#  Copyright (c) 1990 The Regents of the University of California.
#  Copyright (c) 1994-1996 Sun Microsystems, Inc.
#  See the file "license.terms" for information on usage and redistribution
#  of this file, and for a DISCLAIMER OF ALL WARRANTIES.
#
#

=head1 NAME

Tk::bind - Arrange for X events to invoke callbacks

=for category Binding Events and Callbacks

=head1 SYNOPSIS

Retrieve bindings:

S<    >I<$widget>-E<gt>B<bind>

S<    >I<$widget>-E<gt>B<bind>(I<tag>)

S<    >I<$widget>-E<gt>B<bind>(I<sequence>)

S<    >I<$widget>-E<gt>B<bind>(I<tag>,I<sequence>)

Associate and destroy bindings:

S<    >I<$widget>-E<gt>B<bind>(I<sequence>,I<callback>)

S<    >I<$widget>-E<gt>B<bind>(I<tag>,I<sequence>,I<callback>)

=head1 DESCRIPTION

The B<bind> method associates callbacks with X events.
If I<callback> is specified, B<bind> will
arrange for I<callback> to be evaluated whenever
the event(s) given by I<sequence> occur in the window(s)
identified by I<$widget> or I<tag>.
If I<callback> is an empty string then the current binding for
I<sequence> is destroyed, leaving I<sequence> unbound.
In all of the cases where a I<callback> argument is provided,
B<bind> returns an empty string.

If I<sequence> is specified without a I<callback>, then the
callback currently bound to I<sequence> is returned, or
B<undef> is returned if there is no binding for I<sequence>.
If neither I<sequence> nor I<callback> is specified, then the
return value is a list whose elements are all the sequences
for which there exist bindings for I<tag>.

If no I<tag> is specified then the B<bind> refers to I<$widget>.
If I<tag> is specified then it is typically a class name and the B<bind>
refers to all instances of the class on the B<MainWindow> associated
with I<$widget>. (It is possible for I<tag> to be another "widget object"
but this practice is deprecated.) Perl's B<ref>(I<$object>) can be used
to get the class name of any object.
Each window has an associated list of tags, and a binding applies
to a particular window if its tag is among those specified for
the window.
Although the B<bindtags> method may be used to assign an
arbitrary set of binding tags to a window, the default binding
tags provide the following behavior:

If a tag is the name of an internal window the binding applies
to that window.

If the tag is the name of a toplevel window the binding applies
to the toplevel window and all its internal windows.

If the tag is the name of a class of widgets, such as B<Tk::Button>,
the binding applies to all widgets in that class;

If I<tag> has the value B<all>,
the binding applies to all windows descended from the MainWindow
of the application.

=head1 EVENT PATTERNS

The I<sequence> argument specifies a sequence of one or more
event patterns, with optional white space between the patterns.  Each
event pattern has the following syntax:

S<    >'<modifier-modifier-type-detail>'

The entire event pattern is surrounded by angle brackets, and normally
needs to be quoted, as angle brackets are special to perl.
Inside the angle brackets are zero or more modifiers, an event
type, and an extra piece of information (I<detail>) identifying
a particular button or keysym.  Any of the fields may be omitted,
as long as at least one of I<type> and I<detail> is present.
The fields must be separated by white space or dashes.

A second form of pattern is used to specify a user-defined, named virtual
event; see L<Tk::event> for details.  It has the following syntax:

S<    ><<name>>

The entire virtual event pattern is surrounded by double angle brackets.
Inside the angle brackets is the user-defined name of the virtual event.
Modifiers, such as B<Shift> or B<Control>, may not be combined with a
virtual event to modify it.  Bindings on a virtual event may be created
before the virtual event is defined, and if the definition of a virtual
event changes dynamically, all windows bound to that virtual event will
respond immediately to the new definition.

=head1 MODIFIERS

Modifiers consist of any of the following values:

 Control	Mod2, M2
 Shift          Mod3, M3
 Lock          	Mod4, M4
 Button1, B1	Mod5, M5
 Button2, B2	Meta, M
 Button3, B3	Alt
 Button4, B4	Double
 Button5, B5	Triple
 Mod1,    M1

Where more than one value is listed, separated by commas, the values
are equivalent.
Most of the modifiers have the obvious X meanings.
For example, B<Button1> requires that
button 1 be depressed when the event occurs.
For a binding to match a given event, the modifiers in the event
must include all of those specified in the event pattern.
An event may also contain additional modifiers not specified in
the binding.
For example, if button 1 is pressed while the shift and control keys
are down, the pattern B<E<lt>Control-Button-1E<gt>> will match
the event, but B<E<lt>Mod1-Button-1E<gt>> will not.
If no modifiers are specified, then any combination of modifiers may
be present in the event.

B<Meta> and B<M> refer to whichever of the
B<M1> through B<M5> modifiers is associated with the meta
key(s) on the keyboard (keysyms B<Meta_R> and B<Meta_L>).
If there are no meta keys, or if they are not associated with any
modifiers, then B<Meta> and B<M> will not match any events.
Similarly, the B<Alt> modifier refers to whichever modifier
is associated with the alt key(s) on the keyboard (keysyms
B<Alt_L> and B<Alt_R>).

The B<Double> and B<Triple> modifiers are a convenience
for specifying double mouse clicks and other repeated
events. They cause a particular event pattern to be
repeated 2 or 3 times, and also place a time and space requirement
on the sequence:  for a sequence of events to match a B<Double>
or B<Triple> pattern, all of the events must occur close together
in time and without substantial mouse motion in between.
For example, B<E<lt>Double-Button-1E<gt>>
is equivalent to B<E<lt>Button-1E<gt>E<lt>Button-1E<gt>> with the extra
time and space requirement.

=head1 EVENT TYPES

The I<type> field may be any of the standard X event types, with a
few extra abbreviations.  Below is a list of all the valid types;
where two names appear together, they are synonyms.

 ButtonPress, Button	Expose	Map
 ButtonRelease	FocusIn	Motion
 Circulate	FocusOut	Property
 Colormap	Gravity	Reparent
 Configure	KeyPress, Key	Unmap
 Destroy	KeyRelease	Visibility
 Enter	Leave	Activate
 Deactivate

The last part of a long event specification is I<detail>.  In the
case of a B<ButtonPress> or B<ButtonRelease> event, it is the
number of a button (1-5).  If a button number is given, then only an
event on that particular button will match;  if no button number is
given, then an event on any button will match.  Note:  giving a
specific button number is different than specifying a button modifier;
in the first case, it refers to a button being pressed or released,
while in the second it refers to some other button that is already
depressed when the matching event occurs.  If a button
number is given then I<type> may be omitted:  if will default
to B<ButtonPress>.  For example, the specifier B<E<lt>1E<gt>>
is equivalent to B<E<lt>ButtonPress-1E<gt>>.

If the event type is B<KeyPress> or B<KeyRelease>, then
I<detail> may be specified in the form of an X keysym.  Keysyms
are textual specifications for particular keys on the keyboard;
they include all the alphanumeric ASCII characters (e.g. ``a'' is
the keysym for the ASCII character ``a''), plus descriptions for
non-alphanumeric characters (``comma'' is the keysym for the comma
character), plus descriptions for all the non-ASCII keys on the
keyboard (``Shift_L'' is the keysm for the left shift key, and
``F1'' is the keysym for the F1 function key, if it exists).  The
complete list of keysyms is not presented here;  it is
available in other X documentation and may vary from system to
system.
If necessary, you can use the B<'K'> notation described below
to print out the keysym name for a particular key.
If a keysym I<detail> is given, then the
I<type> field may be omitted;  it will default to B<KeyPress>.
For example, B<E<lt>Control-commaE<gt>> is equivalent to
B<E<lt>Control-KeyPress-commaE<gt>>.

=head1 BINDING CALLBACKS AND SUBSTITUTIONS

The I<callback> argument to B<bind> is a perl/Tk callback.
which will be executed whenever the given event sequence occurs.
(See L<Tk::callbacks> for description of the possible forms.)
I<Callback> will be associated with the same B<MainWindow>
that is associated with the I<$widget> that was used to invoke
the B<bind> method, and it will run as though called from B<MainLoop>.
If I<callback> contains
any B<Ev>(I<%>) calls, then each "nested" B<Ev>(I<%>)
"callback" will be evaluated when the event occurs to form arguments
to be passed to the main I<callback>.
The replacement
depends on the character I<%>, as defined in the
list below.  Unless otherwise indicated, the
replacement string is the numeric (decimal) value of the given field from
the current event. Perl/Tk has enhanced this mechanism slightly compared
to the comparable Tcl/Tk mechanism. The enhancements are not yet all
reflected in the list below.
Some of the substitutions are only valid for
certain types of events;  if they are used for other types of events
the value substituted is undefined (not the same as B<undef>!).

=over 4

=item B<'#'>

The number of the last client request processed by the server
(the I<serial> field from the event).  Valid for all event
types.

=item B<'a'>

The I<above> field from the event,
formatted as a hexadecimal number.
Valid only for B<Configure> events.

=item B<'b'>

The number of the button that was pressed or released.  Valid only
for B<ButtonPress> and B<ButtonRelease> events.

=item B<'c'>

The I<count> field from the event.  Valid only for B<Expose> events.

=item B<'d'>

The I<detail> field from the event.  The B<'d'> is replaced by
a string identifying the detail.  For B<Enter>,
B<Leave>, B<FocusIn>, and B<FocusOut> events,
the string will be one of the following:

=over 8

 NotifyAncestor	NotifyNonlinearVirtual
 NotifyDetailNone	NotifyPointer
 NotifyInferior	NotifyPointerRoot
 NotifyNonlinear	NotifyVirtual

For events other than these, the substituted string is undefined.
(Note that this is I<not> the same as Detail part of sequence
use to specify the event.)

=back

=item B<'f'>

The I<focus> field from the event (B<0> or B<1>).  Valid only
for B<Enter> and B<Leave> events.

=item B<'h'>

The I<height> field from the event.  Valid only for B<Configure>,
B<Expose>, and B<GraphicsExpose> events.

=item B<'k'>

The I<keycode> field from the event.  Valid only for B<KeyPress>
and B<KeyRelease> events.

=item B<'m'>

The I<mode> field from the event.  The substituted string is one of
B<NotifyNormal>, B<NotifyGrab>, B<NotifyUngrab>, or
B<NotifyWhileGrabbed>.  Valid only for B<EnterWindow>,
B<FocusIn>, B<FocusOut>, and B<LeaveWindow> events.

=item B<'o'>

The I<override_redirect> field from the event.  Valid only for
B<Map>, B<Reparent>, and B<Configure> events.

=item B<'p'>

The I<place> field from the event, substituted as one of the
strings B<PlaceOnTop> or B<PlaceOnBottom>.  Valid only
for B<Circulate> events.

=item B<'s'>

The I<state> field from the event.  For B<ButtonPress>,
B<ButtonRelease>, B<Enter>, B<KeyPress>, B<KeyRelease>,
B<Leave>, and B<Motion> events, a decimal string
is substituted.  For B<Visibility>, one of the strings
B<VisibilityUnobscured>, B<VisibilityPartiallyObscured>,
and B<VisibilityFullyObscured> is substituted.

=item B<'t'>

The I<time> field from the event.  Valid only for events that
contain a I<time> field.

=item B<'w'>

The I<width> field from the event.  Valid only for
B<Configure>, B<Expose>, and B<GraphicsExpose> events.

=item B<'x'>

The I<x> field from the event.  Valid only for events containing
an I<x> field.

=item B<'y'>

The I<y> field from the event.  Valid only for events containing
a I<y> field.

=item B<'@'>

The string "@I<x,y>" where I<x> and I<y> are as above.
Valid only for events containing I<x> and I<y> fields.
This format is used my methods of B<Tk::Text> and similar widgets.

=item B<'A'>

Substitutes the ASCII character corresponding to the event, or
the empty string if the event doesn't correspond to an ASCII character
(e.g. the shift key was pressed).  B<XLookupString> does all the
work of translating from the event to an ASCII character.
Valid only for B<KeyPress> and B<KeyRelease> events.

=item B<'B'>

The I<border_width> field from the event.  Valid only for
B<Configure> events.

=item B<'E'>

The I<send_event> field from the event.  Valid for all event types.

=item B<'K'>

The keysym corresponding to the event, substituted as a textual
string.  Valid only for B<KeyPress> and B<KeyRelease> events.

=item B<'N'>

The keysym corresponding to the event, substituted as
a decimal
number.  Valid only for B<KeyPress> and B<KeyRelease> events.

=item B<'R'>

The I<root> window identifier from the event.  Valid only for
events containing a I<root> field.

=item B<'S'>

The I<subwindow> window identifier from the event,
as an object if it is one otherwise as a hexadecimal number.
Valid only for events containing a I<subwindow> field.

=item B<'T'>

The I<type> field from the event.  Valid for all event types.

=item B<'W'>

The window to which the event was reported (the
$widget field from the event) - as an perl/Tk object.
Valid for all event types.

=item B<'X'>

The I<x_root> field from the event.
If a virtual-root window manager is being used then the substituted
value is the corresponding x-coordinate in the virtual root.
Valid only for
B<ButtonPress>, B<ButtonRelease>, B<KeyPress>, B<KeyRelease>,
and B<Motion> events.

=item B<'Y'>

The I<y_root> field from the event.
If a virtual-root window manager is being used then the substituted
value is the corresponding y-coordinate in the virtual root.
Valid only for
B<ButtonPress>, B<ButtonRelease>, B<KeyPress>, B<KeyRelease>,
and B<Motion> events.

=back

=head1 MULTIPLE MATCHES

It is possible for several bindings to match a given X event.
If the bindings are associated with different I<tag>'s,
then each of the bindings will be executed, in order.
By default, a class binding will be executed first, followed
by a binding for the widget, a binding for its toplevel, and
an B<all> binding.
The B<bindtags> method may be used to change this order for
a particular window or to associate additional binding tags with
the window.

B<return> and B<Tk-E<gt>break> may be used inside a
callback to control the processing of matching callbacks.
If B<return> is invoked, then the current callback
is terminated but Tk will continue processing callbacks
associated with other I<tag>'s.
If B<Tk-E<gt>break> is invoked within a callback,
then that callback terminates and no other callbacks will be invoked
for the event.
(B<Tk-E<gt>break> is implemented via perl's B<die> with a special value
which is "caught" by the perl/Tk "glue" code.)

If more than one binding matches a particular event and they
have the same I<tag>, then the most specific binding
is chosen and its callback is evaluated.
The following tests are applied, in order, to determine which of
several matching sequences is more specific:
(a) an event pattern that specifies a specific button or key is more specific
than one that doesn't;
(b) a longer sequence (in terms of number
of events matched) is more specific than a shorter sequence;
(c) if the modifiers specified in one pattern are a subset of the
modifiers in another pattern, then the pattern with more modifiers
is more specific.
(d) a virtual event whose physical pattern matches the sequence is less
specific than the same physical pattern that is not associated with a
virtual event.
(e) given a sequence that matches two or more virtual events, one
of the virtual events will be chosen, but the order is undefined.

If the matching sequences contain more than one event, then tests
(c)-(e) are applied in order from the most recent event to the least recent
event in the sequences.  If these tests fail to determine a winner, then the
most recently registered sequence is the winner.

If there are two (or more) virtual events that are both triggered by the
same sequence, and both of those virtual events are bound to the same window
tag, then only one of the virtual events will be triggered, and it will
be picked at random:

 $widget->eventAdd('<<Paste>>' => '<Control-y>');
 $widget->eventAdd('<<Paste>>' => '<Button-2>');
 $widget->eventAdd <<Scroll>>' => '<Button-2>');
 $widget->bind('Tk::Entry','<<Paste>>',sub { print 'Paste'});
 $widget->bind('Tk::Entry','<<Scroll>>', sub {print 'Scroll'});

If the user types Control-y, the B<E<lt>E<lt>PasteE<gt>E<gt>> binding
will be invoked, but if the user presses button 2 then one of
either the B<E<lt>E<lt>PasteE<gt>E<gt>> or the B<E<lt>E<lt>ScrollE<gt>E<gt>> bindings will
be invoked, but exactly which one gets invoked is undefined.

If an X event does not match any of the existing bindings, then the
event is ignored.
An unbound event is not considered to be an error.

=head1 MULTI-EVENT SEQUENCES AND IGNORED EVENTS

When a I<sequence> specified in a B<bind> method contains
more than one event pattern, then its callback is executed whenever
the recent events (leading up to and including the current event)
match the given sequence.  This means, for example, that if button 1 is
clicked repeatedly the sequence B<E<lt>Double-ButtonPress-1E<gt>> will match
each button press but the first.
If extraneous events that would prevent a match occur in the middle
of an event sequence then the extraneous events are
ignored unless they are B<KeyPress> or B<ButtonPress> events.
For example, B<E<lt>Double-ButtonPress-1E<gt>> will match a sequence of
presses of button 1, even though there will be B<ButtonRelease>
events (and possibly B<Motion> events) between the
B<ButtonPress> events.
Furthermore, a B<KeyPress> event may be preceded by any number
of other B<KeyPress> events for modifier keys without the
modifier keys preventing a match.
For example, the event sequence B<aB> will match a press of the
B<a> key, a release of the B<a> key, a press of the B<Shift>
key, and a press of the B<b> key:  the press of B<Shift> is
ignored because it is a modifier key.
Finally, if several B<Motion> events occur in a row, only
the last one is used for purposes of matching binding sequences.

=head1 ERRORS

If an error occurs in executing the callback for a binding then the
B<Tk::Error> mechanism is used to report the error.
The B<Tk::Error> mechanism will be executed at same call level,
and associated with the same B<MainWindow> as
as the callback was invoked.

=head1 SEE ALSO

L<Tk::Error|Tk::Error>
L<Tk::callbacks|Tk::callbacks>
L<Tk::bindtags|Tk::bindtags>

=head1 KEYWORDS

Event, binding

=cut

