Re: Scheme: get current beam-thickness

[David Kastrup]

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...

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

-- 
David Kastrup