Re: treble and bass clef simultaneously

[Werner LEMBERG]

> When staves are part of a group (such as PianoStaff), then it is
> important to use staff-staff-padding, not
> default-staff-staff-padding.  So I goofed there.
> 
> As penance, try out the following: [...]

Very nice, thanks!  Attached is my slightly modified version.

* It uses `alignBelowContext', since otherwise it can happen that
  grobs sticking out vertically of the left-hand staff collide with
  grobs from the right-hand staff.  It has the drawback that
  `staff-staff-spacing' must be set in the main staff also, but I can
  live with that.  As the attached image shows, there still can be
  collisions, but in my music the system distances are sufficiently
  large to avoid that.

* It also replaces `\once\override' with `\override ... \revert' so
  that the second argument of \fakeBassClef can contain skips.

The last missing bit is the hard-coded offset of the fake bass clef
offset, which doesn't take any accidentals (and similar things left of
the note head) into account.


    Werner

\version "2.19.83"


fakeBassClef = #(define-music-function (align-below treble bass)
  ((string? #f) ly:music? ly:music?)

  (define (context-id? id)
    (and (string? id)
         (not (string-null? id))))

  (define prefix-with-bass-clef
    (grob-transformer 'stencil (lambda (grob orig)
      (grob-interpret-markup grob #{
         \markup \with-dimensions-from \stencil $orig {
           \overlay {
             \stencil $orig
             \translate #`(-4 . 0)
               \fontsize #-2 \musicglyph "clefs.F"
           }
         }
      #} ))))

  #{
    % When alignBelowContext is unspecified, attempt to find it.
    \applyContext #(lambda (context)
      (if (not (context-id? align-below))
        (let* ((staff (ly:context-find context 'Staff))
               (id (and (ly:context? staff)
                        (ly:context-id staff))))
          (if (context-id? id)
            (set! align-below id)
            (ly:warning "fakeBassClef: No named Staff found.")))))
    <<
      { #treble }
      \new Staff \with {
        \remove "Time_signature_engraver"
        \remove "Clef_engraver"
        \omit StaffSymbol

        #(ly:make-context-mod `((apply ,(lambda (c)
          (if (context-id? align-below)
            (set! (ly:context-property c 'alignBelowContext) align-below))))))

        % Force overlap by using a very large negative padding.
        \override VerticalAxisGroup.staff-staff-spacing =
          #'((basic-distance . 0)
             (minimum-distance . 0)
             (padding . -100)
             (stretchability . 0))
      } {
        \clef "bass" \voiceTwo
        \override NoteHead.stencil = #prefix-with-bass-clef
        #bass
        \revert NoteHead.stencil
        \oneVoice
      }
    >>
  #} )


%%%%%

\new PianoStaff <<
  \new Staff = "right" {
    \repeat unfold 8 { c'8_[ b''' b''' c'] } |
  }
  \new Staff = "left" \with {
    % necessary for \fakeBassClef
    \override VerticalAxisGroup.staff-staff-spacing =
      #'((basic-distance . 0)
         (minimum-distance . 0)
         (padding . -100)
         (stretchability . 0))
  } \relative c'' {
    c8 g'' a g,, \fakeBassClef { <fis ais cis> g } { c,,,4 } a'''8 g |
    \fakeBassClef { <fis ais cis>8 g } { s cis,,,8 } a'''8 g c g a g |

    \break

    \fakeBassClef { <fis ais cis>8 g } { c,,,4 } a'''8 g c g a g |
    c8 g'' a g,, \fakeBassClef { <fis ais cis> g } { s ces,,,8 } a'''8 g |
  }
>>