1999-01-13 22:28:54 +03:00
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<HTML><BODY>
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<H1 ALIGN=RIGHT><A NAME=events>6 - Handling Events</A></H1>
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This chapter discusses the FLTK event model and how to handle events
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in your program or widget.
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1998-12-29 17:21:17 +03:00
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<H2>The FLTK Event Model</H2>
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2000-04-28 22:15:26 +04:00
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<P>Every time a user moves the mouse pointer, clicks a button, or presses
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a key, an event is generated and sent to your application. Events can also
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come from other programs like the window manager.
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<P>Events are identified by the integer argument passed to the
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<A href=functions.html#handle> <TT>Fl_Widget::handle()</TT></A> virtual
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method. Other information about the most recent event is stored in
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static locations and acquired by calling the <A
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href=#event_xxx><TT>Fl::event_*()</TT></A> methods. This static
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information remains valid until the next event is read from window
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system (i.e. it is ok to look at it outside of the <TT>handle()</TT>
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method).
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1999-01-07 19:36:11 +03:00
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<H2>Mouse Events</H2>
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1999-01-13 22:28:54 +03:00
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<H3>FL_PUSH</H3>
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2000-04-28 22:15:26 +04:00
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A mouse button has gone down with the mouse pointing at this widget.
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1999-01-13 22:28:54 +03:00
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You can find out what button by calling <A href=#event_button><TT>
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Fl::event_button()</TT></A>. You find out the mouse position by
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calling <A href=#event_x><TT>Fl::event_x()</TT></A> and <A href=functions.html#event_y>
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<TT>Fl::event_y()</TT></A>.
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<P>A widget indicates that it "wants" the mouse click by returning
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non-zero from its <A href=functions.html#handle><TT>handle()</TT></A>
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method. It will then become the <A href=functions.html#pushed><TT>
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Fl::pushed()</TT></A> widget and will get <TT>FL_DRAG</TT> and the
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matching <TT>FL_RELEASE</TT> events. If <TT>handle()</TT> returns zero
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then FLTK will try sending the <TT>FL_PUSH</TT> to another widget. </P>
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<H3>FL_DRAG</H3>
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1999-01-27 00:36:02 +03:00
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The mouse has moved with a button held down. The current button state is
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in <a href="#event_state"><tt>Fl::event_state()</tt></a>. The mouse position
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is in <a href="#event_x"><tt>Fl::event_x()</tt></a> and
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<a href="#event_y"><tt>Fl::event_y()</tt></a>.
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1999-06-12 17:53:34 +04:00
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<P>To receive <CODE>FL_DRAG</CODE> events you must also respond to the
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<CODE>FL_PUSH</CODE> and <CODE>FL_RELEASE</CODE> events.
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1999-01-13 22:28:54 +03:00
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<H3>FL_RELEASE</H3>
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A mouse button has been released. You can find out what button by
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calling <A href=#event_button><TT>Fl::event_button()</TT></A>.
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<H3>FL_MOVE</H3>
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The mouse has moved without any mouse buttons held down. This event
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1999-01-27 00:36:02 +03:00
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is sent to the <A href="functions.html#belowmouse"><TT>Fl::belowmouse()</TT></A>
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widget.
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1999-01-07 19:36:11 +03:00
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<H2>Focus Events</H2>
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1999-01-13 22:28:54 +03:00
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<H3>FL_ENTER</H3>
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The mouse has been moved to point at this widget. This can be used
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for highlighting feedback. If a widget wants to highlight or otherwise
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track the mouse, it indicates this by returning non-zero from its <A href=functions.html#handle>
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<TT>handle()</TT></A> method. It then becomes the <A href=functions.html#belowmouse>
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<TT>Fl::belowmouse()</TT></A> widget and will receive <TT>FL_MOVE</TT>
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and <TT>FL_LEAVE</TT> events.
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<H3>FL_LEAVE</H3>
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The mouse has moved out of the widget.
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<H3>FL_FOCUS</H3>
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This indicates an <I>attempt</I> to give a widget the keyboard focus.
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<P>If a widget wants the focus, it should change itself to display the
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fact that it has the focus, and return non-zero from its <A href=functions.html#handle>
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<TT>handle()</TT></A> method. It then becomes the <A href=functions.html#focus>
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<TT>Fl::focus()</TT></A> widget and gets <TT>FL_KEYBOARD</TT> and <TT>
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FL_UNFOCUS</TT> events. </P>
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<P>The focus will change either because the window manager changed
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which window gets the focus, or because the user tried to navigate
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using tab, arrows, or other keys. You can check <A href=functions.html#event_key>
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<TT>Fl::event_key()</TT></A> to figure out why it moved. For
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navigation it will be the key pressed and for instructions from the
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window manager it will be zero. </P>
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<H3>FL_UNFOCUS</H3>
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1999-01-27 00:36:02 +03:00
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Sent to the previous <A href=functions.html#focus><TT>Fl::focus()</TT></A>
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widget when another widget gets the focus.
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1999-01-07 19:36:11 +03:00
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<H2>Keyboard Events</H2>
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1999-01-13 22:28:54 +03:00
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<H3>FL_KEYBOARD</H3>
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A key press. The key pressed can be found in <A href=functions.html#event_key>
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<TT>Fl::event_key()</TT></A>. The text that the key should insert can
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be found with <A href=functions.html#event_text><TT>Fl::event_text()</TT>
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</A> and its length is in <A href=functions.html#event_length><TT>
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Fl::event_length()</TT></A>. If you use the key <TT>handle()</TT>
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1999-06-12 17:53:34 +04:00
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should return 1. If you return zero then FLTK assummes you ignored
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1999-01-13 22:28:54 +03:00
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the key. It will then attempt to send it to a parent widget. If none
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of them want it, it will change the event into a <TT>FL_SHORTCUT</TT>
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1999-06-12 17:53:34 +04:00
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event.
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<P>To receive <CODE>FL_KEYBOARD</CODE> events you must also respond to the
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<CODE>FL_FOCUS</CODE> and <CODE>FL_UNFOCUS</CODE> events.
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2000-02-21 13:45:59 +03:00
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<p>If you are writing a text-editing widget you may also want to call
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the <a href=#compose>Fl::compose()</a> function to translate
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individual keystrokes into foreign characters.
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1999-01-13 22:28:54 +03:00
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<H3>FL_SHORTCUT</H3>
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1999-01-27 00:36:02 +03:00
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If the <A href=functions.html#focus><TT>Fl::focus()</TT></A> widget is zero
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1999-01-13 22:28:54 +03:00
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or ignores an <TT>FL_KEYBOARD</TT> event then FLTK tries sending this
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event to every widget it can, until one of them returns non-zero. <TT>
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FL_SHORTCUT</TT> is first sent to the <TT>belowmouse()</TT> widget,
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then its parents and siblings, and eventually to every widget in the
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window, trying to find an object that returns non-zero. FLTK tries
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really hard to not to ignore any keystrokes!
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<P>You can also make "global" shortcuts by using <A href=osissues.html#add_handler>
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<TT>Fl::add_handler()</TT></A>. A global shortcut will work no matter
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what windows are displayed or which one has the focus. </P>
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1999-01-07 19:36:11 +03:00
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<H2>Widget Events</H2>
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1999-01-13 22:28:54 +03:00
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<H3>FL_DEACTIVATE</H3>
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This widget is no longer active, due to <A href=Fl_Widget.html#Fl_Widget.deactivate>
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<TT>deactivate()</TT></A> being called on it or one of its parents. <TT>
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active()</TT> may still be true after this, the widget is only active
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if <TT>active()</TT> is true on it and all its parents (use <TT>
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active_r()</TT> to check this).
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<H3>FL_ACTIVATE</H3>
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This widget is now active, due to <A href=Fl_Widget.html#Fl_Widget.activate>
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<TT>activate()</TT></A> being called on it or one of its parents.
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<H3>FL_HIDE</H3>
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2000-02-21 13:45:59 +03:00
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This widget is no longer visible, due to <A href=Fl_Widget.html#Fl_Widget.hide><tt>hide()</tt></a> being called on it or one of its
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1999-01-07 19:36:11 +03:00
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parents, or due to a parent window being minimized. <tt>visible()</tt>
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may still be true after this, but the widget is visible only if
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<tt>visible()</tt> is true for it and all its parents (use
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<tt>visible_r()</tt> to check this).
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1998-12-29 17:21:17 +03:00
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1999-01-07 19:36:11 +03:00
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<h3>FL_SHOW</h3>
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1998-12-29 17:21:17 +03:00
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This widget is visible again, due to <a
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2000-02-21 13:45:59 +03:00
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href=Fl_Widget.html#Fl_Widget.show>
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1999-01-13 22:28:54 +03:00
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<TT>show()</TT></A> being called on it or one of its parents, or due to
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a parent window being restored. <I>Child <TT>Fl_Window</TT>s respond to
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this by actually creating the window if not done already, so if you
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subclass a window, be sure to pass <TT>FL_SHOW</TT> to the base class <TT>
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handle()</TT> method!</I>
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1999-01-07 19:36:11 +03:00
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<H2>Clipboard Events</H2>
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1999-01-13 22:28:54 +03:00
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<H3>FL_PASTE</H3>
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You should get this event some time after you call <A href=functions.html#paste>
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<TT>Fl::paste()</TT></A>. The contents of <A href=functions.html#event_text>
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<TT>Fl::event_text()</TT></A> is the text to insert and the number of
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characters is in <A href=functions.html#event_length><TT>
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Fl::event_length()</TT></A>.
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<H3>FL_SELECTIONCLEAR</H3>
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The <A href=functions.html#selection_owner>Fl::selection_owner()</A>
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will get this event before the selection is moved to another widget.
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This indicates that some other widget or program has claimed the
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2000-02-21 13:45:59 +03:00
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selection. Motif programs used this to clear the selection
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indication. Most modern programs ignore this.
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1999-01-13 22:28:54 +03:00
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<H2><A name=event_xxx>Fl::event_*() methods</A></H2>
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FLTK keeps the information about the most recent event in static
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storage. This information is good until the next event is processed.
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Thus it is valid inside <TT>handle()</TT> and <TT>callback()</TT>
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methods.
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<P>These are all trivial inline functions and thus very fast and small: </P>
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<UL>
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1999-01-27 00:36:02 +03:00
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<LI><A href=functions.html#event_button><TT>Fl::event_button</TT></A></LI>
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<LI><A href=functions.html#event_clicks><TT>Fl::event_clicks</TT></A></LI>
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<LI><A href=functions.html#event_inside><TT>Fl::event_inside</TT></A></LI>
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<LI><A href=functions.html#event_is_click><TT>Fl::event_is_click</TT></A></LI>
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<LI><A href=functions.html#event_key><TT>Fl::event_key</TT></A></LI>
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<LI><A href=functions.html#event_length><TT>Fl::event_length</TT></A></LI>
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<LI><A href=functions.html#event_state><TT>Fl::event_state</TT></A></LI>
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<LI><A href=functions.html#event_text><TT>Fl::event_text</TT></A></LI>
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<LI><A href=functions.html#event_x><TT>Fl::event_x</TT></A></LI>
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<LI><A href=functions.html#event_x_root><TT>Fl::event_x_root</TT></A></LI>
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<LI><A href=functions.html#event_y><TT>Fl::event_y</TT></A></LI>
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<LI><A href=functions.html#event_y_root><TT>Fl::event_y_root</TT></A></LI>
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<LI><A href=functions.html#get_key><TT>Fl::get_key</TT></A></LI>
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<LI><A href=functions.html#get_mouse><TT>Fl::get_mouse</TT></A></LI>
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<LI><A href=functions.html#test_shortcut><TT>Fl::test_shortcut</TT></A></LI>
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1999-01-13 22:28:54 +03:00
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</UL>
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<H2><A name=propagation>Event Propagation</A></H2>
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FLTK follows very simple and unchangeable rules for sending events.
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The major innovation is that widgets can indicate (by returning 0 from
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the <TT>handle()</TT> method) that they are not interested in an event,
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and FLTK can then send that event elsewhere. This eliminates the need
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for "interests" (event masks or tables), and this is probably the main
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reason FLTK is much smaller than other toolkits.
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<P>Most events are sent directly to the <TT>handle()</TT> method of the <TT>
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Fl_Window</TT> that the window system says they belong to. The window
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(actually the <TT>Fl_Group</TT> that <TT>Fl_Window</TT> is a subclass
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of) is responsible for sending the events on to any child widgets. To
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make the <TT>Fl_Group</TT> code somewhat easier, FLTK sends some events
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(<TT>FL_DRAG</TT>, <TT>FL_RELEASE</TT>, <TT>FL_KEYBOARD</TT>, <TT>
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FL_SHORTCUT</TT>, <TT>FL_UNFOCUS</TT>, and <TT>FL_LEAVE</TT>) directly
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to leaf widgets. These procedures control those leaf widgets: </P>
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<UL>
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1999-01-27 00:36:02 +03:00
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<LI><A href=osissues.html#add_handler><TT>Fl::add_handler</TT></A></LI>
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<LI><A href=functions.html#belowmouse><TT>Fl::belowmouse</TT></A></LI>
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<LI><A href=functions.html#focus><TT>Fl::focus</TT></A></LI>
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<LI><A href=functions.html#grab><TT>Fl::grab</TT></A></LI>
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<LI><A href=functions.html#modal><TT>Fl::modal</TT></A></LI>
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<LI><A href=functions.html#pushed><TT>Fl::pushed</TT></A></LI>
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<LI><A href=functions.html#release><TT>Fl::release</TT></A></LI>
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<LI><A href=Fl_Widget.html#Fl_Widget.take_focus><TT>Fl_Widget::take_focus</TT></A>
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1999-01-13 22:28:54 +03:00
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</LI>
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</UL>
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1999-01-19 23:53:39 +03:00
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<H2><A name=compose>FLTK Compose-Character Sequences</A></H2>
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2000-02-21 13:45:59 +03:00
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The foreign-letter compose processing done by the <A
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href=Fl_Input.html#compose><tt>Fl_Input</tt></a> widget is provided in
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a function that you can call if you are writing your own text editor
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widget.
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<p>Fltk uses it's own compose processing to allow "preview" of the
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partially composed sequence, which is impossible with the usual
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"dead key" processing.
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<p>Although currently only characters in the ISO-8859-1 character set are
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handled, you should call this in case any enhancements to the
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processing are done in the future. The interface has been designed to
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handle arbitrary UTF-8 encoded text.
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<h4><tt>int Fl::compose(int& del)</tt></h4>
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<p>Use of this function is very simple. Any text editing widget should
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call this for each <tt>FL_KEYBOARD</tt> event.
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<p>If <i>true</i> is returned, then it has modified the
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Fl::event_text() and Fl::event_length() to a set of <i>bytes</i> to
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insert (it may be of zero length!). In will also set the "del"
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parameter to the number of <i>bytes</i> to the left of the cursor to
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delete, this is used to delete the results of the previous call to
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Fl::compose().
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<p>If <i>false</i> is returned, the keys should be treated as function
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keys, and del is set to zero. You could insert the text anyways, if
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you don't know what else to do.
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<p>Though the current implementation returns immediately, future
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versions may take quite awhile, as they may pop up a window or do
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other user-interface things to allow characters to be selected.
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<h4><tt>int Fl::compose_reset()</tt></h4>
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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<p>If the user moves the cursor, be sure to call Fl::compose_reset().
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The next call to Fl::compose() will start out in an initial state. In
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particular it will not set "del" to non-zero. This call is very fast
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so it is ok to call it many times and in many places.
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1999-01-19 23:53:39 +03:00
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2000-02-21 13:45:59 +03:00
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</body></html>
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