Re: Cross staff stem spacing with proportional notation

[David Nalesnik]

On Mon, Mar 13, 2017 at 9:58 AM, David Nalesnik
<address@hidden> wrote:
> Hi Andrew,
>
> On Mon, Mar 13, 2017 at 3:11 AM, Andrew Bernard
> <address@hidden> wrote:
>> This issue has dogged me for a long time, and searching the archives does
>> not produce a reliable answer as far as I can see.
>>
>> When using proportional notation with cross staff beamed groups, it looks
>> vastly better if the stems are evenly spaced, but proportional notation
>> messes this up, and only in the cross staff situation.
>>
>> I have tried using \newSpacing section in my scores and I am so deep in
>> confusion perhaps that I cannot find a way to make this work, while
>> preserving the proportional notation for the score overall.
>>
>> There is a thread concerning this matter here, with no resolution, but
>> pertinent:
>>
>> https://lists.gnu.org/archive/html/lilypond-user/2014-07/msg00303.html
>>
>> It would be great if this could be made to work. What lilypond incantations
>> do I need, or is it a current limitation? Could we have some sort of
>> \spaceStemsEvenly command?
>>
>> Andrew
>>
>> == snip
>>
>> \version "2.19.56"
>>
>> tsd = { \change Staff = treble \stemDown }
>> bsu = { \change Staff = bass \stemUp }
>>
>> treble = {
>>   \clef treble
>>   aes''32[ \bsu c' \tsd d''' \bsu d' \tsd d''' \bsu ees']
>> }
>>
>> bass = {
>>   \clef bass
>>   s4
>> }
>>
>> \score {
>>
>>   \new PianoStaff
>>   <<
>>     \new Staff = "treble" { \treble }
>>     \new Staff = "bass" { \bass }
>>   >>
>>
>>   \layout {
>>   }
>> }
>>
>> \score {
>>
>>   \new PianoStaff
>>   <<
>>     \new Staff = "treble" { \treble }
>>     \new Staff = "bass" { \bass }
>>   >>
>>
>>   \layout {
>>     \context {
>>       \Score
>>       proportionalNotationDuration = #(ly:make-moment 1/32)
>>       \override SpacingSpanner.uniform-stretching = ##t
>>       \override Score.SpacingSpanner.strict-note-spacing = ##t
>>     }
>>   }
>> }
>>
>
> How about this?
>
> It's not a deep solution which adjusts spacing; rather, it adjusts the
> X-offset of NoteColumns based on stem position.
>
> The example shows a corrected group surrounded by default to
> illustrate usage of the music function I've wrapped the correction
> into.
>
> Best,
> David
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> \version "2.19.56"
>
> %% Grob should be a NoteColumn object
> #(define (space-by-stems grob)
>    (let* ((stem (ly:grob-object grob 'stem))
>           (beam (ly:grob-object stem 'beam))
>           (stems (ly:grob-array->list (ly:grob-object beam 'stems)))
>           (note-columns (map (lambda (s) (ly:grob-parent s X)) stems))
>           ;; which NoteColumn am I?
>           (me-nc (memq grob note-columns))
>           (nth (- (length note-columns) (length me-nc)))
>           (orig-stem-pos (map (lambda (s nc)
> (ly:grob-relative-coordinate s nc X))
>                            stems note-columns)))
>      (* -1 (list-ref orig-stem-pos nth))))
>
> spaceStemsEvenly =
> #(define-music-function (mus) (ly:music?)
>    (let ((done #f))
>      #{
>        \override NoteColumn.X-offset = #space-by-stems
>        #mus
>        \revert NoteColumn.X-offset
>      #}))

Oh, there's some extra code.  I decided to use a flag to avoid
redundant calculations, but didn't follow through.  The music function
should read

spaceStemsEvenly =
#(define-music-function (mus) (ly:music?)
   #{
     \override NoteColumn.X-offset = #space-by-stems
     #mus
     \revert NoteColumn.X-offset
   #})

>
> %%%%%%%%%%%%%%%%%% EXAMPLE %%%%%%%%%%%%%%%%%
>
> tsd = { \change Staff = treble \stemDown }
> bsu = { \change Staff = bass \stemUp }
>
> treble = {
>   \clef treble
>   aes''32[ \bsu c' \tsd d''' \bsu d' \tsd d''' \bsu ees']
> }
>
> bass = {
>   \clef bass
>   s8.
> }
>
> \score {
>
>   \new PianoStaff
>   <<
>     \new Staff = "treble" { \treble \spaceStemsEvenly \treble \treble }
>     \new Staff = "bass" { \bass \bass \bass }
>   >>
>
>   \layout {
>     \context {
>       \Score
>       proportionalNotationDuration = #(ly:make-moment 1/32)
>       \override SpacingSpanner.uniform-stretching = ##t
>       \override Score.SpacingSpanner.strict-note-spacing = ##t
>     }
>   }
> }