Re: [Lilypond-auto] Issue 1713 in lilypond: Whole note/dotted note collision in polyphony

[lilypond]

Comment #30 on issue 1713 by address@hidden: Whole note/dotted note  
collision in polyphony
http://code.google.com/p/lilypond/issues/detail?id=1713

@Pavel (comment 22):
"The patch removes several constants [...] but I don't think it's a good  
approach for Lilypond."

Generally i agree, but not in this specific case.  The original code is  
very hard-wired and quite broken.  It produces more bad (completely bad,  
not just imperfect) results than good ones.

"A generic algorithm makes it harder to tweak one distance without tweaking  
other distances."

but a generic algorithm makes it easier to change many things in a  
coordinated, coherent way.

"I believe there should be no slight changes."

If the original code produced at least acceptable results, i would agree.   
But it didn't.  Even if Keith's patch makes 5% of cases slightly worse, it  
makes half of cases significantly better.  In my opinion we should accept  
it, and then improve it.
compare
http://lilypond-stuff.1065243.n5.nabble.com/file/n5705591/close-collisions_current.pdf
with
http://lilypond-stuff.1065243.n5.nabble.com/file/n5705591/close-collisions_new.pdf

"We need a big test, a matrix with all combinations of notes that can  
collide."

I thing the above one is good.  The source is in a comment in Rietveld  
http://codereview.appspot.com/6189048/diff/9003/input/regression/collision-whole.ly#newcode16

"That should cover all styles, all standard shapes of noteheads, all  
durations and all pitch differences."

Are you sure?  A matrix like the above one (or bigger) for 15 styles of  
noteheas and about 15 special shapes used in various shapeNotes?  That's  
about 1000 cases (or more).

I'm not opposed to having an algorithm that would handle all collisions of  
notes with any shape.  But that surely cannot be done with "just-right  
human tweaked numbers"; we would have to teach Lily recognizing the actual  
shape of the noteheads.
I think it is possible to do this: Mike's work on skylines is very  
promising in this regard.  If you haven't followed the discussion about it,  
see issue 2148, http://codereview.appspot.com/5626052/ and compare outlines  
in these files:
http://lilypond-stuff.1065243.n5.nabble.com/file/n5705592/Eja-Mater_master.pdf
http://lilypond-stuff.1065243.n5.nabble.com/file/n5705592/Eja-Mater_skylines.pdf