2cde58f966
I am missing a decent Linux machine. Could someone please check if DND works smoothly on those machines? Just run the 'Input' test and mark and drag text out of the text widgets into another app. Then drag'n'drop text into the FLTK widgets. Finally drag text from one widget into another widget within the same FLTK app. git-svn-id: file:///fltk/svn/fltk/branches/branch-1.1@1972 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
431 lines
18 KiB
HTML
431 lines
18 KiB
HTML
<HTML><BODY>
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<H1 ALIGN=RIGHT><A NAME=subclassing>7 - Adding and Extending Widgets</A></H1>
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This chapter describes how to add your own widgets or extend existing
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widgets in FLTK.
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<H2>Subclassing</H2>
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New widgets are created by <I>subclassing</I> an existing FLTK widget,
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typically <TT>Fl_Widget</TT> for controls and <TT>Fl_Group</TT> for
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composite widgets.
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<P>A control widget typically interacts with the user to receive and/or
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display a value of some sort. </P>
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<P>A composite widget widget holds a list of child widgets and handles moving,
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sizing, showing, or hiding them as needed. <TT>Fl_Group</TT> is the
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main composite widget widget class in FLTK, and all of the other composite widgets (<TT>
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Fl_Pack</TT>, <TT>Fl_Scroll</TT>, <TT>Fl_Tabs</TT>, <TT>Fl_Tile</TT>,
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and <TT>Fl_Window</TT>) are subclasses of it. </P>
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<P>You can also subclass other existing widgets to provide a different
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look or user-interface. For example, the button widgets are all
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subclasses of <TT>Fl_Button</TT> since they all interact with the user
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via a mouse button click. The only difference is the code that draws
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the face of the button. </P>
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<H2>Making a Subclass of Fl_Widget</H2>
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Your subclasses can directly descend from <TT>Fl_Widget</TT> or any
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subclass of <TT>Fl_Widget</TT>. <TT>Fl_Widget</TT> has only four
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virtual methods, and overriding some or all of these may be necessary.
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<H2>The Constructor</H2>
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The constructor should have the following arguments:
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<UL><PRE>
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MyClass(int x, int y, int w, int h, const char *label = 0);
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</PRE></UL>
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This will allow the class to be used in <A href="fluid.html#FLUID">FLUID</A>
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without problems.
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<P>The constructor must call the constructor for the base class and
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pass the same arguments: </P>
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<UL><PRE>
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MyClass::MyClass(int x, int y, int w, int h, const char *label)
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: Fl_Widget(x, y, w, h, label) {
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// do initialization stuff...
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}
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</PRE></UL>
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<TT>Fl_Widget</TT>'s protected constructor sets <TT>x()</TT>, <TT>y()</TT>,
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<TT>w()</TT>, <TT>h()</TT>, and <TT>label()</TT> to the passed values
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and initializes the other instance variables to:
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<UL><PRE>
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type(0);
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box(FL_NO_BOX);
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color(FL_GRAY);
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selection_color(FL_GRAY);
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labeltype(FL_NORMAL_LABEL);
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labelstyle(FL_NORMAL_STYLE);
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labelsize(FL_NORMAL_SIZE);
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labelcolor(FL_BLACK);
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align(FL_ALIGN_CENTER);
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callback(default_callback,0);
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flags(ACTIVE|VISIBLE);
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image(0);
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deimage(0);
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</PRE></UL>
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<H2>Protected Methods of Fl_Widget</H2>
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The following methods are provided for subclasses to use:
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<UL>
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<LI><A href=#clear_visible><TT>Fl_Widget::clear_visible</TT></A></LI>
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<LI><A href=#damage><TT>Fl_Widget::damage</TT></A></LI>
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<LI><A href=#draw_box><TT>Fl_Widget::draw_box</TT></A></LI>
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<LI><A href=#draw_focus><TT>Fl_Widget::draw_focus</TT></A></LI>
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<LI><A href=#draw_label><TT>Fl_Widget::draw_label</TT></A></LI>
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<LI><A href=#set_flag><TT>Fl_Widget::set_flag</TT></A></LI>
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<LI><A href=#set_visible><TT>Fl_Widget::set_visible</TT></A></LI>
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<LI><A href=#test_shortcut><TT>Fl_Widget::test_shortcut</TT></A></LI>
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<LI><A href=#type><TT>Fl_Widget::type</TT></A></LI>
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</UL>
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<H4><A name=damage>void Fl_Widget::damage(uchar mask)
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<BR> void Fl_Widget::damage(uchar mask, int x, int y, int w, int h)
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<BR> uchar Fl_Widget::damage()</A></H4>
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The first form indicates that a partial update of the object is
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needed. The bits in mask are OR'd into <TT>damage()</TT>. Your <TT>
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draw()</TT> routine can examine these bits to limit what it is
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drawing. The public method <TT>Fl_Widget::redraw()</TT> simply does
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<TT> Fl_Widget::damage(FL_DAMAGE_ALL)</TT>, but the implementation of
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your widget can call the private <TT>damage(n)</TT>.
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<P>The second form indicates that a region is damaged. If only these
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calls are done in a window (no calls to <TT>damage(n)</TT>) then FLTK
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will clip to the union of all these calls before drawing anything.
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This can greatly speed up incremental displays. The mask bits are
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OR'd into <TT>damage()</TT> unless this is a <TT>Fl_Window</TT> widget. </P>
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<P>The third form returns the bitwise-OR of all <TT>damage(n)</TT>
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calls done since the last <TT>draw()</TT>.</P>
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<P><I>When redrawing your widgets you should look at the damage bits to
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see what parts of your widget need redrawing.</I> The <tt>handle()</tt>
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method can then set individual damage bits to limit the amount of drawing
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that needs to be done:
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<UL><PRE>
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MyClass::handle(int event) {
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...
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if (change_to_part1) damage(1);
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if (change_to_part2) damage(2);
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if (change_to_part3) damage(4);
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}
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MyClass::draw() {
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if (damage() & FL_DAMAGE_ALL) {
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... draw frame/box and other static stuff ...
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}
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if (damage() & (FL_DAMAGE_ALL | 1)) draw_part1();
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if (damage() & (FL_DAMAGE_ALL | 2)) draw_part2();
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if (damage() & (FL_DAMAGE_ALL | 4)) draw_part3();
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}
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</PRE></UL>
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<H4><A name=draw_box>void Fl_Widget::draw_box() const
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<BR></A>void Fl_Widget::draw_box(Fl_Boxtype b, ulong c) const</H4>
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The first form draws this widget's <TT>box()</TT>, using the
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dimensions of the widget. The second form uses <TT>b</TT> as the box
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type and <TT>c</TT> as the color for the box.
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<H4><A name="draw_focus">void Fl_Widget::draw_focus() const
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<BR>void Fl_Widget::draw_focus(Fl_Boxtype b, int x, int y, int w, int h) const</A></H4>
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<P>Draws a focus box inside the widgets bounding box. The second
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form allows you to specify a different bounding box.
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<H4><A name=draw_label>void Fl_Widget::draw_label() const
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<BR> void Fl_Widget::draw_label(int x, int y, int w, int h) const
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<BR> void Fl_Widget::draw_label(int x, int y, int w, int h, Fl_Align
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align) const</A></H4>
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This is the usual function for a <TT>draw()</TT> method to call to
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draw the widget's label. It does not draw the label if it is supposed
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to be outside the box (on the assumption that the enclosing group will
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draw those labels).
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<P>The second form uses the passed bounding box instead of the widget's
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bounding box. This is useful so "centered" labels are aligned with some
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feature, like a moving slider. </P>
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<P>The third form draws the label anywhere. It acts as though <TT>
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FL_ALIGN_INSIDE</TT> has been forced on so the label will appear inside
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the passed bounding box. This is designed for parent groups to draw
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labels with. </P>
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<H4><A name=set_flag>void Fl_Widget::set_flag(SHORTCUT_LABEL)</A></H4>
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Modifies <TT>draw_label()</TT> so that '&' characters cause an underscore
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to be printed under the next letter.
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<H4><A name=set_visible>void Fl_Widget::set_visible()</A>
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<BR><A name=clear_visible>void Fl_Widget::clear_visible()</A></H4>
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Fast inline versions of <TT>Fl_Widget::hide()</TT> and <TT>
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Fl_Widget::show()</TT>. These do not send the <TT>FL_HIDE</TT> and <TT>
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FL_SHOW</TT> events to the widget.
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<H4><A name=test_shortcut>int Fl_Widget::test_shortcut() const
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<BR> static int Fl_Widget::test_shortcut(const char *s)</A></H4>
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The first version tests <TT>Fl_Widget::label()</TT> against the
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current event (which should be a <TT>FL_SHORTCUT</TT> event). If the
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label contains a '&' character and the character after it matches the key
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press, this returns true. This returns false if the <TT>SHORTCUT_LABEL</TT>
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flag is off, if the label is <TT>NULL</TT> or does not have a
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'&' character in it, or if the keypress does not match the character.
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<P>The second version lets you do this test against an arbitrary
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string. </P>
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<H4><A name=type>uchar Fl_Widget::type() const
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<BR> void Fl_Widget::type(uchar t)</A></H4>
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The property <TT>Fl_Widget::type()</TT> can return an arbitrary 8-bit
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identifier, and can be set with the protected method <TT>type(uchar t)</TT>
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. This value had to be provided for Forms compatibility, but you can
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use it for any purpose you want. Try to keep the value less than 100
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to not interfere with reserved values.
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<P>FLTK does not use RTTI (Run Time Typing Infomation), to enhance
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portability. But this may change in the near future if RTTI becomes
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standard everywhere. </P>
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<P>If you don't have RTTI you can use the clumsy FLTK mechanisim, by
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having <TT>type()</TT> use a unique value. These unique values must
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be greater than the symbol <TT>FL_RESERVED_TYPE</TT> (which is 100).
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Look through the header files for <TT>FL_RESERVED_TYPE</TT> to find an
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unused number. If you make a subclass of <TT>Fl_Window</TT>
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you must use <TT>FL_WINDOW + n</TT> (<TT>n</tt> must be in the
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range 1 to 7). </P>
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<H2><A NAME="handle">Handling Events</A></H2>
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The virtual method <TT>int Fl_Widget::handle(int event)</TT> is called
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to handle each event passed to the widget. It can:
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<UL>
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<LI>Change the state of the widget. </LI>
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<LI>Call <A href=Fl_Widget.html#Fl_Widget.redraw><TT>Fl_Widget::redraw()</TT>
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</A> if the widget needs to be redisplayed. </LI>
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<LI>Call <A href=Fl_Widget.html#Fl_Widget.damage><TT>
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Fl_Widget::damage(n)</TT></A> if the widget needs a partial-update
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(assuming you provide support for this in your <A HREF="#draw"><TT>Fl_Widget::draw()</TT></A>
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method). </LI>
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<LI>Call <A href=Fl_Widget.html#Fl_Widget.do_callback><TT>
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Fl_Widget::do_callback()</TT></A> if a callback should be generated. </LI>
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<LI>Call <TT>Fl_Widget::handle()</TT> on child widgets. </LI>
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</UL>
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Events are identified by the integer argument. Other information
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about the most recent event is stored in static locations and aquired
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by calling the <A href=events.html#events><TT>Fl::event_*()</TT></A>
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functions. This information remains valid until another event is
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handled.
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<P>Here is a sample <TT>handle()</TT> method for a widget that acts as
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a pushbutton and also accepts the keystroke 'x' to cause the callback: </P>
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<UL><PRE>
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int MyClass::handle(int event) {
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switch(event) {
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case FL_PUSH:
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highlight = 1;
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redraw();
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return 1;
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case FL_DRAG: {
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int t = Fl::event_inside(this);
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if (t != highlight) {
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highlight = t;
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redraw();
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}
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}
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return 1;
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case FL_RELEASE:
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if (highlight) {
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highlight = 0;
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redraw();
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do_callback();
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// never do anything after a callback, as the callback
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// may delete the widget!
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}
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return 1;
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case FL_SHORTCUT:
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if (Fl::event_key() == 'x') {
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do_callback();
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return 1;
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}
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return 0;
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default:
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return Fl_Widget::handle(event);
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}
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}
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</PRE></UL>
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<P>You must return non-zero if your <TT>handle()</TT> method
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uses the event. If you return zero, the parent widget will try
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sending the event to another widget.
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<H2><A NAME="draw">Drawing the Widget</A></H2>
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<P>The <TT>draw()</TT> virtual method is called when FLTK wants
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you to redraw your widget. It will be called if and only if
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<TT>damage()</TT> is non-zero, and <TT>damage()</TT> will be
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cleared to zero after it returns. The <TT>draw()</TT> method
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should be declared protected so that it can't be called from
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non-drawing code.
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<P>The <TT>damage()</TT> value contains the bitwise-OR of all
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the <TT>damage(n)</TT> calls to this widget since it was last
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drawn. This can be used for minimal update, by only redrawing
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the parts whose bits are set. FLTK will turn on the
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<TT>FL_DAMAGE_ALL</TT> bit if it thinks the entire widget must
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be redrawn, e.g. for an expose event. </P>
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<P>Expose events (and the above <TT>damage(b,x,y,w,h)</TT>) will cause <TT>
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draw()</TT> to be called with FLTK's <A href=drawing.html#clipping>
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clipping</A> turned on. You can greatly speed up redrawing in some
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cases by testing <TT>fl_not_clipped(x,y,w,h)</TT> or <TT>fl_clip_box(...)</TT> and
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skipping invisible parts. </P>
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<P>Besides the protected methods described above, FLTK provides a large
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number of basic drawing functions, which are described <A href=drawing.html#drawing>
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below</A>. </P>
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<H2>Resizing the Widget</H2>
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The <TT>resize(int x, int y, int w, int h)</TT> method is called when
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the widget is being resized or moved. The arguments are the new
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position, width, and height. <TT>x()</TT>, <TT>y()</TT>, <TT>w()</TT>,
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and <TT>h()</TT> still remain the old size. You must call <TT>resize()</TT>
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on your base class with the same arguments to get the widget size to
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actually change.
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<P>This should <I>not</I> call <TT>redraw()</TT>, at least if only the <TT>
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x()</TT> and <TT>y()</TT> change. This is because composite widgets like <A href=Fl_Scroll.html#Fl_Scroll>
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<TT>Fl_Scroll</TT></A> may have a more efficient way of drawing the new
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position. </P>
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<H2>Making a Composite Widget</H2>
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A "composite" widget contains one or more "child" widgets.
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To make a composite widget you should subclass <A href=Fl_Group.html#Fl_Group><TT>Fl_Group</TT></A>
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. It is possible to make a composite object that is not a subclass of <TT>
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Fl_Group</TT>, but you'll have to duplicate the code in <TT>Fl_Group</TT>
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anyways.
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<P>Instances of the child widgets may be included in the parent: </P>
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<UL><PRE>
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class MyClass : public Fl_Group {
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Fl_Button the_button;
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Fl_Slider the_slider;
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...
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};
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</PRE></UL>
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The constructor has to initialize these instances. They are
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automatically <TT>add()</TT>ed to the group, since the <TT>Fl_Group</TT>
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constructor does <TT>begin()</TT>. <I>Don't forget to call <TT>end()</TT>
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or use the <A href=Fl_End.html#Fl_End><TT>Fl_End</TT></A> pseudo-class:</I>
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<UL><PRE>
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MyClass::MyClass(int x, int y, int w, int h) :
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Fl_Group(x, y, w, h),
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the_button(x + 5, y + 5, 100, 20),
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the_slider(x, y + 50, w, 20)
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{
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...(you could add dynamically created child widgets here)...
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end(); // don't forget to do this!
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}
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</PRE></UL>
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The child widgets need callbacks. These will be called with a pointer
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to the children, but the widget itself may be found in the <TT>parent()</TT>
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pointer of the child. Usually these callbacks can be static private
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methods, with a matching private method:
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<UL><PRE>
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void MyClass::static_slider_cb(Fl_Widget* v, void *) { // static method
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((MyClass*)(v->parent())->slider_cb();
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}
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void MyClass::slider_cb() { // normal method
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use(the_slider->value());
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}
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</PRE></UL>
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If you make the <TT>handle()</TT> method, you can quickly pass all the
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events to the children using the <TT>Fl_Group::handle()</TT> method.
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You don't need to override <TT>handle()</TT> if your composite widget
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does nothing other than pass events to the children:
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<UL><PRE>
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int MyClass::handle(int event) {
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if (Fl_Group::handle(event)) return 1;
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... handle events that children don't want ...
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}
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</PRE></UL>
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<P>If you override <TT>draw()</TT> you need to draw all the
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children. If <TT>redraw()</TT> or <TT>damage()</TT> is called
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on a child, <TT>damage(FL_DAMAGE_CHILD)</TT> is done to the
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group, so this bit of <TT>damage()</TT> can be used to indicate
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that a child needs to be drawn. It is fastest if you avoid
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drawing anything else in this case:
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<UL><PRE>
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int MyClass::draw() {
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Fl_Widget *const*a = array();
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if (damage() == FL_DAMAGE_CHILD) { // only redraw some children
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for (int i = children(); i --; a ++) update_child(**a);
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} else { // total redraw
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... draw background graphics ...
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// now draw all the children atop the background:
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for (int i = children_; i --; a ++) {
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draw_child(**a);
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draw_outside_label(**a); // you may not need to do this
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}
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}
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}
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</PRE></UL>
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<TT>Fl_Group</TT> provides some protected methods to make drawing
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easier:
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<UL>
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<LI><A href=#draw_child>draw_child</A></LI>
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<LI><A href=#draw_outside_label>draw_outside_label</A></LI>
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<LI><A href=#update_child>update_child</A></LI>
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</UL>
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<H4><A name=draw_child>void Fl_Group::draw_child(Fl_Widget&)</A></H4>
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This will force the child's <TT>damage()</TT> bits all to one and call <TT>
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draw()</TT> on it, then clear the <TT>damage()</TT>. You should call
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this on all children if a total redraw of your widget is requested, or
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if you draw something (like a background box) that damages the child.
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Nothing is done if the child is not <TT>visible()</TT> or if it is
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clipped.
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<H4><A name=draw_outside_label>void
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Fl_Group::draw_outside_label(Fl_Widget&) const</A></H4>
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Draw the labels that are <I>not</I> drawn by <A href=#draw_label><TT>
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draw_label()</TT></A>. If you want more control over the label
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positions you might want to call <TT>child->draw_label(x,y,w,h,a)</TT>.
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<H4><A name=update_child>void Fl_Group::update_child(Fl_Widget&)</A></H4>
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Draws the child only if its <TT>damage()</TT> is non-zero. You
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should call this on all the children if your own damage is equal to
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FL_DAMAGE_CHILD. Nothing is done if the child is not <TT>visible()</TT>
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or if it is clipped.
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<H2>Cut and Paste Support</H2>
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FLTK provides routines to cut and paste 8-bit text (in the future this
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may be UTF-8) between applications:
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<UL>
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<LI><A href="Fl.html#Fl.paste"><TT>Fl::paste</TT></A></LI>
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<LI><A href="Fl.html#Fl.selection"><TT>Fl::selection</TT></A></LI>
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<LI><A href="Fl.html#Fl.selection_owner"><TT>Fl::selection_owner</TT></A></LI>
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</UL>
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|
It may be possible to cut/paste non-text data by using <A href=osissues.html#add_handler>
|
|
<TT>Fl::add_handler()</TT></A>.
|
|
|
|
<H2>Drag And Drop Support</H2>
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|
|
|
FLTK provides routines to drag and drop 8-bit text between applications:
|
|
|
|
<P>Drag'n'drop operations are are initiated by copying data to the
|
|
clipboard and calling the function
|
|
<A href="Fl.html#Fl.dnd"><TT>Fl::dnd()</TT></A>.
|
|
|
|
<P>Drop attempts are handled via <A href="events.html#dnd">events</A>:
|
|
<UL>
|
|
<LI><TT>FL_DND_ENTER</TT></LI>
|
|
<LI><TT>FL_DND_DRAG</TT></LI>
|
|
<LI><TT>FL_DND_LEAVE</TT></LI>
|
|
<LI><TT>FL_DND_RELEASE</TT></LI>
|
|
<LI><TT>FL_PASTE</TT></LI>
|
|
</UL>
|
|
|
|
<H2>Making a subclass of Fl_Window</H2>
|
|
|
|
<P>You may want your widget to be a subclass of
|
|
<TT>Fl_Window</TT>, <TT>Fl_Double_Window</TT>, or
|
|
<TT>FL_Gl_Window</TT>. This can be useful if your widget wants
|
|
to occupy an entire window, and can also be used to take
|
|
advantage of system-provided clipping, or to work with a library
|
|
that expects a system window ID to indicate where to draw.
|
|
|
|
<P>Subclassing <TT>Fl_Window</TT>is almost exactly like
|
|
subclassing <TT>Fl_Group</TT>, and in fact you can easily
|
|
switch a subclass back and forth. Watch out for the following
|
|
differences: </P>
|
|
|
|
<OL>
|
|
|
|
<LI><TT>Fl_Window</TT> is a subclass of
|
|
<TT>Fl_Group</TT> so <I>make sure your constructor calls
|
|
<TT>end()</TT></I> unless you actually want children
|
|
added to your window.</LI>
|
|
|
|
<LI>When handling events and drawing, the upper-left
|
|
corner is at 0,0, not <TT>x(),y()</TT> as in other
|
|
<TT>Fl_Widget</TT>'s. For instance, to draw a box
|
|
around the widget, call <TT>draw_box(0, 0, w(),
|
|
h())</TT>, rather than <TT>draw_box(x(), y(), w(),
|
|
h())</TT>.</LI>
|
|
|
|
</OL>
|
|
|
|
<P>You may also want to subclass <TT>Fl_Window</TT> in order to
|
|
get access to different visuals or to change other attributes of
|
|
the windows. See <A href="osissues.html">"Appendix F - Operating
|
|
System Issues"</A> for more information.
|
|
|
|
</BODY>
|
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</HTML>
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