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<HTML><BODY>
<H1 ALIGN=RIGHT><A NAME=events>6 - Handling Events</A></H1>
This chapter discusses the FLTK event model and how to handle events
in your program or widget.
<H2>The FLTK Event Model</H2>
Events are identified by the integer argument passed to the <A href=functions.html#handle>
<TT>Fl_Widget::handle()</TT></A> virtual method. Other information
about the most recent event is stored in static locations and acquired
by calling the <A href=#event_xxx><TT>Fl::event_*()</TT></A> methods.
This static information remains valid until the next event is read from
window system (i.e. it is ok to look at it outside of the <TT>handle()</TT>
method).
<H2>Mouse Events</H2>
<H3>FL_PUSH</H3>
A mouse button has gone down with the mouse pointing at this widget.
You can find out what button by calling <A href=#event_button><TT>
Fl::event_button()</TT></A>. You find out the mouse position by
calling <A href=#event_x><TT>Fl::event_x()</TT></A> and <A href=functions.html#event_y>
<TT>Fl::event_y()</TT></A>.
<P>A widget indicates that it &quot;wants&quot; the mouse click by returning
non-zero from its <A href=functions.html#handle><TT>handle()</TT></A>
method. It will then become the <A href=functions.html#pushed><TT>
Fl::pushed()</TT></A> widget and will get <TT>FL_DRAG</TT> and the
matching <TT>FL_RELEASE</TT> events. If <TT>handle()</TT> returns zero
then FLTK will try sending the <TT>FL_PUSH</TT> to another widget. </P>
<H3>FL_DRAG</H3>
The mouse has moved with a button held down. The current button state is
in <a href="#event_state"><tt>Fl::event_state()</tt></a>. The mouse position
is in <a href="#event_x"><tt>Fl::event_x()</tt></a> and
<a href="#event_y"><tt>Fl::event_y()</tt></a>.
<H3>FL_RELEASE</H3>
A mouse button has been released. You can find out what button by
calling <A href=#event_button><TT>Fl::event_button()</TT></A>.
<H3>FL_MOVE</H3>
The mouse has moved without any mouse buttons held down. This event
is sent to the <A href="functions.html#belowmouse"><TT>Fl::belowmouse()</TT></A>
widget.
<H2>Focus Events</H2>
<H3>FL_ENTER</H3>
The mouse has been moved to point at this widget. This can be used
for highlighting feedback. If a widget wants to highlight or otherwise
track the mouse, it indicates this by returning non-zero from its <A href=functions.html#handle>
<TT>handle()</TT></A> method. It then becomes the <A href=functions.html#belowmouse>
<TT>Fl::belowmouse()</TT></A> widget and will receive <TT>FL_MOVE</TT>
and <TT>FL_LEAVE</TT> events.
<H3>FL_LEAVE</H3>
The mouse has moved out of the widget.
<H3>FL_FOCUS</H3>
This indicates an <I>attempt</I> to give a widget the keyboard focus.
<P>If a widget wants the focus, it should change itself to display the
fact that it has the focus, and return non-zero from its <A href=functions.html#handle>
<TT>handle()</TT></A> method. It then becomes the <A href=functions.html#focus>
<TT>Fl::focus()</TT></A> widget and gets <TT>FL_KEYBOARD</TT> and <TT>
FL_UNFOCUS</TT> events. </P>
<P>The focus will change either because the window manager changed
which window gets the focus, or because the user tried to navigate
using tab, arrows, or other keys. You can check <A href=functions.html#event_key>
<TT>Fl::event_key()</TT></A> to figure out why it moved. For
navigation it will be the key pressed and for instructions from the
window manager it will be zero. </P>
<H3>FL_UNFOCUS</H3>
Sent to the previous <A href=functions.html#focus><TT>Fl::focus()</TT></A>
widget when another widget gets the focus.
<H2>Keyboard Events</H2>
<H3>FL_KEYBOARD</H3>
A key press. The key pressed can be found in <A href=functions.html#event_key>
<TT>Fl::event_key()</TT></A>. The text that the key should insert can
be found with <A href=functions.html#event_text><TT>Fl::event_text()</TT>
</A> and its length is in <A href=functions.html#event_length><TT>
Fl::event_length()</TT></A>. If you use the key <TT>handle()</TT>
should return 1. If you return zero then FLTK assummes you ignored
the key. It will then attempt to send it to a parent widget. If none
of them want it, it will change the event into a <TT>FL_SHORTCUT</TT>
event.
<H3>FL_SHORTCUT</H3>
If the <A href=functions.html#focus><TT>Fl::focus()</TT></A> widget is zero
or ignores an <TT>FL_KEYBOARD</TT> event then FLTK tries sending this
event to every widget it can, until one of them returns non-zero. <TT>
FL_SHORTCUT</TT> is first sent to the <TT>belowmouse()</TT> widget,
then its parents and siblings, and eventually to every widget in the
window, trying to find an object that returns non-zero. FLTK tries
really hard to not to ignore any keystrokes!
<P>You can also make &quot;global&quot; shortcuts by using <A href=osissues.html#add_handler>
<TT>Fl::add_handler()</TT></A>. A global shortcut will work no matter
what windows are displayed or which one has the focus. </P>
<H2>Widget Events</H2>
<H3>FL_DEACTIVATE</H3>
This widget is no longer active, due to <A href=Fl_Widget.html#Fl_Widget.deactivate>
<TT>deactivate()</TT></A> being called on it or one of its parents. <TT>
active()</TT> may still be true after this, the widget is only active
if <TT>active()</TT> is true on it and all its parents (use <TT>
active_r()</TT> to check this).
<H3>FL_ACTIVATE</H3>
This widget is now active, due to <A href=Fl_Widget.html#Fl_Widget.activate>
<TT>activate()</TT></A> being called on it or one of its parents.
<H3>FL_HIDE</H3>
This widget is no longer visible, due to <A #Fl_Widget.show" href="#Fl_Widget.hide><tt>hide()</tt></a> being called on it or one of its
parents, or due to a parent window being minimized. <tt>visible()</tt>
may still be true after this, but the widget is visible only if
<tt>visible()</tt> is true for it and all its parents (use
<tt>visible_r()</tt> to check this).
<h3>FL_SHOW</h3>
This widget is visible again, due to <a
href=">
<TT>show()</TT></A> being called on it or one of its parents, or due to
a parent window being restored. <I>Child <TT>Fl_Window</TT>s respond to
this by actually creating the window if not done already, so if you
subclass a window, be sure to pass <TT>FL_SHOW</TT> to the base class <TT>
handle()</TT> method!</I>
<H2>Clipboard Events</H2>
<H3>FL_PASTE</H3>
You should get this event some time after you call <A href=functions.html#paste>
<TT>Fl::paste()</TT></A>. The contents of <A href=functions.html#event_text>
<TT>Fl::event_text()</TT></A> is the text to insert and the number of
characters is in <A href=functions.html#event_length><TT>
Fl::event_length()</TT></A>.
<H3>FL_SELECTIONCLEAR</H3>
The <A href=functions.html#selection_owner>Fl::selection_owner()</A>
will get this event before the selection is moved to another widget.
This indicates that some other widget or program has claimed the
selection.
<H2><A name=event_xxx>Fl::event_*() methods</A></H2>
FLTK keeps the information about the most recent event in static
storage. This information is good until the next event is processed.
Thus it is valid inside <TT>handle()</TT> and <TT>callback()</TT>
methods.
<P>These are all trivial inline functions and thus very fast and small: </P>
<UL>
<LI><A href=functions.html#event_button><TT>Fl::event_button</TT></A></LI>
<LI><A href=functions.html#event_clicks><TT>Fl::event_clicks</TT></A></LI>
<LI><A href=functions.html#event_inside><TT>Fl::event_inside</TT></A></LI>
<LI><A href=functions.html#event_is_click><TT>Fl::event_is_click</TT></A></LI>
<LI><A href=functions.html#event_key><TT>Fl::event_key</TT></A></LI>
<LI><A href=functions.html#event_length><TT>Fl::event_length</TT></A></LI>
<LI><A href=functions.html#event_state><TT>Fl::event_state</TT></A></LI>
<LI><A href=functions.html#event_text><TT>Fl::event_text</TT></A></LI>
<LI><A href=functions.html#event_x><TT>Fl::event_x</TT></A></LI>
<LI><A href=functions.html#event_x_root><TT>Fl::event_x_root</TT></A></LI>
<LI><A href=functions.html#event_y><TT>Fl::event_y</TT></A></LI>
<LI><A href=functions.html#event_y_root><TT>Fl::event_y_root</TT></A></LI>
<LI><A href=functions.html#get_key><TT>Fl::get_key</TT></A></LI>
<LI><A href=functions.html#get_mouse><TT>Fl::get_mouse</TT></A></LI>
<LI><A href=functions.html#test_shortcut><TT>Fl::test_shortcut</TT></A></LI>
</UL>
<H2><A name=propagation>Event Propagation</A></H2>
FLTK follows very simple and unchangeable rules for sending events.
The major innovation is that widgets can indicate (by returning 0 from
the <TT>handle()</TT> method) that they are not interested in an event,
and FLTK can then send that event elsewhere. This eliminates the need
for &quot;interests&quot; (event masks or tables), and this is probably the main
reason FLTK is much smaller than other toolkits.
<P>Most events are sent directly to the <TT>handle()</TT> method of the <TT>
Fl_Window</TT> that the window system says they belong to. The window
(actually the <TT>Fl_Group</TT> that <TT>Fl_Window</TT> is a subclass
of) is responsible for sending the events on to any child widgets. To
make the <TT>Fl_Group</TT> code somewhat easier, FLTK sends some events
(<TT>FL_DRAG</TT>, <TT>FL_RELEASE</TT>, <TT>FL_KEYBOARD</TT>, <TT>
FL_SHORTCUT</TT>, <TT>FL_UNFOCUS</TT>, and <TT>FL_LEAVE</TT>) directly
to leaf widgets. These procedures control those leaf widgets: </P>
<UL>
<LI><A href=osissues.html#add_handler><TT>Fl::add_handler</TT></A></LI>
<LI><A href=functions.html#belowmouse><TT>Fl::belowmouse</TT></A></LI>
<LI><A href=functions.html#focus><TT>Fl::focus</TT></A></LI>
<LI><A href=functions.html#grab><TT>Fl::grab</TT></A></LI>
<LI><A href=functions.html#modal><TT>Fl::modal</TT></A></LI>
<LI><A href=functions.html#pushed><TT>Fl::pushed</TT></A></LI>
<LI><A href=functions.html#release><TT>Fl::release</TT></A></LI>
<LI><A href=Fl_Widget.html#Fl_Widget.take_focus><TT>Fl_Widget::take_focus</TT></A>
</LI>
</UL>
<H2><A name=compose>FLTK Compose-Character Sequences</A></H2>
The <A href="#Fl_Input"><tt>Fl_Input</tt></a> widget lets you type all the
characters in the standard ISO-8859-1 character set. Most fonts will
display these characters correctly.
<P>To insert them, type the [compose] key and then one or two
characters. The two characters can be in either order. The [compose]
key is any of: Ctrl+Q, the righthand control key, or any key your X server
calls <TT>XK_Multi_key</TT>.
<center><table border=1>
<tr>
<th>Keys</th><th>Char</th>
<th>Keys</th><th>Char</th>
<th>Keys</th><th>Char</th>
<th>Keys</th><th>Char</th>
<th>Keys</th><th>Char</th>
<th>Keys</th><th>Char</th>
</tr>
<tr>
<td align=center><TT>sp</TT></td><td align=center>nbsp</td>
<td align=center><TT>*</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>A`</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>D-</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>a`</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>d-</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>!</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>+-</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>A'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>N~</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>a'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>n~</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>%</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>2</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>A^</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>O`</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>a^</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>o`</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>#</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>3</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>A~</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>O'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>a~</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>o'</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>$</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>A:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>O^</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>a:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>o^</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>y=</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>u</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>A*</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>O~</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>a*</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>o~</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>|</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>p</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>AE</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>O:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>ae</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>o:</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>&amp;</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>.</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>C,</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>x</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>c,</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>-:</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>,</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>E`</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>O/</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>e`</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>o/</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>c</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>1</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>E'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>U`</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>e'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>u`</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>a</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>o</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>E^</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>U'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>e^</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>u'</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>&lt;&lt;</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>>></TT></td><td align=center><EFBFBD></td>
<td align=center><TT>E:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>U^</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>e:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>u^</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>~</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>14</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>I`</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>U:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>i`</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>u:</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>-</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>12</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>I'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>Y'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>i'</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>y'</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>r</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>34</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>I^</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>DD</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>i^</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>dd</TT></td><td align=center><EFBFBD></td>
</tr>
<tr>
<td align=center><TT>_</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>?</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>I:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>ss</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>i:</TT></td><td align=center><EFBFBD></td>
<td align=center><TT>y:</TT></td><td align=center><EFBFBD></td>
</tr>
</table>
</center>
For instance, to type "<22>" type [compose][a]['] or [compose]['][a].
<P>The character "nbsp" (non-breaking space) is typed by using
[compose][space].
<P>The single-character sequences may be followed by a space if
necessary to remove ambiguity. For instance, if you really want to
type "<22>~" rather than "<22>" you must type [compose][a][space][~].
<P>If you wish to use the compose function in your own code, your
widget's <tt>handle()</tt> method must call <tt>fl_compose()</tt>
in response to <tt>FL_KEYPRESS</tt> events:
<h4><TT>int fl_compose(int state, char c, int &amp;del, char *buffer, int &amp;ins)</TT></h4>
Starts or adds a single ASCII character to a compose sequence. This
will return the number of old bytes to delete and a set of new bytes to
insert, and a new <tt>state</tt> value. If this returns zero you can
ignore the result (which just says to insert the character unchanged)
and handle the keystroke yourself.
<P><tt>state</tt> must either be the return value of the last call to
<tt>fl_compose()</tt> or zero to start a new compose sequence. Be sure to reset
to zero if the user ever moves the cursor.
<P><tt>c</tt> is the ASCII character that the user typed.
<P><tt>del</tt> is set to the number of bytes to delete backwards. This
will always be less or equal to the <tt>ins</tt> from the last call to
<tt>fl_compose()</tt>, and will be zero if <tt>state</tt> is zero.
<P><tt>buffer</tt> will have the first <tt>ins</tt> bytes set to the data
to insert and display (it is <I>not</I> nul-terminated).
<P><tt>ins</tt> will be the number of characters to insert.
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