XSetInputFocus, XGetInputFocus - control input focus

display   Specifies the connection to the X server.

       focus     Specifies the window, PointerRoot, or None.

       focus_return
                 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.

       revert_to_return
                 Returns the current focus state (RevertToParent, RevertToPointerRoot, or RevertToNone).

       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 window.

       •    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.

       XSetInputFocus, XGetInputFocus - control input focus

XWarpPointer(3)
       Xlib-CLanguageXInterface

X Version 11                                      libX11 1.8.12                                XSetInputFocus(3)

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

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