Re: Scheme: get current beam-thickness

[Thomas Morley]

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.
To cure, one could add:
#(ly:add-interface
 'flag-interface
 "A flag"
 '(beam-thickness))

Best,
  Harm