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ScriptColumn

ScriptColumn grobs are created by: Script_column_engraver

item-interface

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)
a function that takes the break direction and returns a cons of booleans containing (TRANSPARENT . EMPTY).

Default value: (unset)

breakable (boolean)
boolean indicating if this is a breakable item (clef, barline, key sig, etc.). Default value: (unset)
no-spacing-rods (boolean)
read from grobs: boolean that makes Separation_item ignore this item (MOVE ME TO ITEM). Default value: (unset)

script-column-interface

An interface that sorts scripts according to their script-priority

grob-interface

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)
Store extent. internal use only. Default value: (unset)
X-extent-callback (procedure)
procedure taking an grob and axis argument, returning a number-pair. The return value is the extent of the grob.

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: (unset)

X-offset-callbacks (list)
list of functions, each taking an grob and axis argument. The function determine the position relative to this grob's parent. The last one in the list is called first.

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)
Store extent. internal use only. Default value: (unset)
Y-extent-callback (procedure)
see X-extent-callback. Default value: (unset)
Y-offset-callbacks (list)
see X-offset-callbacks. Default value: (unset)
after-line-breaking-callback (procedure)
Procedure taking a grob as argument. This procedure is called (using dependency resolution) after line breaking. Return value is ignored. Default value: (unset)
before-line-breaking-callback (procedure)
Procedure taking grob as argument. This procedure is called (using dependency resolution) before line breaking, but after generating discretionary items. Return value is ignored. Default value: Script_column::before_line_breaking
cause (any type)
Any kind of causation objects (i.e. music, or perhaps translator) that was the cause for this grob. Default value: (unset)
dependencies (list of grobs)
list of score-grob pointers that indicate who to compute first for certain global passes. Default value: (unset)
extra-X-extent (pair of numbers)
enlarge in X dimension by this much, measured in staff space. Default value: (unset)
extra-Y-extent (pair of numbers)
see extra-Y-extent. Default value: (unset)
extra-offset (pair of numbers)
pair of reals (a cons) forcing an extra offset before outputting. extra-offset is added just before `printing' the grob, so the typesetting engine is completely oblivious to it.

Default value: (unset)

interfaces (list)
list of symbols indicating the interfaces supported by this object. Is initialized from the meta field. Default value: (unset)
layer (number)
The output layer [0..2]. The default is 1. Default value: (unset)
meta (list)
Alist of meta information of this grob.

The alist contains the following entries: name, interfaces.

Default value: '((name . ScriptColumn) (interfaces grob-interface script-column-interface item-interface))

minimum-X-extent (pair of numbers)
minimum size in X dimension, measured in staff space. Default value: (unset)
minimum-Y-extent (pair of numbers)
see minimum-Y-extent. Default value: (unset)
molecule (unknown)
Cached output of the molecule-callback. Default value: (unset)
molecule-callback (procedure)
Function taking grob as argument, returning a smobbed Molecule.

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)
procedure taking grob as argument. This is called after before-line-breaking-callback, but before the actual line breaking itself. Return value is ignored. Default value: (unset)
staff-symbol (grob (GRaphical OBject))
the staff symbol grob that we're in. Default value: (unset)
transparent (boolean)
This is almost the same as setting molecule-callback to #f, but this retains the dimensions of this grob, which means that you can erase grobs individually. . Default value: (unset)

This page is for LilyPond-2.0.1 (stable-branch).

Report errors to <bug-lilypond@gnu.org>.