Re: Change color after a line break

[Marc Hohl]

Am 19.07.2015 um 10:04 schrieb David Kastrup:
> Marc Hohl <address@hidden> writes:
[...]
> This \applyContext is executed at Score level as no other contexts have
> yet been created.
>
> > >     c4\pp\< d e f
> > >     \break \stopStaff
> > >     \applyContext #(override-color-for-all-grobs (x11-color 'red))
>
> This \applyContext is executed at Voice level.  Try
>
> \context Score \applyContext ...
>
> here.  You want Score level rather than Staff level in order to also
> catch stuff like marks, bar numbers and so on.  You might want to use
> \context Staff for the first \applyContext, just to make sure that you
> don't get it executed in some other context due to unrelated stuff.
>
> > >     \startStaff
> > >     \grace { g16[( a g fis]) } g1\ff\!
> > > }

I merely copied the example from lsr, where no explicit contexts are 
given, but I think I understand ...
> > Addendum:
> >
> > I am using the bleeding edge self-compiled lilypond version 2.19.24
> > and tried
> >
> > #(define (override-color-for-all-grobs color)
> >    (lambda (context)
> >     (let loop ((x all-grob-descriptions))
> >      (if (not (null? x))
> >       (let ((grob-name (caar x)))
> >        #{ \override #(list 'Staff grob-name 'color) = #color #}
> >        (loop (cdr x)))))))
>
> Well, you indend this to be the same thing, but evaluating some music
> expression and then throwing it away is not going to cause any visible
> results.

Ah, the same mistake again – I had that before, and you corrected me in 
another thread. I *really* should be more careful.

  By the way, you can write
>    #{ \override Staff . #grob-name . color = #color #}
>
> instead in cases where an override music expression is actually needed.
> Probably #{ \override Staff.#grob-name .color = #color #} would also
> work but it seems nicer not to overdo the compression when putting
> Scheme in the middle.

Ah, ok. I fiddled with the old "Grob #'property" syntax and ended with 
the list construct. Your proposal look quite better.

> > as well as the new overrideProperty command provided by David Kastrup
> > in one of the latest patch series:
> >
> > #(define (override-color-for-all-grobs color)
> >    (lambda (context)
> >     (let loop ((x all-grob-descriptions))
> >      (if (not (null? x))
> >       (let ((grob-name (caar x)))
> >         (overrideProperty (list 'Score grob-name 'color) color)
> >        (loop (cdr x)))))))
>
> No, overrideProperty is a real old thing (and also returns a music
> expression which will use a different mechanism when interpreted).  What
> I provided was propertyOverride (yes, that's a really fabulous naming
> choice that will never cause anybody to confuse the two).

Ah, that's the culprit! I remembered that you provided (override ...)
at Scheme level and renamed the command shortly after that, but somehow
I confused overrideProperty and propertyOverride.


>  Which again
> is just another alias for what you wrote above, and as it is returning a
> music expression, will not do the trick for you in the same way than the
> other overrides.

Yes, I understand.
> Now let's for exercise sake actually try going through a music
> expression here.  If we do that, we cannot go through an \applyContext
> hook since then no iterator will get to see our override any more.  We
> could try creating Override stream events and sending them to the
> context ourselves (that's how the respective iterators work) but that's
> sort of pointless.  Instead, just let us create and use overrides
> directly:
>
> overrideColorForAll =
> #(define-music-function (color) (color?)
> #{ #@(map (lambda (dsc)
>              #{ \override Score . #(car dsc) . color = #color
>              #})
>       all-grob-descriptions)
> #})

Thanks a lot! Just to check that I have understood the underlying 
mechanism, I rewrote that according to

overrideColorForAll =
#(define-music-function (color) (color?)
#{ #@(map (lambda (dsc)
            (propertyOverride (list 'Score (car dsc) 'color) color))
     all-grob-descriptions)
#})

which seems to do the trick as well without switching between Scheme and 
LilyPond whithin overrideColorForAll.

> \relative c' {
>     \overrideColorForAll #(x11-color 'blue)
>     c4\pp\< d e f
>     \break \stopStaff
>     \overrideColorForAll #(x11-color 'red)
>     \startStaff
>     \grace { g16[( a g fis]) } g1\ff\!
> }

Thanks for your detailed explanations!

Marc