MIDI Technique: Contrary Motion

For a long time I wanted a MIDI routine that would take a melodic line and invert it (contrary motion) so that each interval would be a mirror of its original form.  A very common technique used in all styles of music.   Sonar developers have never gotten around to it, so I hired a programmer to create a CAL routine for this. 
 
I'd like to share it with Sonar users, some of you may find it very useful when composing, I know I do....
 
Best,
Jerry
www.jerrygerber.com
 
Here it is:  copy and paste the complete text into a text file and rename the file "Contrary Motion.cal"
****************************************************
;; ContraryMotion.cal - (c)2010 Dallas Hodgson. (MINI version)
;;
;; This CAL script inverts the melodic contour of a monophonic MIDI note
;; sequence beginning from the 2nd note on, for example:
;;
;; F4 (note 53), Bb4 (note 58), C5 (note 60), D5 (note 62) will become
;; F4 (note 53), C4 (note 48), Bb (note 47), Ab (note 45)
;;;
;; Note that running this chromatic script an even number of times over a MIDI
;; sequence is guaranteed to leave it untouched.
;;
;; Dallas Hodgson
;; rockisland@iname.com
;; www.dallashodgson.info

(do
    (include "need20.cal")    ; Require version 2.0 or higher of CAL

    (int lastKey -1)
    (int lastContraryKey -1)
    (int keyDelta -1)
    
    (forEachEvent
        (if (== Event.Kind NOTE)
           (do     
               ;; special case setup for the very first note
               (if (== lastKey -1)
                   (do
                       (= lastKey Note.Key)               
                       (= lastContraryKey Note.Key)
                       (= keyDelta 0)
                   )
               )
 
               ;; Compute rise or fall in pitch of current unshifted note over previous unshifted note (ex: if current note is C62 and last note was C60, keyDelta = 2)
               (= keyDelta (- Note.Key lastKey))
                   
            ;; debug msg            
               ;; (pause Note.Key keyDelta lastKey lastContraryKey isDiatonic fixDir)

            (= lastKey Note.Key)
                    
               ;; Apply contrary motion to current note relative to previous contrary note. (ex: If it went up by 2 semitones, make it go down 2 semitones etc.)
               (= Note.Key (- lastContraryKey keyDelta))
               
               (= lastContraryKey Note.Key)
           );; enddo
        );; endif
    );; endfor
);; enddo


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Great work and very thoughtful to think of the forum.