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

[lilypond]

Comment #1 on issue 3560 by address@hidden: Completion_heads_engraver with  
\scaleDurations
http://code.google.com/p/lilypond/issues/detail?id=3560

I have my problems taking issue 1772 seriously at the same time as this  
issue.

The fundamental problem that we are dealing with is that scaled durations  
are used for multiple purposes.  One purpose is to have basically unmarked  
tuplets where the displayed timing is a differently scaled version of the  
real timing.

Another purpose is to juggle with the onset of the next following  
note/barline/whatever while not actually wanting to change the duration of  
the note as such.

How do we deal with this in Midi?  It should give us a pointer into what we  
want the completion engravers to do.

It also definitely means that either one or the other use cases _will_  
break when using Completion_heads_engraver.  Looking at the code, it seems  
like it makes a distinction between scaled durations that make things  
shorter, and scaled durations that make things longer.  I'm not sure of the  
results (and changing the code around partly lead to infinite loops and  
other stuff), but it's a reasonable guess that the intent is to have the
"scale the durations" interpretation when the factor is smaller than 1 and  
the
"shift next onset but keep the duration" interpretation when the factor is  
larger than 1.

I haven't checked how well this theory holds up in practice.

However, it is worthwhile to note that \times/\tuplet does by far the bulk  
of its work by scaling durations, with tuplet brackets just being the  
topping on the scaled results (probably not even visible to Midi).

So with the current setup, we might not have much of an option other than  
interpreting scaled durations _exclusively_ as scaled durations and nothing  
else, and in that case, most of the examples of issue 1772 are invalid: you  
should work with a combination of unscaled note and subsequent or parallel  
\skip instead if you want Midi interpretation and/or completion engravers  
to have a different view.

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