[MEI-L] page sizes

[Craig Sapp]

Hi Everyone,

In case you were eagerly awaiting it, attached is the final version of my
analysis of staff placement in SCORE.


SCORE data itself has no concept of physical units (with some minor
caveats), so it would be a good model to observe.  The physical units are
defined at the last minute when you are ready to print, and are not defined
while editing the music in the SCORE editor, which matches the idea which
you are headed towards.

See page 50 of the attached PDF for example default spacings in SCORE which
is a good basic roadmap to how default spacing units are defined in SCORE.


> This interline distance (which is already used by MEI) is a musical unit
which describes
> half the distance between two staff lines,

I complain about how you are defining "interline".  Interline is Latin for
"between lines", not "halfway between lines".  This will cause continual
confusion, such as losing your spacecraft:
    http://mars.jpl.nasa.gov/msp98/news/mco990930.html
How about "@semiline", "@hemiline", or "@demiline" instead?   Or maybe
"@halbline" :-)
    http://www.dailywritingtips.com/semi-demi-and-hemi


* The nominal physical length of scoreDef/@interline.size in SCORE is 3.15
points (0.04375 inches, 1.11125 mm).  This is when you print out the music
using the default staff scaling and print size.  Vertical values are always
represented by this step size, and the data files themselves do not
indicate that the final physical rendering is at 3.15 points (which is why
I had to measure it off of the example on page 50).

* So in SCORE, the distance between two staff lines is 2.0 "steps".  And
this means that the height of a staff is 8.0 steps.  Every staff has an
independent scaling factor which only affects the vertical dimension (there
is no staff-level scaling for the horizontal dimension).   So if a staff
has a 50% scaling, all of its steps would be 1/2 of the size of the nominal
height.

* The default "successive staff spacing" is 18.0 steps, so there are 18.0 -
8.0 = 10.0 steps from the top of one staff to the bottom of the next.  This
default spacing is the framework over which individual staves may be
scaled.  This framework is also how SCORE avoids using physical
measurements to place individual staves vertically on the page.  Staves can
be placed anywhere vertically, but their placements are in relation to
their default positions.  For example, a staff could be placed 15 steps
above the top of the staff below by adding an extra offset of 5 steps to
its default position (In SCOREese, set P4=5 for the top staff).

* The staves each have their own scaling factor (called the staff's P5 in
SCOREese).  If P5 is 0.5, then the local staff's step size is now 1/2 of
the default step size.  This scaling factor only affects the height of the
staves, not the length of the staves.  Object placed on a staff will have
the staff's P5 scaling applied to their horizontal and vertical dimensions
(they will shrink by 50% if the staff is scaled by 50%), their vertical
placement will be scaled as well, but not their horizontal placement which
is independent of the staff scaling.  Note that changing the scaling of a
staff does not affect its default position on the page, but if there is a
vertical offset from the default position, that offset will be scaled.

* The horizontal distances in SCORE are described on a different scale than
the vertical distances.  They are described as the fractional position
along the left/right sides of the default staff length.  The nominal length
of a staff is 7.5 inches.  This length is divided up into 200 units, so the
left side of staves are at 0.0, and the right side is at 200.0.  A length
of 540 points (7.5 inches) divided by 200 is 2.7 points, so "200" was
probably used to give an approximately equivalent unit to vertical steps.
It would have been more elegant to set the default horizontal and vertical
units to be the same by using a different vertical scaling...  In any case
the horizontal units are 6/7 of the vertical step units, so if you set a
staff's scaling to 6/7 (85.71428...%), the horizontal units will match the
vertical steps locally for that staff.  Another way of thinking about the
relationship between the horizontal and vertical units in SCORE is that the
default length of staves is 171.428... steps long.  So all vertical and
horizontal units can be related and a final scaling can be given to match
to the specified @interline physical distance between steps.

* horizontal units cannot be scaled within the SCORE editor, and can only
be scaled at print time, such as to match the staff lengths to the distance
between page margins.

For final placement on a physical page, there are three important values:

(1) The distance from the left side of the page to the left side of the
staff (the "left margin", although the system brackets will fall into this
margin, so not exactly the same as a text margin).  The default left margin
is 0.5 inches (plus a fixed extra 0.025 in).

(2) The distance from the bottom of the page to the bottom line of the
first staff.  This is also not exactly a "margin" in the text sense, since
notes/slurs/dynamics can fall within this bottom margin.  The default
bottom margin is 0.75 inches (plus a fixed extra 0.0625 inches).

(3) The page scaling.   This is the method to control the horizontal scale
which is not possible within the SCORE editor (other than trivial
zooming).  But the page scaling will also affect the vertical scale at the
same time.  The origin for the page scaling is the point defined by (1) and
(2) above.  In other words the page scaling does not affect the page
margins, but rather only affects the scaling of the music (you have to
scale the music so that it falls at the correct top and right margin
positions on your page.

Notice that only two margins are defined when printing from SCORE.  This
perhaps gets to the point that Andrew was trying to make:

>  The concept of "physical" unit doesn't really translate well to editions
that are meant for digital consumption only.
> If I have a page meant for a tablet or digital music stand display, what
does the "inch" unit mean? Does it mean
> render it as a physical inch on the screen, regardless of how many pixels
it takes to represent it? Or does it
> mean render it using a fixed number of pixels-per-inch, regardless of how
large or small it makes it from one
> display to another. E-ink displays challenge this concept, since they
don't really have pixels, and high-resolution
> displays also challenge it since the number of pixels it takes to
represent a single physical unit can be completely
> different. So we'll probably need some sort of proportional unit so that
we can say that the page margin is a
> percentage of the rendered display rather than a fixed unit of physical
measurement.

SCORE uses a single origin when printing the music on a page (left and
bottom margins).  And it is up to you to scale the music to correctly fit
within the top and right margins of your desired paper size (or screen
size, e-reader size, etc.).  This could be done by specifying the top and
right margins instead of scaling, but page-level scaling and top/right
margins cannot be controlled independently in SCORE.


-=+Craig
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