[smufl-discuss] Re: Glyph registration proposal

[Emil B. Wojtacki]

Thanks, Joseph, for sharing the html code and starting the work on glyph
registration.
Here are some comments/ideas for glyph registration.

Joseph Berkovitz wrote:
> GENERAL PRINCIPLES
>
>
> - Glyphs that can apply to a staff as a whole (e.g. bar lines, clefs) shall be registered such that the font baseline lies at the nominal Y position of the bottom line of a 5-line staff. If the glyph is specific to a staff other than a regular 5-line staff, then for registration purposes that staff's vertical center shall be exactly aligned with the vertical center of a 5-line staff.
I am not sure if this should apply for clefs. My intuition is, that the
clefs should be placed so, that the note that the clef refers to, is on
the baseline (e.g. F-clef placed so, that one dot is above and the
second below the baseline). Then, there would be no need for additional
vertical adjustment for clef changes/cue clefs.  (Even if clef changes
would be encoded, there are still cue clefs to be positioned correctly)


> TIME SIGNATURES
>
> The spec needs to stipulate that time signature digits are sized to fit
I would add, that they should vertically centred on the baseline. Then,
the scoring application draws them on the 4th (numerator) and 2nd
(denominator) staff line (this behaviour should be possible to override
by the user, e.g. for "handwritten" styles).
It is because for very small staves, the staff lines are relatively
thick, so the height (i.e. the size) of the digits should be adjusted so
that the staff lines do not overshot the digits too much.



> FLAGS (U+E140–U+E15F)
>
> Currently flags' vertical position is dependent on their outline, which will vary unpredictably from font to font. Note that it is not possible to algorithmically determine the stem attachment point from a flag's bounding box.
>
> - All flags shall be vertically positioned so that the stem attachment point lies exactly on the font baseline at X=0. T (Note that it is possible for part of a flag to lie to the left of X=0 if it's drawn in a cursive fashion.)
I would suggest something slightly different:
Vertical position is related to the notehead that is placed on the first
staff line (=on the font baseline), so that scoring app draws the glyph
with no offset from the notehead (unless the stem is shortened when two
voices occur). Please note that in different fonts the
hemidemisemiquavers flags my require different stem length, so this
positioning would make finding the appropriate stem length easier.

For down-stem notes, the reference note head would be on the fifth staff
line.

Since stems have a non-zero width, an addition is needed, that the flag
attachment point is in the middle of the stem width (there is some
overlap needed to ensure that there will no gap between stem and flag,
unless intentional)


> RESTS (U+E1C0–U+E1DF)
>
> Rests are relative to an imaginary staff position, typographically speaking (usually the centerline of a 5-line staff in which the rest assumes its default position). The font baseline should represent this staff position. It is not possible to compute this position from a rest's bounding box, since it may not be the vertical center of the glyph. This implies that most of the rests will move vertically relative to where they are now so that the baseline provides information on where they appear relative to this "reference staff" line.  (If this list allowed attachments, I'd supply a figure here.)

I think that they should be placed rather in reference to the font
baseline, as if they were designed for one-line staff. This would
simplify the placing of the rests when multiple voices occur on the same
staff or in the different (orchestral) percussion staves.

> OPEN QUESTIONS
>
> - 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 think that, in the case of ornaments and articulation, it is enough if
they are optically centred between bearings. For instance, ornaments may
be slightly moved left when they appear on the notehead-side when the
note has an accidental, or slightly moved right, when on stem-side. I
think it should be left to the sophisticated algorithms or to engravers'
eyes.
However, for stem decorations it seems to be a good idea (although I can
still imagine that Sweelinck's shake on stem may be placed differently
for down-stem and up-stem notes).

--
Emil Wojtacki



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