Re: Lyrics break estimation of vertical spacing

[Boris Shingarov]

> I'd rather discuss this point now, because I don't like the extension of
 > Interval (and I'd rather you didn't spend a whole lot of time getting it
 > to work if there is a nicer way)
 
No kidding, neither do I like diluting Interval.  One, it is an extremely
hacky way to do things.  Two, it *does* introduce problems all over the
rest of the code: various idiosyncrasies of C   showing up here and
there, ending up having a donzen of different places fixed already, but
no one knows how many more will surface.  A situation definitely NOT
to be happy about.

> Replace constrained-breaking.cc:461 by
 >
 > Interval begin_extent = sys->begin_of_line_extent (start, end);
 > Interval rest_extent = sys->rest_of_line_extent (start, end);
 
Yes, but how do I implement begin_of_line_extent()?
Grob::pure_height() simply looks up the value of the "Y-extent" property,
which is a Scheme function, and applies it.  The problem that I've been
struggling with during the past several days, is that this is generic.
 
Oh wait.  Are you saying that System has Axis_group_interface?
So that I can call Axis_group_interface::*_of_line_pure_height() on it?
Let me try it right now.