[Lilypond-auto] [LilyIssues-auto] [testlilyissues:issues] #5868 Strange

[issues:#5868] Strange gap behavior with whole-note tremolo beams

Status: New
Created: Fri Mar 27, 2020 02:09 PM UTC by Torsten Hämmerle
Last Updated: Fri Mar 27, 2020 02:09 PM UTC
Owner: Torsten Hämmerle

As reported by Thomas Morley (Harm), the gaps set for whole-note tremolo beams will be become greater than actually set in the Beam.gap property.
See mail Strange gap-behaviour with whole-note tremolo Beams.

Generating test cases

Generated test cases (note the log output) by the following code:

\version "2.20.0" 

\paper { ragged-right = ##f indent = 0 } 

#(define (tst gap) 
  #{ 
    \override Beam.after-line-breaking = 
      #(lambda (grob) 
         (let* ((sys (ly:grob-system grob)) 
                (bound-left (ly:spanner-bound grob LEFT)) 
                (bound-right (ly:spanner-bound grob RIGHT)) 
                (left-nc (ly:grob-parent bound-left X)) 
                (right-nc (ly:grob-parent bound-right X)) 
                (left-nc-ext (ly:grob-extent left-nc sys X)) 
                (right-nc-ext (ly:grob-extent right-nc sys X)) 
                (max-beam-length (- (car right-nc-ext) (cdr left-nc-ext))) 
                (x-pos (ly:grob-property grob 'X-positions)) 
                (beam-length (interval-length x-pos))) 
           (format #t "\nApplied gap: ~a, shortens the Beam by: ~a" 
             gap 
             (- max-beam-length beam-length)))) 

    \override Beam.gap = $gap 

    \repeat tremolo  #8 { a'16 a' } 
  #}) 

$@(map (lambda (gap) (tst gap)) (iota 61 0 0.1))

Log output

And the relevant log output shows the gaps becoming unproportionally wider and wider than actually set as the gap size increases (OK for small gaps, but nearly 10 at the end where it should be only 6):

Applied gap: 0,   shortens the Beam by: 0.0
Applied gap: 0.1, shortens the Beam by: 0.0999999999999943
Applied gap: 0.2, shortens the Beam by: 0.200000000000003
Applied gap: 0.3, shortens the Beam by: 0.299999999999997
Applied gap: 0.4, shortens the Beam by: 0.399999999999999
Applied gap: 0.5, shortens the Beam by: 0.5
Applied gap: 0.6, shortens the Beam by: 0.599999999999994
Applied gap: 0.7, shortens the Beam by: 0.700000000000003
Applied gap: 0.8, shortens the Beam by: 0.799999999999997
Applied gap: 0.9, shortens the Beam by: 0.899999999999999
Applied gap: 1.0, shortens the Beam by: 1.0
Applied gap: 1.1, shortens the Beam by: 1.09999999999999
Applied gap: 1.2, shortens the Beam by: 1.2
Applied gap: 1.3, shortens the Beam by: 1.3
Applied gap: 1.4, shortens the Beam by: 1.4
Applied gap: 1.5, shortens the Beam by: 1.5
Applied gap: 1.6, shortens the Beam by: 1.59999999999999
Applied gap: 1.7, shortens the Beam by: 1.7
Applied gap: 1.8, shortens the Beam by: 1.8
Applied gap: 1.9, shortens the Beam by: 1.9
Applied gap: 2.0, shortens the Beam by: 2.0
Applied gap: 2.1, shortens the Beam by: 2.107998
Applied gap: 2.2, shortens the Beam by: 2.307998
Applied gap: 2.3, shortens the Beam by: 2.507998
Applied gap: 2.4, shortens the Beam by: 2.707998
Applied gap: 2.5, shortens the Beam by: 2.907998
Applied gap: 2.6, shortens the Beam by: 3.107998
Applied gap: 2.7, shortens the Beam by: 3.307998
Applied gap: 2.8, shortens the Beam by: 3.507998
Applied gap: 2.9, shortens the Beam by: 3.707998
Applied gap: 3.0, shortens the Beam by: 3.907998
Applied gap: 3.1, shortens the Beam by: 4.107998
Applied gap: 3.2, shortens the Beam by: 4.307998
Applied gap: 3.3, shortens the Beam by: 4.507998
Applied gap: 3.4, shortens the Beam by: 4.707998
Applied gap: 3.5, shortens the Beam by: 4.907998
Applied gap: 3.6, shortens the Beam by: 5.107998
Applied gap: 3.7, shortens the Beam by: 5.307998
Applied gap: 3.8, shortens the Beam by: 5.507998
Applied gap: 3.9, shortens the Beam by: 5.707998
Applied gap: 4.0, shortens the Beam by: 5.907998
Applied gap: 4.1, shortens the Beam by: 6.107998
Applied gap: 4.2, shortens the Beam by: 6.307998
Applied gap: 4.3, shortens the Beam by: 6.507998
Applied gap: 4.4, shortens the Beam by: 6.707998
Applied gap: 4.5, shortens the Beam by: 6.907998
Applied gap: 4.6, shortens the Beam by: 7.107998
Applied gap: 4.7, shortens the Beam by: 7.307998
Applied gap: 4.8, shortens the Beam by: 7.50799800000001
Applied gap: 4.9, shortens the Beam by: 7.707998
Applied gap: 5.0, shortens the Beam by: 7.907998
Applied gap: 5.1, shortens the Beam by: 8.107998
Applied gap: 5.2, shortens the Beam by: 8.307998
Applied gap: 5.3, shortens the Beam by: 8.50799800000001
Applied gap: 5.4, shortens the Beam by: 8.707998
Applied gap: 5.5, shortens the Beam by: 8.907998
Applied gap: 5.6, shortens the Beam by: 9.107998
Applied gap: 5.7, shortens the Beam by: 9.307998
Applied gap: 5.8, shortens the Beam by: 9.50799800000001
Applied gap: 5.9, shortens the Beam by: 9.707998
Applied gap: 6.0, shortens the Beam by: 9.907998

Obviously caused by thickness of the (invisible) stems

When applying \override Stem.thickness = #100, the ridiculously high value of 100 will make all the deviations in the above examples disappear. A value of 0, however, will make the deviations start even for lower gap values.

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From:	Auto mailings of changes to Lily Issues via Testlilyissues-auto
Subject:	[Lilypond-auto] [LilyIssues-auto] [testlilyissues:issues] #5868 Strange gap behavior with whole-note tremolo beams
Date:	Fri, 27 Mar 2020 14:09:58 -0000