NoteColumn grobs are created by: Rhythmic_column_engraver
Grobs can be distinguished in their role in the horizontal spacing.
Many grobs define constraints on the spacing by their sizes. For
example, note heads, clefs, stems, and all other symbols with a fixed
shape. These grobs form a subtype called Item
.
Some items need special treatment for line breaking. For example, a clef is normally only printed at the start of a line (i.e. after a line break). To model this, `breakable' items (clef, key signature, bar lines, etc.) are copied twice. Then we have three versions of each breakable item: one version if there is no line break, one version that is printed before the line break (at the end of a system), one version that is printed after the line break.
Whether these versions are visible and take up space, is determined by
the outcome of the break-visibility
. This grob property is a
function taking a direction (-1, 0 or 1) as argument. It returns a
cons of booleans, signifying whether this grob should be transparent
and have no extent.
break-visibility
(procedure)
Default value: (unset)
breakable
(boolean)
no-spacing-rods
(boolean)
Stem and noteheads combined
accidentals
(list)
arpeggio
(grob (GRaphical OBject))
force-hshift
(number)
horizontal-shift
(integer)
note-heads
(list of grobs)
rest
(grob (GRaphical OBject))
rest-collision
(grob (GRaphical OBject))
stem
(grob (GRaphical OBject))
a group of coupled grobs
axes
(list)
'(0 1)
In music notation, lots of symbols are related in some way. You can think of music notation as a graph where nodes are formed by the symbols, and the arcs by their relations. A grob is a node in that graph. The directed edges in the graph are formed by references to other grobs (i.e. pointers). This big graph of grobs specifies the notation problem. The solution of this problem is a description of the printout in closed form, i.e. a list of values. These values are Molecules.
All grobs have an X and Y-position on the page. These X and Y positions are stored in a relative format, so they can easily be combined by stacking them, hanging one grob to the side of another, and coupling them into a grouping-grob.
Each grob has a reference point (a.k.a. parent): the position of a grob is stored relative to that reference point. For example the X-reference point of a staccato dot usually is the note head that it applies to. When the note head is moved, the staccato dot moves along automatically.
A grob is often associated with a symbol, but some grobs do not print any symbols. They take care of grouping objects. For example, there is a separate grob that stacks staves vertically. The NoteCollision is also an abstract grob: it only moves around chords, but doesn't print anything.
X-extent
(pair of numbers)
X-extent-callback
(procedure)
The size of a grob are determined through callbacks, settable with
grob properties X-extent-callback
and Y-extent-callback
.
There can be only one extent-callback for each axis. No callback
(Scheme value #f
) means: `empty in this direction'. If you fill
in a pair of numbers, that pair hard-codes the extent in that
coordinate.
Default value: Axis_group_interface::group_extent_callback
X-offset-callbacks
(list)
Offsets of grobs are relative to a parent reference point. Most positions are not known when an object is created, so these are calculated as needed. This is done by adding a callback for a specific direction.
Offset callbacks can be stacked, i.e.
property .... override #'Y-offset-callbacks = #(list callback1 callback2 callback3)
The callbacks will be executed in the order callback3 callback2
callback1
. This is used for quantized positioning: the staccato dot is
above or below a note head, and it must not be on a staff-line. To
achieve this, the staccato dot has two callbacks: one that positions the
grob above or below the note head, and one that rounds the Y-position of
the grob to the nearest open space.
Default value: (unset)
Y-extent
(pair of numbers)
Y-extent-callback
(procedure)
X-extent-callback
.
Default value: Axis_group_interface::group_extent_callback
Y-offset-callbacks
(list)
X-offset-callbacks
.
Default value: (unset)
after-line-breaking-callback
(procedure)
before-line-breaking-callback
(procedure)
cause
(any type)
dependencies
(list of grobs)
extra-X-extent
(pair of numbers)
extra-Y-extent
(pair of numbers)
extra-Y-extent
.
Default value: (unset)
extra-offset
(pair of numbers)
extra-offset
is added just before `printing' the grob, so the
typesetting engine is completely oblivious to it.
Default value: (unset)
interfaces
(list)
meta
field.
Default value: (unset)
layer
(number)
meta
(list)
The alist contains the following entries: name, interfaces.
Default value: '((name . NoteColumn) (interfaces grob-interface axis-group-interface note-column-interface item-interface))
minimum-X-extent
(pair of numbers)
minimum-Y-extent
(pair of numbers)
minimum-Y-extent
.
Default value: (unset)
molecule
(unknown)
molecule-callback
(procedure)
All visible, i.e. non-transparent, grobs have a callback to create a
Molecule. The callback should be a Scheme function taking one argument
(the grob) and returning a Molecule. Most molecule callbacks are
written in C++, but you can also write them in Scheme. An example is
provided in input/regression/molecule-hacking.ly
.
Default value: (unset)
spacing-procedure
(procedure)
staff-symbol
(grob (GRaphical OBject))
transparent
(boolean)
This page is for LilyPond-2.0.0 (stable-branch).