Re: ly:stencil-extent gives not the exact value?

[David Nalesnik]

Hi Harm,

On Sat, Oct 22, 2011 at 11:35 AM, harm6 <address@hidden> wrote:

Hi,

the following function should rebuild a beam.

\version "2.14.2"

#(set-global-staff-size 20)

#(define (test-stencil grob)
 (let* ((beam (ly:beam::print grob))
       (beam-extent-x (ly:stencil-extent beam X))
       (beam-length-x (interval-length beam-extent-x))
       (single-beam-thickness (ly:grob-property grob 'beam-thickness))
       (beam-positions (ly:grob-property grob 'positions))
       (mrkp (markup #:beam    (* beam-length-x 0.97)  ;; why??
                       0               ;; level Beams only!
                       single-beam-thickness))
       (new-Beam (ly:stencil-in-color
                   (ly:stencil-translate-axis
                     (ly:stencil-translate-axis
                       (grob-interpret-markup grob mrkp)
                       -0.025 X)               ;; why??
                     (car beam-positions)
                     Y)
                     1 0 0)))

  new-Beam))

\relative c' {
 \override Beam #'layer = #-4
 \once \override Beam #'stencil = #test-stencil
 e'8 [e]
 \override Beam #'color = #green
 f8 [f]
}

But I noticed two problems:
First I have to adjust the beam-length. (This needs to be done in addiction
to the global-staff-size.) Seems that ly:stencil-extent gives not the exact
value!?
What am I missing?

I'm guessing that it's an issue with the markup command \beam.  Looking at the definition in define-markup-commands.scm, it seems that 'blot-diameter isn't taken into account in the calculation of width and thickness.   (Is this intentional or a defect?)  The following fixes the problem with the beam's length and thickness, and will work when you change the staff size:

\version "2.14.2"

#(set-global-staff-size 24)

#(define (test-stencil grob)

 (let* ((beam (ly:beam::print grob))

        (b-d (ly:output-def-lookup (ly:grob-layout grob) 'blot-diameter))

        (beam-extent-x (ly:stencil-extent beam X))

        (beam-length-x (interval-length beam-extent-x))

        (single-beam-thickness (ly:grob-property grob 'beam-thickness))

        (beam-positions (ly:grob-property grob 'positions))

        (mrkp (markup #:beam (- beam-length-x b-d)

                             0               ;; level Beams only!

                             (- single-beam-thickness b-d)))

        (new-Beam (ly:stencil-in-color

                    (ly:stencil-translate-axis

                      (ly:stencil-translate-axis

                        (grob-interpret-markup grob mrkp)

                        -0.024 X)               ;; why??

                      (car beam-positions)

                      Y)

                    1 0 0)))

    new-Beam))

\relative c' {

 \override Beam #'layer = #-4

 \once \override Beam #'stencil = #test-stencil

 e'8 [e]

 \once \override Beam #'color = #red

 e [e]

 \override Beam #'color = #green

 f8 [f]

}

And second there's need to use ly:stencil-translate-axis to move the new
beam a little in X-axis-direction. But why?

I can't figure this one out...

HTH,

David