Appendix B: Glossary

A

abstract

(class) An abstract class cannot be instantiated ; it serves only as a parent class to derive other classes.

access function

A function (or method ) that allows read or write access to a field inside an object. In the GObject convention, the function name usually contains _get_ or _set_ . The GObject property system abstracts and unifies access functions.

accessibility

(also Ally) For disabled persons. For example, an accessibile application might have an interface to represent text in Braille, offer a screen reader, and have interfaces for alternative input methods such as voice input and head/mouth sticks. Many organizations require accessibility features for software. In GTK+ and GNOME, ATK provides accessibility.

accumulator

(signal) During signal emission, many signal handlers may each return values. However, GSignal can return only one value to the code that emitted the signal. An accumulator is a special callback that GSignal invokes after each signal handler to collect and/or process the handler return values, passing the final result back after the emission.

alpha channel

The part of an RGBA value in a bitmap that determines transparency. Images without alpha channels have no transparency information and therefore cannot contain features such as translucent areas.

antialiasing

Edge smoothing. With no special help, a bitmap representation of a diagonal line exhibits "jaggies" at edges between bright and dark pixels. Text displayed on a monitor is especially prone to this phenomenon due to an especially large number of shapes crammed into a small area. Antialiasing attempts to ameliorate this situation by filling neighboring pixels with interpolated colors, and in some cases, the results can significantly improve legibility. However, antialiasing can also distort characters badly , especially without the use of font hinting.

API

Application programming interface. The API is the part of a software package that a programmer uses. An API consists of exported constants, variables , functions, classes, macros, and more. In the C programming language, header files normally define API elements.

application identifier

A GNOME application's symbolic name (for example, gnome-terminal for GNOME Terminal). Use the application identifier in any place where you must represent the application in a pathname: for example, in executable names , application-specific installation directories, help files, and menu item files. Several GNOME library functions use the application identifier.

asynchronous

Offline; the opposite of synchronous. In asynchronous I/O, program execution is not blocked during system access, but rather, the I/O access runs in the background. The main program can retrieve the result later, or the I/O system can interrupt the main program with a callback function when the operation completes. Some programs that use asynchronous I/O interact much better to user input ” in particular, Nautilus and any usable Web browser ” because the window does not freeze when waiting for user input. GnomeVFS offers asynchronous I/O for GNOME.

ATK

Accessibility Toolkit. The library supporting accessibility features in GTK+ and GNOME. ATK receives information about the user interface structure and then allows the user to operate the interface with tools such as touch screens and magnification windows .

atom

A block of data, usually small and one of several similar blocks; memory chunks are efficient means of creating atoms .

attribute

1. In object-oriented programming, a part of a class that defines a piece of data inside a class; see property for GObject-specific information. 2. In XML, a key-value pair that expands the information inside tag: For example, sauce=worcester .