Re: Feature request: Display bezier control-points

[David Nalesnik]

Hi Urs,

> It would be a really valuable feature if one could let LilyPond display
> > the control-points of a bezier curve.
> > I would imagine something like a cross or a point at the middle two
> > control-points.
>

I think this would be very helpful, so that you can visualize exactly what
these control-points are that you're setting.  (It must be a common
misconception that they are points on the actual curve.)

I'm not sure what impact this may have on the layout, but you could do
something like the following:

\version "2.15.37"

#(define (make-cross-stencil coords)
  (ly:stencil-add
    (make-line-stencil 0.1 (- (car coords) 0.2) (- (cdr coords) 0.2)
   (+ (car coords) 0.2) (+ (cdr coords) 0.2))
    (make-line-stencil 0.1 (- (car coords) 0.2) (+ (cdr coords) 0.2)
   (+ (car coords) 0.2) (- (cdr coords) 0.2))))

#(define display-control-points
  (lambda (grob)
    (let ((stencil (ly:slur::print grob))
          (cps (ly:grob-property grob 'control-points)))

      (ly:stencil-add stencil
      (make-cross-stencil (second cps))
      (make-cross-stencil (third cps))))))

\relative c'' {
  \override Slur #'stencil = #display-control-points
  c( d e f)
}

Hope you find this helpful!

-David