Chapter 7. Event Management

Table of Contents

While Xlib allows the reading and processing of events anywhere in an application, widgets in the X Toolkit neither directly read events nor grab the server or pointer. Widgets register procedures that are to be called when an event or class of events occurs in that widget.

A typical application consists of startup code followed by an event loop that reads events and dispatches them by calling the procedures that widgets have registered. The default event loop provided by the Intrinsics is XtAppMainLoop.

The event manager is a collection of functions to perform the following tasks:

Add or remove event sources other than X server events (in particular, timer interrupts, file input, or POSIX signals).
Query the status of event sources.
Add or remove procedures to be called when an event occurs for a particular widget.
Enable and disable the dispatching of user-initiated events (keyboard and pointer events) for a particular widget.
Constrain the dispatching of events to a cascade of pop-up widgets.
Register procedures to be called when specific events arrive.
Register procedures to be called when the Intrinsics will block.
Enable safe operation in a multi-threaded environment.

Most widgets do not need to call any of the event handler functions explicitly. The normal interface to X events is through the higher-level translation manager, which maps sequences of X events, with modifiers, into procedure calls. Applications rarely use any of the event manager routines besides XtAppMainLoop.

Adding and Deleting Additional Event Sources

While most applications are driven only by X events, some applications need to incorporate other sources of input into the Intrinsics event-handling mechanism. The event manager provides routines to integrate notification of timer events and file data pending into this mechanism.

The next section describes functions that provide input gathering from files. The application registers the files with the Intrinsics read routine. When input is pending on one of the files, the registered callback procedures are invoked.

Adding and Removing Input Sources

To register a new file as an input source for a given application context, use XtAppAddInput.

XtInputId XtAppAddInput(XtAppContext app_context, int source, XtPointer condition, XtInputCallbackProc proc, XtPointer client_data);

XtInputId XtAppAddInput(XtAppContext app_context, int source, XtPointer condition, XtInputCallbackProc proc, XtPointer client_data);

app_context	Specifies the application context that identifies the application.
source	Specifies the source file descriptor on a POSIX-based system or other operating-system-dependent device specification.
condition	Specifies the mask that indicates a read, write, or exception condition or some other operating-system-dependent condition.
proc	Specifies the procedure to be called when the condition is found.
client_data	Specifies an argument passed to the specified procedure when it is called.

The XtAppAddInput function registers with the Intrinsics read routine a new source of events, which is usually file input but can also be file output. Note that file should be loosely interpreted to mean any sink or source of data. XtAppAddInput also specifies the conditions under which the source can generate events. When an event is pending on this source, the callback procedure is called.

The legal values for the condition argument are operating-system-dependent. On a POSIX-based system, source is a file number and the condition is some union of the following:

XtInputReadMask	Specifies that proc is to be called when source has data to be read.
XtInputWriteMask	Specifies that proc is to be called when source is ready for writing.
XtInputExceptMask	Specifies that proc is to be called when source has exception data.

Callback procedure pointers used to handle file events are of type (*XtInputCallbackProc).

typedef void (*XtInputCallbackProc)(XtPointer client_data, int *source, XtInputId *id);

typedef void (*XtInputCallbackProc)(XtPointer client_data, int *source, XtInputId *id);

client_data	Passes the client data argument that was registered for this procedure in `XtApp\%AddInput`.
source	Passes the source file descriptor generating the event.
id	Passes the id returned from the corresponding `XtAppAddInput` call.

See the section called “Using the Intrinsics in a Multi-Threaded Environment” for information regarding the use of XtAppAddInput in multiple threads.

To discontinue a source of input, use XtRemoveInput.

void XtRemoveInput(XtInputId id);

id	Specifies the id returned from the corresponding `XtAppAddInput` call.

The XtRemoveInput function causes the Intrinsics read routine to stop watching for events from the file source specified by id.

See the section called “Using the Intrinsics in a Multi-Threaded Environment” for information regarding the use of XtRemoveInput in multiple threads.

Adding and Removing Blocking Notifications

Occasionally it is desirable for an application to receive notification when the Intrinsics event manager detects no pending input from file sources and no pending input from X server event sources and is about to block in an operating system call.

To register a hook that is called immediately prior to event blocking, use XtAppAddBlockHook.

XtBlockHookId XtAppAddBlockHook(XtAppContext app_context, XtBlockHookProc proc, XtPointer client_data);

app_context	Specifies the application context that identifies the application.
proc	Specifies the procedure to be called before blocking.
client_data	Specifies an argument passed to the specified procedure when it is called.

The XtAppAddBlockHook function registers the specified procedure and returns an identifier for it. The hook procedure proc is called at any time in the future when the Intrinsics are about to block pending some input.

The procedure pointers used to provide notification of event blocking are of type *XtBlockHookProc.

void *XtBlockHookProc(XtPointer client_data);

void *XtBlockHookProc(XtPointer client_data);

client_data

Passes the client data argument that was registered for this procedure in XtApp\%AddBlockHook.

To discontinue the use of a procedure for blocking notification, use XtRemoveBlockHook.

void XtRemoveBlockHook(XtBlockHookId id);

id	Specifies the identifier returned from the corresponding call to `XtAppAddBlockHook`.

The XtRemoveBlockHook function removes the specified procedure from the list of procedures that are called by the Intrinsics read routine before blocking on event sources.

Adding and Removing Timeouts

The timeout facility notifies the application or the widget through a callback procedure that a specified time interval has elapsed. Timeout values are uniquely identified by an interval id.

To register a timeout callback, use XtAppAddTimeOut.

XtIntervalId XtAppAddTimeOut(XtAppContext app_context, unsigned long interval, XtTimerCallbackProc proc, XtPointer client_data);

XtIntervalId XtAppAddTimeOut(XtAppContext app_context, unsigned long interval, XtTimerCallbackProc proc, XtPointer client_data);

app_context	Specifies the application context for which the timer is to be set.
interval	Specifies the time interval in milliseconds.
proc	Specifies the procedure to be called when the time expires.
client_data	Specifies an argument passed to the specified procedure when it is called.

The XtAppAddTimeOut function creates a timeout and returns an identifier for it. The timeout value is set to interval. The callback procedure proc is called when XtAppNextEvent or XtAppProcessEvent is next called after the time interval elapses, and then the timeout is removed.

Callback procedure pointers used with timeouts are of type *XtTimerCallbackProc.

void *XtTimerCallbackProc(XtPointer client_data, XtIntervalId *timer);

void *XtTimerCallbackProc(XtPointer client_data, XtIntervalId *timer);

client_data	Passes the client data argument that was registered for this procedure in `XtApp\%AddTimeOut`.
timer	Passes the id returned from the corresponding `XtAppAddTimeOut` call.

See the section called “Using the Intrinsics in a Multi-Threaded Environment” for information regarding the use of XtAppAddTimeOut in multiple threads.

To clear a timeout value, use XtRemoveTimeOut.

void XtRemoveTimeOut(XtIntervalId timer);

timer

Specifies the id for the timeout request to be cleared.

The XtRemoveTimeOut function removes the pending timeout. Note that timeouts are automatically removed once they trigger.

Please refer to Section 7.12 for information regarding the use of XtRemoveTimeOut in multiple threads.

Adding and Removing Signal Callbacks

The signal facility notifies the application or the widget through a callback procedure that a signal or other external asynchronous event has occurred. The registered callback procedures are uniquely identified by a signal id.

Prior to establishing a signal handler, the application or widget should call XtAppAddSignal and store the resulting identifier in a place accessible to the signal handler. When a signal arrives, the signal handler should call XtNoticeSignal to notify the Intrinsics that a signal has occured. To register a signal callback use XtAppAddSignal.

XtSignalId XtAppAddSignal(XtAppContext app_context, XtSignalCallbackProc proc, XtPointer client_data);

app_context	Specifies the application context that identifies the application.
proc	Specifies the procedure to be called when the signal is noticed.
client_data	Specifies an argument passed to the specified procedure when it is called.

The callback procedure pointers used to handle signal events are of type (*XtSignalCallbackProc).

typedef void (*XtSignalCallbackProc)(XtPointer client_data, XtSignalId *id);

typedef void (*XtSignalCallbackProc)(XtPointer client_data, XtSignalId *id);

client_data	Passes the client data argument that was registered for this procedure in `XtAppAddSignal`.
id	Passes the id returned from the corresponding `XtAppAddSignal` call.

To notify the Intrinsics that a signal has occured, use XtNoticeSignal.

void XtNoticeSignal(XtSignalId id);

id	Specifies the id returned from the corresponding `XtAppAddSignal` call.

On a POSIX-based system, XtNoticeSignal is the only Intrinsics function that can safely be called from a signal handler. If XtNoticeSignal is invoked multiple times before the Intrinsics are able to invoke the registered callback, the callback is only called once. Logically, the Intrinsics maintain “pending” flag for each registered callback. This flag is initially False and is set to True by XtNoticeSignal. When XtAppNextEvent or XtAppProcessEvent (with a mask including XtIMSignal) is called, all registered callbacks with “pending” True are invoked and the flags are reset to False.

If the signal handler wants to track how many times the signal has been raised, it can keep its own private counter. Typically the handler would not do any other work; the callback does the actual processing for the signal. The Intrinsics never block signals from being raised, so if a given signal can be raised multiple times before the Intrinsics can invoke the callback for that signal, the callback must be designed to deal with this. In another case, a signal might be raised just after the Intrinsics sets the pending flag to False but before the callback can get control, in which case the pending flag will still be True after the callback returns, and the Intrinsics will invoke the callback again, even though all of the signal raises have been handled. The callback must also be prepared to handle this case.

To remove a registered signal callback, call XtRemoveSignal.

void XtRemoveSignal(XtSignalId id);

void XtRemoveSignal(XtSignalId id);

id	Specifies the id returned by the corresponding call to `XtAppAddSignal`.

The client should typically disable the source of the signal before calling XtRemoveSignal. If the signal could have been raised again before the source was disabled and the client wants to process it, then after disabling the source but before calling XtRemoveSignal the client can test for signals with XtAppPending and process them by calling XtAppProcessEvent with the mask XtIMSignal.

Constraining Events to a Cascade of Widgets

Modal widgets are widgets that, except for the input directed to them, lock out user input to the application.

When a modal menu or modal dialog box is popped up using XtPopup, user events (keyboard and pointer events) that occur outside the modal widget should be delivered to the modal widget or ignored. In no case will user events be delivered to a widget outside the modal widget.

Menus can pop up submenus, and dialog boxes can pop up further dialog boxes to create a pop-up cascade. In this case, user events may be delivered to one of several modal widgets in the cascade.

Display-related events should be delivered outside the modal cascade so that exposure events and the like keep the application's display up-to-date. Any event that occurs within the cascade is delivered as usual. The user events delivered to the most recent spring-loaded shell in the cascade when they occur outside the cascade are called remap events and are KeyPress, KeyRelease, ButtonPress, and ButtonRelease. The user events ignored when they occur outside the cascade are MotionNotify and EnterNotify. All other events are delivered normally. In particular, note that this is one way in which widgets can receive LeaveNotify events without first receiving EnterNotify events; they should be prepared to deal with this, typically by ignoring any unmatched LeaveNotify events.

XtPopup uses the XtAddGrab and XtRemoveGrab functions to constrain user events to a modal cascade and subsequently to remove a grab when the modal widget is popped down.

To constrain or redirect user input to a modal widget, use XtAddGrab.

void XtAddGrab(Widget w, Boolean exclusive, Boolean spring_loaded);

w	Specifies the widget to add to the modal cascade. Must be of class Core or any subclass thereof.
exclusive	Specifies whether user events should be dispatched exclusively to this widget or also to previous widgets in the cascade.
spring_loaded	Specifies whether this widget was popped up because the user pressed a pointer button.

The XtAddGrab function appends the widget to the modal cascade and checks that exclusive is True if spring_loaded is True. If this condition is not met, XtAddGrab generates a warning message.

The modal cascade is used by XtDispatchEvent when it tries to dispatch a user event. When at least one modal widget is in the widget cascade, XtDispatchEvent first determines if the event should be delivered. It starts at the most recent cascade entry and follows the cascade up to and including the most recent cascade entry added with the exclusive parameter True.

This subset of the modal cascade along with all descendants of these widgets comprise the active subset. User events that occur outside the widgets in this subset are ignored or remapped. Modal menus with submenus generally add a submenu widget to the cascade with exclusive False. Modal dialog boxes that need to restrict user input to the most deeply nested dialog box add a subdialog widget to the cascade with exclusive True. User events that occur within the active subset are delivered to the appropriate widget, which is usually a child or further descendant of the modal widget.

Regardless of where in the application they occur, remap events are always delivered to the most recent widget in the active subset of the cascade registered with spring_loaded True, if any such widget exists. If the event occurred in the active subset of the cascade but outside the spring-loaded widget, it is delivered normally before being delivered also to the spring-loaded widget. Regardless of where it is dispatched, the Intrinsics do not modify the contents of the event.

To remove the redirection of user input to a modal widget, use XtRemoveGrab.

void XtRemoveGrab(Widget w);

void XtRemoveGrab(Widget w);

w	Specifies the widget to remove from the modal cascade.

The XtRemoveGrab function removes widgets from the modal cascade starting at the most recent widget up to and including the specified widget. It issues a warning if the specified widget is not on the modal cascade.

Requesting Key and Button Grabs

The Intrinsics provide a set of key and button grab interfaces that are parallel to those provided by Xlib and that allow the Intrinsics to modify event dispatching when necessary. X Toolkit applications and widgets that need to passively grab keys or buttons or actively grab the keyboard or pointer should use the following Intrinsics routines rather than the corresponding Xlib routines.

To passively grab a single key of the keyboard, use XtGrabKey.

void XtGrabKey(Widget widget, KeyCode keycode, Modifiers modifiers, Boolean owner_events, int pointer_mode);

void XtGrabKey(Widget widget, KeyCode keycode, Modifiers modifiers, Boolean owner_events, int pointer_mode);

widget	Specifies the widget in whose window the key is to be grabbed. Must be of class Core or any subclass thereof.
keycode , modifiers , owner_events , pointer_mode , keyboard_mode	Specify arguments to `XGrabKey`; see Section 12.2 in Xlib — C Language X Interface.

XtGrabKey calls XGrabKey specifying the widget's window as the grab window if the widget is realized. The remaining arguments are exactly as for XGrabKey. If the widget is not realized, or is later unrealized, the call to XGrabKey is performed (again) when the widget is realized and its window becomes mapped. In the future, if XtDispatchEvent is called with a KeyPress event matching the specified keycode and modifiers (which may be AnyKey or AnyModifier, respectively) for the widget's window, the Intrinsics will call XtUngrabKeyboard with the timestamp from the KeyPress event if either of the following conditions is true:

There is a modal cascade and the widget is not in the active subset of the cascade and the keyboard was not previously grabbed, or
XFilterEvent returns True.

To cancel a passive key grab, use XtUngrabKey.

void XtUngrabKey(Widget widget, KeyCode keycode, Modifiers modifiers);

void XtUngrabKey(Widget widget, KeyCode keycode, Modifiers modifiers);

widget	Specifies the widget in whose window the key was grabbed.
keycode , modifiers	Specify arguments to `XUngrabKey`; see Section 12.2 in Xlib — C Language X Interface.

The XtUngrabKey procedure calls XUngrabKey specifying the widget's window as the ungrab window if the widget is realized. The remaining arguments are exactly as for XUngrabKey. If the widget is not realized, XtUngrabKey removes a deferred XtGrabKey request, if any, for the specified widget, keycode, and modifiers.

To actively grab the keyboard, use XtGrabKeyboard.

int XtGrabKeyboard(Widget widget, Boolean owner_events, int pointer_mode, Time time);

int XtGrabKeyboard(Widget widget, Boolean owner_events, int pointer_mode, Time time);

widget	Specifies the widget for whose window the keyboard is to be grabbed. Must be of class Core or any subclass thereof.
owner_events , pointer_mode , keyboard_mode , time	Specify arguments to `XGrabKeyboard`; see Section 12.2 in Xlib — C Language X Interface.

If the specified widget is realized, XtGrabKeyboard calls XGrabKeyboard specifying the widget's window as the grab window. The remaining arguments and return value are exactly as for XGrabKeyboard. If the widget is not realized, XtGrabKeyboard immediately returns GrabNotViewable. No future automatic ungrab is implied by XtGrabKeyboard.

To cancel an active keyboard grab, use XtUngrabKeyboard.

void XtUngrabKeyboard(Widget widget, Time time);

void XtUngrabKeyboard(Widget widget, Time time);

widget	Specifies the widget that has the active keyboard grab.
time	Specifies the additional argument to `XUngrabKeyboard`; see Section 12.2 in Xlib — C Language X Interface.

XtUngrabKeyboard calls XUngrabKeyboard with the specified time.

To passively grab a single pointer button, use XtGrabButton.

void XtGrabButton(Widget widget, int button, Modifiers modifiers, Boolean owner_events, unsigned int event_mask, int pointer_mode, Window confine_to, Cursor cursor);

void XtGrabButton(Widget widget, int button, Modifiers modifiers, Boolean owner_events, unsigned int event_mask, int pointer_mode, Window confine_to, Cursor cursor);

widget	Specifies the widget in whose window the button is to be grabbed. Must be of class Core or any subclass thereof.
button , modifiers , owner_events , event_mask , pointer_mode , keyboard_mode , confine_to , cursor	Specify arguments to `XGrabButton`; see Section 12.1 in Xlib — C Language X Interface.

XtGrabButton calls XGrabButton specifying the widget's window as the grab window if the widget is realized. The remaining arguments are exactly as for XGrabButton. If the widget is not realized, or is later unrealized, the call to XGrabButton is performed (again) when the widget is realized and its window becomes mapped. In the future, if XtDispatchEvent is called with a ButtonPress event matching the specified button and modifiers (which may be AnyButton or AnyModifier, respectively) for the widget's window, the Intrinsics will call XtUngrabPointer with the timestamp from the ButtonPress event if either of the following conditions is true:

There is a modal cascade and the widget is not in the active subset of the cascade and the pointer was not previously grabbed, or
XFilterEvent returns True.

To cancel a passive button grab, use XtUngrabButton.

void XtUngrabButton(Widget widget, unsigned int button, Modifiers modifiers);

void XtUngrabButton(Widget widget, unsigned int button, Modifiers modifiers);

widget	Specifies the widget in whose window the button was grabbed.
button , modifiers	Specify arguments to `XUngrabButton`; see Section 12.1 in Xlib — C Language X Interface.

The XtUngrabButton procedure calls XUngrabButton specifying the widget's window as the ungrab window if the widget is realized. The remaining arguments are exactly as for XUngrabButton. If the widget is not realized, XtUngrabButton removes a deferred XtGrabButton request, if any, for the specified widget, button, and modifiers.

To actively grab the pointer, use XtGrabPointer.

int XtGrabPointer(Widget widget, Boolean owner_events, unsigned int event_mask, int pointer_mode, Window confine_to, Cursor cursor, Time time);

int XtGrabPointer(Widget widget, Boolean owner_events, unsigned int event_mask, int pointer_mode, Window confine_to, Cursor cursor, Time time);

widget	Specifies the widget for whose window the pointer is to be grabbed. Must be of class Core or any subclass thereof.
owner_events , event_mask , pointer_mode , keyboard_mode , confine_to , cursor , time	Specify arguments to `XGrabPointer`; see Section 12.1 in Xlib — C Language X Interface.

If the specified widget is realized, XtGrabPointer calls XGrabPointer, specifying the widget's window as the grab window. The remaining arguments and return value are exactly as for XGrabPointer. If the widget is not realized, XtGrabPointer immediately returns GrabNotViewable. No future automatic ungrab is implied by XtGrabPointer.

To cancel an active pointer grab, use XtUngrabPointer.

void XtUngrabPointer(Widget widget, Time time);

void XtUngrabPointer(Widget widget, Time time);

widget	Specifies the widget that has the active pointer grab.
time	Specifies the time argument to `XUngrabPointer`; see Section 12.1 in Xlib — C Language X Interface.

XtUngrabPointer calls XUngrabPointer with the specified time.

Focusing Events on a Child

To redirect keyboard input to a normal descendant of a widget without calling XSetInputFocus, use XtSetKeyboardFocus.

void XtSetKeyboardFocus(Widget subtree);

subtree	Specifies the subtree of the hierarchy for which the keyboard focus is to be set. Must be of class Core or any subclass thereof.
descendant	Specifies either the normal (non-pop-up) descendant of subtree to which keyboard events are logically directed, or `None`. It is not an error to specify `None` when no input focus was previously set. Must be of class Object or any subclass thereof.

XtSetKeyboardFocus causes XtDispatchEvent to remap keyboard events occurring within the specified subtree and dispatch them to the specified descendant widget or to an ancestor. If the descendant's class is not a subclass of Core, the descendant is replaced by its closest windowed ancestor.

When there is no modal cascade, keyboard events can be dispatched to a widget in one of five ways. Assume the server delivered the event to the window for widget E (because of X input focus, key or keyboard grabs, or pointer position).

If neither E nor any of E's ancestors have redirected the keyboard focus, or if the event activated a grab for E as specified by a call to XtGrabKey with any value of owner_events, or if the keyboard is actively grabbed by E with owner_events False via XtGrabKeyboard or XtGrabKey on a previous key press, the event is dispatched to E.
Beginning with the ancestor of E closest to the root that has redirected the keyboard focus or E if no such ancestor exists, if the target of that focus redirection has in turn redirected the keyboard focus, recursively follow this focus chain to find a widget F that has not redirected focus.
- If E is the final focus target widget F or a descendant of F, the event is dispatched to E.
- If E is not F, an ancestor of F, or a descendant of F, and the event activated a grab for E as specified by a call to XtGrabKey for E, XtUngrabKeyboard is called.
- If E is an ancestor of F, and the event is a key press, and either
- - E has grabbed the key with XtGrabKey and owner_events False, or
  - E has grabbed the key with XtGrabKey and owner_events True, and the coordinates of the event are outside the rectangle specified by E's geometry, then the event is dispatched to E.
- Otherwise, define A as the closest common ancestor of E and F:
- - If there is an active keyboard grab for any widget via either XtGrabKeyboard or XtGrabKey on a previous key press, or if no widget between F and A (noninclusive) has grabbed the key and modifier combination with XtGrabKey and any value of owner_events, the event is dispatched to F.
  - Else, the event is dispatched to the ancestor of F closest to A that has grabbed the key and modifier combination with XtGrabKey.

When there is a modal cascade, if the final destination widget as identified above is in the active subset of the cascade, the event is dispatched; otherwise the event is remapped to a spring-loaded shell or discarded. Regardless of where it is dispatched, the Intrinsics do not modify the contents of the event.

When subtree or one of its descendants acquires the X input focus or the pointer moves into the subtree such that keyboard events would now be delivered to the subtree, a FocusIn event is generated for the descendant if FocusChange events have been selected by the descendant. Similarly, when subtree loses the X input focus or the keyboard focus for one of its ancestors, a FocusOut event is generated for descendant if FocusChange events have been selected by the descendant.

A widget tree may also actively manage the X server input focus. To do so, a widget class specifies an accept_focus procedure.

The accept_focus procedure pointer is of type *XtAcceptFocusProc.

Boolean *XtAcceptFocusProc(Widget w, Time *time);

Boolean *XtAcceptFocusProc(Widget w, Time *time);

w	Specifies the widget.
time	Specifies the X time of the event causing the accept focus.

Widgets that need the input focus can call XSetInputFocus explicitly, pursuant to the restrictions of the Inter-Client Communication Conventions Manual.. To allow outside agents, such as the parent, to cause a widget to take the input focus, every widget exports an accept_focus procedure. The widget returns a value indicating whether it actually took the focus or not, so that the parent can give the focus to another widget. Widgets that need to know when they lose the input focus must use the Xlib focus notification mechanism explicitly (typically by specifying translations for FocusIn and FocusOut events). Widgets classes that never want the input focus should set the accept_focus field to NULL.

To call a widget's accept_focus procedure, use XtCallAcceptFocus.

Boolean XtCallAcceptFocus(Widget w, Time *time);

Boolean XtCallAcceptFocus(Widget w, Time *time);

w	Specifies the widget. Must be of class Core or any subclass thereof.
time	Specifies the X time of the event that is causing the focus change.

The XtCallAcceptFocus function calls the specified widget's accept_focus procedure, passing it the specified widget and time, and returns what the accept_focus procedure returns. If accept_focus is NULL, XtCallAcceptFocus returns False.

Events for Drawables That Are Not a Widget's Window

Sometimes an application must handle events for drawables that are not associated with widgets in its widget tree. Examples include handling GraphicsExpose and NoExpose events on Pixmaps, and handling PropertyNotify events on the root window.

To register a drawable with the Intrinsics event dispatching, use XtRegisterDrawable.

void XtRegisterDrawable(Display *display, Drawable drawable, Widget widget);

void XtRegisterDrawable(Display *display, Drawable drawable, Widget widget);

display	Specifies the drawable's display.
drawable	Specifies the drawable to register.
widget	Specifies the widget to register the drawable for.

XtRegisterDrawable associates the specified drawable with the specified widget so that future calls to XtWindowToWidget with the drawable will return the widget. The default event dispatcher will dispatch future events that arrive for the drawable to the widget in the same manner as events that contain the widget's window.

If the drawable is already registered with another widget, or if the drawable is the window of a widget in the client's widget tree, the results of calling XtRegisterDrawable are undefined.

To unregister a drawable with the Intrinsics event dispatching, use XtUnregisterDrawable.

void XtUnregisterDrawable(Display *display, Drawable drawable);

void XtUnregisterDrawable(Display *display, Drawable drawable);

display	Specifies the drawable's display.
drawable	Specifies the drawable to unregister.

XtUnregisterDrawable removes an association created with XtRegisterDrawable. If the drawable is the window of a widget in the client's widget tree the results of calling XtUnregisterDrawable are undefined.

Querying Event Sources

The event manager provides several functions to examine and read events (including file and timer events) that are in the queue. The next three functions are Intrinsics equivalents of the XPending, XPeekEvent, and XNextEvent Xlib calls.

To determine if there are any events on the input queue for a given application, use XtAppPending.

XtInputMask XtAppPending(XtAppContext app_context);

app_context

Specifies the application context that identifies the application to check.

The XtAppPending function returns a nonzero value if there are events pending from the X server, timer pending, other input sources pending, or signal sources pending. The value returned is a bit mask that is the OR of XtIMXEvent, XtIMTimer, XtIMAlternateInput, and XtIMSignal (see XtAppProcessEvent ). If there are no events pending, XtAppPending flushes the output buffers of each Display in the application context and returns zero.

To return the event from the head of a given application's input queue without removing input from the queue, use XtAppPeekEvent.

Boolean XtAppPeekEvent(XtAppContext app_context, XEvent *event_return);

Boolean XtAppPeekEvent(XtAppContext app_context, XEvent *event_return);

app_context	Specifies the application context that identifies the application.
event_return	Returns the event information to the specified event structure.

If there is an X event in the queue, XtAppPeekEvent copies it into event_return and returns True. If no X input is on the queue, XtAppPeekEvent flushes the output buffers of each Display in the application context and blocks until some input is available (possibly calling some timeout callbacks in the interim). If the next available input is an X event, XtAppPeekEvent fills in event_return and returns True. Otherwise, the input is for an input source registered with XtAppAddInput, and XtAppPeekEvent returns False. The sample implementations provides XtAppPeekEvent as described. Timeout callbacks are called while blocking for input. If some input for an input source is available, XtAppPeekEvent will return True without returning an event.

To remove and return the event from the head of a given application's X event queue, use XtAppNextEvent.

void XtAppNextEvent(XtAppContext app_context, XEvent *event_return);

void XtAppNextEvent(XtAppContext app_context, XEvent *event_return);

app_context	Specifies the application context that identifies the application.
event_return	Returns the event information to the specified event structure.

If the X event queue is empty, XtAppNextEvent flushes the X output buffers of each Display in the application context and waits for an X event while looking at the other input sources and timeout values and calling any callback procedures triggered by them. This wait time can be used for background processing; see the section called “Adding Background Work Procedures”.

Dispatching Events

The Intrinsics provide functions that dispatch events to widgets or other application code. Every client interested in X events on a widget uses XtAddEventHandler to register which events it is interested in and a procedure (event handler) to be called when the event happens in that window. The translation manager automatically registers event handlers for widgets that use translation tables; see Chapter 10, Translation Management.

Applications that need direct control of the processing of different types of input should use XtAppProcessEvent.

void XtAppProcessEvent(XtAppContext app_context, XtInputMask mask);

app_context	Specifies the application context that identifies the application for which to process input.
mask	Specifies what types of events to process. The mask is the bitwise inclusive OR of any combination of `XtIMXEvent`, `XtIMTimer`, `XtIMAlternateInput`, and `XtIMSignal`. As a convenience, `Intrinsic.h` defines the symbolic name `XtIMAll` to be the bitwise inclusive OR of these four event types.

The XtAppProcessEvent function processes one timer, input source, signal source, or X event. If there is no event or input of the appropriate type to process, then XtAppProcessEvent blocks until there is. If there is more than one type of input available to process, it is undefined which will get processed. Usually, this procedure is not called by client applications; see XtAppMainLoop. XtAppProcessEvent processes timer events by calling any appropriate timer callbacks, input sources by calling any appropriate input callbacks, signal source by calling any appropriate signal callbacks, and X events by calling XtDispatchEvent.

When an X event is received, it is passed to XtDispatchEvent, which calls the appropriate event handlers and passes them the widget, the event, and client-specific data registered with each procedure. If no handlers for that event are registered, the event is ignored and the dispatcher simply returns.

To dispatch an event returned by XtAppNextEvent, retrieved directly from the Xlib queue, or synthetically constructed, to any registered event filters or event handlers, call XtDispatchEvent.

Boolean XtDispatchEvent(XEvent *event);

Boolean XtDispatchEvent(XEvent *event);

event

Specifies a pointer to the event structure to be dispatched to the appropriate event handlers.

The XtDispatchEvent function first calls XFilterEvent with the event and the window of the widget to which the Intrinsics intend to dispatch the event, or the event window if the Intrinsics would not dispatch the event to any handlers. If XFilterEvent returns True and the event activated a server grab as identified by a previous call to XtGrabKey or XtGrabButton, XtDispatchEvent calls XtUngrabKeyboard or XtUngrabPointer with the timestamp from the event and immediately returns True. If XFilterEvent returns True and a grab was not activated, XtDispatchEvent just immediately returns True. Otherwise, XtDispatchEvent sends the event to the event handler functions that have been previously registered with the dispatch routine. XtDispatchEvent returns True if XFilterEvent returned True, or if the event was dispatched to some handler, and False if it found no handler to which to dispatch the event. XtDispatchEvent records the last timestamp in any event that contains a timestamp (see XtLastTimestampProcessed ), regardless of whether it was filtered or dispatched. If a modal cascade is active with spring_loaded True, and if the event is a remap event as defined by XtAddGrab, XtDispatchEvent may dispatch the event a second time. If it does so, XtDispatchEvent will call XFilterEvent again with the window of the spring-loaded widget prior to the second dispatch, and if XFilterEvent returns True, the second dispatch will not be performed.

The Application Input Loop

To process all input from a given application in a continuous loop, use the convenience procedure XtAppMainLoop.

void XtAppMainLoop(XtAppContext app_context);

void XtAppMainLoop(XtAppContext app_context);

app_context

Specifies the application context that identifies the application.

The XtAppMainLoop function first reads the next incoming X event by calling XtAppNextEvent and then dispatches the event to the appropriate registered procedure by calling XtDispatchEvent. This constitutes the main loop of X Toolkit applications. There is nothing special about XtAppMainLoop; it simply calls XtAppNextEvent and then XtDispatchEvent in a conditional loop. At the bottom of the loop, it checks to see if the specified application context's destroy flag is set. If the flag is set, the loop breaks. The whole loop is enclosed between a matching XtAppLock and XtAppUnlock.

Applications can provide their own version of this loop, which tests some global termination flag or tests that the number of top-level widgets is larger than zero before circling back to the call to XtAppNextEvent.

Setting and Checking the Sensitivity State of a Widget

Many widgets have a mode in which they assume a different appearance (for example, are grayed out or stippled), do not respond to user events, and become dormant.

When dormant, a widget is considered to be insensitive. If a widget is insensitive, the event manager does not dispatch any events to the widget with an event type of KeyPress, KeyRelease, ButtonPress, ButtonRelease, MotionNotify, EnterNotify, LeaveNotify, FocusIn, or FocusOut.

A widget can be insensitive because its sensitive field is False or because one of its ancestors is insensitive and thus the widget's ancestor_sensitive field also is False. A widget can but does not need to distinguish these two cases visually.

Note

Pop-up shells will have ancestor_sensitive False if the parent was insensitive when the shell was created. Since XtSetSensitive on the parent will not modify the resource of the pop-up child, clients are advised to include a resource specification of the form “*TransientShell.ancestorSensitive: True” in the application defaults resource file or to otherwise ensure that the parent is sensitive when creating pop-up shells.

To set the sensitivity state of a widget, use XtSetSensitive.

void XtSetSensitive(Widget w, Boolean sensitive);

w	Specifies the widget. Must be of class RectObj or any subclass thereof.
sensitive	Specifies whether the widget should receive keyboard, pointer, and focus events.

The XtSetSensitive function first calls XtSetValues on the current widget with an argument list specifying the XtNsensitive resource and the new value. If sensitive is False and the widget's class is a subclass of Composite, XtSetSensitive recursively propagates the new value down the child tree by calling XtSetValues on each child to set ancestor_sensitive to False. If sensitive is True and the widget's class is a subclass of Composite and the widget's ancestor_sensitive field is True, XtSetSensitive sets the ancestor_sensitive of each child to True and then recursively calls XtSetValues on each normal descendant that is now sensitive to set ancestor_sensitive to True.

XtSetSensitive calls XtSetValues to change the sensitive and ancestor_sensitive fields of each affected widget. Therefore, when one of these changes, the widget's set_values procedure should take whatever display actions are needed (for example, graying out or stippling the widget).

XtSetSensitive maintains the invariant that, if the parent has either sensitive or ancestor_sensitive False, then all children have ancestor_sensitive False.

To check the current sensitivity state of a widget, use XtIsSensitive.

Boolean XtIsSensitive(Widget w);

w	Specifies the object. Must be of class Object or any subclass thereof.

The XtIsSensitive function returns True or False to indicate whether user input events are being dispatched. If object's class is a subclass of RectObj and both sensitive and ancestor_sensitive are True, XtIsSensitive returns True; otherwise, it returns False.

Adding Background Work Procedures

The Intrinsics have some limited support for background processing. Because most applications spend most of their time waiting for input, you can register an idle-time work procedure that is called when the toolkit would otherwise block in XtAppNextEvent or XtAppProcessEvent. Work procedure pointers are of type (*XtWorkProc).

typedef Boolean (*XtWorkProc)(XtPointer client_data);

client_data

Passes the client data specified when the work procedure was registered.

This procedure should return True when it is done to indicate that it should be removed. If the procedure returns False, it will remain registered and called again when the application is next idle. Work procedures should be very judicious about how much they do. If they run for more than a small part of a second, interactive feel is likely to suffer.

To register a work procedure for a given application, use XtAppAddWorkProc.

XtWorkProcId XtAppAddWorkProc(XtAppContext app_context, XtWorkProc proc, XtPointer client_data);

app_context	Specifies the application context that identifies the application.
proc	Specifies the procedure to be called when the application is idle.
client_data	Specifies the argument passed to the specified procedure when it is called.

The XtAppAddWorkProc function adds the specified work procedure for the application identified by app_context and returns an opaque unique identifier for this work procedure. Multiple work procedures can be registered, and the most recently added one is always the one that is called. However, if a work procedure adds another work procedure, the newly added one has lower priority than the current one.

To remove a work procedure, either return True from the procedure when it is called or use XtRemoveWorkProc outside of the procedure.

void XtRemoveWorkProc(XtWorkProcId id);

void XtRemoveWorkProc(XtWorkProcId id);

id	Specifies which work procedure to remove.

The XtRemoveWorkProc function explicitly removes the specified background work procedure.

X Event Filters

The event manager provides filters that can be applied to specific X events. The filters, which screen out events that are redundant or are temporarily unwanted, handle pointer motion compression, enter/leave compression, and exposure compression.

Pointer Motion Compression

Widgets can have a hard time keeping up with a rapid stream of pointer motion events. Furthermore, they usually do not care about every motion event. To throw out redundant motion events, the widget class field compress_motion should be True. When a request for an event would return a motion event, the Intrinsics check if there are any other motion events for the same widget immediately following the current one and, if so, skip all but the last of them.

Enter/Leave Compression

To throw out pairs of enter and leave events that have no intervening events, as can happen when the user moves the pointer across a widget without stopping in it, the widget class field compress_enterleave should be True. These enter and leave events are not delivered to the client if they are found together in the input queue.

Exposure Compression

Many widgets prefer to process a series of exposure events as a single expose region rather than as individual rectangles. Widgets with complex displays might use the expose region as a clip list in a graphics context, and widgets with simple displays might ignore the region entirely and redisplay their whole window or might get the bounding box from the region and redisplay only that rectangle.

In either case, these widgets do not care about getting partial exposure events. The compress_exposure field in the widget class structure specifies the type and number of exposure events that are dispatched to the widget's expose procedure. This field must be initialized to one of the following values:

#define XtExposeNoCompress ((XtEnum)False)
#define XtExposeCompressSeries ((XtEnum)True)
#define XtExposeCompressMultiple <implementation-defined>
#define XtExposeCompressMaximal <implementation-defined>

optionally ORed with any combination of the following flags (all with implementation-defined values): XtExposeGraphicsExpose, XtExposeGraphicsExposeMerged, XtExposeNoExpose, and XtExposeNoRegion.

If the compress_exposure field in the widget class structure does not specify XtExposeNoCompress, the event manager calls the widget's expose procedure only once for a series of exposure events. In this case, all Expose or GraphicsExpose events are accumulated into a region. When the final event is received, the event manager replaces the rectangle in the event with the bounding box for the region and calls the widget's expose procedure, passing the modified exposure event and (unless XtExposeNoRegion is specified) the region. For more information on regions, see Section 16.5 in Xlib — C Language X Interface..)

The values have the following interpretation:

XtExposeNoCompress

No exposure compression is performed; every selected event is individually dispatched to the expose procedure with a region argument of NULL.

XtExposeCompressSeries

Each series of exposure events is coalesced into a single event, which is dispatched when an exposure event with count equal to zero is reached.

XtExposeCompressMultiple

Consecutive series of exposure events are coalesced into a single event, which is dispatched when an exposure event with count equal to zero is reached and either the event queue is empty or the next event is not an exposure event for the same widget.

XtExposeCompressMaximal

All expose series currently in the queue for the widget are coalesced into a single event without regard to intervening nonexposure events. If a partial series is in the end of the queue, the Intrinsics will block until the end of the series is received.

The additional flags have the following meaning:

XtExposeGraphicsExpose

Specifies that GraphicsExpose events are also to be dispatched to the expose procedure. GraphicsExpose events are compressed, if specified, in the same manner as Expose events.

XtExposeGraphicsExposeMerged

Specifies in the case of XtExposeCompressMultiple and XtExposeCompressMaximal that series of GraphicsExpose and Expose events are to be compressed together, with the final event type determining the type of the event passed to the expose procedure. If this flag is not set, then only series of the same event type as the event at the head of the queue are coalesced. This flag also implies XtExposeGraphicsExpose.

XtExposeNoExpose

Specifies that NoExpose events are also to be dispatched to the expose procedure. NoExpose events are never coalesced with other exposure events or with each other.

XtExposeNoRegion

Specifies that the final region argument passed to the expose procedure is NULL. The rectangle in the event will still contain bounding box information for the entire series of compressed exposure events. This option saves processing time when the region is not needed by the widget.

Widget Exposure and Visibility

Every primitive widget and some composite widgets display data on the screen by means of direct Xlib calls. Widgets cannot simply write to the screen and forget what they have done. They must keep enough state to redisplay the window or parts of it if a portion is obscured and then reexposed.

Redisplay of a Widget: The expose Procedure

The expose procedure pointer in a widget class is of type (*XtExposeProc).

typedef void (*XtExposeProc)(Widget w, XEvent *event, Region region);

typedef void (*XtExposeProc)(Widget w, XEvent *event, Region region);

w	Specifies the widget instance requiring redisplay.
event	Specifies the exposure event giving the rectangle requiring redisplay.
region	Specifies the union of all rectangles in this exposure sequence.

The redisplay of a widget upon exposure is the responsibility of the expose procedure in the widget's class record. If a widget has no display semantics, it can specify NULL for the expose field. Many composite widgets serve only as containers for their children and have no expose procedure.

Note

If the expose procedure is NULL, XtRealizeWidget fills in a default bit gravity of NorthWestGravity before it calls the widget's realize procedure.

If the widget's compress_exposure class field specifies XtExposeNoCompress or XtExposeNoRegion, or if the event type is NoExpose (see the section called “Exposure Compression”), region is NULL. If XtExposeNoCompress is not specified and the event type is not NoExpose, the event is the final event in the compressed series but x, y, width, and height contain the bounding box for all the compressed events. The region is created and destroyed by the Intrinsics, but the widget is permitted to modify the region contents.

A small simple widget (for example, Label) can ignore the bounding box information in the event and redisplay the entire window. A more complicated widget (for example, Text) can use the bounding box information to minimize the amount of calculation and redisplay it does. A very complex widget uses the region as a clip list in a GC and ignores the event information. The expose procedure is not chained and is therefore responsible for exposure of all superclass data as well as its own.

However, it often is possible to anticipate the display needs of several levels of subclassing. For example, rather than implement separate display procedures for the widgets Label, Pushbutton, and Toggle, you could write a single display routine in Label that uses display state fields like

Boolean invert;
Boolean highlight;
Dimension highlight_width;

Label would have invert and highlight always False and highlight_width zero. Pushbutton would dynamically set highlight and highlight_width, but it would leave invert always False. Finally, Toggle would dynamically set all three. In this case, the expose procedures for Pushbutton and Toggle inherit their superclass's expose procedure; see the section called “Inheritance of Superclass Operations”.

Widget Visibility

Some widgets may use substantial computing resources to produce the data they will display. However, this effort is wasted if the widget is not actually visible on the screen, that is, if the widget is obscured by another application or is iconified.

The visible field in the core widget structure provides a hint to the widget that it need not compute display data. This field is guaranteed to be True by the time an exposure event is processed if any part of the widget is visible, but is False if the widget is fully obscured.

Widgets can use or ignore the visible hint. If they ignore it, they should have visible_interest in their widget class record set False. In such cases, the visible field is initialized True and never changes. If visible_interest is True, the event manager asks for VisibilityNotify events for the widget and sets visible to True on VisibilityUnobscured or VisibilityPartiallyObscured events and False on VisibilityFullyObscured events.

X Event Handlers

Event handlers are procedures called when specified events occur in a widget. Most widgets need not use event handlers explicitly. Instead, they use the Intrinsics translation manager. Event handler procedure pointers are of the type (*XtEventHandler).

typedef void (*XtEventHandler)(Widget w, XtPointer client_data, XEvent *event, Boolean *continue_to_dispatch);

typedef void (*XtEventHandler)(Widget w, XtPointer client_data, XEvent *event, Boolean *continue_to_dispatch);

w	Specifies the widget for which the event arrived.
client_data	Specifies any client-specific information registered with the event handler.
event	Specifies the triggering event.
continue_to_dispatch	Specifies whether the remaining event handlers registered for the current event should be called.

After receiving an event and before calling any event handlers, the Boolean pointed to by continue_to_dispatch is initialized to True. When an event handler is called, it may decide that further processing of the event is not desirable and may store False in this Boolean, in which case any handlers remaining to be called for the event are ignored.

The circumstances under which the Intrinsics may add event handlers to a widget are currently implementation-dependent. Clients must therefore be aware that storing False into the continue_to_dispatch argument can lead to portability problems.

Event Handlers That Select Events

To register an event handler procedure with the dispatch mechanism, use XtAddEventHandler.

void XtAddEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data);

void XtAddEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data);

w	Specifies the widget for which this event handler is being registered. Must be of class Core or any subclass thereof.
event_mask	Specifies the event mask for which to call this procedure.
nonmaskable	Specifies whether this procedure should be called on the nonmaskable events `( GraphicsExpose`, `NoExpose`, `SelectionClear`, `SelectionRequest`, `SelectionNotify`, `ClientMessage`, and `MappingNotify ).`
proc	Specifies the procedure to be called.
client_data	Specifies additional data to be passed to the event handler.

The XtAddEventHandler function registers a procedure with the dispatch mechanism that is to be called when an event that matches the mask occurs on the specified widget. Each widget has a single registered event handler list, which will contain any procedure/client_data pair exactly once regardless of the manner in which it is registered. If the procedure is already registered with the same client_data value, the specified mask augments the existing mask. If the widget is realized, XtAddEventHandler calls XSelectInput, if necessary. The order in which this procedure is called relative to other handlers registered for the same event is not defined.

To remove a previously registered event handler, use XtRemoveEventHandler.

void XtRemoveEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data);

w	Specifies the widget for which this procedure is registered. Must be of class Core or any subclass thereof.
event_mask	Specifies the event mask for which to unregister this procedure.
nonmaskable	Specifies whether this procedure should be removed on the nonmaskable events `( GraphicsExpose`, `NoExpose`, `SelectionClear`, `SelectionRequest`, `SelectionNotify`, `ClientMessage`, and `MappingNotify ).`
proc	Specifies the procedure to be removed.
client_data	Specifies the registered client data.

The XtRemoveEventHandler function unregisters an event handler registered with XtAddEventHandler or XtInsertEventHandler for the specified events. The request is ignored if client_data does not match the value given when the handler was registered. If the widget is realized and no other event handler requires the event, XtRemoveEventHandler calls XSelectInput. If the specified procedure has not been registered or if it has been registered with a different value of client_data, XtRemoveEventHandler returns without reporting an error.

To stop a procedure registered with XtAddEventHandler or XtInsertEventHandler from receiving all selected events, call XtRemoveEventHandler with an event_mask of XtAllEvents and nonmaskable True. The procedure will continue to receive any events that have been specified in calls to XtAddRawEventHandler or XtInsertRawEventHandler.

To register an event handler procedure that receives events before or after all previously registered event handlers, use XtInsertEventHandler.

typedef enum {XtListHead, XtListTail} XtListPosition;

void XtInsertEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data, XtListPosition position);

void XtInsertEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data, XtListPosition position);

w	Specifies the widget for which this event handler is being registered. Must be of class Core or any subclass thereof.
event_mask	Specifies the event mask for which to call this procedure.
nonmaskable	Specifies whether this procedure should be called on the nonmaskable events `( GraphicsExpose`, `NoExpose`, `SelectionClear`, `SelectionRequest`, `SelectionNotify`, `ClientMessage`, and `MappingNotify ).`
proc	Specifies the procedure to be called.
client_data	Specifies additional data to be passed to the client's event handler.
position	Specifies when the event handler is to be called relative to other previously registered handlers.

XtInsertEventHandler is identical to XtAddEventHandler with the additional position argument. If position is XtListHead, the event handler is registered so that it is called before any event handlers that were previously registered for the same widget. If position is XtListTail, the event handler is registered to be called after any previously registered event handlers. If the procedure is already registered with the same client_data value, the specified mask augments the existing mask and the procedure is repositioned in the list.

Event Handlers That Do Not Select Events

On occasion, clients need to register an event handler procedure with the dispatch mechanism without explicitly causing the X server to select for that event. To do this, use XtAddRawEventHandler.

void XtAddRawEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data);

w	Specifies the widget for which this event handler is being registered. Must be of class Core or any subclass thereof.
event_mask	Specifies the event mask for which to call this procedure.
nonmaskable	Specifies whether this procedure should be called on the nonmaskable events `( GraphicsExpose`, `NoExpose`, `SelectionClear`, `SelectionRequest`, `SelectionNotify`, `ClientMessage`, and `MappingNotify ).`
proc	Specifies the procedure to be called.
client_data	Specifies additional data to be passed to the client's event handler.

The XtAddRawEventHandler function is similar to XtAddEventHandler except that it does not affect the widget's event mask and never causes an XSelectInput for its events. Note that the widget might already have those mask bits set because of other nonraw event handlers registered on it. If the procedure is already registered with the same client_data, the specified mask augments the existing mask. The order in which this procedure is called relative to other handlers registered for the same event is not defined.

To remove a previously registered raw event handler, use XtRemoveRawEventHandler.

void XtRemoveRawEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data);

void XtRemoveRawEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data);

w	Specifies the widget for which this procedure is registered. Must be of class Core or any subclass thereof.
event_mask	Specifies the event mask for which to unregister this procedure.
nonmaskable	Specifies whether this procedure should be removed on the nonmaskable events `( GraphicsExpose`, `NoExpose`, `SelectionClear`, `SelectionRequest`, `SelectionNotify`, `ClientMessage`, and `MappingNotify ).`
proc	Specifies the procedure to be registered.
client_data	Specifies the registered client data.

The XtRemoveRawEventHandler function unregisters an event handler registered with XtAddRawEventHandler or XtInsertRawEventHandler for the specified events without changing the window event mask. The request is ignored if client_data does not match the value given when the handler was registered. If the specified procedure has not been registered or if it has been registered with a different value of client_data, XtRemoveRawEventHandler returns without reporting an error.

To stop a procedure registered with XtAddRawEventHandler or XtInsertRawEventHandler from receiving all nonselected events, call XtRemoveRawEventHandler with an event_mask of XtAllEvents and nonmaskable True. The procedure will continue to receive any events that have been specified in calls to XtAddEventHandler or XtInsertEventHandler.

To register an event handler procedure that receives events before or after all previously registered event handlers without selecting for the events, use XtInsertRawEventHandler.

void XtInsertRawEventHandler(Widget w, EventMask event_mask, Boolean nonmaskable, XtEventHandler proc, XtPointer client_data, XtListPosition position);

w	Specifies the widget for which this event handler is being registered. Must be of class Core or any subclass thereof.
event_mask	Specifies the event mask for which to call this procedure.
nonmaskable	Specifies whether this procedure should be called on the nonmaskable events `( GraphicsExpose`, `NoExpose`, `SelectionClear`, `SelectionRequest`, `SelectionNotify`, `ClientMessage`, and `MappingNotify ).`
proc	Specifies the procedure to be registered.
client_data	Specifies additional data to be passed to the client's event handler.
position	Specifies when the event handler is to be called relative to other previously registered handlers.

The XtInsertRawEventHandler function is similar to XtInsertEventHandler except that it does not modify the widget's event mask and never causes an XSelectInput for the specified events. If the procedure is already registered with the same client_data value, the specified mask augments the existing mask and the procedure is repositioned in the list.

Current Event Mask

To retrieve the event mask for a given widget, use XtBuildEventMask.

EventMask XtBuildEventMask(Widget w);

w	Specifies the widget. Must be of class Core or any subclass thereof.

The XtBuildEventMask function returns the event mask representing the logical OR of all event masks for event handlers registered on the widget with XtAddEventHandler and XtInsertEventHandler and all event translations, including accelerators, installed on the widget. This is the same event mask stored into the XSetWindowAttributes structure by XtRealizeWidget and sent to the server when event handlers and translations are installed or removed on the realized widget.

Event Handlers for X11 Protocol Extensions

To register an event handler procedure with the Intrinsics dispatch mechanism according to an event type, use XtInsertEventTypeHandler.

void XtInsertEventTypeHandler(Widget widget, int event_type, XtPointer select_data, XtEventHandler proc, XtPointer client_data, XtListPosition position);

void XtInsertEventTypeHandler(Widget widget, int event_type, XtPointer select_data, XtEventHandler proc, XtPointer client_data, XtListPosition position);

widget	Specifies the widget for which this event handler is being registered. Must be of class Core or any subclass thereof.
event_type	Specifies the event type for which to call this event handler.
select_data	Specifies data used to request events of the specified type from the server, or NULL.
proc	Specifies the event handler to be called.
client_data	Specifies additional data to be passed to the event handler.
position	Specifies when the event handler is to be called relative to other previously registered handlers.

XtInsertEventTypeHandler registers a procedure with the dispatch mechanism that is to be called when an event that matches the specified event_type is dispatched to the specified widget.

If event_type specifies one of the core X protocol events, then select_data must be a pointer to a value of type EventMask, indicating the event mask to be used to select for the desired event. This event mask is included in the value returned by XtBuildEventMask. If the widget is realized, XtInsertEventTypeHandler calls XSelectInput if necessary. Specifying NULL for select_data is equivalent to specifying a pointer to an event mask containing 0. This is similar to the XtInsertRawEventHandler function.

If event_type specifies an extension event type, then the semantics of the data pointed to by select_data are defined by the extension selector registered for the specified event type.

In either case the Intrinsics are not required to copy the data pointed to by select_data, so the caller must ensure that it remains valid as long as the event handler remains registered with this value of select_data.

The position argument allows the client to control the order of invocation of event handlers registered for the same event type. If the client does not care about the order, it should normally specify XtListTail, which registers this event handler after any previously registered handlers for this event type.

Each widget has a single registered event handler list, which will contain any procedure/client_data pair exactly once if it is registered with XtInsertEventTypeHandler, regardless of the manner in which it is registered and regardless of the value(s) of select_data. If the procedure is already registered with the same client_data value, the specified mask augments the existing mask and the procedure is repositioned in the list.

To remove an event handler registered with XtInsertEventTypeHandler, use XtRemoveEventTypeHandler.

void XtRemoveEventTypeHandler(Widget widget, int event_type, XtPointer select_data, XtEventHandler proc, XtPointer client_data);

void XtRemoveEventTypeHandler(Widget widget, int event_type, XtPointer select_data, XtEventHandler proc, XtPointer client_data);

widget	Specifies the widget for which the event handler was registered. Must be of class Core or any subclass thereof.
event_type	Specifies the event type for which the handler was registered.
select_data	Specifies data used to deselect events of the specified type from the server, or NULL.
proc	Specifies the event handler to be removed.
client_data	Specifies the additional client data with which the procedure was registered.

The XtRemoveEventTypeHandler function unregisters an event handler registered with XtInsertEventTypeHandler for the specified event type. The request is ignored if client_data does not match the value given when the handler was registered.

If event_type specifies one of the core X protocol events, select_data must be a pointer to a value of type EventMask, indicating the event mask to be used to deselect for the appropriate event. If the widget is realized, XtRemoveEventTypeHandler calls XSelectInput if necessary. Specifying NULL for select_data is equivalent to specifying a pointer to an event mask containing 0. This is similar to the XtRemoveRawEventHandler function.

If event_type specifies an extension event type, then the semantics of the data pointed to by select_data are defined by the extension selector registered for the specified event type.

To register a procedure to select extension events for a widget, use XtRegisterExtensionSelector.

void XtRegisterExtensionSelector(Display *display, int min_event_type, int max_event_type, XtExtensionSelectProc proc, XtPointer client_data);

void XtRegisterExtensionSelector(Display *display, int min_event_type, int max_event_type, XtExtensionSelectProc proc, XtPointer client_data);

display	Specifies the display for which the extension selector is to be registered.
min_event_type
max_event_type	Specifies the range of event types for the extension.
proc	Specifies the extension selector procedure.
client_data	Specifies additional data to be passed to the extension selector.

The XtRegisterExtensionSelector function registers a procedure to arrange for the delivery of extension events to widgets.

If min_event_type and max_event_type match the parameters to a previous call to XtRegisterExtensionSelector for the same display, then proc and client_data replace the previously registered values. If the range specified by min_event_type and max_event_type overlaps the range of the parameters to a previous call for the same display in any other way, an error results.

When a widget is realized, after the core.realize method is called, the Intrinsics check to see if any event handler specifies an event type within the range of a registered extension selector. If so, the Intrinsics call each such selector. If an event type handler is added or removed, the Intrinsics check to see if the event type falls within the range of a registered extension selector, and if it does, calls the selector. In either case the Intrinsics pass a list of all the widget's event types that are within the selector's range. The corresponding select data are also passed. The selector is responsible for enabling the delivery of extension events required by the widget.

An extension selector is of type (*XtExtensionSelectProc).

typedef void (*XtExtensionSelectProc)(Widget widget, int *event_types, XtPointer *select_data, int count, XtPointer client_data);

typedef void (*XtExtensionSelectProc)(Widget widget, int *event_types, XtPointer *select_data, int count, XtPointer client_data);

widget	Specifies the widget that is being realized or is having an event handler added or removed.
event_types	Specifies a list of event types that the widget has registered event handlers for.
select_data	Specifies a list of the select_data parameters specified in `XtInsertEventTypeHandler`.
count	Specifies the number of entries in the event_types and select_data lists.
client_data	Specifies the additional client data with which the procedure was registered.

The event_types and select_data lists will always have the same number of elements, specified by count. Each event type/select data pair represents one call to XtInsertEventTypeHandler.

To register a procedure to dispatch events of a specific type within XtDispatchEvent, use XtSetEventDispatcher.

XtEventDispatchProc XtSetEventDispatcher(Display *display, int event_type, XtEventDispatchProc proc);

XtEventDispatchProc XtSetEventDispatcher(Display *display, int event_type, XtEventDispatchProc proc);

display	Specifies the display for which the event dispatcher is to be registered.
event_type	Specifies the event type for which the dispatcher should be invoked.
proc	Specifies the event dispatcher procedure.

The XtSetEventDispatcher function registers the event dispatcher procedure specified by proc for events with the type event_type. The previously registered dispatcher (or the default dispatcher if there was no previously registered dispatcher) is returned. If proc is NULL, the default procedure is restored for the specified type.

In the future, when XtDispatchEvent is called with an event type of event_type, the specified proc (or the default dispatcher) is invoked to determine a widget to which to dispatch the event.

The default dispatcher handles the Intrinsics modal cascade and keyboard focus mechanisms, handles the semantics of compress_enterleave and compress_motion, and discards all extension events.

An event dispatcher procedure pointer is of type (*XtEventDispatchProc).

typedef Boolean (*XtEventDispatchProc)(XEvent *event);

typedef Boolean (*XtEventDispatchProc)(XEvent *event);

event

Passes the event to be dispatched.

The event dispatcher procedure should determine whether this event is of a type that should be dispatched to a widget.

If the event should be dispatched to a widget, the event dispatcher procedure should determine the appropriate widget to receive the event, call XFilterEvent with the window of this widget, or None if the event is to be discarded, and if XFilterEvent returns False, dispatch the event to the widget using XtDispatchEventToWidget. The procedure should return True if either XFilterEvent or XtDispatchEventToWidget returned True and False otherwise.

If the event should not be dispatched to a widget, the event dispatcher procedure should attempt to dispatch the event elsewhere as appropriate and return True if it successfully dispatched the event and False otherwise.

Some dispatchers for extension events may wish to forward events according to the Intrinsics' keyboard focus mechanism. To determine which widget is the end result of keyboard event forwarding, use XtGetKeyboardFocusWidget.

Widget XtGetKeyboardFocusWidget(Widget widget);

widget

Specifies the widget to get forwarding information for.

The XtGetKeyboardFocusWidget function returns the widget that would be the end result of keyboard event forwarding for a keyboard event for the specified widget.

To dispatch an event to a specified widget, use XtDispatchEventToWidget.

Boolean XtDispatchEventToWidget(Widget widget, XEvent *event);

Boolean XtDispatchEventToWidget(Widget widget, XEvent *event);

widget	Specifies the widget to which to dispatch the event.
event	Specifies a pointer to the event to be dispatched.

The XtDispatchEventToWidget function scans the list of registered event handlers for the specified widget and calls each handler that has been registered for the specified event type, subject to the continue_to_dispatch value returned by each handler. The Intrinsics behave as if event handlers were registered at the head of the list for Expose, NoExpose, GraphicsExpose, and VisibilityNotify events to invoke the widget's expose procedure according to the exposure compression rules and to update the widget's visible field if visible_interest is True. These internal event handlers never set continue_to_dispatch to False.

XtDispatchEventToWidget returns True if any event handler was called and False otherwise.

Using the Intrinsics in a Multi-Threaded Environment

The Intrinsics may be used in environments that offer multiple threads of execution within the context of a single process. A multi-threaded application using the Intrinsics must explicitly initialize the toolkit for mutually exclusive access by calling XtToolkitThreadInitialize.

Initializing a Multi-Threaded Intrinsics Application

To test and initialize Intrinsics support for mutually exclusive thread access, call XtToolkitThreadInitialize.

Boolean XtToolkitThreadInitialize();

XtToolkitThreadInitialize returns True if the Intrinsics support mutually exclusive thread access, otherwise it returns False. XtToolkitThreadInitialize must be called before XtCreateApplicationContext, XtAppInitialize, XtOpenApplication, or XtSetLanguageProc is called. XtToolkitThreadInitialize may be called more than once; however, the application writer must ensure that it is not called simultaneously by two or more threads.

Locking X Toolkit Data Structures

The Intrinsics employs two levels of locking: application context and process. Locking an application context ensures mutually exclusive access by a thread to the state associated with the application context, including all displays and widgets associated with it. Locking a process ensures mutually exclusive access by a thread to Intrinsics process global data.

A client may acquire a lock multiple times and the effect is cumulative. The client must ensure that the lock is released an equal number of times in order for the lock to be acquired by another thread.

Most application writers will have little need to use locking as the Intrinsics performs the necessary locking internally. Resource converters are an exception. They require the application context or process to be locked before the application can safely call them directly, for example:

...
XtAppLock(app_context);
XtCvtStringToPixel(dpy, args, num_args, fromVal, toVal, closure_ret);
XtAppUnlock(app_context);
...

When the application relies upon XtConvertAndStore or a converter to provide the storage for the results of a conversion, the application should acquire the process lock before calling out and hold the lock until the results have been copied.

Application writers who write their own utility functions, such as one which retrieves the being_destroyed field from a widget instance, must lock the application context before accessing widget internal data. For example:

#include <X11/CoreP.h>
Boolean BeingDestroyed (widget)
Widget widget;
{
Boolean ret;
XtAppLock(XtWidgetToApplicationContext(widget));
ret = widget->core.being_destroyed;
XtAppUnlock(XtWidgetToApplicationContext(widget));
return ret;
}

A client that wishes to atomically call two or more Intrinsics functions must lock the application context. For example:

...
XtAppLock(XtWidgetToApplicationContext(widget));
XtUnmanageChild (widget1);
XtManageChild (widget2);
XtAppUnlock(XtWidgetToApplicationContext(widget));
...

Locking the Application Context

To ensure mutual exclusion of application context, display, or widget internal state, use XtAppLock.

void XtAppLock(XtAppContext app_context);

void XtAppLock(XtAppContext app_context);

app_context

Specifies the application context to lock.

XtAppLock blocks until it is able to acquire the lock. Locking the application context also ensures that only the thread holding the lock makes Xlib calls from within Xt. An application that makes its own direct Xlib calls must either lock the application context around every call or enable thread locking in Xlib.

To unlock a locked application context, use XtAppUnlock.

void XtAppUnlock(XtAppContext app_context);

app_context

Specifies the application context that was previously locked.

Locking the Process

To ensure mutual exclusion of X Toolkit process global data, a widget writer must use XtProcessLock.

void XtProcessLock();

void XtProcessLock();

XtProcessLock blocks until it is able to acquire the lock. Widget writers may use XtProcessLock to guarantee mutually exclusive access to widget static data.

To unlock a locked process, use XtProcessUnlock.

void XtProcessUnlock();

To lock both an application context and the process at the same time, call XtAppLock first and then XtProcessLock. To release both locks, call XtProcessUnlock first and then XtAppUnlock. The order is important to avoid deadlock.

Event Management in a Multi-Threaded Environment

In a nonthreaded environment an application writer could reasonably assume that it is safe to exit the application from a quit callback. This assumption may no longer hold true in a multi-threaded environment; therefore it is desirable to provide a mechanism to terminate an event-processing loop without necessarily terminating its thread.

To indicate that the event loop should terminate after the current event dispatch has completed, use XtAppSetExitFlag.

void XtAppSetExitFlag(XtAppContext app_context);

void XtAppSetExitFlag(XtAppContext app_context);

app_context

Specifies the application context.

XtAppMainLoop tests the value of the flag and will return if the flag is True.

Application writers who implement their own main loop may test the value of the exit flag with XtAppGetExitFlag.

Boolean XtAppGetExitFlag(XtAppContext app_context);

app_context

Specifies the application context.

XtAppGetExitFlag will normally return False, indicating that event processing may continue. When XtAppGetExitFlag returns True, the loop must terminate and return to the caller, which might then destroy the application context.

Application writers should be aware that, if a thread is blocked in XtAppNextEvent, XtAppPeekEvent, or XtAppProcessEvent and another thread in the same application context opens a new display, adds an alternate input, or a timeout, any new source(s) will not normally be "noticed" by the blocked thread. Any new sources are "noticed" the next time one of these functions is called.

The Intrinsics manage access to events on a last-in, first-out basis. If multiple threads in the same application context block in XtAppNextEvent, XtAppPeekEvent, or XtAppProcessEvent, the last thread to call one of these functions is the first thread to return.