Centering a stencil on another stencil

[Paul Morris]

After I didn’t find anything for it in the LSR or mailing list, I came up with a scheme procedure for centering one stencil on another, on either the X or Y axis.  I uploaded it to the LSR and I’m posting it here for future seekers of centered stencils.

http://lsr.di.unimi.it/LSR/Item?id=1009

Cheers,
-Paul


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\version "2.18.2"

#(define (center-stencil-on-stencil axis stil-a stil-b)
   "Return a copy of stencil @var{stil-b} that has been 
    moved so it is centered on stencil @var{stil-a} on 
    @var{axis}. @var{axis} is 0 for X axis, 1 for Y axis."
   (let* ((ext-a (ly:stencil-extent stil-a axis))
          (ext-b (ly:stencil-extent stil-b axis))
          (width-a (- (cdr ext-a) (car ext-a)))
          (width-b (- (cdr ext-b) (car ext-b)))
          (width-diff (- width-a width-b))
          (position-diff (- (car ext-a) (car ext-b)))
          (offset (+ position-diff (/ width-diff 2)))
          (new-stil-b (ly:stencil-translate-axis stil-b offset axis)))
     new-stil-b))

%%%%%%%%%%%%%

circle = #(make-circle-stencil 3 0.4 #f)

square =
#(stencil-with-color
  (make-connected-path-stencil
   '((0 0) (3 0) (3 3) (0 3) (0 0))
   0.4 1 1 #f #f)
  blue)

\markup \line {
  \stencil #(ly:stencil-add circle square)
  "   "
  \stencil #(ly:stencil-add circle (center-stencil-on-stencil X circle square))
  "   "
  \stencil #(ly:stencil-add circle (center-stencil-on-stencil Y circle square))
  "   "
  \stencil #(ly:stencil-add circle (center-stencil-on-stencil Y circle
                                     (center-stencil-on-stencil X circle square)))
}

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