Trouble connecting different staffs in Lilypond

Question

I'm quite new to Lilypond, and have been trying to produce something like in the attached picture:

Here's a minimal example of what I tried, which doesn't work. How do I prevent the note in the upper staff to be shifted so much to the right? Should I use an entirely different approach?

Would be very grateful for any help!

\version "2.20.0"  % necessary for upgrading to future LilyPond versions.

upper = \relative c' {
  \clef treble
  \key c \major
  \time 4/4
<<f4 a>> <<f a>> <<f a>> <<e g>> |

}

lower = \relative c' {
  \clef bass
  \key c \major
  \time 4/4


<< f, a {\(c \change Staff = "upper" c \)}>>\change Staff = "lower"
<< f, a {\(c \change Staff = "upper" c\)} >>\change Staff = "lower"
<< f, a {\(c \change Staff = "upper" c\)} >>\change Staff = "lower"
<< c, g'{\(c \change Staff = "upper" c\)} >>\change Staff = "lower"
 
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%
\score {
  \new PianoStaff  

  <<
    \new Staff = "upper" \upper
    \new Staff = "lower" \lower
  >>
\layout {}
  \midi { }
}

Answer 1

You need to use multiple voices for the bass notes and the changing 8th notes and then have them be 8th notes instead of quarters. Here is a fixed version of your code:

\version "2.20.0"  % necessary for upgrading to future LilyPond versions.

upper = \relative c' {
  \clef treble
  \key c \major
  \time 4/4
<f a>4 <f a> <f a> <e g> |

}

lower = \relative c' {
  \clef bass
  \key c \major
  \time 4/4


<< 
  \new Voice { \repeat unfold 4 {
    <>^\markup\with-dimensions #'(-0.1 . 0.1) #'(-2.55 . 0) " " %%% This hack serves as little spacer to increase the distance to the top staff
    \override Stem.length-fraction = #0.7 %%% make stems a bit shorter
    \voiceOne c8[ \change Staff = "upper" \voiceTwo c] \change Staff = "lower"
  } }
  { \voiceTwo <f, a>4 <f a> <f a> <c g'> }
>>
 
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%
\score {
  \new PianoStaff  

  <<
    \new Staff = "upper" \upper
    \new Staff = "lower" \lower
  >>
\layout {}
  \midi { }
}

Edit: You might also want to check out this part of the manual: https://lilypond.org/doc/v2.22/Documentation/notation/multiple-voices

Answer 2

Like Lazy, I've also had a go at fixing your code. It looks like our codes are actually quite similar, but I thought I'd post my code anyway.

A first point I would make is that chords should be written within a single pair of chevrons, with the duration on the outside, i.e. <f a>4 rather that <<f4 a>>.

The main problem with your attempt is that you need to write the quavers that change staff as a seperate voice from the chords. These will be in \voiceOne when in lower staff, but become \voiceTwo when we change to the upper staff.

I don't know why you've got phrasing slurs.

The main difference between my code and Lazy's is that I've use a beam position override to get flat horizontal beams.

PS: I haven't used \relative, because it's gross.

\version "2.20.0"

upper = {
    \clef treble
    \key c \major
    \omit\time 4/4
        \once\override DynamicText.self-alignment-X = #1.25
        <f' a'>4\mp^- 4^- 4^- <e' g'!> |
}

lower = {
    \clef bass
    \key c \major
    \omit\time 4/4      
        << 
            {
                \repeat unfold 4 {
                    \voiceOne
                    \once\override Beam.positions = #'( 4.5 . 4.5)
                        c'8[
                    \change Staff = "upper"
                    \voiceTwo
                            c']
                    \change Staff = "lower"
                } |
            } \\
            {
                <f a>4 4 4 <c g!> |
            }
        >>
}

\score {
    \new PianoStaff
        <<
            \new Staff = "upper" \upper
            \new Staff = "lower" \lower
        >>
    \layout {}
    \midi {}
}