5411396ea6
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.1@5607 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
371 lines
13 KiB
HTML
371 lines
13 KiB
HTML
<HTML>
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<TITLE>6 - Handling Events</TITLE>
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<H1 ALIGN="RIGHT"><A NAME="events">6 - Handling Events</A></H1>
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<P>This chapter discusses the FLTK event model and how to handle
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events in your program or widget.
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<H2>The FLTK Event Model</H2>
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<P>Every time a user moves the mouse pointer, clicks a button,
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or presses a key, an event is generated and sent to your
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application. Events can also come from other programs like the
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window manager.
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<P>Events are identified by the integer argument passed to the
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<A href="subclassing.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 the window
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system, so it is ok to look at it outside of the <TT>handle()</TT>
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method.
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<H2>Mouse Events</H2>
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<H3>FL_PUSH</H3>
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<P>A mouse button has gone down with the mouse pointing at this
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widget. You can find out what button by calling <A
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href="Fl.html#Fl.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
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href="Fl.html#Fl.event_x"><TT>Fl::event_x()</TT></A> and <A
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href="Fl.html#Fl.event_y"> <TT>Fl::event_y()</TT></A>.
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<P>A widget indicates that it "wants" the mouse click
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by returning non-zero from its <A
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href="subclassing.html#handle"><TT>handle()</TT></A> method. It
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will then become the <A href="Fl.html#Fl.pushed"><TT>
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Fl::pushed()</TT></A> widget and will get <TT>FL_DRAG</TT> and
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the matching <TT>FL_RELEASE</TT> events. If <TT>handle()</TT>
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returns zero then FLTK will try sending the <TT>FL_PUSH</TT> to
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another widget. </P>
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<H3>FL_DRAG</H3>
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<P>The mouse has moved with a button held down. The current
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button state is in <a
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href="Fl.html#Fl.event_state"><tt>Fl::event_state()</tt></a>.
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The mouse position is in <a
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href="Fl.html#Fl.event_x"><tt>Fl::event_x()</tt></a> and <a
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href="Fl.html#Fl.event_y"><tt>Fl::event_y()</tt></a>.
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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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<H3>FL_RELEASE</H3>
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<P>A mouse button has been released. You can find out what
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button by calling <A
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href="Fl.html#Fl.event_button"><TT>Fl::event_button()</TT></A>.
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<H3>FL_MOVE</H3>
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<P>The mouse has moved without any mouse buttons held down.
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This event is sent to the <A
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href="Fl.html#Fl.belowmouse"><TT>Fl::belowmouse()</TT></A>
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widget.
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<H3>FL_MOUSEWHEEL</H3>
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<P>The user has moved the mouse wheel. The <A
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HREF="Fl.html#Fl.event_dx"><TT>Fl::event_dx()</TT></A> and <A
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HREF="Fl.html#Fl.event_dy"><TT>Fl::event_dy()</TT></A> methods
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can be used to find the amount to scroll horizontally and
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vertically.
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<H2>Focus Events</H2>
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<H3>FL_ENTER</H3>
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<P>The mouse has been moved to point at this widget. This can
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be used for highlighting feedback. If a widget wants to
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highlight or otherwise track the mouse, it indicates this by
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returning non-zero from its <A
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href="Fl.html#Fl.handle"><TT>handle()</TT></A> method. It then
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becomes the <A
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href="Fl.html#Fl.belowmouse"><TT>Fl::belowmouse()</TT></A>
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widget and will receive <TT>FL_MOVE</TT> and <TT>FL_LEAVE</TT>
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events.
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<H3>FL_LEAVE</H3>
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<P>The mouse has moved out of the widget.
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<H3>FL_FOCUS</H3>
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<P>This indicates an <I>attempt</I> to give a widget the
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keyboard focus.
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<P>If a widget wants the focus, it should change itself to
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display the fact that it has the focus, and return non-zero from
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its <A
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href="Fl_Widget.html#Fl_Widget.handle"><TT>handle()</TT></A>
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method. It then becomes the <A
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href="Fl.html#Fl.focus"><TT>Fl::focus()</TT></A> widget and gets
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<TT>FL_KEYDOWN</TT>, <TT>FL_KEYUP</TT>, and <TT>FL_UNFOCUS</TT>
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events.
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<P>The focus will change either because the window manager
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changed which window gets the focus, or because the user tried
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to navigate using tab, arrows, or other keys. You can check <A
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href="Fl.html#Fl.event_key"><TT>Fl::event_key()</TT></A> to
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figure out why it moved. For navigation it will be the key
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pressed and interaction with the window manager it will be
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zero.
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<H3>FL_UNFOCUS</H3>
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<P>This event is sent to the previous <A
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href="Fl.html#Fl.focus"><TT>Fl::focus()</TT></A> widget when
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another widget gets the focus or the window loses focus.
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<H2>Keyboard Events</H2>
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<H3>FL_KEYDOWN, FL_KEYUP</H3>
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<P>A key was pressed or released. The key can be found in <A
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href="Fl.html#Fl.event_key"><TT>Fl::event_key()</TT></A>. The
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text that the key should insert can be found with <A
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href="Fl.html#Fl.event_text"><TT>Fl::event_text()</TT></A> and
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its length is in <A
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href="Fl.html#Fl.event_length"><TT>Fl::event_length()</TT></A>.
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If you use the key <TT>handle()</TT> should return 1. If you
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return zero then FLTK assumes you ignored the key and will
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then attempt to send it to a parent widget. If none of them want
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it, it will change the event into a <TT>FL_SHORTCUT</TT> event.
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<P>To receive <CODE>FL_KEYBOARD</CODE> events you must also
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respond to the <CODE>FL_FOCUS</CODE> and <CODE>FL_UNFOCUS</CODE>
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events.
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<P>If you are writing a text-editing widget you may also want to
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call the <a href="Fl.html#Fl.compose"><TT>Fl::compose()</TT></a>
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function to translate individual keystrokes into foreign
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characters.
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<P><code>FL_KEYUP</code> events are sent to the widget that
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currently has focus. This is not necessarily the same widget
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that received the corresponding <code>FL_KEYDOWN</code> event
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because focus may have changed between events.
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<H3>FL_SHORTCUT</H3>
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<P>If the <A href="Fl.html#Fl.focus"><TT>Fl::focus()</TT></A>
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widget is zero or ignores an <TT>FL_KEYBOARD</TT> event then
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FLTK tries sending this event to every widget it can, until one
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of them returns non-zero. <TT>FL_SHORTCUT</TT> is first sent to
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the <TT>Fl::belowmouse()</TT> widget, then its parents and
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siblings, and eventually to every widget in the window, trying
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to find an object that returns non-zero. FLTK tries really hard
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to not to ignore any keystrokes!
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<P>You can also make "global" shortcuts by using <A
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href="Fl.html#Fl.add_handler"><TT>Fl::add_handler()</TT></A>. A
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global shortcut will work no matter what windows are displayed
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or which one has the focus.</P>
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<H2>Widget Events</H2>
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<H3>FL_DEACTIVATE</H3>
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<P>This widget is no longer active, due to <A
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href="Fl_Widget.html#Fl_Widget.deactivate"><TT>deactivate()</TT></A>
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being called on it or one of its parents. <TT> active()</TT> may
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still be true after this, the widget is only active if
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<TT>active()</TT> is true on it and all its parents (use <TT>active_r()</TT> to check this).
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<H3>FL_ACTIVATE</H3>
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<P>This widget is now active, due to <A
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href="Fl_Widget.html#Fl_Widget.activate"><TT>activate()</TT></A>
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being called on it or one of its parents.
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<H3>FL_HIDE</H3>
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<P>This widget is no longer visible, due to <A
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href="Fl_Widget.html#Fl_Widget.hide"><tt>hide()</tt></a> being
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called on it or one of its parents, or due to a parent window
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being minimized. <tt>visible()</tt> may still be true after
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this, but the widget is visible only if <tt>visible()</tt> is
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true for it and all its parents (use <tt>visible_r()</tt> to
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check this).
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<h3>FL_SHOW</h3>
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<P>This widget is visible again, due to <a
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href="Fl_Widget.html#Fl_Widget.show"><TT>show()</TT></A> being
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called on it or one of its parents, or due to a parent window
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being restored. <I>Child <TT>Fl_Window</TT>s respond to this by
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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
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class <TT>handle()</TT> method!</I>
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<H2>Clipboard Events</H2>
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<H3>FL_PASTE</H3>
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<P>You should get this event some time after you call <A
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href="Fl.html#Fl.paste"><TT>Fl::paste()</TT></A>. The contents
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of <A href="Fl.html#Fl.event_text"><TT>Fl::event_text()</TT></A>
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is the text to insert and the number of characters is in <A
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href="Fl.html#Fl.event_length"><TT>Fl::event_length()</TT></A>.
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<H3>FL_SELECTIONCLEAR</H3>
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<P>The <A
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href="Fl.html#Fl.selection_owner"><TT>Fl::selection_owner()</TT></A>
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will get this event before the selection is moved to another
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widget. This indicates that some other widget or program has
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claimed the selection. Motif programs used this to clear the
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selection indication. Most modern programs ignore this.
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<H2><A NAME="dnd">Drag And Drop Events</A></H2>
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<H3>FL_DND_ENTER</H3>
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<P>The mouse has been moved to point at this widget. A widget
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that is interested in receiving drag'n'drop data must return 1
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to receive FL_DND_DRAG, FL_DND_LEAVE and FL_DND_RELEASE events.
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<H3>FL_DND_DRAG</H3>
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<P>The mouse has been moved inside a widget while dragging data.
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A widget that is interested in receiving drag'n'drop data should
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indicate the possible drop position.
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<H3>FL_DND_LEAVE</H3>
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<P>The mouse has moved out of the widget.
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<H3>FL_DND_RELEASE</H3>
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<P>The user has released the mouse button dropping data into
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the widget. If the widget returns 1, it will receive the data in
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the immediatly following FL_PASTE event.
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<!-- NEED 6in -->
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<H2><A name="event_xxx">Fl::event_*() methods</A></H2>
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<P>FLTK keeps the information about the most recent event in
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static storage. This information is good until the next event is
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processed. Thus it is valid inside <TT>handle()</TT> and
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<TT>callback()</TT> 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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<LI><A HREF="Fl.html#Fl.event_button"><TT>Fl::event_button</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_clicks"><TT>Fl::event_clicks</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_dx"><TT>Fl::event_dx</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_dy"><TT>Fl::event_dy</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_inside"><TT>Fl::event_inside</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_is_click"><TT>Fl::event_is_click</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_key"><TT>Fl::event_key</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_length"><TT>Fl::event_length</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_state"><TT>Fl::event_state</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_text"><TT>Fl::event_text</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_x"><TT>Fl::event_x</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_x_root"><TT>Fl::event_x_root</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_y"><TT>Fl::event_y</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.event_y_root"><TT>Fl::event_y_root</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.get_key"><TT>Fl::get_key</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.get_mouse"><TT>Fl::get_mouse</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.test_shortcut"><TT>Fl::test_shortcut</TT></A></LI>
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</UL>
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<H2><A name=propagation>Event Propagation</A></H2>
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<P>FLTK follows very simple and unchangeable rules for sending
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events. The major innovation is that widgets can indicate (by
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returning 0 from the <TT>handle()</TT> method) that they are not
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interested in an event, and FLTK can then send that event
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elsewhere. This eliminates the need for "interests"
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(event masks or tables), and this is probably the main reason
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FLTK is much smaller than other toolkits.
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<P>Most events are sent directly to the <TT>handle()</TT> method
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of the <TT>Fl_Window</TT> that the window system says they
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belong to. The window (actually the <TT>Fl_Group</TT> that
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<TT>Fl_Window</TT> is a subclass of) is responsible for sending
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the events on to any child widgets. To make the
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<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>,
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<TT>FL_SHORTCUT</TT>, <TT>FL_UNFOCUS</TT>, and
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<TT>FL_LEAVE</TT>) directly to leaf widgets. These procedures
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control those leaf widgets:
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<UL>
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<LI><A HREF="Fl.html#Fl.add_handler"><TT>Fl::add_handler</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.belowmouse"><TT>Fl::belowmouse</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.focus"><TT>Fl::focus</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.grab"><TT>Fl::grab</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.modal"><TT>Fl::modal</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.pushed"><TT>Fl::pushed</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.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></LI>
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</UL>
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<H2><A name="compose">FLTK Compose-Character Sequences</A></H2>
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<P>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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<p>FLTK uses its own compose processing to allow "preview" of
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the partially composed sequence, which is impossible with the
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usual "dead key" processing.
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<p>Although currently only characters in the ISO-8859-1
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character set are handled, you should call this in case any
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enhancements to the processing are done in the future. The
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interface has been designed to handle arbitrary UTF-8 encoded
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text.
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<P>The following methods are provided for character composition:
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<UL>
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<LI><A HREF="Fl.html#Fl.compose"><TT>Fl::compose()</TT></A></LI>
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<LI><A HREF="Fl.html#Fl.compose_reset"><TT>Fl::compose_reset()</TT></A></LI>
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</UL>
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</BODY>
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</HTML>
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