Re: Plan for discussions

[address@hidden]

On 14 mai 2012, at 11:22, Joseph Rushton Wakeling wrote:

> On 14/05/12 09:56, David Kastrup wrote:
>> <URL:http://lilypond.org/doc/v2.15/Documentation/source/Documentation/notation/skipping-corrected-music>
> 
> Yes, but that wasn't the use-case I had in mind.  The sort of thing I was 
> thinking of was:
> 
>    (i) I have a full, complete score, which I have compiled.
> 
>   (ii) I spot a typo (say, an A that should be A-flat).
> 
>  (iii) I correct the wrong note and recompile.  The recompilation process
>        ought to be significantly faster than the original complete-score
>        compilation process, even though a full score is being produced as
>        output.

This is very hard because of the butterfly effect - an A-flat in an 
already-crammed line could lead to new line breaking, which means new vertical 
spacing etc..

I only see two ways of handling this:

1)  An aux file that is able to act as a sort of diff to the current file so 
that the creation of Grobs is accelerated during the interpretation process (a 
speed up of about 15% on orchestral scores, 1-ish% if that on simple scores).

2) LilyPond running in server mode on your machine where it takes an input file 
and runs a lot of "contingencies" as a background process.  That is, it starts 
with the most recent successfully compiled score and rules-out different line 
breaking configurations.  For example, it'd add accidentals to groups of notes 
to test what that did to line-breaking and come up with categories of cases 
where the line breaking didn't change.  If a new run of LilyPond on a corrected 
score falls into one of these categories of cases, then LilyPond uses a stashed 
result for line breaking.  Machines 20 years ago would have died doing this, 
but I actually think its possible now.  One of the reasons that Instagram is so 
cool is because it does a similar thing: it starts uploading a photo while 
you're writing captions and browsing through filters and applies certain 
filters to the uploaded file and to the local file once the decision is made.  
As a result, the upload seems instantaneous.  But for us, this would easily 
take a Google summer of code...and fall of code...and winter of code...and...

Cheers,
MS