Re: order of engravers

[David Kastrup]

Kieren MacMillan <address@hidden> writes:

> Hi Graham et al,
>
>> Talking about
>> http://code.google.com/p/lilypond/issues/detail?id=673
>> problem with order of \consists
>> 
>> 1)  Add a sentence about default_bar_line_engraver and
>> timing_translator  (or whatever Werner was talking about on 673).  I
>> know we've already said "there order may matter; here's one example,
>> but there may be others", but we might as well list this case since it
>> came up.
>> 
>> 2)  Do some trawling through the IR and/or code (as per Han-Wen's
>> comment 5 in the issue)  and try to discover all dependency chains of
>> engravers, then list all those in Notation.  If you go to this much
>> effort, we might as well make a separate section (well,
>> unnumberedsubsubsec) in the docs for these dependency chains.
>
> From the "header" comments in IR:
>
>     Auto_beam_engraver requires Stem_engraver
>     Bar_number_engraver requires Staff_collecting_engraver
>     Default_bar_line_engraver should be at the same level as Timing_translator
>     Mark_engraver should stay with Staff_collecting_engraver
>     Metronome_mark_engraver requires Staff_collecting_engraver
>
> From comments in engraver-init.ly:
>
>     Bar_engraver must be first so default bars aren't overwritten with empty 
> ones.

And so on.  One could automate documentation generation by making it
possible to specify order/dependencies when defining engravers.

And if each engraver specifies what engravers it is relying on in a
machine-readable manner (or the respective order in which it wants to be
applied), then Lilypond can actually do the required sorting and figure
out a proper order at runtime.

-- 
David Kastrup