goeyvaerts-rotation

dear all

here's a function (revised, should work correct now) to work with rotations - based on the work of karel  goeyvaerts

(defun goeyvaerts-rotation* (&key pitches 
                                 static-pitches
                                 generations
                                 goeyvaerts-transpose-interval
                                 (direction 'up)
                                 low-border
                                 high-border
                                 correction-interval)

  (let ((pitches (filter-remove (pitch-to-midi static-pitches) (pitch-to-midi pitches))))
    (midi-to-pitch (append  (list (append pitches (pitch-to-midi static-pitches)))

                            (cond ((equal direction 'up)
                                   (loop repeat generations
                                     for x in (gen-repeat 50 goeyvaerts-transpose-interval)
                                     collect (append 
                                              (setf pitches (append (loop for i in pitches
                                                                      
                                                                      when (> (+ i x) (pitch-to-midi high-border))
                                                                      collect (+ x (- i (abs correction-interval)))
                                                                      else collect (+ i x))))
                                              (pitch-to-midi static-pitches))))

                                  ((equal direction 'down)
                                   (loop repeat generations
                                     for x in (gen-repeat 50 goeyvaerts-transpose-interval)
                                     collect (append 
                                              (setf pitches (append (loop for i in pitches
                                                                      
                                                                      when (< (- i x)  (pitch-to-midi low-border))
                                                                      collect (+ i correction-interval)
                                                                      else collect (- i x))))
                                              (pitch-to-midi static-pitches)))))))))

EXAMPLE:

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;;; an example with multiple objects inside a chord / GOEYVAERTS uses it woth octave-rotations and with static pitches
;;; here i do it different....

;;; :goeyvaerts-transpose-interval => in every generation the elements are transposed by next interval (circular)
;;; :static-pitches =>  will not rotate!!
;;; :high-border => if a pitch  is higher then this it will be transposed down by :correction-interval

;;; EVALUATE THIS

(setf groups (loop for i in (goeyvaerts-rotation* :pitches '(b3 d4 eb4 gb4 f5 e5 g5 ab5 a4 bb4 db5 c6)
                                                  :static-pitches nil;'(e4 eb5)
                                                  :direction 'up
                                                  :generations 20
                                                  :goeyvaerts-transpose-interval '(2 3 5 7 5 3)
                                                  :low-border 'a2
                                                  :high-border 'eb6
                                                  :correction-interval -36)

               collect  (gen-divide '(5 3 2 2) i)))

;;; AND THIS / cmd1 => so you see the chords an see the rotation etc..

(setf chordized-groups (loop for i in groups 
                         collect (chordize i)))


=> you see the process of the elements