Re: When (in seconds) does each page begin?

[Matt Wallis]

On 28/05/2020 23:15, Valentin Villenave wrote:
> On 5/28/20, Matt Wallis <m7956@acumen-it.co.uk> wrote:
> > The output from event-listener is so close. I just need to get it to
> > listen to the appropriate events ... if that is possible.
>
> Then you should definitely have a look at the last link I sent
> (lilypond-html-video); IIRC it uses a Scheme engraver (so no patching
> Lily itself) to output svg with additional timing information encoded
> as data- attributes for each rhythmic event. Then one can use that to
> get a cursor, change CSS attributes on the fly (e.g. noteheads
> opacity), switch from one page to the next, etc.  It’s still very much
> WIP, but you can have a look at the examples (particularly the
> vibraphone one) to get an idea.

Many thanks for the pointer. I had not encountered lilypond-html-video 
before.

It is very informative to see how the Grob_metadata_engraver is 
constructed in 
https://gitlab.com/sigmate/lilypond-html-live-score/-/blob/master/grob-inspector.ily. 
 I finally have a reason to look into what a grob is - did I mention I 
was new to this? :-)

But it is working on a single SVG (one long line) using 
one-line-auto-height-page-breaking, whereas I want a sequence of pages, 
and to know when each page starts (in seconds).

From my initial reading, I suspect there is a way of inferring from the 
grobs when a new page begins. I find myself asking: if I have one System 
per page, can I infer a page has started by acknowledging all System 
grobs?.
But I would rather do this more directly by listening to the 
page-break-event (or something like that).

> I’m CCing Mathieu as it’s his project. Mathieu, you can read Matt’s
> previous message here:
> https://lists.gnu.org/archive/html/lilypond-user/2020-05/msg00527.html

And my original question is here:

https://lists.gnu.org/archive/html/lilypond-user/2020-05/msg00521.html

BTW, I didn't see a vibraphone example. I scanned a few branches, but 
maybe I didn't try the right branch.

All the best, Matt