Re: attachment points for vertical spacing dimensions

[Alexander Kobel]

On 2010-10-07 04:11, Joe Neeman wrote:
> On Wed, Oct 6, 2010 at 1:26 AM, Mark Polesky <address@hidden
> <mailto:address@hidden>> wrote:
>     Joe Neeman wrote:
>     >  I would argue that the baseline is more natural then the
>     >  bottom.  Moreover, using the baseline as a reference point
>     >  will result in more even spacing of multiple consecutive
>     >  lines of markup.
>
>     Okay, that's a good point, so I agree -- baseline is better
>     than bottom.  But do you agree with Carl and Trevor that we
>     should always use the same reference point for markups?  I
>     was specifically proposing to use the bottom of the upper
>     markup and the top of the lower markup for
>     between-title-spacing, but Carl argued eloquently against
>     it.  Carl's argument is probably much more solid than mine,
>     but just for the record, what do you think?
>
> I don't care so much about one versus two reference points (although the
> current code only works with one), but I do think that the reference
> points should not depend on any ascenders or descenders.

Hm, I'm not sure.  The baseline in some sense is the natural place to 
attach references to - that's how it's done in most applications I can 
think of.  On the other, hand, these typically deal with single lines on 
their own...
For a markup placed /above/ a staff (or another markup, by the same 
argument), the baseline of the lowest line of the markup is a sensible 
reference (even better than the bottom corner, since, as you pointed 
out, this does not depend on an ascender).  However, this is a poor 
choice for markups (like footer) /below/ a staff - if you add a line 
here, you'd have to redo spacing.  Using the baseline of the top-most 
line would be better, but looks far harder to code.
Furthermore, both baselines don't allow a good handling of the case of 
non-character markups (a score - What's the baseline there? The middle 
line of some staff? -, a figure, whatever) which has larger height than 
a letter of the default font.  And font sizing doesn't change the 
baseline, but the ascender and descender height.

Honestly, I don't think it's worth the hassle.  IMHO, we should try to 
give reasonable definitions, but not to deal with each and every 
possible use case; the user needs to tweak, and he probably won't find 
the optimal values for all these spacing variables by anything but 
trial-and-error.  Let's not complicate this by overcluttering with a 
huge bunch of options.
As for fonts, it's not too hard to guess the extent of a line, 
especially since baseline-skip is given in staff units.  The topmost 
point as anchor works fine in many cases, and padding additionally is 
there to avoid trouble.

The only point the current layout does not work well for me is tweaking 
the pages s.t. the topmost and bottommost (center lines of) staves align 
over all pages, but even there I can perfectly live with a manual 
positioning of the footer and, optionally, a \with-dimension #'(0 . 0) 
#'(0 . 0) there.  And if the very last line of a score is slightly above 
the others, I don't feel it disturbs the overall impression.  Things are 
easier for the top, since the first page has the book header, and the 
page number has the same extent on all the others.

>     I've noticed that in many traditionally-engraved scores, [...]
>     For example, say score1 has title/subtitle/etc. in the usual
>     place (top center), and piece/opus also in the usual place
>     (flush left and flush right just above the top system), and
>     the top system has no protruding skyline.  Now score2 has
>     all the same titling but the top system has a really high
>     note just before the rightmost barline.
>
>     To prevent a collision between the last note and the opus,
>     LilyPond will shift the first system down.  Fine.  But what
>     I've noticed in the classic scores is that in this
>     situation, the top system is not shifted down, but rather
>     the opus is shifted *up*.  This is an important difference!
>
>     It means that the placement of the top system is determined
>     by the bookTitleMarkup, and the scoreTitleMarkup is
>     determined by the top system.  And it usually looks better
>     this way (and more consistent from score to score). [...]
>
> I won't say it's more trouble than it's worth, but I don't think it's
> trivial. In lilypond-spacing-backend terms, I think you want to treat
> the opus markup as a "loose line."

Now, that'd be an feature...  Even assuming that we'd have to take opus 
out of the header tags - can one manually add "loose lines" besides Lyrics?


Cheers,
Alexander