
          (elementarray (ly:grob-object papercolumn 'elements))
          (xref (ly:grob-common-refpoint-of-array grob elementarray X))
          (yref (ly:grob-common-refpoint-of-array grob elementarray Y))
          (elements (ly:grob-array->list elementarray))
          (dir (ly:grob-property grob 'direction))
          (below? (if (> dir 0) < >))
          (goodstems (filter (connectableStem? xref yref grob dir below?) elements))
          (beststems (sort goodstems (lowerStem? yref below?)))
          (peer (car (append beststems (list grob)))))
     (if (equal? grob peer)
         (begin (ly:programming-error "No suitable stem to connect to") 4)
         (if (> dir 0)
             (* 2 (- (car (ly:grob-extent peer yref Y))
                     (car (ly:grob-extent grob yref Y))))
             (* 2 (- (cdr (ly:grob-extent grob yref Y))
                     (cdr (ly:grob-extent peer yref Y))))))))

\score {
  \new StaffGroup <<
    \new Staff = "staffone" <<
      \new Voice {
        \voiceOne c''
      }
      \new Voice {
        \override Stem #'cross-staff = ##t
        \override Stem #'length = #crossStaffLength
        \voiceTwo c'
      }
      \new Voice {
        \voiceThree g' c'
      }
    >>
    \new Staff = "stafftwo" <<
      \new Voice {
        \clef bass \voiceOne g
      }
      \new Voice {
        \clef bass \voiceTwo e,
      }
      \new Voice {
        \clef bass \voiceThree d
        \override Stem #'cross-staff = ##t
        \override Stem #'length = #crossStaffLength
        f
      }
    >>
    \new Staff = "staffthree" <<
      \new Voice {
        \clef bass \voiceOne f
      }
      \new Voice {
        \clef bass \voiceTwo g,
      }
      \new Voice {
        \override Stem #'cross-staff = ##t
        \override Stem #'length = #crossStaffLength
        \clef bass \voiceThree c c
      }
    >>
  >>
  \layout { }
}