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       XSetInputFocus, XGetInputFocus - control input focus


       int XSetInputFocus(Display *display, Window focus, int revert_to, Time time);

       int XGetInputFocus(Display *display, Window *focus_return, int *revert_to_return);


       display   Specifies the connection to the X server.

       focus     Specifies the window, PointerRoot, or None.

                 Returns the focus window, PointerRoot, or None.

       revert_to Specifies where the input focus reverts to if the window becomes not viewable.
                 You can pass RevertToParent, RevertToPointerRoot, or RevertToNone.

                 Returns the current focus state (RevertToParent, RevertToPointerRoot, or

       time      Specifies the time.  You can pass either a timestamp or CurrentTime.


       The XSetInputFocus function changes the input focus and the last-focus-change time.  It
       has no effect if the specified time is earlier than the current last-focus-change time or
       is later than the current X server time.  Otherwise, the last-focus-change time is set to
       the specified time (CurrentTime is replaced by the current X server time).  XSetInputFocus
       causes the X server to generate FocusIn and FocusOut events.

       Depending on the focus argument, the following occurs:

       ·    If focus is None, all keyboard events are discarded until a new focus window is set,
            and the revert_to argument is ignored.

       ·    If focus is a window, it becomes the keyboard's focus window.  If a generated
            keyboard event would normally be reported to this window or one of its inferiors, the
            event is reported as usual.  Otherwise, the event is reported relative to the focus

       ·    If focus is PointerRoot, the focus window is dynamically taken to be the root window
            of whatever screen the pointer is on at each keyboard event.  In this case, the
            revert_to argument is ignored.

       The specified focus window must be viewable at the time XSetInputFocus is called, or a
       BadMatch error results.  If the focus window later becomes not viewable, the X server
       evaluates the revert_to argument to determine the new focus window as follows:

       ·    If revert_to is RevertToParent, the focus reverts to the parent (or the closest
            viewable ancestor), and the new revert_to value is taken to be RevertToNone.

       ·    If revert_to is RevertToPointerRoot or RevertToNone, the focus reverts to PointerRoot
            or None, respectively.  When the focus reverts, the X server generates FocusIn and
            FocusOut events, but the last-focus-change time is not affected.

       XSetInputFocus can generate BadMatch, BadValue, and BadWindow errors.

       The XGetInputFocus function returns the focus window and the current focus state.


       BadValue  Some numeric value falls outside the range of values accepted by the request.
                 Unless a specific range is specified for an argument, the full range defined by
                 the argument's type is accepted.  Any argument defined as a set of alternatives
                 can generate this error.

       BadWindow A value for a Window argument does not name a defined Window.


       Xlib - C Language X Interface