+----Fl_Box, Fl_Browser_, Fl_Button, Fl_Chart, Fl_Clock,
Fl_Free, Fl_Group, Fl_Input_, Fl_Menu_, Fl_Positioner,
Fl_Widget is the base class for all widgets in FLTK. You can't
create one of these because the constructor is not public. However you
can subclass it.
All "property" accessing methods, such as color(),
parent(), or argument() are implemented as trivial inline
functions and thus are as fast and small as accessing fields in a
structure. Unless otherwise noted, the property setting methods such as
color(n) or label(s) are also trivial inline functions,
even if they change the widget's appearance. It is up to the user code
to call redraw() after these.
Fl_Widget::Fl_Widget(int x, int y, int w, int h, const char*
This is the protected constructor for an Fl_Widget, but all derived
widgets have a matching public constructor. It takes a value for x(),
y(), w(), h(), and an optional value for label().
Destroying single widgets is not very common. It is your
responsibility to either remove() them from any enclosing group, or to
destroy that group immediately after destroying the children.
uchar Fl_Widget::type() const;
This value is used for Forms compatability and to simulate RTTI.
The position of the upper-left corner of the widget in its enclosing
Fl_Window (not its parent if that is not an Fl_Window), and its
width and height.
Change the size or position of the widget. This is a virtual function
so the widget may implement its own handling of resizing. The default
version does not do redraw(), that is the parent widget's
responsibility (this is because the parent may know a faster way to
update the display, such as scrolling from the old position).
position(x,y) is a shortcut for resize(x,y,w(),h())
, and size(w,h) is a shortcut for resize(x(),y(),w,h)
Return a pointer to the Fl_Window
that this widget is in (it will skip any and all parent widgets
between this and the window). Returns NULL if none. Note:
for an Fl_Window, this returns its parent window (if
any), not this window.
The box() identifies a routine that draws the background of
the widget. See Box Types for the
available types. The default depends on the widget, but is usually
FL_NO_BOX or FL_UP_BOX.
This color is passed to the box routine. Color is an index into an
internal table of rgb colors. For most widgets this defaults to
FL_GRAY. See the
enumeration list for predefined colors. Use
Fl::set_color() to redefine colors.
For Forms compatibility a second color is defined. This is usually
used to color the widget when it is selected, although some widgets use
this color for other purposes. You can set both colors at once with
The label is printed somewhere on the widget or next to it. The
string is not copied, the passed pointer is stored unchanged in
A labeltype identifies a routine that
draws the label of the widget. This can be used for special effects
such as emboss, or to use the label() pointer as another form
of data such as a bitmap. The value FL_NORMAL_LABEL prints
the label as text.
How the label is printed next to or inside the widget. The default
value is FL_ALIGN_CENTER, which centers the label. The value
can be any of these constants or'd together:
This color is passed to the labeltype routine, and is typically the
color of the label text. This defaults to FL_BLACK.
Fonts are identified by small 8-bit indexes into a table. See the
enumeration list for predefined typefaces. The default value uses a
Helvetica typeface (Arial for Microsoft® Windows®). The function
Fl::set_font() can define new typefaces.
Fonts are further identified by a point size. The default is 14.
Each widget has a single callback. You can set it or examine it with
You can also just change the void * second argument to the
callback with the user_data methods.
For convenience you can also define the callback as taking a long
argument. This is implemented by casting this to a Fl_Callback
and casting the long to a void * and may not be
portable to some machines.
void Fl_Widget::callback(void (*)(Fl_Widget*))
For convenience you can also define the callback as taking only one
argument. This is implemented by casting this to a Fl_Callback
and may not be portable to some machines.
You can cause a widget to do its callback at any time, and even pass
Fl_Widget::changed() is a flag that is turned on when the user
changes the value stored in the widget. This is only used by
subclasses of Fl_Widget that store values, but is in the base
class so it is easier to scan all the widgets in a panel and
do_callback() on the changed ones in response to an "OK" button.
Most widgets turn this flag off when they do the callback, and when
the program sets the stored value.
Fl_Widget::when() is a set of bitflags used by subclasses of
Fl_Widget to decide when to do the callback. If the value is zero
then the callback is never done. Other values are described in the
individual widgets. This field is in the base class so that you can
scan a panel and do_callback() on all the ones that don't do
their own callbacks in response to an "OK" button.
The default callback, which puts a pointer to the widget on the queue
returned by Fl::readqueue()
. You may want to call this from your own callback.
An invisible widget never gets redrawn and does not get events. The
visible() method returns true if the widget is set to be
visible.The visible_r() method returns true if the widget and
all of its parents are visible. A widget is only visible if
visible() is true on it and all of its parents.
Changing it will send FL_SHOW or FL_HIDE
events to the widget. Do not change it if the parent is not
visible, as this will send false FL_SHOW or FL_HIDE
events to the widget. redraw() is called if necessary on
this or the parent.
Fl_Widget::active() returns whether the widget is active.
Fl_Widget::active_r() returns whether the widget and all of
its parents are active. An inactive widget does not get any events,
but it does get redrawn. A widget is only active if active() is
true on it and all of its parents.
Changing this value will send FL_ACTIVATE or
FL_DEACTIVATE to the widget if active_r() is true.
Currently you cannot deactivate Fl_Window widgets.
output() means the same as !active() except it does
not change how the widget is drawn. The widget will not recieve any
events. This is useful for making scrollbars or buttons that work as
displays rather than input devices.
This is the same as (active() && visible() &&
!output()) but is faster.
Mark the widget as needing its draw() routine called.
Non-zero if draw() needs to be called. Actually this is a
bit field that the widget subclass can use to figure out what parts to
Returns a pointer to the parent widget. Usually this is a Fl_Group or Fl_Window. Returns
NULL if none.
Returns true if b is a child of this widget, or is equal to
this widget. Returns false if b is NULL.
Returns true if this is a child of a, or is equal to a
. Returns false if a is NULL.
Tries to make this widget be the Fl::focus() widget, by first
sending it an FL_FOCUS event, and if it returns non-zero,
setting Fl::focus() to this widget. You should use this
method to assign the focus to an widget. Returns true if the widget
accepted the focus.