filter and selectively delay X events

## NAME

Tk_RestrictEvents - filter and selectively delay X events

## SYNOPSIS

#include <tk.h>

Tk_RestrictProc * Tk_RestrictEvents(proc, arg, prevArgPtr)

## ARGUMENTS

`Tk_RestrictProc *proc` (in)
  Predicate procedure to call to filter incoming X events. NULL means do not restrict events at all.
`char *arg` (in)
  Arbitrary argument to pass to proc.
`char **prevArgPtr` (in/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 or deferred until some later time (e.g. when the event restriction is lifted). Proc is a standard X predicate procedure, of the sort passed to XCheckIfEvent. It must have arguments and result that match the type Tk_RestrictProc:
typedef Bool Tk_RestrictProc( Display *display, XEvent *eventPtr, char *arg);
The display argument to proc is the display from which eventPtr was received, and eventPtr points to an event under consideration. The arg argument is a copy of the arg passed to Tk_RestrictEvents; it may be used to provide proc with information it needs to filter events. Proc must return True or False. True means the event should be processed immediately and False means the event should not be processed now, but should be saved for some later time.

Tk_RestrictEvents uses its return value and prevArgPtr 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. Please use it only where it is absolutely necessary. If only a local restriction is needed, it can probably be achieved more cleanly by changing event-to-Tcl bindings or by calling Tk_DeleteEventHandler.

## KEYWORDS

delay, event, filter, restriction