Re: [Lilypond-auto] Issue 3560 in lilypond: Completion_heads_engraver with \scaleDurations

[lilypond]

Comment #12 on issue 3560 by address@hidden: Completion_heads_engraver with  
\scaleDurations
http://code.google.com/p/lilypond/issues/detail?id=3560

Well, the problem is that you'll have a1*5 behave one way, and a1*9/8*5  
another (for a five measure note in 9/8 time).  I just don't see that we  
can draw a safe dividing line here, and tuplets _are_ being done using  
scaled time (see the new regtest).  If you mix tuplets with other scalings,  
sometimes whole factors arise, sometimes not.

In addition, currently the completion_heads_engraver messes with a note's  
scale factor whenever it crosses a boundary but leaves it intact when it  
doesn't.  So if you write
\new Voice \with {
  \remove "Note_heads_engraver"
  \consists "Completion_heads_engraver"
}
{ r16*2 \repeat unfold 15 c8*2 r16*2 }
The results are fabulously inconsistent.

Which of the two appended results would you rather have?  Unscaled  
durations can't express arbitrary rational numbers.  That's a limitation of  
musical notation.  With scaled durations (like tuplets), the visual  
appearance no longer matches the actual musical duration.  If the  
Completion_heads_engraver reverses this mismatch, but only sometimes,  
depending on whether a note crosses some boundary or not, does not really  
deliver useful value.

I certainly agree with Keith that the listed use cases would be "nice to  
have".  But seeing the price tag makes me shelve them.

We would need an actual _switch_ for the completion engravers to flip  
between behaviors, and if you flipped that switch to the "lazy long  
durations" setting, syncopated tuplets are impossible.  We might provide  
settings, but I don't think that a default setting that treats c1*3/2*3  
differently from c1*3/2*4 is a reasonable idea for specifying this kind of  
duration, and never mind that c1*3/2*1, not crossing any boundary at all,  
will look different _again_.

Attachments:
        ddd.preview.png  6.3 KB
        eee.preview.png  6.6 KB

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