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## Bar Line Layering

 From: Dan Eble Subject: Bar Line Layering Date: Sat, 25 Oct 2014 11:41:09 -0400

I am proposing an approach to the issue "Manual barlines overwrite repeat

I think this issue could be addressed by introducing the concept of bar line
layers.  The bar lines created automatically at measure boundaries would be in
one layer.  The bar lines created automatically by repeat structures would be
in a layer on top of them.

top      bar lines created specially by user (is it useful?)
repeat   bar lines created automatically by repeat structures
main     bar lines created with \bar x
timing   bar lines created automatically at measure boundaries
bottom   bar lines created specially by the user (use described later)

I’m not sure that the “timing" layer should be separate from the “main” layer,

The definition of the set of glyphs to use for a bar line type (normal,
end-of-line, beginning-of-line) would need to indicate when the lower layer
should show through.  Whether this would need to be a new option (e.g. #f) or
just a new meaning for “” is discussed later.

The bar engraver would compose the bar types from all layers into a set of
glyphs to assign to the BarLine.  For the example in the issue,

norm   eol   bol
repeat     (“.|:”,  #f, “.|:”)
main       (“||”, “||”, “||”)
timing     (“|”,   “|”, “|”)
-------------------------
result     (“.|:”, “||”, “.|:”)

BOTTOM-LAYER USE CASE: I want a bar line which

1. does not have the problems with repeat bar lines
that are described in the tracker

2. looks different than an automatic bar line

3. does not require me to pay attention to the measure
position to avoid clobbering automatic bar lines

4. is visible at the end of the line only

I’ve seen this in hymns where lines are broken in mid-measure with a double bar
or a thick bar when the break corresponds to the end of a line of the poem.  I
currently use a command \meterBar which takes care of 2-4 with some
hoop-jumping and code that seems fragile.  It think bar line layers would solve
the whole problem more easily.

BAR ERASURE: \bar “” currently erases automatic bar lines.  Is this important
or just a side effect?  What should \bar “” mean in a layered scheme?

Option 1. The intended use of \bar “” is just to allow a line break; erasing an
automatic bar line is a side effect nobody cares for.  It is fine if \bar “” is
changed to allow a lower-layer bar to appear.  There are separate layers for
“timing” and “main” bar lines, and \bar “” adds a transparent bar line to the
“main” layer.  We do not need to add #f as an option in the glyph sets.

Option 2. Erasing an automatic bar line with \bar “” is useful, but it is not
generally useful to allow one layer to hide what is under it without drawing
anything in its place.  There is one combined layer for “timing” and “main” bar
lines, and \bar “” overrides the type of bar in this layer (like the current
code).  We do not need to add #f as an option in the glyph sets.

Option 3. It is generally useful to allow one layer to hide what is under it
without drawing anything in its place, and this is what \bar “” does in a
separate “main” layer above the “timing” layer.  This needs to be represented
in the glyph sets.

There’s a lot more to consider, but that’s enough for now.  Thanks for your
feedback.
—
Dan