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Re: Feature request: Display bezier control-points


From: Urs Liska
Subject: Re: Feature request: Display bezier control-points
Date: Fri, 04 May 2012 10:56:46 +0200
User-agent: Mozilla/5.0 (X11; Linux i686; rv:11.0) Gecko/20120329 Thunderbird/11.0.1

Am 04.05.2012 08:09, schrieb James:
Hello,

On 4 May 2012 01:31, Urs Liska<address@hidden>  wrote:
Am 04.05.2012 02:08, schrieb 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!
Wow, extremely!
Of course I would prefer to have this built-in.
And as you I can't really judge if this has side effects.
But this really _is_ helping to find suitable values for the control-points.

  * Although I know bezier curves from vector graphics software, I also
   was convinced that the 'control-points' were four points on the
   curve that define its shape.
  * In fact the first and last are such points, whereas the middle two
   'control-points' are the 'handles'.
   ->  Is this explained somewhere?
http://lilypond.org/doc/v2.14/Documentation/notation-big-page.html#modifying-ties-and-slurs
OK, that's a thorough explanation ...
I must have read this - but probably I didn't understand it then and therefore forgot it more effectively than if I hadn't seen it at all ;-)

Best
Urs

?

James




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