Re: whack-a-regression

[Keith OHara]

Janek Warchoł <janek.lilypond <at> gmail.com> writes:

> > Janek Warchoł <janek.lilypond <at> gmail.com> writes:
> >
> >> i've decided that instead of complaining about slowed development
> >> process, i can do some bug-fixing instead.

> 2013/7/2 Keith OHara <k-ohara5a5a <at> oco.net>:
> > The problem seems to need text that uses skylines being placed outside
> > the staff.  Tiny changes to the text avoid the problem, including adding
> > spaces to the start of the text.  I have not investigated whether the
> > problem affects lyrics (which are place in their own verticalAxisGroup)
> > or dynamics (which can be placed against the staff or in a Dynamics).
> 
> \new Lyrics \lyricmode { \markup \bold Largo }
> compiled fine.
> 

And changing the text, it always seems to compile fine.  So there seems 
to be no problem in forming a skyline around Lyric Text.

The problem appeared when placing text in relation to other things, so try
<< \new Lyrics \lyricmode { a }
   \new Lyrics \lyricmode { u } >>
LilyPond on Windows runs forever on that, depending on the text.

Two lines of Lyrics do not use the code that does outside-staff placement,
so it was not my change that caused the problem.  It must be the changes
to the implementation of Skylines for issue 3344. 

One thing that LilyPond must do in both buggy cases is to merge skylines 
together.  The function merge() has lots of loops that step by the width 
of a segment in a skyline, and the skylines around text seem to have 
vertical segments.  To fix the bug we need to skip near-zero-width 
segments or make those loops robust to zero-width segments.