\version "2.22.0" % "2.23.3"

\paper {
  indent = 0
  ragged-right = ##f
  line-width = 120
}

\layout {
  \context {
    \Voice
    \override Glissando.layer = 1000
    \override Glissando.bound-details.left.padding = 0
    \override Glissando.bound-details.right.padding = 0
    \override Glissando.breakable = ##t
  }
}

%% cross stensil
#(define*
   (make-cross-stencil coords #:optional (thick 0.1) (sz 0.2))
   (ly:stencil-add
     (make-line-stencil
       thick
       (- (car coords) sz)
       (- (cdr coords) sz)
       (+ (car coords) sz)
       (+ (cdr coords) sz))
     (make-line-stencil
       thick
       (- (car coords) sz)
       (+ (cdr coords) sz)
       (+ (car coords) sz)
       (- (cdr coords) sz))))

%% glissando stencil
#(define glissando-stencil-proc (lambda (grob) (ly:line-spanner::print grob)))

%% get start/end points
#(define gliss-data
  (lambda (grob)
(let* ((simple-y? (and (ly:grob-property grob 'simple-Y)
                       (not (ly:grob-property grob 'cross-staff))))
       (lbi (ly:grob-property grob 'left-bound-info))
       (rbi (ly:grob-property grob 'right-bound-info))
       (common-x (ly:grob-common-refpoint grob
                  (ly:grob-common-refpoint
                   (ly:spanner-bound grob LEFT)
                   (ly:spanner-bound grob RIGHT) X) X))
       (scaling (magstep (ly:grob-property grob 'font-size 0)))
       (left-padding (ly:assoc-get 'padding lbi 0))
       (left-stencil (ly:assoc-get 'stencil lbi #f))
       (left-common-y (ly:assoc-get 'common-y lbi grob))
       (right-padding (ly:assoc-get 'padding rbi 0))
       (right-stencil (ly:assoc-get 'stencil rbi #f))
       (right-common-y (ly:assoc-get 'common-y rbi grob))
       (common-y (ly:grob-common-refpoint left-common-y right-common-y Y))
       (normalized-endpoints (ly:grob-property grob 'normalized-endpoints '(0 . 1)))
       (span-left-x (ly:assoc-get 'X lbi 0))
       (span-left-y (ly:assoc-get 'Y lbi 0))
       (span-right-x (ly:assoc-get 'X rbi 0))
       (span-right-y (ly:assoc-get 'Y rbi 0)))
  (if (not simple-y?)
   (begin
    (set! span-left-y (+ span-left-y
     (ly:grob-relative-coordinate left-common-y common-y Y)))
    (set! span-right-y (+ span-right-y
     (ly:grob-relative-coordinate right-common-y common-y Y)))))
  (let ((y-length (- span-right-y span-left-y)))
   (set! span-left-y (+ span-left-y
    (* (car normalized-endpoints) y-length)))
   (set! span-right-y (- span-right-y
    (* (- 1 (cdr normalized-endpoints)) y-length))))
  (let* ((span-dx (- span-right-x span-left-x))
         (span-dy (- span-right-y span-left-y))
         (span-length (sqrt (+ (* span-dx span-dx) (* span-dy span-dy)))))
   (if (> (+ left-padding right-padding) span-length) '()
    (let* ((grad-dx (/ span-dx span-length))
           (grad-dy (/ span-dy span-length)))
     (set! span-left-x (+ span-left-x (* left-padding scaling grad-dx)))
     (set! span-left-y (+ span-left-y (* left-padding scaling grad-dy)))
     (set! span-right-x (- span-right-x (* right-padding scaling grad-dx)))
     (set! span-right-y (- span-right-y (* right-padding scaling grad-dy)))
     (if (and (ly:stencil? left-stencil)
              (not (ly:stencil-empty? left-stencil)))
      (let ((factor (/ (cdr (ly:stencil-extent left-stencil X)) grad-dx)))
       (set! span-left-x (+ span-left-x (* factor grad-dx)))
       (set! span-left-y (+ span-left-y (* factor grad-dy)))))
     (if (and (ly:stencil? right-stencil)
              (not (ly:stencil-empty? right-stencil)))
      (let ((factor (/ (car (ly:stencil-extent right-stencil X)) grad-dx)))
       (set! span-right-x (+ span-right-x (* factor grad-dx)))
       (set! span-right-y (+ span-right-y (* factor grad-dy)))))
     (let* ((dx (ly:grob-relative-coordinate grob common-x X))
            (dy (if simple-y? 0 (ly:grob-relative-coordinate grob common-y Y)))
            (system (ly:grob-system grob))
            (dy-right (ly:grob-relative-coordinate grob system Y)))
      (set! span-left-x (- span-left-x dx))
      (set! span-left-y (- span-left-y dy))
      (set! span-right-x (- span-right-x dx))
      (set! span-right-y (- span-right-y dy dy-right))
      (cons (cons span-left-x span-left-y)
            (cons span-right-x span-right-y)))))))))

#(define gliss-stencil-with-crosses
  (lambda (grob)
    (let* ((cross-coords (gliss-data grob)))
      (ly:stencil-add
        ;; left cross
        (stencil-with-color
          (make-cross-stencil (car cross-coords) 0.2 0.2) blue)
        ;; right cross
        (stencil-with-color
          (make-cross-stencil (cdr cross-coords) 0.2 0.2) red)
        ;; glissando
        (stencil-with-color (glissando-stencil-proc grob) magenta)))))

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Examples
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%% Simple

{
  \override Glissando.stencil = #gliss-stencil-with-crosses
  e''1\glissando s2 e'
}

%% Padding

{
  \override Glissando.stencil = #gliss-stencil-with-crosses
  \override Glissando.bound-details.left.padding = #3
  \override Glissando.bound-details.right.padding = #5
  e''1\glissando s2 e'
}

%% Stencils

{
  \override Glissando.stencil = #gliss-stencil-with-crosses
  \override Glissando.font-size = #3
  \override Glissando.bound-details.left.text =
    \markup \vcenter \box \left-align "lorem"
  \override Glissando.bound-details.right.text =
    \markup \vcenter \box \right-align "ipsum"
  e''1\glissando s2 e'
}

%% cross-staff

\new PianoStaff
  <<
    \new Staff = "top"
      \with {
        \override VerticalAxisGroup.staff-staff-spacing.padding = 10
      }
      \relative c'' {
        \override Glissando.stencil = #gliss-stencil-with-crosses
        c1\glissando
        \change Staff = "bottom"
        s2
        g,,2
      }

    \new Staff = "bottom" { \clef "bass" s1*2 }
  >>

%% with line break

{
  \override Glissando.stencil = #gliss-stencil-with-crosses

  e'''1\glissando
  \break
  s2 c''
}