Tk_RestrictEvents(3) Tk Tk_RestrictEvents(3)
_________________________________________________________________
NAME
Tk_RestrictEvents - filter and selectively delay X events
SYNOPSIS
#include <tk.h>
Tk_RestrictProc *
Tk_RestrictEvents(proc, clientData, prevClientDataPtr)
ARGUMENTS
Tk_RestrictProc *proc (in) Predicate
procedure
to call to
filter
incoming X
events.
NULL means
do not
restrict
events at
all.
ClientData clientData (in) Arbitrary
argument
to pass to
proc.
ClientData *prevClientDataPtr (out) Pointer to
place to
save
argument
to
previous
restrict
procedure.
_________________________________________________________________
DESCRIPTION
This procedure is useful in certain situations where
applications are only prepared to receive certain X events.
After Tk_RestrictEvents is called, Tk_DoOneEvent (and hence
Tk_MainLoop) will filter X input events through proc. Proc
indicates whether a given event is to be processed
immediately, deferred until some later time (e.g. when the
event restriction is lifted), or discarded. Proc is a
procedure with arguments and result that match the type
Tk_RestrictProc:
typedef Tk_RestrictAction Tk_RestrictProc(
ClientData clientData,
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Tk_RestrictEvents(3) Tk Tk_RestrictEvents(3)
XEvent *eventPtr);
The clientData argument is a copy of the clientData passed
to Tk_RestrictEvents; it may be used to provide proc with
information it needs to filter events. The eventPtr points
to an event under consideration. Proc returns a restrict
action (enumerated type Tk_RestrictAction) that indicates
what Tk_DoOneEvent should do with the event. If the return
value is TK_PROCESS_EVENT, then the event will be handled
immediately. If the return value is TK_DEFER_EVENT, then
the event will be left on the event queue for later
processing. If the return value is TK_DISCARD_EVENT, then
the event will be removed from the event queue and discarded
without being processed.
Tk_RestrictEvents uses its return value and
prevClientDataPtr to return information about the current
event restriction procedure (a NULL return value means there
are currently no restrictions). These values may be used to
restore the previous restriction state when there is no
longer any need for the current restriction.
There are very few places where Tk_RestrictEvents is needed.
In most cases, the best way to restrict events is by
changing the bindings with the bind Tcl command or by
calling Tk_CreateEventHandler and Tk_DeleteEventHandler from
C. The main place where Tk_RestrictEvents must be used is
when performing synchronous actions (for example, if you
need to wait for a particular event to occur on a particular
window but you don't want to invoke any handlers for any
other events). The ``obvious'' solution in these situations
is to call XNextEvent or XWindowEvent, but these procedures
cannot be used because Tk keeps its own event queue that is
separate from the X event queue. Instead, call
Tk_RestrictEvents to set up a filter, then call
Tk_DoOneEvent to retrieve the desired event(s).
KEYWORDS
delay, event, filter, restriction
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