XLIB Programming Manual, Rel. 5, Third Edition

16.2 Substructure Redirection

The window manager enforces its window layout policy using substructure redirection. When the window manager selects SubstructureRedirectMask on the root window, an attempt by any other client to change the configuration of any child of the root window will fail. Instead an event describing the layout change request will be sent to the window manager. The window manager then reads the event and determines whether to honor the request, modify it, or deny it completely. If it decides to honor the request, it calls the routine that the client called that triggered the event with the same arguments. If it decides to modify the request, it calls the same routine but with modified arguments.

The structure, as the term is used here, is the location, size, stacking order, border width, and mapping status of a window. The substructure is all these statistics about the children of a particular window. This is the complete set of information about screen layout that the window manager might need in order to implement its policy. Redirection means that an event is sent to the client selecting redirection (usually the window manager), and the original structure-changing request is not executed.

The events that are selected by SubstructureRedirectMask and the routines that are intercepted are as follows:

• CirculateRequest events report when an Xlib function, such as XCirculateSubwindows(), XCirculateSubwindowsDown(), XCirculateSubwindowsUp(), or XRestackWindows(), is ...