Re: feature requests: scalable \shape values; (stem) for \shapeII

[Thomas Morley]

Am Mi., 7. Okt. 2020 um 10:35 Uhr schrieb Martín Rincón Botero
<martinrinconbotero@gmail.com>:
>
> Now that we’ve been talking about \shape and \shapeII, I would like to ask if 
> it’s possible that values put for \shape(II) could scale according to staff 
> size. Whenever I have a smaller staff, whatever values work for a 20 points 
> staff are too much for smaller staves (either with a smaller font size or 
> with \magnify). It would be great, from a user perspective, that a (0 . 1) 
> value would produce a similar/proportional result no matter the size of the 
> staff, instead of being always in a different “scale” every time you have 
> different staff sizes (so that you have to put smaller values for smaller 
> staves). That would also be useful if you decide later to increase or 
> decrease the font size used.

Hi Martín,

\shape adds your settings to the calculated control-points of the curve.
Though, those control-points are calculated differently depending on
staff-space.
Look at the example below, you will notice the default control-points
are always different.
In the attached image I let print the second and third control-point.

\layout {
  \context {
      \Voice
      \override NoteHead.stencil = #point-stencil
  }
}

mus = { b'1_~ b'1 }

\new Staff \with { \magnifyStaff #4 } \mus
\new Staff \with { \magnifyStaff #1 } \mus
\new Staff \with { \magnifyStaff #1/4 } \mus

This means \shape always gets different control-points to work with,
thus the result will never be consistent even for scaled
offset-values.

Nevertheless, it's not too hard to code a shape-version, which will
scale it's offset-values according to current staff-space:

\version "2.20.0"

shape-h =
#(define-music-function (offsets item)
   (list? key-list-or-music?)
   (_i "Offset control-points of @var{item} by @var{offsets}.  The
argument is a list of number pairs or list of such lists.  Each
element of a pair represents an offset to one of the coordinates of a
control-point.  If @var{item} is a string, the result is
@code{\\once\\override} for the specified grob type.  If @var{item} is
a music expression, the result is the same music expression with an
appropriate tweak applied.")
   (define (shape-curve grob coords)
     (let* ((orig (ly:grob-original grob))
            (siblings (if (ly:spanner? grob)
                          (ly:spanner-broken-into orig) '()))
            (total-found (length siblings))
            (staff-space (ly:staff-symbol-staff-space grob))
            (offsets
              (map
                (lambda (offset)
                  (if (number-pair? offset)
                      (cons (car offset) (* (cdr offset) staff-space))
                      offset))
                offsets)))
       (define (offset-control-points offsets)
         (if (null? offsets)
             coords
             (map coord-translate coords offsets)))

       (define (helper sibs offs)
         (if (pair? offs)
             (if (eq? (car sibs) grob)
                 (offset-control-points (car offs))
                 (helper (cdr sibs) (cdr offs)))
             coords))

       ;; we work with lists of lists
       (if (or (null? offsets)
               (not (list? (car offsets))))
           (set! offsets (list offsets)))

       (if (>= total-found 2)
           (helper siblings offsets)
           (offset-control-points (car offsets)))))

   (once (propertyTweak 'control-points
                        (grob-transformer 'control-points shape-curve)
                        item)))

\layout {
  \context {
      \Voice
      \override NoteHead.stencil = #point-stencil
  }
}

mus = { b'1 \shape-h #'((0 . 1) (0 . 0) (0 . 0) (0 . 0)) _~ b'1 }

\new Staff \with { \magnifyStaff #4 } \mus
\new Staff \with { \magnifyStaff #1 } \mus
\new Staff \with { \magnifyStaff #1/4 } \mus

See second image.

Cheers,
  Harm

atest-105.cropped.pdf
Description: Adobe PDF document

atest-105-scaled-shape.cropped.pdf
Description: Adobe PDF document