[MEI-L] slur and @curvedir; moving Bezier control points

Wed Feb 11 23:57:08 CET 2015

This is such an interesting discussion with, as Perry suggests, no perfect
solution.

I am attaching two pertinent examples from Computing in Musicology (Vol.
7, 1991) that show (a) the famous but unlikely beam/slur crossings in
Ravel's "Scarbo" unlikely slur crossings and (b) Grieg's requirements for
beams of unusual length.

The beam example becomes more cumbersome when the width of the layout
(particularly for examples in books and articles) is inadequate to
accommodate the beam and/or slur groupings shown.  A significant problem
in notation programs has been the book-keeping on slurs that need to
continue to the next system.  With beams,  continuation is not always a
viable option.

Eleanor

Eleanor Selfridge-Field
Consulting Professor, Music (and, by courtesy, Symbolic Systems)
Braun Music Center #129
Stanford University
Stanford, CA 94305-3076, USA
http://web.stanford.edu/~esfield/  +1/ 650 725-9242

-----Original Message-----
From: mei-l [mailto:mei-l-bounces at lists.uni-paderborn.de] On Behalf Of
Byrd, Donald A.
Sent: Wednesday, February 11, 2015 5:02 AM
To: Music Encoding Initiative
Cc: Roland, Perry D. (pdr4h)
Subject: Re: [MEI-L] slur and @curvedir; moving Bezier control points

A belated comment on Perry's message of a week ago, just below. I don't
see how moving the Bezier control points "along with everything else" can
possibly change the shape of the curve. If you move everything 5.347 mm to
the right and 2.718 mm down, the curve will have exactly the same shape;
it'll just be 5.347 mm to the right and 2.718 mm down, and in precisely
the same position relative to the rest of the notation.

Nightingale stores Bezier control points as offsets from note heads. If
you move the note heads, of course the curve follows along; the
coordinates actually used to draw the curve are the new coordinates of the
note heads plus the offsets.

Or am I misunderstanding?

--Don

> On Tue, Feb 3, 2015 at 3:50 PM, Roland, Perry D. (pdr4h)
<pdr4h at eservices.virginia.edu> wrote:
> Hi Raffaele,
>
> Using @bezier only "locks" the rendering if the control points are
specified as absolute page coordinates.  If they're given as offsets from
something else, such as a particular note, then the rendition of the slur
is dependent on the position of that thing.
>
> This is how I envision it working.  It's possible that moving the bezier
control points (even if they're moved relative to everything else) will
change the shape of the curve.  If that's true, then our only mechanism
for controlling a slur is through the use of @bulge.  For automatic layout
without any user intervention, the only mechanism is @curvedir --
remembering that values in @curvedir cannot possibly result in a perfect
rendition every time.  It seems there truly is no way to have the cake and
eat it too, hence the comment which began my initial response to Benni.
>
> Of course, only those with more knowledge and experience with this stuff
can say for sure.
> Laurent?  Craig?  Zoltan?  Want to join in?
>
> --
> p.
>
> __________________________
> Perry Roland
> Music Library
> University of Virginia
> P. O. Box 400175
> Charlottesville, VA 22904
> 434-982-2702 (w)
> pdr4h (at) virginia (dot) edu
> From: mei-l [mei-l-bounces at lists.uni-paderborn.de] on behalf of
> Raffaele Viglianti [raffaeleviglianti at gmail.com]
> Sent: Tuesday, February 03, 2015 9:29 AM
> To: Music Encoding Initiative
> Subject: Re: [MEI-L] slur and @curvedir
>
> Hi all,
>
> I find Perry's explanation really helpful and interesting, particularly
concerning the the sharing of responsibilities between the encoder and the
renderer. Encoding @bezier before rendering locks the encoding into only
one possible rendering, which is not great for the reflowing that a truly
dynamic score should allow. Unless the aim of the encoder is to
represent/document the curvature of one specific written source, which is
a totally legitimate approach (and might be what Benni is after?).
>
> Having two slurs and joining them, instead, seems conceptually wrong to
me: there is only one slur and no real XML overlapping (or other
limitation) that would justify, arguably, splitting the element in two.
>
> Raff
>
> On Tue, Feb 3, 2015 at 5:27 AM, Axel Teich Geertinger <atge at kb.dk>
wrote:
> Hi Perry
>
>
>
> Thanks for your elaborate reply. As always I wasn’t aware of any worms
> involved, but I did realize that there is no single or easy answer :-)
>
>
>
> Drawing a complex slur that not only avoids collisions with other
objects but is also aesthetically satisfying can be quite a challenge. My
deepest respect for people working on rendering slurs!
>
> As you say, it almost always requires visual control and corrections to
get it right. But recording the corrections also means that they will have
to be encodable somehow, that is, in more detail than possible with
@bezier, for instance. I have no immediate ideas about how to solve this
in a medium as fluid as music notation.
>
>
>
> Best,
>
> Axel
>
>
>
> Fra: mei-l [mailto:mei-l-bounces at lists.uni-paderborn.de] På vegne af
> Roland, Perry D. (pdr4h)
> Sendt: 2. februar 2015 20:14
>
>
> Til: Music Encoding Initiative
> Emne: Re: [MEI-L] slur and @curvedir
>
>
>
> Hi Axel,
>
>
>
> One comment before I answer your questions -- This is a huge can of
worms for which it seems there can never be a single, universally
satisfying answer.
>
>
>
> @curvedir only provides minimal information about the slur so a renderer
must "figure out" the rest. This is the easiest method for the encoder,
but requires a lot more intelligence on the part of the rendering engine,
for example with regard to collision avoidance. From another angle,
however, it provides the greatest amount of flexibility for the renderer
to arrive at the final shape of the slur.  Like I said before, aside from
providing a more detailed classification purpose, allowing curvdir="above
below above below (and so on)" doesn't really provide much rendering help
because, just as you've observed, it says nothing about the location of
the points where the slur is supposed to bend back on itself.
>
>
>
> @bulge attempts to provide this missing information by indicating
distance from an imaginary line between the end points of the slur.
Providing two values means the distance between the end points should be
halved and a curve drawn that passes through the starting point, the point
indicated by the 1st value in @bulge, the mid-point of the line, the point
indicated by the 2nd value, and the ending point.  Three values would mean
dividing the distance between the end points by thirds, etc.
>
>
>
> "Simple" slurs (i.e., ones that don't alternate sides of the imaginary
line) can be drawn with @bulge by supplying only a single value or by
giving only positive or only negative values.  Doing this, instead of
using @curvedir, places the shape of the slur in the control of the
encoder instead of the rendering engine, but puts the burden of "scribing"
the shape on the encoder.  The ability to draw "simple" slurs is why
@bulge can't be constrained to alternating positive and negative values.
>
>
>
> The example provided in the Guidelines should use the values -2 and 1.
The diagram is also misleading in that the lines connecting the curve with
the imaginary line should divide their respective sections of the curve
into equal parts; that is, the line illustrating point 1 should be drawn
at the "highest" point of the curve, mid-way between the mid-point of the
imaginary line and the end point of the slur.
>
>
>
> @bezier provides the most encoder control over the rendition of the
slur.  But unless the control points of the curve are expressed as offsets
from some musical feature (like a note, for instance), then re-flowing the
notation will "disconnect" the slur from it and the slur will end up in
the wrong place on the page.  So, the bezier control points have to be
*offsets* from something, presumably from the features pointed at by the
@startid and @endid attributes, as long as the notation is expected to be
"edit-able".  The @startid, @endid, @bezier combination will move the slur
with the notation.  The problem with bezier control points is the same as
with @bulge values -- it's nearly impossible for one to create them
without the aid of some kind of drawing environment or iterative
"code/view/code" workflow.
>
>
>
> Without a doubt, a better explanation of this stuff is desperately
needed the Guidelines. But, there may also be better ways of recording the
information necessary for drawing slurs than what is provided by the
current set of attributes.  I welcome contributions on either front.
>
>
>
> --
>
> p.
>
>
>
> __________________________
> Perry Roland
> Music Library
>
> University of Virginia
>
> P. O. Box 400175
>
> Charlottesville, VA 22904
> 434-982-2702 (w)
> pdr4h (at) virginia (dot) edu
>
> From: mei-l [mei-l-bounces at lists.uni-paderborn.de] on behalf of Axel
> Teich Geertinger [atge at kb.dk]
> Sent: Monday, February 02, 2015 3:29 AM
> To: Music Encoding Initiative
> Subject: Re: [MEI-L] slur and @curvedir
>
> Hi all
>
>
>
> Just out of curiosity: None of the solutions I have seen (@bulge,
@bezier, or @curvedir=”above below”) do indicate explicitly where the slur
changes position from above the notes to below – that is, where the slur
intersects the melodic line, so to speak. I guess that the use of @bezier
will give the desired result in most situations, but as the actual
rendering of the slur must  be dependent to some degree on other factors
such as the note spacing or system breaks, I wonder how we can be sure
that it will always cross the melodic line at the desired place. With
@bulge or @curvedir (with extended values as suggested by Zoltan) this
must be even more uncertain, right? In principle, a rendering algorithm
may draw the slur in Benni’s example above the first three groups of notes
and below only the last group when using @bulge or @curvedir. How do we
avoid that?
>
>
>
> One more question about @bulge, again just out of curiosity: Should it
be defined that a sequence of values for @bulge must an alternating
sequence of positive and negative values, either in the guidelines or the
schema? Or would a sequence like the one in the guidelines example
(@bulge=”2 1”) make any sense in any situation?
>
>
>
> Best,
>
> Axel
>
>
>
>
>
> Fra: mei-l [mailto:mei-l-bounces at lists.uni-paderborn.de] På vegne af
> Komíves Zoltán
> Sendt: 2. februar 2015 07:08
> Til: Music Encoding Initiative
> Emne: Re: [MEI-L] slur and @curvedir
>
>
>
> Hi Perry,
>
>
>
> I think extending the data type of @curvedir attribute could be
justified simply base on the argument of classification: @curvdir provides
a classification mechanism, but this classification is rather incomplete,
the current values of @curvedir do not cover all the cases that are out
there (see Benni's example: nor "above" neither "below" is appropriate,
and the omission of the attribute surely cannot imply what we want to
convey, that is the curve goes also above and below). This has nothing to
do with rendering, since in order to render a slur or phrase mark, the
actual curve needs to be calculated anyway, even when "above" or "below"
is applied.
>
>
>
> Out of Benni's suggestions I quite like "above-below" / "below-above".
(Note that his question concerns @curvedir not @place.) In fact, it occurs
to me, we could even allow an alternating sequence of the values "below"
and "above". Benni's example would be encoded as <slur curvedir="above
below"/>. This, beside conveying the fact that the curve goes first below,
then above, could also be applied to curves with multiple inflection
points. I have no literary example for this at hand, but wouldn't be
surprised if there was some in existence.
>
>
>
> Best
>
> Zoltan
>
>
>
>
>
>
>
> 2015-02-01 17:04 GMT+00:00 Roland, Perry D. (pdr4h)
<pdr4h at eservices.virginia.edu>:
>
>
>
> Laurent is correct, the values in the example should be -2 and 1.
>
>
>
> The place attribute is for describing the placement of an entity in
general terms.  For phrase marks and slurs, it also generically describes
the curvature of the mark, and therefore functions as short hand for a
more detailed description given by the bulge or bezier attributes. It
would be possible to add a value to @place for slurs/phrases with multiple
inflection points, such as "mixed" or perhaps "complex", but this would
only fulfill a classification purpose -- it wouldn't provide any
information regarding how to draw the slur/phrase.  So, one would still
need to use @bulge or @bezier for rendering.
>
>
>
> Another complicating factor is that @place is used by a number of
elements other than slur and phrase.  Adding "mixed" directly to @place
would introduce the possibility of nonsense in the case of, say, <accid>
or <breath>.  Of course, a specialized form of @place for slur/phrase is a
possibility, but would need careful handling.
>
>
>
> --
>
> p.
>
>
>
>
> __________________________
> Perry Roland
> Music Library
>
> University of Virginia
>
> P. O. Box 400175
>
> Charlottesville, VA 22904
> 434-982-2702 (w)
> pdr4h (at) virginia (dot) edu
>
> From: mei-l [mei-l-bounces at lists.uni-paderborn.de] on behalf of
> Laurent Pugin [laurent at music.mcgill.ca]
> Sent: Sunday, February 01, 2015 8:27 AM
> To: Music Encoding Initiative
> Subject: Re: [MEI-L] slur and @curvedir
>
> Hi Benni,
>
>
>
> Have you looked at @bulge? There is an example in the guidelines:
> http://music-encoding.org/documentation/guidelines2013/userSymbols#ind
> ex.xml-body.1_div.23_div.3_div.4
>
>
>
> I would have expected the values to be -2 1 for the given example, so I
am not sure I understand it correctly.
>
>
>
> Laurent
>
>
>
> On Fri, Jan 30, 2015 at 2:13 PM, Benjamin Wolff Bohl <bohl at edirom.de>
wrote:
>
> Dear MEI-L,
>
> Freschütz has a question concerning encoding mixed direction slurs.
>
>
>
> <image001.png>
>
> In case the picture doesn't come through, please see:
> https://github.com/Freischuetz-Digital/proofMEIdata/issues/25
>
>
>
> This slur may not be properly encoded in MEI using @curvedir that only
> allows 'above' or 'below' as values. Nevertheless, using @bezier is
> much more verbose than needed

>
> Maybe a value like 'mixed' / 'above-below' / 'below-above' / 'changing'
/ 'alternating' would be applicable? Of course the schema would have to be
modified to allow this. Are there any comparable values in other parts of
the schema?
>
>
>
> This is no "special", rather quite often in printed music from the 19th
century.
>
>
>
> All the best,
>
> Benjamin
>
>
>
> <Screenshot from 2015-02-10
> 17:33:03.png>_______________________________________________
> mei-l mailing list
> mei-l at lists.uni-paderborn.de
> https://lists.uni-paderborn.de/mailman/listinfo/mei-l

---
Donald Byrd
Woodrow Wilson Indiana Teaching Fellow
Adjunct Associate Professor of Informatics Visiting Scientist, Research
Technologies Indiana University Bloomington

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