# 3 - Common Widgets and Attributes

This chapter describes many of the widgets that are provided with FLTK and covers how to query and set the standard attributes.

## Buttons

FLTK provides many types of buttons:

- `Fl_Button` - A standard push button.
- `Fl_Check_Button` - A button with a check box.
- `Fl_Light_Button` - A push button with a light.
- `Fl_Repeat_Button` - A push button that repeats when held.
- `Fl_Return_Button` - A push button that is activated by the `Enter` key.
- `Fl_Round_Button` - A button with a radio circle.

Figure 3-1: FLTK Button Widgets

All of these buttons just need the corresponding `<FL/Fl_xyz_Button.H>` header file. The constructor takes the bounding box of the button and optionally a label string:

    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");

Each button has an associated `type()` which allows it to behave as a push button, toggle button, or radio button:

    button->type(FL_NORMAL_BUTTON);
    lbutton->type(FL_TOGGLE_BUTTON);
    rbutton->type(FL_RADIO_BUTTON);

For toggle and radio buttons, the `value()` method returns the current button state (0 = off, 1 = on). The `set()` and `clear()` methods can be used on toggle buttons to turn a toggle button on or off, respectively. Radio buttons can be turned on with the `setonly()` method; this will also turn off other radio buttons in the same group.

## Text

FLTK provides several text widgets for displaying and receiving text:

- `Fl_Input` - A one-line text input field.
- `Fl_Output` - A one-line text output field.
- `Fl_Multiline_Input` - A multi-line text input field.
- `Fl_Multiline_Output` - A multi-line text output field.
- `Fl_Text_Display` - A multi-line text display widget.
- `Fl_Text_Editor` - A multi-line text editing widget.
- `Fl_Help_View` - A HTML text display widget.

The `Fl_Output` and `Fl_Multiline_Output` widgets allow the user to copy text from the output field but not change it.

The `value()` method is used to get or set the string that is displayed:

    Fl_Input *input = new Fl_Input(x, y, width, height, "label");
    input->value("Now is the time for all good men...");

The string is copied to the widget's own storage when you set the `value()` of the widget.

The `Fl_Text_Display` and `Fl_Text_Editor` widgets use an associated `Fl_Text_Buffer` class for the value, instead of a simple string.

## Valuators

Unlike text widgets, valuators keep track of numbers instead of strings. FLTK provides the following valuators:

- `Fl_Counter` - A widget with arrow buttons that shows the current value.
- `Fl_Dial` - A round knob.
- `Fl_Roller` - An SGI-like dolly widget.
- `Fl_Scrollbar` - A standard scrollbar widget.
- `Fl_Slider` - A scrollbar with a knob.
- `Fl_Value_Slider` - A slider that shows the current value.

Figure 3-2: FLTK valuator widgets

The `value()` method gets and sets the current value of the widget. The `minimum()` and `maximum()` methods set the range of values that are reported by the widget.

## Groups

The `Fl_Group` 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:

- `Fl_Double_Window` - A double-buffered window on the screen.
- `Fl_Gl_Window` - An OpenGL window on the screen.
- `Fl_Group` - The base container class; can be used to group any widgets together.
- `Fl_Pack` - A collection of widgets that are packed into the group area.
- `Fl_Scroll` - A scrolled window area.
- `Fl_Tabs` - Displays child widgets as tabs.
- `Fl_Tile` - A tiled window area.
- `Fl_Window` - A window on the screen.

## Setting the Size and Position of Widgets

The size and position of widgets is usually set when you create them. You can access them with the `x()`, `y()`, `w()`, and `h()` methods.

You can change the size and position by using the `position()`, `resize()`, and `size()` methods:

    button->position(x, y);
    group->resize(x, y, width, height);
    window->size(width, height);

If you change a widget's size or position after it is displayed you will have to call `redraw()` on the widget's parent.

## Colors

FLTK stores the colors of widgets as an 32-bit unsigned number that is either an index into a color palette of 256 colors or a 24-bit RGB color. The color palette is not the X or WIN32 colormap, but instead is an internal table with fixed contents.

There are symbols for naming some of the more common colors:

- `FL_BLACK`
- `FL_RED`
- `FL_GREEN`
- `FL_YELLOW`
- `FL_BLUE`
- `FL_MAGENTA`
- `FL_CYAN`
- `FL_WHITE`

These symbols are the default colors for all FLTK widgets. They are explained in more detail in the chapter Enumerations

- `FL_FOREGROUND_COLOR`
- `FL_BACKGROUND_COLOR`
- `FL_INACTIVE_COLOR`
- `FL_SELECTION_COLOR`

RGB colors can be set using the `fl_rgb_color()` function:

    Fl_Color c = fl_rgb_color(85, 170, 255);

The widget color is set using the `color()` method:

    button->color(FL_RED);

Similarly, the label color is set using the `labelcolor()` method:

    button->labelcolor(FL_WHITE);

## Box Types

The type `Fl_Boxtype` stored and returned in `Fl_Widget::box()` is an enumeration defined in `<Enumerations.H>`. Figure 3-3 shows the standard box types included with FLTK.

Figure 3-3: FLTK box types

`FL_NO_BOX` means nothing is drawn at all, so whatever is already on the screen remains. The `FL_..._FRAME` types only draw their edges, leaving the interior unchanged. The blue color in Figure 3-3 is the area that is not drawn by the frame types.

### Making Your Own Boxtypes

You can define your own boxtypes by making a small function that draws the box and adding it to the table of boxtypes.

Note: This interface has changed in FLTK 2.0!

#### The Drawing Function

The drawing function is passed the bounding box and background color for the widget:

    void xyz_draw(int x, int y, int w, int h, Fl_Color c) {
    ...
    }

A simple drawing function might fill a rectangle with the given color and then draw a black outline:

    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);
    }

#### Fl_Boxtype fl_down(Fl_Boxtype)

`fl_down` returns the "pressed" or "down" version of a box. If no "down" version of a given box exists, the behavior of this function is undefined and some random box or frame is returned. See also: fl_frame drawing.

#### Fl_Boxtype fl_frame(Fl_Boxtype)

`fl_frame` returns the unfilled, frame-only version of a box. If no frame version of a given box exists, the behavior of this function is undefined and some random box or frame is returned. See also: fl_frame drawing.

#### Fl_Boxtype fl_box(Fl_Boxtype)

`fl_box` returns the filled version of a frame. If no filled version of a given frame exists, the behavior of this function is undefined and some random box or frame is returned. See also: `fl_frame`.

#### Adding Your Box Type

The `Fl::set_boxtype()` method adds or replaces the specified box type:

    #define XYZ_BOX FL_FREE_BOXTYPE

    Fl::set_boxtype(XYZ_BOX, xyz_draw, 1, 1, 2, 2);

The last 4 arguments to `Fl::set_boxtype()` are the offsets for the x, y, width, and height values that should be subtracted when drawing the label inside the box.

A complete box design contains four box types in this order: a filled, neutral box (`UP_BOX`), a filled, depressed box (`DOWN_BOX`), and the same as outlines only (`UP_FRAME` and `DOWN_FRAME`). The function `fl_down(Fl_Boxtype)` expects the neutral design on a boxtype with a numerical value evenly dividable by two. `fl_frame(Fl_Boxtype)` expects the `UP_BOX` design at a value dividable by four.

## Labels and Label Types

The `label()`, `align()`, `labelfont()`, `labelsize()`, `labeltype()`, `image()`, and `deimage()` methods control the labeling of widgets.

### label()

The `label()` method sets the string that is displayed for the label. Symbols can be included with the label string by escaping them using the "@" symbol - "@@" displays a single at sign. Figure 3-4 shows the available symbols.

Figure 3-4: FLTK label symbols

The @ sign may also be followed by the following optional "formatting" characters, in this order:

- '#' forces square scaling, rather than distortion to the widget's shape.
- +[1-9] or -[1-9] tweaks the scaling a little bigger or smaller.
- '$' flips the symbol horizontally, '%' flips it vertically.
- [0-9] - rotates by a multiple of 45 degrees. '5' and '6' do no rotation while the others point in the direction of that key on a numeric keypad. '0', followed by four more digits rotates the symbol by that amount in degrees.

Thus, to show a very large arrow pointing downward you would use the label string "@+92->".

### align()

The `align()` method positions the label. The following constants are defined and may be OR'd together as needed:

- `FL_ALIGN_CENTER` - center the label in the widget.
- `FL_ALIGN_TOP` - align the label at the top of the widget.
- `FL_ALIGN_BOTTOM` - align the label at the bottom of the widget.
- `FL_ALIGN_LEFT` - align the label to the left of the widget.
- `FL_ALIGN_RIGHT` - align the label to the right of the widget.
- `FL_ALIGN_INSIDE` - align the label inside the widget.
- `FL_ALIGN_CLIP` - clip the label to the widget's bounding box.
- `FL_ALIGN_WRAP` - wrap the label text as needed.
- `FL_TEXT_OVER_IMAGE` - show the label text over the image.
- `FL_IMAGE_OVER_TEXT` - show the label image over the text (default).

### labeltype()

The `labeltype()` method sets the type of the label. The following standard label types are included:

- `FL_NORMAL_LABEL` - draws the text.
- `FL_NO_LABEL` - does nothing.
- `FL_SHADOW_LABEL` - draws a drop shadow under the text.
- `FL_ENGRAVED_LABEL` - draws edges as though the text is engraved.
- `FL_EMBOSSED_LABEL` - draws edges as thought the text is raised.
- `FL_ICON_LABEL` - draws the icon associated with the text.

### image() and deimage()

The `image()` and `deimage()` methods set an image that will be displayed with the widget. The `deimage()` method sets the image that is shown when the widget is inactive, while the `image()` method sets the image that is shown when the widget is active.

To make an image you use a subclass of `Fl_Image`.

#### Making Your Own Label Types

Label types are actually indexes into a table of functions that draw them. The primary purpose of this is to use this to draw the labels in ways inaccessible through the `fl_font` mechanism (e.g. `FL_ENGRAVED_LABEL`) or with program-generated letters or symbology.

Note: This interface has changed in FLTK 2.0!

##### Label Type Functions

To setup your own label type you will need to write two functions: one to draw and one to measure the label. The draw function is called with a pointer to a `Fl_Label` structure containing the label information, the bounding box for the label, and the label alignment:

    void xyz_draw(const Fl_Label *label, int x, int y, int w, int h, Fl_Align align) {
    ...
    }

The label should be drawn inside this bounding box, even if `FL_ALIGN_INSIDE` is not enabled. The function is not called if the label value is `NULL`.

The measure function is called with a pointer to a `Fl_Label` structure and references to the width and height:

    void xyz_measure(const Fl_Label *label, int &w, int &h) {
    ...
    }

The function should measure the size of the label and set `w` and `h` to the size it will occupy.

##### Adding Your Label Type

The `Fl::set_labeltype` method creates a label type using your draw and measure functions:

    #define XYZ_LABEL FL_FREE_LABELTYPE

    Fl::set_labeltype(XYZ_LABEL, xyz_draw, xyz_measure);

The label type number `n` can be any integer value starting at the constant `FL_FREE_LABELTYPE`. Once you have added the label type you can use the `labeltype()` method to select your label type.

The `Fl::set_labeltype` method can also be used to overload an existing label type such as `FL_NORMAL_LABEL`.

#### Making your own symbols

It is also possible to define your own drawings and add them to the symbol list, so they can be rendered as part of any label.

To create a new symbol, you implement a drawing function `void drawit(Fl_Color c)` which typically uses the complex drawing functions to generate a vector shape inside a two-by-two units sized box around the origin. This function is then linked into the symbols table using `fl_add_symbol`:

    int fl_add_symbol(const char *name, void (*drawit)(Fl_Color), int scalable)

name is the name of the symbol without the "@"; scalable must be set to 1 if the symbol is generated using scalable vector drawing functions.

    int fl_draw_symbol(const char *name,int x,int y,int w,int h,Fl_Color col)

This function draw a named symbol fitting the given rectangle.

## Callbacks

Callbacks are functions that are called when the value of a widget changes. A callback function is sent a `Fl_Widget` pointer of the widget that changed and a pointer to data that you provide:

    void xyz_callback(Fl_Widget *w, void *data) {
    ...
    }

The `callback()` method sets the callback function for a widget. You can optionally pass a pointer to some data needed for the callback:

    int xyz_data;

    button->callback(xyz_callback, &xyz_data);

Normally callbacks are performed only when the value of the widget changes. You can change this using the `when()` method:

    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);

Note:

You cannot delete a widget inside a callback, as the widget may still be accessed by FLTK after your callback is completed. Instead, use the `Fl::delete_widget()` method to mark your widget for deletion when it is safe to do so.

Hint:

Many programmers new to FLTK or C++ try to use a non-static class method instead of a static class method or function for their callback. Since callbacks are done outside a C++ class, the `this` pointer is not initialized for class methods.

To work around this problem, define a static method in your class that accepts a pointer to the class, and then have the static method call the class method(s) as needed. The data pointer you provide to the `callback()` method of the widget can be a pointer to the instance of your class.

    class Foo {
      void my_callback(Fl_Widget *w);
      static void my_static_callback(Fl_Widget *w, void *f) { ((Foo *)f)->my_callback(w); }
      ...
    }

    ...

    w->callback(my_static_callback, (void *)this);

## Shortcuts

Shortcuts are key sequences that activate widgets such as buttons or menu items. The `shortcut()` method sets the shortcut for a widget:

    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');
    button->shortcut(0); // no shortcut

The shortcut value is the key event value - the ASCII value or one of the special keys like `FL_Enter` - combined with any modifiers like `Shift`, `Alt`, and `Control`.