Re: markup column with baseline-skip relative to font size

[Aaron Hill]

On 2018-11-17 4:39 am, Kieren MacMillan wrote:
> I really don’t understand why Lilypond’s text handling is so fussy. It
> should be easy for the user to say “lines in a multi-line markup must
> be exactly *this* far apart [regardless of individual glyph height]” —
> in fact, it should be the default.

As far as I can see, LilyPond really does try to space lines from 
baseline to baseline by the amount specified.  However if a line is too 
tall, the underlying composition of stencils does not permit overlap and 
results in lines being further away than expected.  But if you can 
choose a suitably large value for baseline-skip, then the spacing really 
is how you describe.

Consider this extravagantly contrived example:

%%%%
\version "2.19.82"

#(define-markup-command (show-baseline-skip layout props args) (markup?)
  #:properties ((baseline-skip 0))
  (let* ((stencil (interpret-markup layout props args))
         (x-extent (ly:stencil-extent stencil 0))
         (y-extent (ly:stencil-extent stencil 1))
         (x-center (* (+ (car x-extent) (cdr x-extent)) 0.5))
         (path `((moveto ,(car x-extent) 0)(lineto ,(cdr x-extent) 0)
                 (lineto ,x-center ,(- baseline-skip))(closepath)))
         (thickness (* 0.5 (ly:output-def-lookup layout 
'line-thickness))))
    (interpret-markup layout props (markup #:combine args
      #:with-dimensions x-extent y-extent
      #:with-color (rgb-color 1 0.2 0.4)
      #:path thickness path))))
#(define-markup-command (show-extents layout props args) (markup?)
  (let* ((stencil (interpret-markup layout props args))
         (x-extent (ly:stencil-extent stencil 0))
         (y-extent (ly:stencil-extent stencil 1))
         (path `((moveto ,(car x-extent) ,(car y-extent))
                 (lineto ,(cdr x-extent) ,(car y-extent))
                 (lineto ,(cdr x-extent) ,(cdr y-extent))
                 (lineto ,(car x-extent) ,(cdr y-extent))(closepath)))
         (thickness (* 0.5 (ly:output-def-lookup layout 
'line-thickness))))
    (interpret-markup layout props (markup #:combine args
      #:with-dimensions x-extent y-extent
      #:with-color (rgb-color 0.2 0.4 1)
      #:path thickness path))))

\fixed c'' {
  \mark \markup \fontsize #-2 {
    \center-column {
      \show-extents \show-baseline-skip "qb"
      \show-extents \show-baseline-skip "qb"
      \show-extents \show-baseline-skip "qb"
    }
    \center-column {
      \show-extents \show-baseline-skip "x"
      \show-extents \show-baseline-skip "x"
      \show-extents \show-baseline-skip "x"
    }
  }
  \override Fingering.stencil = #(lambda (grob)
    (let* ((text (ly:grob-property grob 'text))
           (font-size (ly:grob-property grob 'font-size 0))
           (baseline-skip (ly:grob-property grob 'baseline-skip 2))
           (new-baseline-skip (* baseline-skip (magstep font-size))))
      (grob-interpret-markup grob (markup #:text
        #:override (cons 'baseline-skip new-baseline-skip)
        #:center-column ((#:show-baseline-skip #:show-extents "^")
                         (#:show-baseline-skip #:show-extents text)
                         (#:show-baseline-skip #:show-extents text))))))
  \override Fingering.font-size = #0
  \override Fingering.baseline-skip = #2
  g16[-\finger "q" f-\finger "x" e-\finger "b"]
  \override Fingering.font-size = #3
  g16[-\finger "q" f-\finger "x" e-\finger "b"]
  \override Fingering.baseline-skip = #0.75
  g16[-\finger "q" f-\finger "x" e-\finger "b"]
}
%%%%

The blue outlines are showing the extents of the stencils and the red 
triangles are visualizing the baseline-skip.  If lines are being spaced 
properly, the point of a triangle will lie exactly on the baseline of 
the subsequent line.  Any gap between triangles indicates that the 
baseline-skip was not honored.

Right away, you can see the default baseline-skip for RehearsalMarks is 
too small for the font size, and so the lines with both ascenders and 
descenders end up being further apart than expected because 
\center-column does not want to overlap stencils.

My version of your fingering stencil function computes a idealized 
baseline-skip based on the current font-size and baseline-skip.  This 
should be close to what you originally requested, I suspect; but be 
advised that in the right-most example, I have constrained the 
baseline-skip such that again we see abutting stencils where there 
should be overlapping, if baseline-skip were strict.

-- Aaron Hill

markuplines.cropped.png
Description: PNG image