Re: [Lilypond-auto] Issue 1320 in lilypond: Enhancement: user-customizable barlines through a Scheme interface.

[Marc Hohl]

Am 21.07.2012 15:02, schrieb address@hidden:
> Updates:
>     Labels: -Patch-new Patch-needs_work
>
> Comment #35 on issue 1320 by address@hidden: Enhancement: 
> user-customizable barlines through a Scheme interface.
> http://code.google.com/p/lilypond/issues/detail?id=1320#c35
>
> Patchy the autobot says: Again, lots of small changes across the bar.  
> The shifts for repeats appear fixed. breathing-sign-ancient.ly looks 
> like it is losing the third breathing sign, however that may be a 
> rasterization artifact of the regtest checker.  There are small 
> effects like isolated letters in text shifted likely by one pixel.  
> That makes it likely that we are seeing the effects of 
> rounding/quantization artifacts.  Are there some calculations done in 
> C++ that use integers and/or rounding?  I would suspect that those are 
> probably done with exact numbers or reals or different rounding modes 
> in Scheme.  Remember that (/ 1 2) yields 1/2, not 0 in Scheme.

Thanks for your comment.

I did some experimenting with the stencils in order to
find out what's fishy here.

A small test file:

#(define (bar-line-print-info grob)
         (let* ((stencil (bar-line::print grob))
                ;;(stencil (ly:bar-line::print grob))
                (glyph (ly:grob-property grob 'glyph))
                (x-extent (ly:stencil-extent stencil X))
                (y-extent (ly:stencil-extent stencil Y)))

               (display "\nBar Line - glyph: ")(display glyph)
               (display ", X-extent: ")(display x-extent)
               (display ", Y-extent: ")(display y-extent)
               stencil))

music = \relative f {
  \override Staff.BarLine #'stencil = #bar-line-print-info
  c'4 c c c \bar "|"
  c c c c \bar "."
  c c c c \bar ":"
  c c c c \bar "'"
  c c c c \bar "S"
  c c c c \bar "kievan"
  c c c c \bar "dashed"
}

\score {
  \new Staff {
     \new Voice { \music }
  }
}

was processed twice; first a build from current master, then again with
a build from my local branch:

[master]

address@hidden ~/sandbox/issue1320$ Lilypond show-extents.ly
GNU LilyPond 2.15.42
»show-extents.ly« wird verarbeitet
Analysieren...
Interpreting music...[8][8]
Vorverarbeitung der grafischen Elemente...
Bar Line - glyph: |, X-extent: (0.0 . 0.19), Y-extent: (-1.99875 . 1.99875)
Bar Line - glyph: ., X-extent: (0.0 . 0.6), Y-extent: (-1.99875 . 1.99875)
Bar Line - glyph: :, X-extent: (0.0 . 0.449996), Y-extent: (-1.725 . 1.725)
Bar Line - glyph: ', X-extent: (0.0 . 0.1), Y-extent: (1.49875 . 2.49875)
Bar Line - glyph: S, X-extent: (-1.25 . 1.25), Y-extent: (-4.0 . 4.0)
Bar Line - glyph: kievan, X-extent: (-0.0 . 1.59999), Y-extent: 
(-2.095008 . 2.904992)
Bar Line - glyph: |, X-extent: (0.0 . 0.19), Y-extent: (-1.99875 . 1.99875)
Bar Line - glyph: ., X-extent: (0.0 . 0.6), Y-extent: (-1.99875 . 1.99875)
Bar Line - glyph: :, X-extent: (0.0 . 0.449996), Y-extent: (-1.725 . 1.725)
Bar Line - glyph: :, X-extent: (0.0 . 0.0), Y-extent: (-1.99875 . 1.99875)
Bar Line - glyph: ', X-extent: (0.0 . 0.1), Y-extent: (1.49875 . 2.49875)
Bar Line - glyph: S, X-extent: (-0.3 . 0.38), Y-extent: (-1.99875 . 1.99875)
Bar Line - glyph: S, X-extent: (-1.25 . 1.25), Y-extent: (-4.0 . 4.0)
Bar Line - glyph: kievan, X-extent: (-0.0 . 1.59999), Y-extent: 
(-2.095008 . 2.904992)
Bar Line - glyph: kievan, X-extent: (0.0 . 0.0), Y-extent: (-1.99875 . 
1.99875)
Bar Line - glyph: dashed, X-extent: (0.0 . 0.19), Y-extent: (-1.99875 . 
1.99875)
Bar Line - glyph: dashed, X-extent: (0.0 . 0.19), Y-extent: (-1.99875 . 
1.99875)
Ideale Seitenanzahl wird gefunden...
Musik wird auf eine Seite angepasst...
Systeme erstellen...
Layout nach »show-extents.ps« ausgeben...
Konvertierung nach »./show-extents.pdf«...
Kompilation erfolgreich beendet

[barlineI]

address@hidden ~/sandbox/issue1320$ Lilypond show-extents.ly
GNU LilyPond 2.15.42
»show-extents.ly« wird verarbeitet
Analysieren...
Interpreting music...[8][8]
Vorverarbeitung der grafischen Elemente...
Bar Line - glyph: |, X-extent: (0.0 . 0.19), Y-extent: (-2.05 . 2.05)
Bar Line - glyph: ., X-extent: (0.0 . 0.6), Y-extent: (-2.05 . 2.05)
Bar Line - glyph: :, X-extent: (0.0 . 0.449996), Y-extent: (-1.725 . 1.725)
Bar Line - glyph: ', X-extent: (0.0 . 0.1), Y-extent: (1.55 . 2.55)
Bar Line - glyph: S, X-extent: (-1.25 . 1.25), Y-extent: (-4.0 . 4.0)
Bar Line - glyph: kievan, X-extent: (-0.0 . 1.59999), Y-extent: 
(-2.095008 . 2.904992)
Bar Line - glyph: |, X-extent: (0.0 . 0.19), Y-extent: (-2.05 . 2.05)
Bar Line - glyph: ., X-extent: (0.0 . 0.6), Y-extent: (-2.05 . 2.05)
Bar Line - glyph: :, X-extent: (0.0 . 0.449996), Y-extent: (-1.725 . 1.725)
Bar Line - glyph: :, X-extent: (0.0 . 0.0), Y-extent: (-2.05 . 2.05)
Bar Line - glyph: ', X-extent: (0.0 . 0.1), Y-extent: (1.55 . 2.55)
Bar Line - glyph: S, X-extent: (-0.3 . 0.38), Y-extent: (-2.05 . 2.05)
Bar Line - glyph: S, X-extent: (-1.25 . 1.25), Y-extent: (-4.0 . 4.0)
Bar Line - glyph: kievan, X-extent: (-0.0 . 1.59999), Y-extent: 
(-2.095008 . 2.904992)
Bar Line - glyph: kievan, X-extent: (0.0 . 0.0), Y-extent: (-2.05 . 2.05)
Bar Line - glyph: dashed, X-extent: (-0.095 . 0.095), Y-extent: (-2.05 . 
2.05)
Bar Line - glyph: dashed, X-extent: (-0.095 . 0.095), Y-extent: (-2.05 . 
2.05)
Ideale Seitenanzahl wird gefunden...
Musik wird auf eine Seite angepasst...
Systeme erstellen...
Layout nach »show-extents.ps« ausgeben...
Konvertierung nach »./show-extents.pdf«...
Kompilation erfolgreich beendet

The x-extent of all bar lines is identical except for the dashed
bar line (the newer version is centered around x=0, but the width is 
identical),
so IIUC, rounding errors may not a problem here.

Interestingly, the y-coordinates differ in some cases; this shouldn't
affect the spacing, but I'll try to correct this anyway.

So the main question is: where do the shifted pixels come from?

Regards,

Marc

>