Anchor points of Slurs / Phrasing slurs

[Valentin Petzel]

Hello.


I’ve been thinking about how to get these S-shaped slurs you tend to find in 
piano music (e.g. in Staff changes) done properly in Lilypond. Usually this is 
done by manually overriding the Coefficients to the Bernsteinpolynomials, which 
I think should be avoided if possible. 

I guess Lilypond’s optimizing algorithm might actually be able to this fine, 
potentially with a slight variation of the parameters to the penalty 
functional. But for this we’d need to have more freedom about the slur’s 
anchor points:

Currently the anchor points are set both over or both under the starting / 
ending note, depending on the slur’s direction. For the S-shape we would need 
the control points to differ in directions, so one point above and one point 
beneath the respective notes.

So I try to do do at least one of these two things:

A) Have both the the slur end point take a direction [ i.e. something like
c^( ... c_)  ]
B) Add a modifier '((x1 . x2) (y1 . y2)) to the slur interface to specify the 
relative anchor points or an offset

I’m just stuck there, because I can’t figure out the part that actually 
calculates the anchor points, so I hope that one of you has more insight into 
the lilypond code regarding that matter.


Regards,
Valentin

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