+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; beam slope
+
+;; calculates each slope of a broken beam individually
+(define-public (beam::place-broken-parts-individually grob)
+ (ly:beam::quanting grob '(+inf.0 . -inf.0) #f))
+
+;; calculates the slope of a beam as a single unit,
+;; even if it is broken. this assures that the beam
+;; will pick up where it left off after a line break
+(define-public (beam::align-with-broken-parts grob)
+ (ly:beam::quanting grob '(+inf.0 . -inf.0) #t))
+
+;; uses the broken beam style from edition peters combines the
+;; values of place-broken-parts-individually and align-with-broken-parts above,
+;; favoring place-broken-parts-individually when the beam naturally has a steeper
+;; incline and align-with-broken-parts when the beam is flat
+(define-public (beam::slope-like-broken-parts grob)
+ (define (slope y x)
+ (/ (- (cdr y) (car y)) (- (cdr x) (car x))))
+ (let* ((quant1 (ly:beam::quanting grob '(+inf.0 . -inf.0) #t))
+ (original (ly:grob-original grob))
+ (siblings (if (ly:grob? original)
+ (ly:spanner-broken-into original)
+ '())))
+ (if (null? siblings)
+ quant1
+ (let* ((quant2 (ly:beam::quanting grob '(+inf.0 . -inf.0) #f))
+ (x-span (ly:grob-property grob 'X-positions))
+ (slope1 (slope quant1 x-span))
+ (slope2 (slope quant2 x-span))
+ (quant2 (if (not (= (sign slope1) (sign slope2)))
+ '(0 . 0)
+ quant2))
+ (factor (/ (atan (abs slope1)) PI-OVER-TWO))
+ (base (cons-map
+ (lambda (x)
+ (+ (* (x quant1) (- 1 factor))
+ (* (x quant2) factor)))
+ (cons car cdr))))
+ (ly:beam::quanting grob base #f)))))