Re: Scheme: get current beam-thickness

[David Kastrup]

Aaron Hill <address@hidden> writes:

> 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
> }
> %%%%
>
> I am unaware of any simpler approach, as it is my understanding that
> grobs do not persist the entire context within which they were
> created.

How would they then make it to the page?  Suicided grobs have their
properties deleted prematurely, but those are not the rule.

> Mind you, I would love to be shown that I am incorrect.

This is Scheme anyway.  In general, objects persist as long as you are
able to reference them.

-- 
David Kastrup