Re: Coloring adjacent notes by interval

[Michael Käppler]

Thanks David,
at the bottom is what I got so far.

Two problems I could not tackle so far:
1. I would like the engraver to be usable in two modes of operation:
A. acknowledging grobs from the note-head-engraver, coloring them
B. directly listening to note-events, output some kind of text, graphviz 
output etc.
even when there is no note-head-engraver present in the context.
Is it somehow possible to merge these two approaches into one engraver? 
The only
possibility I can think of at this moment is to use the 
listener-approach and
to override and revert NoteHead.color as a context property.
Would this be the right way to go?

2. At this moment the engraver colors only the second note of the 
interval found.
I would like to color also the first note, this would however require 
some kind of lookahead
because when the engraver acknowledges the first NoteHead grob it does 
not know which
step will follow.

Any advice is kindly appreciated.

Michael

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

\version "2.19.21"

% Interval definitions
% Number determines the interval type, 1=prime, 2=second, 3=third ...
% plus and minus signs determine variant, no sign=perfect interval, 
+=major ++=augmented
% -=minor, --=diminished
% This list may be extended or completely overwritten
% Usage: #(display (assoc-get "4--" intervaldefs))

#(define intervaldefs
   '(("1++" . (0 . 1))
     ("1" . (0 . 0))
     ("2-" . (1 . 1))
     ("2--" . (1 . 0))
     ("2+" . (1 . 2))
     ("2++" . (1 . 3))
     ("3-" . (2 . 3))
     ("3--" . (2 . 2))
     ("3+" . (2 . 4))
     ("3++" . (2 . 5))
     ("4--" . (3 . 4))
     ("4++" . (3 . 6))
     ("4" . (3 . 5))
     ("5--" . (4 . 6))
     ("5++" . (4 . 8))
     ("5" . (4 . 7))
     ("6-" . (5 . 8))
     ("6--" . (5 . 7))
     ("6+" . (5 . 9))
     ("6++" . (5 . 10))
     ("7-" . (6 . 10))
     ("7--" . (6 . 9))
     ("7+" . (6 . 11))
     ("7++" . (6 . 12))
     ("8--" . (7 . 11))
     ("8++" . (7 . 13))
     ("8" . (7 . 12))
     ("9-" . (8 . 13))
     ("9--" . (8 . 12))
     ("9+" . (8 . 14))
     ("9++" . (8 . 15))
     ("10-" . (9 . 15))
     ("10--" . (9 . 14))
     ("10+" . (9 . 16))
     ("10++" . (9 . 17))
     ("11--" . (10 . 16))
     ("11++" . (10 . 18))
     ("11" . (10 . 17))
     ("12--" . (11 . 18))
     ("12" . (11 . 19))))


interval-color-engraver = #(define-scheme-function (interval 
intervaldefs color)
                             (string? list? color?)
                             (lambda (context)
                               (let ((last-pitch #f))
                                 (make-engraver
                                  (acknowledgers
                                   ((note-head-interface engraver grob 
source-engraver)
                                    (let* ((current-pitch 
(ly:event-property (ly:grob-property grob 'cause) 'pitch))
                                           (current-interval-dt-st (if 
last-pitch
(cons
(- (ly:pitch-steps current-pitch)
(ly:pitch-steps last-pitch))
(- (ly:pitch-semitones current-pitch)
(ly:pitch-semitones last-pitch)))
(cons #f #f)))
                                           (given-interval-dt-st 
(assoc-get interval intervaldefs))
                                           (color-grob? (equal? 
current-interval-dt-st given-interval-dt-st)))
                                      (format (current-error-port) 
"Previous pitch: ~a\n" last-pitch)
                                      (format (current-error-port) 
"Current pitch: ~a\n" current-pitch)
                                      (format (current-error-port) 
"Diatonic diff: ~a\n" (car current-interval-dt-st))
                                      (format (current-error-port) 
"Semitonic diff: ~a\n" (cdr current-interval-dt-st))
                                      (format (current-error-port) 
"Color grob?: ~a\n" color-grob?)
                                      (if color-grob?
                                          (set! (ly:grob-property grob 
'color) color))
                                      (set! last-pitch 
current-pitch))))))))


\layout {
  \context {
    \Voice
    \consists \interval-color-engraver #"2-" #intervaldefs #red
  }
}

\relative c'' { c4 c cis c des c d c }

Am 30.11.2019 um 21:47 schrieb David Kastrup:
> Michael Käppler <address@hidden> writes:
>
> > Am 29.11.2019 um 23:27 schrieb David Kastrup:
> > > Michael Käppler <address@hidden> writes:
> > >
> > > > Hi all,
> > > > I would like to color all successive notes in a voice that span a
> > > > certain interval, like e.g. a perfect fifth upwards.
> > > > Seems to me the most straightforward and extensible way would be to
> > > > write a scheme engraver for this, right?
> > > No, just a callback function for a NoteHead's color property should be
> > > fine.
> > That means it is possible to access properties of a preceding or
> > subsequent event from within a callback?
> Ah, no.  I didn't really get what you meant using "successive" here.
> Yes, this sounds like something that you'd use an engraver for.