9.2.4 Layout interfaces

The HTML page that we found in the previous section, describes the layout object called Fingering. Such an object is a symbol within the score. It has properties that store numbers (like thicknesses and directions), but also pointers to related objects. A layout object is also called a Grob, which is short for Graphical Object. For more details about Grobs, see grob-interface.

The page for Fingering lists the definitions for the Fingering object. For example, the page says

padding (dimension, in staff space):

0.6

which means that the number will be kept at a distance of at least 0.6 of the note head.

Each layout object may have several functions as a notational or typographical element. For example, the Fingering object has the following aspects

• Its size is independent of the horizontal spacing, unlike slurs or beams.
• It is a piece of text. Granted, it is usually a very short text.
• That piece of text is typeset with a font, unlike slurs or beams.
• Horizontally, the center of the symbol should be aligned to the center of the notehead.
• Vertically, the symbol is placed next to the note and the staff.
• The vertical position is also coordinated with other super- and subscript symbols.

Each of these aspects is captured in so-called interfaces, which are listed on the Fingering page at the bottom

This object supports the following interfaces: item-interface, self-alignment-interface, side-position-interface, text-interface, text-script-interface, font-interface, finger-interface, and grob-interface.

Clicking any of the links will take you to the page of the respective object interface. Each interface has a number of properties. Some of them are not user-serviceable (“Internal properties”), but others are.

We have been talking of the Fingering object, but actually it does not amount to much. The initialization file scm/define-grobs.scm shows the soul of the `object',

(Fingering
  . ((print-function . ,Text_interface::print)
     (padding . 0.6)
     (staff-padding . 0.6)
     (self-alignment-X . 0)
     (self-alignment-Y . 0)
     (script-priority . 100)
     (font-size . -5)
     (meta . ((interfaces . (finger-interface font-interface
                             text-script-interface text-interface
                             side-position-interface
                             self-alignment-interface
                             item-interface))))))

As you can see, the Fingering object is nothing more than a bunch of variable settings, and the webpage in the Program Reference is directly generated from this definition.

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