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<HTML>
<BODY>
<H1 ALIGN=RIGHT><A NAME="common">3 - Common Widgets and Attributes</A></H1>
This chapter describes many of the widgets that are provided with FLTK and covers how
to query and set the standard attributes.
<H2>Buttons</H2>
FLTK provides many types of buttons:
<ul>
<li><tt>Fl_Button</tt> - A standard push button.
<li><tt>Fl_Check_Button</tt> - A button with a check box.
<li><tt>Fl_Light_Button</tt> - A push button with a light.
<li><tt>Fl_Repeat_Button</tt> - A push button that repeats when held.
<li><tt>Fl_Return_Button</tt> - A push button that is activated by the Enter key.
<li><tt>Fl_Round_Button</tt> - A button with a check circle.
</ul>
For all of these buttons you just need to include the corresponding
<tt><FL/Fl_xyz_Button.H></tt> header file. The constructor takes the
bounding box of the button and optionally a label string:
<ul><pre>
Fl_Button *button = new Fl_Button(x, y, width, height, "label");
Fl_Light_Button *lbutton = new Fl_Light_Button(x, y, width, height);
Fl_Round_Button *rbutton = new Fl_Round_Button(x, y, width, height, "label");
</pre></ul>
Each button has an associated <a href="#Fl_Button.type"><tt>type()</tt></a>
which allows it to behave as a push button, toggle button, or radio button:
<ul><pre>
button->type(0);
lbutton->type(FL_TOGGLE_BUTTON);
rbutton->type(FL_RADIO_BUTTON);
</pre></ul>
For toggle and radio buttons, the <a href="#Fl_Button.value"><tt>value()</tt></a>
method returns the current button state (0 = off, 1 = on). The
<a href="#Fl_Widget.set"><tt>set()</tt></a> and
<a href="#Fl_Widget.clear"><tt>clear()</tt></a> methods can be used on toggle
buttons to turn a toggle button on or off, respectively. Radio buttons can
be turned on with the <a href="#Fl_Widget.setonly"><tt>setonly()</tt></a>
method; this will also turn off other radio buttons in the current group.
<H2>Text</H2>
FLTK provides several text widgets for displaying and receiving text:
<ul>
<li><tt>Fl_Input</tt> - A standard one-line text input field.
<li><tt>Fl_Output</tt> - A standard one-line text output field.
<li><tt>Fl_Multiline_Input</tt> - A standard multi-line text input field.
<li><tt>Fl_Multiline_Output</tt> - A standard multi-line text output field.
</ul>
The <tt>Fl_Output</tt> and <tt>Fl_Multiline_Output</tt> widgets allow the
user to copy text from the output field but not change it.
<p>The <a href="#Fl_Input.value"><tt>value()</tt></a> method is used to get or
set the string that is displayed:
<ul><pre>
Fl_Input *input = new Fl_Input(x, y, width, height, "label");
input->value("Now is the time for all good men...");
</pre></ul>
<H2>Valuators</H2>
Unlike text widgets, valuators keep track of numbers instead of strings.
FLTK provides the following valuators:
<ul>
<li><tt>Fl_Counter</tt> - A widget with arrow buttons that shows the
current value.
<li><tt>Fl_Dial</tt> - A round knob.
<li><tt>Fl_Roller</tt> - An SGI-like dolly widget.
<li><tt>Fl_Scrollbar</tt> - A standard scrollbar widget.
<li><tt>Fl_Slider</tt> - A scrollbar with a knob.
<li><tt>Fl_Value_Slider</tt> - A slider that shows the current value.
</ul>
The <a href="#Fl_Valuator.value"><tt>value()</tt></a> method gets and sets the
current value of the widget. The <a href="#Fl_Valuator.minimum">
<tt>minimum()</tt></a> and <a href="#Fl_Valuator.maximum"><tt>maximum</tt></a>
methods set the range of values that are reported by the widget.
<H2>Groups</H2>
The <tt>Fl_Group</tt> widget class is used as a general purpose "container"
widget. Besides grouping radio buttons, the groups are used to encapsulate
windows, tabs, and scrolled windows. The following group classes are available
with FLTK:
<ul>
<li><tt>Fl_Double_Window</tt> - A double-buffered window on the screen.
<li><tt>Fl_Gl_Window</tt> - An OpenGL window on the screen.
<li><tt>Fl_Group</tt> - The base container class; can be used to group any widgets together.
<li><tt>Fl_Scroll</tt> - A scrolled window area.
<li><tt>Fl_Tabs</tt> - Displays child widgets as tabs.
<li><tt>Fl_Window</tt> - A window on the screen.
</ul>
<H2>Setting the Size and Position of Widgets</H2>
The size and position of widgets is usually set when you create them. You
can change this at any time using the <tt>position</tt>, <tt>resize()</tt>,
and <tt>size</tt> methods:
<ul><pre>
button->position(x, y);
group->resize(x, y, width, height);
window->size(width, height);
</pre></ul>
Changing the size or position of a widget will cause a redraw of that widget
and its children.
<H2><A NAME="colors">Colors</A></H2>
FLTK manages a virtual color palette of "standard" colors. The
standard colors are:
<ul>
<li><tt>FL_BLACK</tt>
<li><tt>FL_RED</tt>
<li><tt>FL_GREEN</tt>
<li><tt>FL_YELLOW</tt>
<li><tt>FL_BLUE</tt>
<li><tt>FL_MAGENTA</tt>
<li><tt>FL_CYAN</tt>
<li><tt>FL_WHITE</tt>
<li><tt>FL_GRAY</tt>
</ul>
The widget color can be set using the <tt>color()</tt> method:
<ul><pre>
button->color(FL_RED);
</pre></ul>
Similarly, the label color can be set using the <tt>labelcolor()</tt> method:
<ul><pre>
button->labelcolor(FL_WHITE);
</pre></ul>
<H2><A NAME="boxtypes">Box Types</A></H2>
<p>The type <tt>Fl_Boxtype</tt> stored and returned in <a href="#Fl_Widget.box">
<tt>Fl_Widget::box()</tt></a> is an enumeration defined in
<a href="#enumerations"><tt><FL/Enumerations.H></tt></a>:
<center><img src=boxtypes.gif width=80%></center>
<tt>FL_NO_BOX</tt> means nothing is drawn at all, so whatever is
already on the screen remains. The <tt>FL_..._FRAME</tt> types only
draw their edges, leaving the center unchanged. In the above diagram
the blue color is the area that is not drawn by the box.
<H3>Making your own Boxtypes</H3>
You can define your own boxtypes by making a small function that
draws the box and adding a pointer to it to a table of boxtypes.
<H4>The Drawing Function</H4>
The drawing function is passed the bounding box and background
color for the widget:
<ul><pre>
void xyz_draw(int x, int y, int w, int h, Fl_Color c) {
...
}
</pre></ul>
A simple drawing function might fill a rectangle with the given
color and then draw a black outline:
<ul><pre>
void xyz_draw(int x, int y, int w, int h, Fl_Color c) {
fl_color(c);
fl_rectf(x, y, w, h);
fl_color(FL_BLACK);
fl_rect(x, y, w, h);
}
</pre></ul>
<H4>Adding Your Box Type</H4>
The <tt>Fl::set_boxtype()</tt> method adds or replaces the
specified box type:
<ul><pre>
#define XYZ_BOX FL_FREE_BOXTYPE
Fl::set_boxtype(XYZ_BOX, xyz_draw, 1, 1, 2, 2);
</pre></ul>
The last 4 arguments to <tt>Fl::set_boxtype()</tt> are the offsets
for the bounding box that should be subtracted when drawing the label
inside the box.
<H2><A NAME="labels">Labels and Label Types</A></H2>
The <tt>label()</tt>, <tt>align</tt>, <tt>labelfont()</tt>, <tt>labelsize()</tt>,
and <tt>labeltype()</tt> methods control the labeling of widgets.
<H3>label()</H3>
The <tt>label()</tt> method sets the string that is displayed for the label.
For the <tt>FL_SYMBOL_LABEL</tt> and image label types the string contains
the actual symbol or image data.
<H3>align()</H3>
The <tt>align()</tt> method positions the label. The following constants are
defined:
<ul>
<li><tt>FL_ALIGN_CENTER</tt> - center the label in the widget.
<li><tt>FL_ALIGN_TOP</tt> - align the label at the top of the widget.
<li><tt>FL_ALIGN_BOTTOM</tt> - align the label at the bottom of the widget.
<li><tt>FL_ALIGN_LEFT</tt> - align the label to the left of the widget.
<li><tt>FL_ALIGN_RIGHT</tt> - align the label to the right of the widget.
<li><tt>FL_ALIGN_INSIDE</tt> - align the label inside the widget.
<li><tt>FL_ALIGN_CLIP</tt> - clip the label to the widget's bounding box.
<li><tt>FL_ALIGN_WRAP</tt> - wrap the label text as needed.
</ul>
<H3>labeltype()</H3>
The <tt>labeltype()</tt> method sets the type of the label. The following
standard label types are included:
<ul>
<li><tt>FL_NORMAL_LABEL</tt> - draws the text.
<li><tt>FL_NO_LABEL</tt> - does nothing
<li><tt>FL_SYMBOL_LABEL</tt> - draws "@xyz" labels, see "<a href=#symbols>Symbol Labels</a>"
<li><tt>FL_SHADOW_LABEL</tt> - draws a drop shadow under the text
<li><tt>FL_ENGRAVED_LABEL</tt> - draws edges as though the text is engraved
<li><tt>FL_EMBOSSED_LABEL</tt> - draws edges as thought the text is raised
</ul>
To make bitmaps or pixmaps you use a method on the
<a href="#Fl_Bitmap"><tt>Fl_Bitmap</tt></a> or
<a href="#Fl_Pixmap"><tt>Fl_Pixmap</tt></a> objects.
<H4>Making Your Own Label Types</H4>
Label types are actually indexes into a table of functions to draw
them. The primary purpose of this is to let you reuse the
<tt>label()</tt> pointer as a pointer to arbitrary data such as a
bitmap or pixmap. You can also use this to draw the labels in ways
inaccessible through the <tt>fl_font</tt> mechanisim (e.g.
<tt>FL_ENGRAVED_LABEL</tt>) or with program-generated letters or
symbology.
<H5>Label Type Functions</H5>
To setup your own label type you will need to write two functions
to draw and measure the label. The draw function is called with a
pointer to a <a href="#Fl_Label"><tt>Fl_Label</tt></a> structure
containing the label information, the bounding box for the label,
and the label alignment:
<ul><pre>
void xyz_draw(Fl_Label *label, int x, int y, int w, int h, Fl_Align align) {
...
}
</pre></ul>
The label should be drawn <i>inside</i> this bounding box, even if
<tt>FL_ALIGN_INSIDE</tt> is not enabled. The function is not called if
the label value is <tt>NULL</tt>.
<p>The measure function is called with a pointer to a <a href="#Fl_Label"><tt>Fl_Label</tt></a> structure
and references to the width and height:
<ul><pre>
void xyz_measure(Fl_Label *label, int &w, int &h) {
...
}
</pre></ul>
It should measure the size of the label and set <tt>w</tt> and <tt>h</tt> to
the size it will occupy.
<H5>Adding Your Label Type</H5>
The <tt>Fl::set_labeltype</tt> method creates a label type using your
draw and measure functions:
<ul><pre>
#define XYZ_LABEL FL_FREE_LABELTYPE
Fl::set_labeltype(XYZ_LABEL, xyz_draw, xyz_measure);
</pre></ul>
The label type number <tt>n</tt> can be any integer value starting at
the constant <tt>FL_FREE_LABELTYPE</tt>. Once you have added the label
type you can use the <tt>labeltype()</tt> method to select your label
type.
<p>The <tt>Fl::set_labeltype</tt> method can also be used to overload an
existing label type such as <tt>FL_NORMAL_LABEL</tt>.
<H4><a name="symbols">Symbol Labels</H4>
<p>The <tt>FL_SYMBOL_LABEL</tt> label type uses the <tt>label()</tt>
string to look up a small drawing procedure in a hash table. For
historical reasons the string always starts with '@', if it starts with
something else (or the symbol is not found) the label is drawn
normally:
<center><img src=symbols.gif></center>
The @ sign may be followed by the following optional "formatting"
characters, in this order:
<ul>
<li>'#' forces square scaling, rather than distortion to the
widget's shape.
<li>+[1-9] or -[1-9] tweaks the scaling a little bigger or
smaller.
<li>[1-9] - rotates by a multiple of 45 degrees. '6' does
nothing, the others point in the direction of that key on a
numeric keypad.
</ul>
<H2>Callbacks</H2>
Callbacks are functions that are called when the value of a widget changes.
A callback function is sent a <tt>Fl_Widget</tt> pointer of the widget that
changed and optionally a pointer to data of some sort:
<ul><pre>
void xyz_callback(Fl_Widget *w, void *data) {
...
}
</pre></ul>
The <tt>callback()</tt> method sets the callback function for a widget. You
can optionally pass a pointer to some data needed for the callback:
<ul><pre>
int xyz_data;
button->callback(xyz_callback, &xyz_data);
</pre></ul>
Normally callbacks are performed only when the value of the widget
changes. You can change this using the
<a href="#Fl_Widget.when"><tt>when()</tt></a> method:
<ul><pre>
button->when(FL_WHEN_NEVER);
button->when(FL_WHEN_CHANGED);
button->when(FL_WHEN_RELEASE);
button->when(FL_WHEN_RELEASE_ALWAYS);
button->when(FL_WHEN_ENTER_KEY);
button->when(FL_WHEN_ENTER_KEY_ALWAYS);
button->when(FL_WHEN_CHANGED | FL_WHEN_NOT_CHANGED);
</pre></ul>
<H2>Shortcuts</H2>
Shortcuts are key sequences that activate widgets (usually buttons or menu
items). The <tt>shortcut()</tt> method registers a shortcut for a widget:
<ul><pre>
button->shortcut(FL_Enter);
button->shortcut(FL_SHIFT + 'b');
button->shortcut(FL_CTRL + 'b');
button->shortcut(FL_ALT + 'b');
button->shortcut(FL_CTRL + FL_ALT + 'b');
</pre></ul>
The shortcut value is the key event value (the ASCII value or one of
the special keys like <tt>FL_Enter</tt>) combined with any modifiers
(like shift, alt, and control).
</BODY>
</HTML>
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