[smufl-discuss] Re: Glyph registration proposal

[Joseph Berkovitz]

>> Currently, the registration roughly centers each staff vertically
>> (within a half staff line) with respect to the center line of a 5-
>> line staff, but takes an unclear approach for staves with an even
>> number of lines that seems to round off the vertical placement. The
>> glyphs for 2-, 4- and 6-line staves should be adjusted so the staff
>> line symbols all have their vertical center aligned with the center
>> of the middle line of the 5-line staff glyph.
>
> I have adjusted Bravura to match this recommendation, but I'm not 100%
> sure that e.g. a 2-line staff should conceptually be centered on the
> middle line of a 5-line staff; there is presumably some argument about how
> changes in the number of staff lines (e.g. midway through a system) should
> be handled: should there be any continuity between the positions of staff
> lines when switching between a 5-line and, say, a 2-line staff?
>
> I imagine that few (if any) scoring applications will actually choose to
> use these symbols for drawing staves anyway, so this is somewhat academic,
> I suppose.

Actually, this is not an academic point when it comes to clefs, especially clefs that can be used on non-5-line-staves. I should have called this point out more clearly. The staff glyphs are really the least of the concerns; as you point out few applications will use them. It's the clefs that motivated this rule.

For example consider the 4-line TAB and 6-line TAB clefs. These were already centered in the way that the rule prescribes (maintaining a vertical centerline at Y=0.5 em).

Also, the percussion clef is usable on a staff with any number of lines, and the preservation of the centerline means that the glyph is already in the prescribed registration, regardless of what sort of staff it is considered to belong to.

Given the importance of clefs, I felt it was best to come up with a rule that made it easy to position clefs consistently, as opposed to trying to fudge things to preserve line continuity in the staff glyphs which are of limited utility anyway.

>
>> NOTES (U+E100–U+E11F)
>>
>> These should be vertically centered on the baseline. Currently only
>> the breve and semibreve are centered.
>
> I had already added "duplicates" of the breve and semibreve notes into the
> Noteheads range, which are centered on the baseline (I had already made
> this change earlier in SMuFL 0.5's development, ditto for accidentals),
> and had left all of the notes in the Notes range sitting on the baseline.
> My justification for doing this was that precomposed notes would
> presumably only be used for text-like purposes. However, since we all seem
> to be agreed that we need separate fonts for text-based applications
> anyway, that justification is no longer valid.

But perhaps your point is still valid. These code points seem designed for use in metronome markings and it seems desirable to have metronome marking glyphs ready and available in the non-textual font. I think you are right that precomposed notes are not going to be used except in a text-like setting, I simply wasn't thinking about that.

So perhaps the note glyphs should remain as they were, set up well for metronome markings (with the breve/semibreve made consistent).

>> - Should the vertical line at X=0 in design space be used to define
>> the nominal alignment point of ornaments, articulations, stem
>> decorations (such as single note tremolos), much as the baseline is
>> used to align note heads etc.? Note that it's quite common to have
>> glyphs that have bits to the left of X=0, such as the "combining
>> diacritical marks" range of Unicode.
>
> I wonder if this gains us anything? I guess that the most common kinds of
> alignment for these kinds of objects is above/below notes; unless we want
> to propose that noteheads should also be centered on x=0, then I'm not
> sure centering things like ornaments and articulations on x=0 would help.
> Would substantively worse results be had by centering the center of the
> glyph's bounding box on the center of the notehead's bounding box, I
> wonder?

Well, really, in spite of raising this point, I don't think we gain very much from it since note heads tend to be symmetrical and applications will need to calculate glyph bounding boxes in general anyway. So I think the metadata proposal can  carry this burden by allowing optional horizontal anchor points to be defined for note heads and ornaments -- but typically they won't, in which case the recommended positioning is to do exactly what you said: place "the center of the glyph's bounding box on the center of the notehead's bounding box".

…Joe


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