Re: what does it take to produce a new output block

[Flaming Hakama by Elaine]

> ---------- Forwarded message ----------
> From: Flaming Hakama by Elaine <elaine@flaminghakama.com>
> To: lilypond-devel <lilypond-devel@gnu.org>
> Cc:
> Bcc:
> Date: Tue, 31 May 2022 14:02:51 -0700
> Subject: what does it take to produce a new output block
> Hi,
>
> I am interesting in seeing what it would take to enhance lilypond to output
> in this text format
>
> https://www.irealpro.com/ireal-pro-file-format
>
> My first idea would be to add something along the lines of the midi block,
> where if you add this new output, you will get output in this text format,
> which is essentially an HTML link.
>
> \score {
>   … music …
>   \layout { }
>   \midi { }
>   \ireal { }
> }
>
>
> I suppose it should support similar features for command line and scheme:
>
> -direal-extension=html
> #(ly:set-option 'ireal-extension "html")
>
>
> To look into implementing this, where would I get started?
>
> Is there any documentation that describes what exactly is a block, what it
> takes as input, etc.?
>
> Where would I find the code for the layout and midi blocks?
>
>
> Thanks,
>
> Elaine
>
>
>
>
> ---------- Forwarded message ----------
> From: Jean Abou Samra <jean@abou-samra.fr>
> To: Flaming Hakama by Elaine <elaine@flaminghakama.com>, lilypond-devel <
> lilypond-devel@gnu.org>
> Cc:
> Bcc:
> Date: Tue, 31 May 2022 23:24:44 +0200
> Subject: Re: what does it take to produce a new output block
> Hi,
>
> A minor point of procedure: even though you changed the subject, it
> appears that you started this thread from a previous thread about time
> signatures in your email client. The email contains headers that make it
> appear in that thread for others. In the future, start a new thread
> every time.
>
>
> Le 31/05/2022 à 23:02, Flaming Hakama by Elaine a écrit :
> > Hi,
> >
> > I am interesting in seeing what it would take to enhance lilypond to
> output
> > in this text format
> >
> > https://www.irealpro.com/ireal-pro-file-format
> >
> > My first idea would be to add something along the lines of the midi
> block,
> > where if you add this new output, you will get output in this text
> format,
> > which is essentially an HTML link.
> >
> > \score {
> >    … music …
> >    \layout { }
> >    \midi { }
> >    \ireal { }
> > }
> >
> >
> > I suppose it should support similar features for command line and scheme:
> >
> > -direal-extension=html
> > #(ly:set-option 'ireal-extension "html")
> >
> >
> > To look into implementing this, where would I get started?
>
>
>
> I would start by writing Scheme engravers living in \layout
> that take the content and format it together. The only disadvantage
> is that won't have ireal output without at the same time doing
> layout output (well, unless you go for calling (exit) at the
> end of the translation step if that's really a problem ...).
> The big advantage is that you can start doing this right now
> in a .ly file, without touching LilyPond's code at all, post
> it on the user list and get feedback.
>
> There is no official documentation for engravers, but there
> is an unofficial resource (by me):
>
> https://extending-lilypond.readthedocs.io/en/latest/translation.html
>
>
>
> > Is there any documentation that describes what exactly is a block, what
> it
> > takes as input, etc.?
>
>
> Well, LilyPond doesn't really have a notion of a "block".
> The objects you create with \midi and \layout are called
> "output definitions" (output defs for shorts), a category
> which actually also encompasses \paper blocks. I guess the
> closest you get as documentation about output defs is
>
>
> https://lilypond.org/doc/v2.23/Documentation/notation/modifying-context-plug_002dins.html
>
> but this is not really descriptive of the internals, and
> I don't think it needs to be: output defs are an overarching
> concept where many tweaks take place; the way these tweaks
> are arranged internally isn't really relevant to the user.
>
> Most importantly, \layout and \midi are hardcoded. You
> cannot create you own type of "block" without touching
> the C++ sources.
>
>
>
> > Where would I find the code for the layout and midi blocks?
>
>
> A bit all over the place, really. lily/lexer.ll and lily/parser.hh
> have the parsing logic, with some bits in lily/lily-lexer.cc
> and lily/lily-parser.cc. The Output_def class is found in
> lily/output-def.cc. The Scheme interfaces for manipulating
> it are in lily/output-def-scheme.cc. A central element of output
> defs is context defs (the \context blocks); that class is
> in lily/context-def.cc with Scheme interfaces in
> lily/context-def-scheme.cc. Then you have files like
> lily/engraver.cc, lily/score-engraver.cc, lily/performer.cc,
> lily/score-performer.cc which define the classes of
> translators that \layout and \midi respectively run.
>
> But as I said above, I don't think the code for \layout
> and \midi is the most relevant part of LilyPond to
> look at for solving your problem, at least until you get
> to a state where it's working fully and you want to contribute
> it to LilyPond with that kind of interface. Start with
> learning how to code an engraver first.
>
> Best,
> Jean
>
>
>
Thanks, this is very helpful.