Re: Some questions related to score video generation

[Urs Liska]

Hi Knut,

very interesting project (which should be included in my plan for an
additional "interesting uses" page on lilypond.org). Some comments (but
explicitly without any warranty):


Am 07.07.2017 um 09:55 schrieb Knut Petersen:
> Hi everybody!
>
> I extended my video generation script to allow coloring notes as they
> are played.
> Currently that works for noteheads and rests, see this example I
> uploaded to youtube <https://www.youtube.com/watch?v=Z6MtIydbe-I>.
>
> Question 1: I use an after-line-breaking override for NoteHead, Rest
> and MultiMeasureRest
> events to encode the moment and the duration in the color fields of
> the notehead
> grobs, translate to postscript and postprocess the postscript files to
> tell ghostscript
> to generate images for every moment that has one of those events. Does
> anybody
> know a less hackish way to generate  multiple copies of the systems of
> a score
> with changes to only the color of some grobs?

What about generating the score as SVG and coloring the objects with CSS
? you could store a consecutive *index* in the grobs (rather than actual
moments) and create a list with all moments when the coloring should change.

In a post-processing step you could iterate over the list, color the
elements with the corresponding index and produce an image from that.
In a second post-processing step you could iterate over the list to
compile the generated images according to the moments in the list.

>
> Question 2: I also would like to change the color of the stems, flags
> and dots that
> belong to a notehead, but those have no 'duration. Does anybody have
> an idea
> how to give a certain color to those grobs from inside the code called
> by the
> notehead after-line-breaking override?

If nh is the name of your grob in the callback then

  (ly:grob-object nh 'stem)
will give you the stem.

AFAIK the Flag etc. are not all accessible this way but you can do (in a
(let)):
  (nc (ly:item-get-column nh)) ; get the note column for the note head
  (elements (ly:grob-array->list (ly:grob-object nc 'elements)))
which gives you a list of all items in the note column to iterate over.

HTH
Urs

>
> Knut
>
>
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