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EVENT(3)	      DragonFly Library Functions Manual	      EVENT(3)

NAME

event_init, event_dispatch, event_loop, event_loopexit, event_loopbreak, event_set, event_base_dispatch, event_base_loop, event_base_loopexit, event_base_loopbreak, event_base_set, event_base_free, event_add, event_del, event_once, event_base_once, event_pending, event_initialized, event_priority_init, event_priority_set, evtimer_set, evtimer_add, evtimer_del, evtimer_pending, evtimer_initialized, signal_set, signal_add, signal_del, signal_pending, signal_initialized, bufferevent_new, bufferevent_free, bufferevent_write, bufferevent_write_buffer, bufferevent_read, bufferevent_enable, bufferevent_disable, bufferevent_settimeout, bufferevent_base_set, evbuffer_new, evbuffer_free, evbuffer_add, evbuffer_add_buffer, evbuffer_add_printf, evbuffer_add_vprintf, evbuffer_drain, evbuffer_write, evbuffer_read, evbuffer_find, evbuffer_readline, evhttp_new, evhttp_bind_socket, evhttp_free -- execute a function when a specific event occurs

SYNOPSIS

#include <sys/time.h> #include <event.h> struct event_base * event_init(void); int event_dispatch(void); int event_loop(int flags); int event_loopexit(struct timeval *tv); int event_loopbreak(void); void event_set(struct event *ev, int fd, short event, void (*fn)(int, short, void *), void *arg); int event_base_dispatch(struct event_base *base); int event_base_loop(struct event_base *base, int flags); int event_base_loopexit(struct event_base *base, struct timeval *tv); int event_base_loopbreak(struct event_base *base); int event_base_set(struct event_base *base, struct event *); void event_base_free(struct event_base *base); int event_add(struct event *ev, struct timeval *tv); int event_del(struct event *ev); int event_once(int fd, short event, void (*fn)(int, short, void *), void *arg, struct timeval *tv); int event_base_once(struct event_base *base, int fd, short event, void (*fn)(int, short, void *), void *arg, struct timeval *tv); int event_pending(struct event *ev, short event, struct timeval *tv); int event_initialized(struct event *ev); int event_priority_init(int npriorities); int event_priority_set(struct event *ev, int priority); void evtimer_set(struct event *ev, void (*fn)(int, short, void *), void *arg); void evtimer_add(struct event *ev, struct timeval *); void evtimer_del(struct event *ev); int evtimer_pending(struct event *ev, struct timeval *tv); int evtimer_initialized(struct event *ev); void signal_set(struct event *ev, int signal, void (*fn)(int, short, void *), void *arg); void signal_add(struct event *ev, struct timeval *); void signal_del(struct event *ev); int signal_pending(struct event *ev, struct timeval *tv); int signal_initialized(struct event *ev); struct bufferevent * bufferevent_new(int fd, evbuffercb readcb, evbuffercb writecb, everrorcb, void *cbarg); void bufferevent_free(struct bufferevent *bufev); int bufferevent_write(struct bufferevent *bufev, void *data, size_t size); int bufferevent_write_buffer(struct bufferevent *bufev, struct evbuffer *buf); size_t bufferevent_read(struct bufferevent *bufev, void *data, size_t size); int bufferevent_enable(struct bufferevent *bufev, short event); int bufferevent_disable(struct bufferevent *bufev, short event); void bufferevent_settimeout(struct bufferevent *bufev, int timeout_read, int timeout_write); int bufferevent_base_set(struct event_base *base, struct bufferevent *bufev); struct evbuffer * evbuffer_new(void); void evbuffer_free(struct evbuffer *buf); int evbuffer_add(struct evbuffer *buf, const void *data, size_t size); int evbuffer_add_buffer(struct evbuffer *dst, struct evbuffer *src); int evbuffer_add_printf(struct evbuffer *buf, const char *fmt, ...); int evbuffer_add_vprintf(struct evbuffer *buf, const char *fmt, va_list ap); void evbuffer_drain(struct evbuffer *buf, size_t size); int evbuffer_write(struct evbuffer *buf, int fd); int evbuffer_read(struct evbuffer *buf, int fd, int size); u_char * evbuffer_find(struct evbuffer *buf, const u_char *data, size_t size); char * evbuffer_readline(struct evbuffer *buf); struct evhttp * evhttp_new(struct event_base *base); int evhttp_bind_socket(struct evhttp *http, const char *address, u_short port); void evhttp_free(struct evhttp *http); int (*event_sigcb)(void); volatile sig_atomic_t event_gotsig;

DESCRIPTION

The event API provides a mechanism to execute a function when a specific event on a file descriptor occurs or after a given time has passed. The event API needs to be initialized with event_init() before it can be used. In order to process events, an application needs to call event_dispatch(). This function only returns on error, and should replace the event core of the application program. The function event_set() prepares the event structure ev to be used in future calls to event_add() and event_del(). The event will be prepared to call the function specified by the fn argument with an int argument indicating the file descriptor, a short argument indicating the type of event, and a void * argument given in the arg argument. The fd indicates the file descriptor that should be monitored for events. The events can be either EV_READ, EV_WRITE, or both, indicating that an application can read or write from the file descriptor respectively without blocking. The function fn will be called with the file descriptor that triggered the event and the type of event which will be either EV_TIMEOUT, EV_SIGNAL, EV_READ, or EV_WRITE. Additionally, an event which has regis- tered interest in more than one of the preceeding events, via bitwise-OR to event_set(), can provide its callback function with a bitwise-OR of more than one triggered event. The additional flag EV_PERSIST makes an event_add() persistent until event_del() has been called. Once initialized, the ev structure can be used repeatedly with event_add() and event_del() and does not need to be reinitialized unless the function called and/or the argument to it are to be changed. How- ever, when an ev structure has been added to libevent using event_add() the structure must persist until the event occurs (assuming EV_PERSIST is not set) or is removed using event_del(). You may not reuse the same ev structure for multiple monitored descriptors; each descriptor needs its own ev. The function event_add() schedules the execution of the ev event when the event specified in event_set() occurs or in at least the time specified in the tv. If tv is NULL, no timeout occurs and the function will only be called if a matching event occurs on the file descriptor. The event in the ev argument must be already initialized by event_set() and may not be used in calls to event_set() until it has timed out or been removed with event_del(). If the event in the ev argument already has a sched- uled timeout, the old timeout will be replaced by the new one. The function event_del() will cancel the event in the argument ev. If the event has already executed or has never been added the call will have no effect. The functions evtimer_set(), evtimer_add(), evtimer_del(), evtimer_initialized(), and evtimer_pending() are abbreviations for common situations where only a timeout is required. The file descriptor passed will be -1, and the event type will be EV_TIMEOUT. The functions signal_set(), signal_add(), signal_del(), signal_initialized(), and signal_pending() are abbreviations. The event type will be a persistent EV_SIGNAL. That means signal_set() adds EV_PERSIST. In order to avoid races in signal handlers, the event API provides two variables: event_sigcb and event_gotsig. A signal handler sets event_gotsig to indicate that a signal has been received. The applica- tion sets event_sigcb to a callback function. After the signal handler sets event_gotsig, event_dispatch will execute the callback function to process received signals. The callback returns 1 when no events are reg- istered any more. It can return -1 to indicate an error to the event library, causing event_dispatch() to terminate with errno set to EINTR. The function event_once() is similar to event_set(). However, it sched- ules a callback to be called exactly once and does not require the caller to prepare an event structure. This function supports EV_TIMEOUT, EV_READ, and EV_WRITE. The event_pending() function can be used to check if the event specified by event is pending to run. If EV_TIMEOUT was specified and tv is not NULL, the expiration time of the event will be returned in tv. The event_initialized() macro can be used to check if an event has been initialized. The event_loop function provides an interface for single pass execution of pending events. The flags EVLOOP_ONCE and EVLOOP_NONBLOCK are recog- nized. The event_loopexit function exits from the event loop. The next event_loop() iteration after the given timer expires will complete nor- mally (handling all queued events) then exit without blocking for events again. Subsequent invocations of event_loop() will proceed normally. The event_loopbreak function exits from the event loop immediately. event_loop() will abort after the next event is completed; event_loopbreak() is typically invoked from this event's callback. This behavior is analogous to the "break;" statement. Subsequent invocations of event_loop() will proceed normally. It is the responsibility of the caller to provide these functions with pre-allocated event structures.

EVENT PRIORITIES

By default libevent schedules all active events with the same priority. However, sometimes it is desirable to process some events with a higher priority than others. For that reason, libevent supports strict priority queues. Active events with a lower priority are always processed before events with a higher priority. The number of different priorities can be set initially with the event_priority_init() function. This function should be called before the first call to event_dispatch(). The event_priority_set() function can be used to assign a priority to an event. By default, libevent assigns the middle priority to all events unless their priority is explicitly set.

THREAD SAFE EVENTS

Libevent has experimental support for thread-safe events. When initial- izing the library via event_init(), an event base is returned. This event base can be used in conjunction with calls to event_base_set(), event_base_dispatch(), event_base_loop(), event_base_loopexit(), bufferevent_base_set() and event_base_free(). event_base_set() should be called after preparing an event with event_set(), as event_set() assigns the provided event to the most recently created event base. bufferevent_base_set() should be called after preparing a bufferevent with bufferevent_new(). event_base_free() should be used to free memory associated with the event base when it is no longer needed.

BUFFERED EVENTS

libevent provides an abstraction on top of the regular event callbacks. This abstraction is called a buffered event. A buffered event provides input and output buffers that get filled and drained automatically. The user of a buffered event no longer deals directly with the IO, but instead is reading from input and writing to output buffers. A new bufferevent is created by bufferevent_new(). The parameter fd specifies the file descriptor from which data is read and written to. This file descriptor is not allowed to be a pipe(2). The next three parameters are callbacks. The read and write callback have the following form: void (*cb)(struct bufferevent *bufev, void *arg). The error call- back has the following form: void (*cb)(struct bufferevent *bufev, short what, void *arg). The argument is specified by the fourth parameter cbarg. A bufferevent struct pointer is returned on success, NULL on error. Both the read and the write callback may be NULL. The error callback has to be always provided. Once initialized, the bufferevent structure can be used repeatedly with bufferevent_enable() and bufferevent_disable(). The flags parameter can be a combination of EV_READ and EV_WRITE. When read enabled the buffer- event will try to read from the file descriptor and call the read call- back. The write callback is executed whenever the output buffer is drained below the write low watermark, which is 0 by default. The bufferevent_write() function can be used to write data to the file descriptor. The data is appended to the output buffer and written to the descriptor automatically as it becomes available for writing. bufferevent_write() returns 0 on success or -1 on failure. The bufferevent_read() function is used to read data from the input buffer, returning the amount of data read. If multiple bases are in use, bufferevent_base_set() must be called before enabling the bufferevent for the first time. NON-BLOCKING HTTP SUPPORT libevent provides a very thin HTTP layer that can be used both to host an HTTP server and also to make HTTP requests. An HTTP server can be cre- ated by calling evhttp_new(). It can be bound to any port and address with the evhttp_bind_socket() function. When the HTTP server is no longer used, it can be freed via evhttp_free(). To be notified of HTTP requests, a user needs to register callbacks with the HTTP server. This can be done by calling evhttp_set_cb(). The sec- ond argument is the URI for which a callback is being registered. The corresponding callback will receive an struct evhttp_request object that contains all information about the request. This section does not document all the possible function calls; please check event.h for the public interfaces.

ADDITIONAL NOTES

It is possible to disable support for epoll, kqueue, devpoll, poll or select by setting the environment variable EVENT_NOEPOLL, EVENT_NOKQUEUE, EVENT_NODEVPOLL, EVENT_NOPOLL or EVENT_NOSELECT, respectively. By set- ting the environment variable EVENT_SHOW_METHOD, libevent displays the kernel notification method that it uses.

RETURN VALUES

Upon successful completion event_add() and event_del() return 0. Other- wise, -1 is returned and the global variable errno is set to indicate the error.

SEE ALSO

kqueue(2), poll(2), select(2), evdns(3), timeout(9)

HISTORY

The event API manpage is based on the timeout(9) manpage by Artur Grabowski. The port of libevent to Windows is due to Michael A. Davis. Support for real-time signals is due to Taral.

AUTHORS

The event library was written by Niels Provos.

BUGS

This documentation is neither complete nor authoritative. If you are in doubt about the usage of this API then check the source code to find out how it works, write up the missing piece of documentation and send it to me for inclusion in this man page. DragonFly 4.1 August 8, 2000 DragonFly 4.1 event(n) Tk Built-In Commands event(n) ______________________________________________________________________________

NAME

event - Miscellaneous event facilities: define virtual events and generate events

SYNOPSIS

event option ?arg arg ...? ______________________________________________________________________________

DESCRIPTION

The event command provides several facilities for dealing with window system events, such as defining virtual events and synthesizing events. The command has several different forms, determined by the first argument. The following forms are currently supported: event add <<virtual>> sequence ?sequence ...? Associates the virtual event virtual with the physical event sequence(s) given by the sequence arguments, so that the virtual event will trigger whenever any one of the sequences occurs. Virtual may be any string value and sequence may have any of the values allowed for the sequence argument to the bind command. If virtual is already defined, the new physical event sequences add to the existing sequences for the event. event delete <<virtual>> ?sequence sequence ...? Deletes each of the sequences from those associated with the virtual event given by virtual. Virtual may be any string value and sequence may have any of the values allowed for the sequence argument to the bind command. Any sequences not currently associated with virtual are ignored. If no sequence argument is provided, all physical event sequences are removed for virtual, so that the virtual event will not trigger anymore. event generate window event ?option value option value ...? Generates a window event and arranges for it to be processed just as if it had come from the window system. Window gives the path name of the window for which the event will be generated; it may also be an identifier (such as returned by winfo id) as long as it is for a window in the current application. Event provides a basic description of the event, such as <Shift- Button-2> or <<Paste>>. If Window is empty the whole screen is meant, and coordinates are relative to the screen. Event may have any of the forms allowed for the sequence argument of the bind command except that it must consist of a single event pattern, not a sequence. Option-value pairs may be used to specify additional attributes of the event, such as the x and y mouse position; see EVENT FIELDS below. If the -when option is not specified, the event is processed immediately: all of the handlers for the event will complete before the event generate command returns. If the -when option is specified then it determines when the event is processed. Certain events, such as key events, require that the window has focus to receive the event properly. event info ?<<virtual>>? Returns information about virtual events. If the <<virtual>> argument is omitted, the return value is a list of all the virtual events that are currently defined. If <<virtual>> is specified then the return value is a list whose elements are the physical event sequences currently defined for the given virtual event; if the virtual event is not defined then an empty string is returned. Note that virtual events that are not bound to physical event sequences are not returned by event info.

EVENT FIELDS

The following options are supported for the event generate command. These correspond to the "%" expansions allowed in binding scripts for the bind command. -above window Window specifies the above field for the event, either as a window path name or as an integer window id. Valid for Configure events. Corresponds to the %a substitution for binding scripts. -borderwidth size Size must be a screen distance; it specifies the border_width field for the event. Valid for Configure events. Corresponds to the %B substitution for binding scripts. -button number Number must be an integer; it specifies the detail field for a ButtonPress or ButtonRelease event, overriding any button number provided in the base event argument. Corresponds to the %b substitution for binding scripts. -count number Number must be an integer; it specifies the count field for the event. Valid for Expose events. Corresponds to the %c substitution for binding scripts. -data string String may be any value; it specifies the user_data field for the event. Only valid for virtual events. Corresponds to the %d substitution for virtual events in binding scripts. -delta number Number must be an integer; it specifies the delta field for the MouseWheel event. The delta refers to the direction and magnitude the mouse wheel was rotated. Note the value is not a screen distance but are units of motion in the mouse wheel. Typically these values are multiples of 120. For example, 120 should scroll the text widget up 4 lines and -240 would scroll the text widget down 8 lines. Of course, other widgets may define different behaviors for mouse wheel motion. This field corresponds to the %D substitution for binding scripts. -detail detail Detail specifies the detail field for the event and must be one of the following: NotifyAncestor NotifyNonlinearVirtual NotifyDetailNone NotifyPointer NotifyInferior NotifyPointerRoot NotifyNonlinear NotifyVirtual Valid for Enter, Leave, FocusIn and FocusOut events. Corresponds to the %d substitution for binding scripts. -focus boolean Boolean must be a boolean value; it specifies the focus field for the event. Valid for Enter and Leave events. Corresponds to the %f substitution for binding scripts. -height size Size must be a screen distance; it specifies the height field for the event. Valid for Configure events. Corresponds to the %h substitution for binding scripts. -keycode number Number must be an integer; it specifies the keycode field for the event. Valid for KeyPress and KeyRelease events. Corresponds to the %k substitution for binding scripts. -keysym name Name must be the name of a valid keysym, such as g, space, or Return; its corresponding keycode value is used as the keycode field for event, overriding any detail specified in the base event argument. Valid for KeyPress and KeyRelease events. Corresponds to the %K substitution for binding scripts. -mode notify Notify specifies the mode field for the event and must be one of NotifyNormal, NotifyGrab, NotifyUngrab, or NotifyWhileGrabbed. Valid for Enter, Leave, FocusIn, and FocusOut events. Corresponds to the %m substitution for binding scripts. -override boolean Boolean must be a boolean value; it specifies the override_redirect field for the event. Valid for Map, Reparent, and Configure events. Corresponds to the %o substitution for binding scripts. -place where Where specifies the place field for the event; it must be either PlaceOnTop or PlaceOnBottom. Valid for Circulate events. Corresponds to the %p substitution for binding scripts. -root window Window must be either a window path name or an integer window identifier; it specifies the root field for the event. Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease, Enter, Leave, and Motion events. Corresponds to the %R substitution for binding scripts. -rootx coord Coord must be a screen distance; it specifies the x_root field for the event. Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease, Enter, Leave, and Motion events. Corresponds to the %X substitution for binding scripts. -rooty coord Coord must be a screen distance; it specifies the y_root field for the event. Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease, Enter, Leave, and Motion events. Corresponds to the %Y substitution for binding scripts. -sendevent boolean Boolean must be a boolean value; it specifies the send_event field for the event. Valid for all events. Corresponds to the %E substitution for binding scripts. -serial number Number must be an integer; it specifies the serial field for the event. Valid for all events. Corresponds to the %# substitution for binding scripts. -state state State specifies the state field for the event. For KeyPress, KeyRelease, ButtonPress, ButtonRelease, Enter, Leave, and Motion events it must be an integer value. For Visibility events it must be one of VisibilityUnobscured, VisibilityPartiallyObscured, or VisibilityFullyObscured. This option overrides any modifiers such as Meta or Control specified in the base event. Corresponds to the %s substitution for binding scripts. -subwindow window Window specifies the subwindow field for the event, either as a path name for a Tk widget or as an integer window identifier. Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease, Enter, Leave, and Motion events. Similar to %S substitution for binding scripts. -time integer Integer must be an integer value; it specifies the time field for the event. Additonally the special value current is allowed, this value will be substituted by the current event time. Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease, Enter, Leave, Motion, and Property events. Corresponds to the %t substitution for binding scripts. -warp boolean boolean must be a boolean value; it specifies whether the screen pointer should be warped as well. Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease, and Motion events. The pointer will only warp to a window if it is mapped. -width size Size must be a screen distance; it specifies the width field for the event. Valid for Configure events. Corresponds to the %w substitution for binding scripts. -when when When determines when the event will be processed; it must have one of the following values: now Process the event immediately, before the command returns. This also happens if the -when option is omitted. tail Place the event on Tcl's event queue behind any events already queued for this application. head Place the event at the front of Tcl's event queue, so that it will be handled before any other events already queued. mark Place the event at the front of Tcl's event queue but behind any other events already queued with -when mark. This option is useful when generating a series of events that should be processed in order but at the front of the queue. -x coord Coord must be a screen distance; it specifies the x field for the event. Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease, Motion, Enter, Leave, Expose, Configure, Gravity, and Reparent events. Corresponds to the %x substitution for binding scripts. If Window is empty the coordinate is relative to the screen, and this option corresponds to the %X substitution for binding scripts. -y coord Coord must be a screen distance; it specifies the y field for the event. Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease, Motion, Enter, Leave, Expose, Configure, Gravity, and Reparent events. Corresponds to the %y substitution for binding scripts. If Window is empty the coordinate is relative to the screen, and this option corresponds to the %Y substitution for binding scripts. Any options that are not specified when generating an event are filled with the value 0, except for serial, which is filled with the next X event serial number.

PREDEFINED VIRTUAL EVENTS

Tk defines the following virtual events for the purposes of notification: <<AltUnderlined>> This is sent to widget to notify it that the letter it has underlined (as an accelerator indicator) with the -underline option has been pressed in combination with the Alt key. The usual response to this is to either focus into the widget (or some related widget) or to invoke the widget. <<Invoke>> This can be sent to some widgets (e.g. button, listbox, menu) as an alternative to <space>. <<ListboxSelect>> This is sent to a listbox when the set of selected item(s) in the listbox is updated. <<MenuSelect>> This is sent to a menu when the currently selected item in the menu changes. It is intended for use with context-sensitive help systems. <<Modified>> This is sent to a text widget when the contents of the widget are changed. <<Selection>> This is sent to a text widget when the selection in the widget is changed. <<ThemeChanged>> This is sent to all widgets when the ttk theme changed. The ttk widgets listen to this event and redisplay themselves when it fires. The legacy widgets ignore this event. <<TkWorldChanged>> This event is sent to all widgets when a font is changed, for example, by the use of [font configure]. The user_data field (%d) will have the value "FontChanged". For other system wide changes, this event will be sent to all widgets, and the user_data field will indicate the cause of the change. NOTE: all tk and ttk widgets already handle this event internally. <<TraverseIn>> This is sent to a widget when the focus enters the widget because of a user-driven "tab to widget" action. <<TraverseOut>> This is sent to a widget when the focus leaves the widget because of a user-driven "tab to widget" action. <<UndoStack>> This is sent to a text widget when its undo stack or redo stack becomes empty or unempty. <<WidgetViewSync>> This is sent to a text widget when its internal data become obsolete, and again when these internal data are back in sync with the widget view. The detail field (%d substitution) is either true (when the widget is in sync) or false (when it is not). Tk defines the following virtual events for the purposes of unifying bindings across multiple platforms. Users expect them to behave in the following way: <<Clear>> Delete the currently selected widget contents. <<Copy>> Copy the currently selected widget contents to the clipboard. <<Cut>> Move the currently selected widget contents to the clipboard. <<LineEnd>> Move to the end of the line in the current widget while deselecting any selected contents. <<LineStart>> Move to the start of the line in the current widget while deselecting any selected contents. <<NextChar>> Move to the next item (i.e., visible character) in the current widget while deselecting any selected contents. <<NextLine>> Move to the next line in the current widget while deselecting any selected contents. <<NextPara>> Move to the next paragraph in the current widget while deselecting any selected contents. <<NextWord>> Move to the next group of items (i.e., visible word) in the current widget while deselecting any selected contents. <<Paste>> Replace the currently selected widget contents with the contents of the clipboard. <<PasteSelection>> Insert the contents of the selection at the mouse location. (This event has meaningful %x and %y substitutions). <<PrevChar>> Move to the previous item (i.e., visible character) in the current widget while deselecting any selected contents. <<PrevLine>> Move to the previous line in the current widget while deselecting any selected contents. <<PrevPara>> Move to the previous paragraph in the current widget while deselecting any selected contents. <<PrevWindow>> Traverse to the previous window. <<PrevWord>> Move to the previous group of items (i.e., visible word) in the current widget while deselecting any selected contents. <<Redo>> Redo one undone action. <<SelectAll>> Set the range of selected contents to the complete widget. <<SelectLineEnd>> Move to the end of the line in the current widget while extending the range of selected contents. <<SelectLineStart>> Move to the start of the line in the current widget while extending the range of selected contents. <<SelectNextChar>> Move to the next item (i.e., visible character) in the current widget while extending the range of selected contents. <<SelectNextLine>> Move to the next line in the current widget while extending the range of selected contents. <<SelectNextPara>> Move to the next paragraph in the current widget while extending the range of selected contents. <<SelectNextWord>> Move to the next group of items (i.e., visible word) in the current widget while extending the range of selected contents. <<SelectNone>> Reset the range of selected contents to be empty. <<SelectPrevChar>> Move to the previous item (i.e., visible character) in the current widget while extending the range of selected contents. <<SelectPrevLine>> Move to the previous line in the current widget while extending the range of selected contents. <<SelectPrevPara>> Move to the previous paragraph in the current widget while extending the range of selected contents. <<SelectPrevWord>> Move to the previous group of items (i.e., visible word) in the current widget while extending the range of selected contents. <<ToggleSelection>> Toggle the selection. <<Undo>> Undo the last action.

EXAMPLES

MAPPING KEYS TO VIRTUAL EVENTS In order for a virtual event binding to trigger, two things must happen. First, the virtual event must be defined with the event add command. Second, a binding must be created for the virtual event with the bind command. Consider the following virtual event definitions: event add <<Paste>> <Control-y> event add <<Paste>> <Button-2> event add <<Save>> <Control-X><Control-S> event add <<Save>> <Shift-F12> if {[tk windowingsystem] eq "aqua"} { event add <<Save>> <Command-s> } In the bind command, a virtual event can be bound like any other builtin event type as follows: bind Entry <<Paste>> {%W insert [selection get]} The double angle brackets are used to specify that a virtual event is being bound. If the user types Control-y or presses button 2, or if a <<Paste>> virtual event is synthesized with event generate, then the <<Paste>> binding will be invoked. If a virtual binding has the exact same sequence as a separate physical binding, then the physical binding will take precedence. Consider the following example: event add <<Paste>> <Control-y> <Meta-Control-y> bind Entry <Control-y> {puts Control-y} bind Entry <<Paste>> {puts Paste} When the user types Control-y the <Control-y> binding will be invoked, because a physical event is considered more specific than a virtual event, all other things being equal. However, when the user types Meta-Control-y the <<Paste>> binding will be invoked, because the Meta modifier in the physical pattern associated with the virtual binding is more specific than the <Control-y> sequence for the physical event. Bindings on a virtual event may be created before the virtual event exists. Indeed, the virtual event never actually needs to be defined, for instance, on platforms where the specific virtual event would be meaningless or ungeneratable. When a definition of a virtual event changes at run time, all windows will respond immediately to the new definition. Starting from the preceding example, if the following code is executed: bind Entry <Control-y> {} event add <<Paste>> <Key-F6> the behavior will change such in two ways. First, the shadowed <<Paste>> binding will emerge. Typing Control-y will no longer invoke the <Control-y> binding, but instead invoke the virtual event <<Paste>>. Second, pressing the F6 key will now also invoke the <<Paste>> binding. MOVING THE MOUSE POINTER Sometimes it is useful to be able to really move the mouse pointer. For example, if you have some software that is capable of demonstrating directly to the user how to use the program. To do this, you need to "warp" the mouse around by using event generate, like this: for {set xy 0} {$xy < 200} {incr xy} { event generate . <Motion> -x $xy -y $xy -warp 1 update after 50 } Note that it is usually considered bad style to move the mouse pointer for the user because it removes control from them. Therefore this technique should be used with caution. Also note that it is not guaranteed to function on all platforms.

SEE ALSO

bind(n)

KEYWORDS

event, binding, define, handle, virtual event Tk 8.3 event(n)

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