Re: Vibrato (wavy lines) notation

[Valentin Petzel]

Hello Jean,

That makes sense, thank you (I supposed it was something legacy, else why 
would it be there?).

Cheers,
Valentin

Am Freitag, 14. Jänner 2022, 21:59:31 CET schrieb Jean Abou Samra:
> Le 14/01/2022 à 20:41, Valentin Petzel a écrit :
> > Hello Richard,
> > 
> > The file you’ve given us has a lot of nonsensical quoting in lines
> > 149-153.
> 
> Actually, not completely nonsensical, but legacy. There used to
> be one more level of quoting inside stencil expressions until
> 
> commit 06ba7f0823a14da773391ccf3c10244a54e812d4
> Author: Han-Wen Nienhuys <hanwenn@gmail.com>
> Date:   Sun Aug 2 21:47:25 2020 +0200
> 
>      Dispatch stencil routines using explicit tables
> 
>      scm_eval in GUILE became much more elaborate to deal with byte code
>      (2.2) and JIT compilation (3.0). This means that scm_eval has more
>      overhead for single shot code:
> 
>       * setup temporary storage for bytecode/JIT'd x86 code
>       * run up and down the syntax tree applying optimizations
>       * other magic that compiler folks do to make things run faster
> 
>      The Scheme expressions for stencils aren't generalized code; they are
>      just a device-independent description of the output. In particular,
>      they have no advanced construct (loops, conditionals, tail calls,
>      variable bindings, variable references), also, they are run only
>      once. So all the work that scm_eval does to produce faster code is
>      just overhead.
> 
>      The change makes it explicit that the data is just literal data, and
>      does the one thing to specialize it from device-independent to
>      device-specific, which is replacing symbols with their definitions
>      from output-ps.scm
> 
>      Because output expression do not pass through eval anymore, we stop
>      quoting symbol and list values.
> 
>      Backend implementors should take the following changes into account:
> 
>      * placebox is removed. Instead each stencil expression is surrounded
>        by settranslation and resettranslation
> 
>      * ly:make-paper-outputter takes a single function as argument. The
>        function takes the Scheme expression, for example,
> 
>           (circle 10 0.1 #t)
> 
>        as argument.
> 
>      * A paper-outputter no longer is associated with a module. For the SVG
>        backend, this is solved by creating some backend-specific
>        expressions (set-paper, set-unit-length) which the eval-svg function
>        treats specially.
> 
>      Markup/stencil implementors should take the following changes into
>      account:
> 
>      * Stencil expressions are no longer passed through the eval
>        function. This means that all inner (quasi)quoting should be
>        removed.
> 
>      Tested
>        lilypond -dbackend=svg input/regression/les-nereides
> 
>      Timing
> 
>      In verbose mode, the backend output phase will print timing. This
>      timing leads to the following data for (MSDM-reduced, 2Ghz CPU):
> 
>      Current master
>      - Guile 1.8: 0.74s
>      - Guile 2.2: 4.73s
>      - Guile 3.0: 2.49s
> 
>      This commit
>      - Guile 1.8: 0.80s
>      - Guile 2.2: 1.41s
>      - Guile 3.0: 1.20s
> 
> > Basically `(path ...) is already quasi-quoted, so there is no reason to
> > quote the symbol round (as it is already quoted).
> 
> Well, but there was.
> 
> `round
> => round
> 
> `'round
> => (quote round)
> 
> This extra quote was necessary in 2.20.
> 
> > Also you will get an error for
> > line 150 where we have
> > 
> > `(,@',(concatenate path-final))
> > 
> > So we first quasi-quote something that is already quasi-quoted, then we
> > create a list, use an unquote splice operator (,@), which basically
> > evaluates the expression to a list and then gives the entries of the list
> > instead of the list (note we are CREATING a list first just to splice
> > something into it – instead of this we can simply do ,(concatenate
> > path-final)), then we are quoting the whole thing we just unquoted again
> > to add another unquote, which does not work as the last quote was not a
> > quasi-quote.
> > 
> > So to get it to work closest to what’s in the file we’d need to do
> > 
> > (,@`,(concatenate path-final))
> > 
> > Or alternatively
> > 
> > ,`(,@`,(concatenate path-final))
> > 
> > But much more intelligent would be simply doing this:
> > 
> > ,(concatenate path-final)
> 
> Yes, in 2.22, and in 2.20 you are right that it
> can be simplified, but to ',(concatenate path-final)
> with an extra quote at the beginning.
> 
> Anyway, here is a largely simplified version of this
> snippet:
> 
> 
> \version "2.22.1"
> 
> #(use-modules (ice-9 match))
> 
> #(set-object-property! 'curvature-factor 'backend-type? number?)
> 
> vibrato =
> #(define-music-function (amplitudes wave-length) (list? number?)
>     #{
>       \once \override TrillSpanner.normalized-endpoints =
>         #ly:spanner::calc-normalized-endpoints
>       \once \override TrillSpanner.curvature-factor = 0.35
>       \once \override TrillSpanner.stencil =
>         #(let* ((n-amplitudes-1 (1- (length amplitudes))))
>            (grob-transformer
>             'stencil
>             (lambda (grob original)
>               (if
>                (ly:stencil? original)
>                (match-let* (((left . right) (ly:grob-property grob
> 'normalized-endpoints))
>                              (left-idx (inexact->exact (round (*
> n-amplitudes-1 left))))
>                              (right-idx (inexact->exact (round (*
> n-amplitudes-1 right))))
>                              (sublist (match (drop (take amplitudes
>                                                     (1+ right-idx))
>                                               left-idx)
>                                        ((one) (list one one))
>                                        (lst lst)))
>                              (original-ext (ly:stencil-extent original X))
>                              (len (interval-length original-ext))
>                              ((start . end) original-ext)
>                              (position-increment (/ len (1- (length
> sublist))))
>                              (thickness (* (ly:grob-property grob
> 'thickness 1.0)
> (ly:staff-symbol-line-thickness grob)))
>                              (factor (ly:grob-property grob
> 'curvature-factor)))
>                  (make-path-stencil
>                   (append
>                    `(moveto ,start 0.0)
>                    (let loop ((position start)
>                               (tail sublist)
>                               (last-exact start)
>                               (current-sign 1)
>                               (acc '()))
>                      (if (>= position end)
>                          (reverse! acc)
>                          (match-let* ((next-position (+ position
> wave-length))
>                                       (intermediate1 (+ position (*
> wave-length factor)))
>                                       (intermediate2 (+ position (*
> wave-length (- 1 factor))))
>                                       (from-last (- position last-exact))
>                                       ((previous-height next-height . _)
> tail)
>                                       (height (* current-sign
> (interval-index
> (cons previous-height next-height)
>                                                                (+ -1 (*
> 2 (/ from-last position-increment))))))
>                                       (path-component `(curveto
> ,intermediate1 ,height
> ,intermediate2 ,height
> ,next-position 0.0))
>                                 (new-acc (append-reverse path-component
> acc)))
>                            (if (>= from-last position-increment)
>                                (loop next-position
>                                      (cdr tail)
>                                      (+ last-exact position-increment)
>                                      (- current-sign)
>                                      new-acc)
>                                (loop next-position
>                                      tail
>                                      last-exact
>                                      (- current-sign)
>                                      new-acc))))))
>                   thickness
>                   1
>                   1
>                   #f))
>                '()))))
>      #})
> 
> {
>    \vibrato #'(0.5) #0.5
>    c'2\startTrillSpan d' e'\stopTrillSpan
> }
> 
> {
>    \vibrato #'(0.5 2.0) #0.5
>    c'2\startTrillSpan d' e'\stopTrillSpan
> }
> 
> {
>    \override TrillSpanner.thickness = 2
>    \vibrato #'(0.0 2.0) #3.0
>    c'1\startTrillSpan d' \break
>    e' e'\stopTrillSpan
> }
> 
> {
>    \override TrillSpanner.bound-details.left.padding = -2
>    \vibrato #'(0.5 0.5 8 0.0) #0.8
>    c'1\startTrillSpan d' \break
>    e' e'\stopTrillSpan
> }
> 
> {
>    \override TrillSpanner.bound-details.left.padding = -2
>    \vibrato #'(2.5 3.5 8 0.0) #0.8
>    c'1\startTrillSpan d' \break
>    e' e'\stopTrillSpan
> }
> 
> 
> Best regards,
> Jean

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