[Lilypond-auto] [LilyIssues-auto] [testlilyissues:issues] #5539 TextSpan

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[Lilypond-auto] [LilyIssues-auto] [testlilyissues:issues] #5539 TextSpanner: left text incorrectly influences dashes

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Sat, 20 Jul 2019 09:11:06 -0000

Hi Werner,

I disagree.
The dashed line of a TextSpanner must start right after left-text. It must end right before right-text or as in your example at the target NoteColumn. (for line-breaks similar).

This can't be warranted while exactly following the user-setted dash-period/fraction.
Some scaling is always needed. Otherwise the dashed line will be too short or too long.

In your eample:
If I read out the dashed-line-settings from the 'stencil I get:

%% im      
      (dashed-line
        0.1
        0.672281764072063
        6.05053587664857
        14.1179170455133
        0.0
        0.0))

%% immer
      (dashed-line
        0.1
        0.926494248232063
        8.33844823408857
        10.1914367305527
        0.0
        0.0)

dashed-line has settings for thickness, on, off, x-destination, y-destination and phase (in this order)

IIUC:
on, off are the here relevant variables, influenced by dash-period/fraction,
note: dash-fraction is a percentage not an absolute value.
'on' is the printed part
'off' is the white space part

So in the first example (+ on off on off on) should lead to the x-destination, which is correct.
In the second example (+ on off on) should lead to the x-destination, which is correct as well.

OTOH (+ on off) is in both cases not the setted dash-period:
6.722817640720633 for the first, 9.264942482320633 for the second stencil.

Looks like lily scales both, the length of the printed dash and the white space between them to find an accaptable trade-off.

Whether current approach is the best, may be discussable, but you can't avoid scaling, imho.
In the draw-dashed-line-markup which I implementd some time ago, I scaled 'on' only for a rare corner case (very short line) otherwise only 'off' is tackled.

[issues:#5539] TextSpanner: left text incorrectly influences dashes

Status: New
Created: Sat Jul 20, 2019 08:17 AM UTC by Werner LEMBERG
Last Updated: Sat Jul 20, 2019 08:19 AM UTC
Owner: nobody
Attachments:

text-spanner-wrong-dash-spacing.png (4.6 kB; image/png)

[git commit 49f41bf1c64ae1e2490571e73a85cbc4b2a9fb27]

\version "2.21.0"

\header { texidoc = "
  For a text spanner, the length of the (left) text element
  must not influence the distance between and the length of
  dashes.

  Here is a counterexample.
" }

\relative c' {
  \override TextSpanner.dash-period = #8
  \override TextSpanner.dash-fraction= #0.1

  \override TextSpanner.bound-details.left.text = "im"
  e1\startTextSpan e1 e1\stopTextSpan

  \override TextSpanner.bound-details.left.text = "immer"
  e1\startTextSpan e1 e1\stopTextSpan
}

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