X Window Manager - How X Window Managers Work

How X Window Managers Work

When a window manager is running, some kinds of interaction between the X server and its clients are redirected through the window manager. In particular, whenever an attempt to show a new window is made, this request is redirected to the window manager, which decides the initial position of the window. Additionally, most modern window managers are reparenting, which usually leads to a banner being placed at the top of the window and a decorative frame being drawn around the window. These two elements are controlled by the window manager rather than the program. Therefore, when the user clicks or drags these elements, it is the window manager that takes the appropriate actions (such as moving or resizing the window).

Window managers are also responsible for icons. Indeed, icons do not exist at the X Window System core protocol level. When the user requests a window to be iconified, the window manager unmaps it (makes it non-visible) and takes the appropriate actions to show an icon in its place. Most modern window managers do not literally show icons to represent iconified windows anymore. Often, an auxiliary toolbar program will allow access to iconified windows.

While the main aim of a window manager is to manage the windows, many window managers have additional features such as handling mouse clicks in the root window, presenting panes and other visual elements, handling some keystrokes (e.g., Alt-F4 may close a window), deciding which application to run at start-up, etc.

Standardized protocols exist to allow normal clients to communicate with the window manager. The original one is Inter-Client Communication Conventions Manual (ICCCM) but this has been superseded by the Extended Window Manager Hints (EWMH).