Re: building pairs in music functions

[Kevin Barry]

On Fri, Mar 13, 2015 at 3:34 PM, Stephen MacNeil <address@hidden> wrote:

\version "2.18.2"

rotateBracket =

#(define-music-function (parser location input) (pair?)

#{

\once \override HorizontalBracket.bracket-flare = $input

#})

Actually I wanted to build the bracket flare from a single value, but I had stripped away most of the code for the purposes of the question. I do a lot of analytic music examples and for that I often angle the HorizontalBrackets, but each time I rotate one it requires using trigonometry (seriously) to calculate the right bracket-flare values, so I just wanted to do that automatically. I eventually got something that works. Here it is in case anyone is interested:

\version "2.18.2"

startAngledGroup =

#(define-event-function (parser location num)

   (integer?)

   (let* ((rot-angle (degrees->radians num))

          (left-flare (- (tan rot-angle)))

          (right-flare (tan rot-angle))

          (y-offset (- (/ num 10))))

     (define flare-callback

       (lambda (grob)

         (ly:grob-set-property! grob 'rotation (list num 0 0))

         (if (= UP (ly:grob-property grob 'direction))

              (ly:grob-set-property! grob 'bracket-flare (cons right-flare left-flare))

              (ly:grob-set-property! grob 'bracket-flare (cons left-flare right-flare)))))

     #{

       \single \override HorizontalBracket.before-line-breaking = #flare-callback

       \startGroup

     #}))

\relative {

  b\startAngledGroup #10 e\stopGroup

}

\layout {

  \context {

    \Voice

    \consists "Horizontal_bracket_engraver"

  }

}