Using GTK+ on the X Window System
Using GTK+ on the X Window System — X11 aspects of using GTK+
GTK+ for the X Window System
On UNIX, the X backend is the default build for GTK+. So you don't need to do anything special when compiling it, and everything should "just work."
To mix low-level Xlib routines into a GTK program,
X11-specific commandline options
The X backend understands some additional command line arguments.
The name of the X display to open instead of the one specified
DISPLAY environment variable.
The number of the screen within the default display. This overrides
any screen number specified in the display name specified by
--display command line option or
DISPLAY environment variable. If this screen
cannot be opened, then GTK+ will fall back to the screen
specified in the display name. This option is not useful
interactively; the intended purposes is that when a program
registers its command line with a session
manager for later restarting, it can save the
screen it is on, without having to worry if it might be
restarted on a different display.
Makes all X requests synchronously. This is a useful option for
debugging, but it will slow down the performance considerably.
Understanding the X11 architecture
People coming from a Windows or MacOS background often find certain aspects of the X Window System surprising. This section introduces some basic X concepts at a high level. For more details, the book most people use is called the Xlib Programming Manual by Adrian Nye; this book is volume one in the O'Reilly X Window System series.
Standards are another important resource if you're poking in low-level X11 details, in particular the ICCCM and the Extended Window Manager Hints specifications. freedesktop.org has links to many relevant specifications.
The GDK manual covers
Server, client, window manager
Other window systems typically put all their functionality in the application itself. With X, each application involves three different programs: the X server, the application (called a client because it's a client of the X server), and a special client called the window manager.
The X server is in charge of managing resources, processing drawing requests, and dispatching events such as keyboard and mouse events to interested applications. So client applications can ask the X server to create a window, draw a circle, or move windows around.
The window manager is in charge of rendering the frame or borders around windows; it also has final say on the size of each window, and window states such as minimized, maximized, and so forth. On Windows and MacOS the application handles most of this. On X11, if you wish to modify the window's state, or change its frame, you must ask the window manager to do so on your behalf, using an established convention.
GTK+ has functions for asking the window manager to do various things; see for example gtk_window_iconify() or gtk_window_maximize() or gtk_window_set_decorated(). Keep in mind that gtk_window_move() and window sizing are ultimately controlled by the window manager as well and most window managers will ignore certain requests from time to time, in the interests of good user interface.