[MEI-L] slur and @curvedir

Tue Feb 3 11:27:10 CET 2015

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<mailto: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<tel:434-982-2702> (w)
pdr4h (at) virginia (dot) edu
________________________________
From: mei-l [mei-l-bounces at lists.uni-paderborn.de<mailto:mei-l-bounces at lists.uni-paderborn.de>] on behalf of Laurent Pugin [laurent at music.mcgill.ca<mailto: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#index.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<mailto:bohl at edirom.de>> wrote:

Dear MEI-L,
Freschütz has a question concerning encoding mixed direction slurs.

[bildschirmfoto 2015-01-30 um 14 05 39]<https://cloud.githubusercontent.com/assets/2430401/5976008/319371e8-a889-11e4-9a4c-7fe5cc246dfe.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<https://github.com/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

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