Re: Setting Slur.positions to 0s can still move slurs

[Aaron Hill]

On 2021-04-07 7:52 am, Nate Whetsell wrote:
> Setting Slur.positions to #'(0 . 0) appears to still move slurs.

The Internals reference [1] comments on the the positions property of 
the slur-interface:

"For slurs, this value selects which slur candidate to use; if extreme 
positions are requested, the closest one is taken."

The snippet [2] you mentioned is poorly worded in my opinion.  Setting 
positions does not move the Slur, rather it tells LilyPond to try to use 
a Slur that has its ends points on the specified staff position.  As 
such, #'(0 . 0) does not mean there is to be no effect on the Slur, 
rather it instructs LilyPond to prefer a Slur where the ends lie on the 
center line.

To actually move a Slur, you could adjust its control-points property, 
which holds the shape of the candidate Slur that was selected by 
LilyPond.  The \shape command [3] is typically used to do this as it 
allows you to specify individual offsets to be applied to each control 
point.

[1]: 
https://lilypond.org/doc/v2.22/Documentation/internals/slur_002dinterface
[2]: https://lsr.di.unimi.it/LSR/Item?id=684
[3]: 
https://lilypond.org/doc/v2.22/Documentation/notation/modifying-shapes


-- Aaron Hill