Fl_Group

Fl_Group is the main FLTK container widget that maintains an ordered list of child widgets. Children can be any widget including other Fl_Groups. The most important subclass is Fl_Window, but groups are also used for layout management (Fl_Pack, Fl_Flex, Fl_Grid) and controlling radio buttons. The Tab and arrow keys move focus between widgets in a group.

Constructor

Fl_Group(int x, int y, int w, int h, const char *label = 0);

x, y

int

required

Position relative to parent window

w, h

int

required

Size in pixels

label

const char*

Optional label text

Description: Creates a new group. The default boxtype is FL_NO_BOX.

Group Management

begin()

Begins adding widgets to this group.

void begin();

Description: Makes this group the current group. All widgets created after this call are automatically added as children until end() is called.

end()

Ends adding widgets to this group.

void end();

Description: Sets the current group back to the previous group. Example:

Fl_Group *group = new Fl_Group(10, 10, 200, 100);
group->begin();
  Fl_Button *btn1 = new Fl_Button(20, 20, 80, 30, "Button 1");
  Fl_Button *btn2 = new Fl_Button(110, 20, 80, 30, "Button 2");
group->end();

current()

Gets or sets the current group.

static Fl_Group *current();
static void current(Fl_Group *g);

Fl_Group*

Group to make current (for setter)

Returns: Pointer to current group (for getter)

Child Management

children()

Gets the number of children.

int children() const;

Returns: Number of child widgets

child()

Gets a child by index.

Fl_Widget *child(int n) const;

int

required

Child index (0 to children()-1)

Returns: Pointer to child widget or nullptr if index is out of range Example:

for (int i = 0; i < group->children(); i++) {
  Fl_Widget *w = group->child(i);
  printf("Child %d: %s\n", i, w->label());
}

array()

Gets array of all children.

Fl_Widget* const* array() const;

Returns: Pointer to internal array of child pointers

find()

Finds the index of a child widget.

int find(const Fl_Widget* widget) const;
int find(const Fl_Widget& widget) const;

Widget to find

Returns: Index of child, or children() if not found

Adding Children

add()

Adds a widget as a child.

void add(Fl_Widget& widget);
void add(Fl_Widget* widget);

Widget to add

Description: Adds the widget to the end of the child list. The widget is removed from its current parent if it has one. Example:

Fl_Button *btn = new Fl_Button(10, 10, 80, 30, "Click");
group->add(btn);

insert()

Inserts a widget at a specific position.

void insert(Fl_Widget& widget, int i);
void insert(Fl_Widget& widget, Fl_Widget* before);

Widget to insert

int

Index to insert at

before

Fl_Widget*

Insert before this widget

Description: Inserts the widget at the specified position or before the specified widget.

Removing Children

remove()

Removes a widget from the group.

void remove(int index);
void remove(Fl_Widget& widget);
void remove(Fl_Widget* widget);

index

int

Index of widget to remove

Widget to remove

Description: Removes the widget from the group but does not delete it. To delete a widget, use delete. Example:

group->remove(button);   // Remove from group
delete button;           // Delete the widget

clear()

Removes all children.

void clear();

Description: Removes all children from the group. The children are not deleted, only removed.

delete_child()

Deletes a child by index.

virtual int delete_child(int n);

int

required

Index of child to delete

Returns: 0 if successful Description: Removes and deletes the child widget at the specified index.

Resizing

resizable()

Gets or sets the resizable widget.

Fl_Widget* resizable() const;
void resizable(Fl_Widget* widget);
void resizable(Fl_Widget& widget);

Widget to use as resizable

Description: The resizable widget defines the resize behavior:

NULL: Fixed size group, all children maintain position/size
this: All children resize proportionally
child widget: Widgets inside the resizable bounds are scaled, widgets outside are moved

Important: The resizable must be NULL, the group itself, or a direct child of the group. Example:

// Make the group itself resizable
group->resizable(group);

// Use a specific child as the resize box
Fl_Box *box = new Fl_Box(20, 20, 100, 60);
group->resizable(box);

add_resizable()

Adds a widget and makes it resizable.

void add_resizable(Fl_Widget& widget);

Widget to add and make resizable

Description: Convenience method that adds the widget and sets it as the resizable.

init_sizes()

Initializes internal resize data.

void init_sizes();

Description: Records the current sizes and positions of all children for use by the resizing code. Called automatically by resize().

Drawing

clip_children()

Gets or sets child clipping.

unsigned int clip_children();
void clip_children(int c);

int

required

1 to enable clipping, 0 to disable

Returns: True if clipping is enabled (for getter) Description: When enabled, child widgets are clipped to the group’s bounding box. Default is disabled. Example:

group->clip_children(1);  // Enable clipping

Protected Drawing Methods

draw_child()

Draws a single child widget.

void draw_child(Fl_Widget& widget) const;

Child widget to draw

Description: For use in custom draw() methods to draw specific children.

draw_children()

Draws all child widgets.

void draw_children();

Description: Called by the default draw() method to draw all children.

draw_outside_label()

Draws a child’s outside label.

void draw_outside_label(const Fl_Widget& widget) const;

Child widget whose label to draw

update_child()

Updates (redraws) a specific child.

void update_child(Fl_Widget& widget) const;

Child widget to update

Type Checking

as_group()

Returns this as an Fl_Group pointer.

Fl_Group* as_group() override;

Returns: Pointer to this group

Example: Radio Button Group

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Group.H>
#include <FL/Fl_Radio_Button.H>

int main() {
  Fl_Window *window = new Fl_Window(300, 200);
  
  // Create a group for radio buttons
  Fl_Group *radio_group = new Fl_Group(10, 10, 280, 100);
  radio_group->begin();
    new Fl_Radio_Button(20, 20, 100, 25, "Option 1");
    new Fl_Radio_Button(20, 50, 100, 25, "Option 2");
    new Fl_Radio_Button(20, 80, 100, 25, "Option 3");
  radio_group->end();
  
  window->end();
  window->show();
  return Fl::run();
}

Example: Resizable Group

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Group.H>
#include <FL/Fl_Button.H>
#include <FL/Fl_Box.H>

int main() {
  Fl_Window *win = new Fl_Window(400, 300);
  
  Fl_Group *group = new Fl_Group(10, 10, 380, 280);
  group->box(FL_DOWN_BOX);
  group->begin();
  
    // Fixed position buttons
    new Fl_Button(20, 20, 80, 30, "Top Left");
    new Fl_Button(290, 20, 80, 30, "Top Right");
    
    // Resizable area in the middle
    Fl_Box *resizable_box = new Fl_Box(110, 60, 180, 180);
    resizable_box->box(FL_FLAT_BOX);
    
    new Fl_Button(20, 250, 80, 30, "Bottom Left");
    new Fl_Button(290, 250, 80, 30, "Bottom Right");
  
  group->end();
  group->resizable(resizable_box);
  
  win->end();
  win->resizable(group);
  win->show();
  
  return Fl::run();
}

Fl_Widget - Base widget class
Fl_Window - Window class (derived from Fl_Group)
Fl (Global Namespace) - Global functions

Core Classes

Basic Widgets

Menu Widgets

Container Widgets

Complex Widgets

Drawing & Graphics

Constructor

Group Management

begin()

end()

current()

Child Management

children()

child()

array()

find()

Adding Children

add()

insert()

Removing Children

remove()

clear()

delete_child()

Resizing

resizable()

add_resizable()

init_sizes()

Drawing

clip_children()

Protected Drawing Methods

draw_child()

draw_children()

draw_outside_label()

update_child()

Type Checking

as_group()

Example: Radio Button Group

Example: Resizable Group

Core Classes

Basic Widgets

Menu Widgets

Container Widgets

Complex Widgets

Drawing & Graphics

Documentation Index

​Constructor

​Group Management

​begin()

​end()

​current()

​Child Management

​children()

​child()

​array()

​find()

​Adding Children

​add()

​insert()

​Removing Children

​remove()

​clear()

​delete_child()

​Resizing

​resizable()

​add_resizable()

​init_sizes()

​Drawing

​clip_children()

​Protected Drawing Methods

​draw_child()

​draw_children()

​draw_outside_label()

​update_child()

​Type Checking

​as_group()

​Example: Radio Button Group

​Example: Resizable Group

​Related

Constructor

Group Management

begin()

end()

current()

Child Management

children()

child()

array()

find()

Adding Children

add()

insert()

Removing Children

remove()

clear()

delete_child()

Resizing

resizable()

add_resizable()

init_sizes()

Drawing

clip_children()

Protected Drawing Methods

draw_child()

draw_children()

draw_outside_label()

update_child()

Type Checking

as_group()

Example: Radio Button Group

Example: Resizable Group

Related