GType in Font

Generator DataMatrix in Font GType

G_TYPE_NONE G_TYPE_CHAR G_TYPE_INT G_TYPE_LONG G_TYPE_BOOLEAN G_TYPE_ENUM G_TYPE_FLAGS G_TYPE_FLOAT

An empty type that is equivalent to void. Equivalent to the standard C char type. Equivalent to the standard C int type. Values must be within the range of G_MININT to G_MAXINT. Equivalent to the standard C long type. Values must be within the range of G_MINLONG to G_MAXLONG. A standard Boolean type that holds either TRUE or FALSE. A standard enumeration equivalent to the C enum type. Bit fields holding Boolean flags. Equivalent to the standard C float type. Values must be within the range of negative G_MAXFLOAT to G_MAXFLOAT.

Equivalent to the standard C double type. Values must be within the range of negative G_MAXDOUBLE to G_MAXDOUBLE. Equivalent to NULL-terminated C strings. An untyped pointer type similar to void*.

GObject provides GTK+ with two other vital data types: GValue and GObject. GValue is a generic container that can hold any structure of which the system is already aware. This allows functions to return a piece of data of an arbitrary type. Without GValue, the object-oriented nature of GTK+ would not be possible. G_TYPE_GOBJECT, or GObject, is the fundamental type that the widget class inheritance structure of GTK+ is based on. It allows widgets to inherit the properties of their parents, including style properties and signals. GObject is a singly-inherited system, where each child class can only have one parent class. The derived child inherits all characteristics of the parent, because in every way, the child is the parent. You will learn how to use this system to derive custom GTK+ widgets in 11. GObject also provides widgets with a signal system, an object properties system, and memory management. We will explore all of these concepts in the next chapter.

The GIMP Drawing Kit (GDK) is a computer graphics library originally designed for the X Window System that wraps around low-level drawing and window functions. GDK acts as the intermediary between Xlib and GTK+. It renders drawings, raster graphics, cursors, and fonts in all GTK+ applications. Also, since it is implemented in every GTK+ program, GDK provides drag-and-drop support and window events. GDK provides GTK+ widgets the ability to be drawn to the screen. To do this, every widget has an associated GdkWindow object, except for a few widgets that will be discussed in a later chapter. A GdkWindow is essentially a rectangular area located on the screen in which the widget is drawn. GdkWindow objects also allow widgets to detect X Window System events, which will be covered in the next chapter. GDK has been ported to Windows and Mac OS X. It has also included support for Cairo since the release of GTK+ 2.8.

GdkPixbuf is a small library that provides client-side image manipulation functions. It was created as a replacement for the GNOME Imaging Model (Imlib). Images can be loaded from files or image data can be fed directly into the library functions. We will use this library when adding images to tree views and when creating new GtkImage widgets in later chapters. One advantage of GdkPixbuf images is that images can be reference-counted. This means that a GdkPixbuf image can be displayed in multiple locations, while only being stored in memory once. It will only be destroyed when all reference counts are decremented.

The GdkPixbuf library takes advantage of Libart, a 2-D drawing library distributed with GNOME, to apply transformations to images. Because of this, you can shear, scale, and rotate images to your heart s delight. The images are then rendered using the GdkRGB library and drawable areas. By using such a wide variety of specialized tools, GdkPixbuf can provide image rendering of a very high class. GdkPixbuf, while it is a small library, provides a wide variety of functions for manipulating and displaying images. The library will be put to only the most basic of uses throughout this book. For more information on advanced GdkPixbuf topics, you should reference its API documentation.