Re: Scheme: get current beam-thickness

[Thomas Morley]

Am So., 26. Jan. 2020 um 12:41 Uhr schrieb David Kastrup <address@hidden>:
>
> Thomas Morley <address@hidden> writes:
>
> > Am Sa., 25. Jan. 2020 um 20:31 Uhr schrieb Aaron Hill
> > <address@hidden>:
> >>
> >> On 2020-01-25 10:39 am, David Stephen Grant wrote:
> >> > I'm trying to create a custom flag stencil, and would like to get the
> >> > current _beam_ thickness. As a first step, in the following example I
> >> > would
> >> > expect 0.5, then 1, to be printed to the console. Is there a way of
> >> > doing
> >> > this?
> >>
> >> With a little bit of encouragement, yes:
> >>
> >> %%%%
> >> \version "2.19.83"
> >>
> >> BeamThicknessToFlag_engraver = #(lambda (...)
> >>    `((acknowledgers
> >>        (flag-interface . ,(lambda (engraver grob source-engraver)
> >>          (ly:grob-set-property! grob 'beam-thickness
> >>            (ly:assoc-get 'beam-thickness
> >>              (ly:context-grob-definition
> >>                (ly:translator-context engraver)
> >>                'Beam))))))))
> >>
> >> customFlag = #(lambda (grob)
> >>    (let ((bt (ly:grob-property grob 'beam-thickness)))
> >>      (grob-interpret-markup grob #{ \markup #(number->string bt) #})))
> >>
> >> \new Voice
> >> \with { \consists \BeamThicknessToFlag_engraver }
> >> {
> >>    \override Flag.stencil = \customFlag
> >>
> >>    c'8 r8
> >>
> >>    \override Beam.beam-thickness = #0.5
> >>    c'8 r8
> >>
> >>    \override Beam.beam-thickness = #1.0
> >>    c'8 r8
> >>
> >>    \revert Beam.beam-thickness
> >>    c'8 r8
> >> }
> >> %%%%
> >
> > Hi Aaron,
> >
> > I stand corrected, it is possible.
> > Alas, going for a custom-engraver feels overdone, if not really
> > needed. Thus I asked about the final goal.
> >
> > Even at the risk being regarded as a nitpicker and also being aware we
> > have similar codings (wrt to juggling grob-properties) in our docs,
> > the code will return several programming errors if compiled with
> > -dcheck-internal-types.
>
> I have some incomplete work in branches that would significantly speed
> up property accesses but would not support undeclared properties.
>
> Not that we have a good interface for adding them yet...

Furthermore, ly:add-interface obviously creates a _new_ interface, not
adding something to a probably preexistent one, as I naively assumed.

So below should better read:

#(ly:add-interface
 'flag-interface
 "A flag"
 '(beam-thickness
   glyph-name
   stroke-style
   style))
>
> > To cure, one could add:
> > #(ly:add-interface
> >  'flag-interface
> >  "A flag"
> >  '(beam-thickness))
>
> --
> David Kastrup

Cheers,
  Harm