A conforming implementation shall support the following libraries from the GTK+ stack which provide interfaces for creating rich graphical user interface applications.
A general-purpose utility library, not specific to graphical user interfaces. Glib is implemented as several libraries, providing a type system, a signal system, data conversion routines, string utilities, a filesystem abstraction and file utility routines, threading support and a main loop abstraction.
ATK is the Accessibility Toolkit. It provides a set of generic interfaces allowing accessibility technologies to interact with a graphical user interface. For example, a screen reader uses ATK to discover the text in an interface and read it to blind users. GTK+ widgets have built-in support for accessibility using the ATK framework.
Pango is a library for laying out and rendering text. It centers around the PangoLayout object, representing a paragraph of text. Pango provides the engine for GtkTextView, GtkLabel, GtkEntry, and other widgets that display text.
This is a small library which allows you to create GdkPixbuf ("pixel buffer") objects from image data or image files. Use a GdkPixbuf in combination with GtkImage to display images.
GDK is the abstraction layer that allows GTK+ to support multiple windowing systems. GDK provides drawing and window system facilities on X11, Windows, and the Linux framebuffer device.
The GTK+ library contains widgets, that is, GUI components such as GtkButton or GtkTextView.
There are three main parts to the definition of each of these libraries.
The "Interfaces" section defines the required library name and version, and the required public symbols (interfaces and global data), as well as symbol versions, if any.
The "Interface Definitions" section provides complete or partial definitions of certain interfaces where either this specification is the source specification, or where there are variations from the source specification. If an interface definition requires one or more header files, one of those headers shall include the function prototype for the interface.
For source definitions of interfaces which include a reference to a header file, the contents of such header files form a part of the specification. The "Data Definitions" section provides the binary-level details for the header files from the source specifications, such as values for macros and enumerated types, as well as structure layouts, sizes and padding, etc. These data definitions, although presented in the form of header files for convenience, should not be taken a representing complete header files, as they are a supplement to the source specifications. Application developers should follow the guidelines of the source specifications when determining which header files need to be included to completely resolve all references.
Note: While the Data Definitions supplement the source specifications, this specification itself does not require conforming implementations to supply any header files.