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Fl_Box

The Fl_Box widget simply draws its box and optionally its label. It is useful as a visual frame around other widgets or as a placeholder in layouts.

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Header File

#include <FL/Fl_Box.H>

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Class Overview

Fl_Box is a simple widget that displays a box with an optional label. While invisible by default (with FL_NO_BOX), it can be made visible by setting an appropriate box type. It’s commonly used to:
  • Draw frames around groups of widgets
  • Display static text labels
  • Serve as placeholders in resizable layouts
  • Act as Fl_Group::resizable() values

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Inheritance

Fl_Widget
  └── Fl_Box
Inherits from: Fl_Widget

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Constructors

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Default Constructor

Fl_Box(int X, int Y, int W, int H, const char *L = 0)
Creates a new Fl_Box widget with the given coordinates, size, and label.
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X
int
The X coordinate of the widget relative to the enclosing window
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Y
int
The Y coordinate of the widget relative to the enclosing window
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W
int
Width of the widget in pixels
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H
int
Height of the widget in pixels
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L
const char*
default:"nullptr"
Optional text for the widget label
This constructor sets box() to FL_NO_BOX, making the widget invisible by default. Use box(Fl_Boxtype) to make it visible.

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Boxtype Constructor

Fl_Box(Fl_Boxtype B, int X, int Y, int W, int H, const char *L)
Creates a new Fl_Box widget with a specific box type.
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B
Fl_Boxtype
The box type to display (e.g., FL_UP_BOX, FL_DOWN_BOX, FL_BORDER_BOX)
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X
int
The X coordinate of the widget relative to the enclosing window
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Y
int
The Y coordinate of the widget relative to the enclosing window
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W
int
Width of the widget in pixels
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H
int
Height of the widget in pixels
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L
const char*
Text for the widget label (can be nullptr)

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Public Methods

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handle()

int handle(int event) override
Handles events for the widget. Returns 1 if the event was handled, 0 otherwise.
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event
int
The FLTK event type (e.g., FL_PUSH, FL_DRAG, FL_RELEASE)
Returns: int - 1 if handled, 0 otherwise

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Protected Methods

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draw()

void draw() override
Draws the box and its label. This method is called automatically by FLTK and should not be called directly.

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Inherited Methods

As a subclass of Fl_Widget, Fl_Box inherits all standard widget methods including:
  • box() / box(Fl_Boxtype) - Get or set the box type
  • label() / label(const char*) - Get or set the label text
  • color() / color(Fl_Color) - Get or set the background color
  • labelcolor() / labelcolor(Fl_Color) - Get or set the label color
  • labelfont() / labelfont(Fl_Font) - Get or set the label font
  • labelsize() / labelsize(Fl_Fontsize) - Get or set the label size
  • align() / align(Fl_Align) - Get or set label alignment

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Usage Example

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

int main(int argc, char **argv) {
  Fl_Window *window = new Fl_Window(340, 180);
  
  // Create a visible box with a border as a frame
  Fl_Box *frame = new Fl_Box(FL_UP_BOX, 10, 10, 320, 160, "Information Panel");
  frame->labelsize(16);
  frame->labelfont(FL_BOLD);
  frame->align(FL_ALIGN_TOP | FL_ALIGN_INSIDE);
  
  // Create an invisible box as a label holder
  Fl_Box *label = new Fl_Box(20, 50, 300, 30, "This is a static text display");
  label->align(FL_ALIGN_LEFT | FL_ALIGN_INSIDE);
  
  // Create a box with custom styling
  Fl_Box *colorbox = new Fl_Box(FL_FLAT_BOX, 20, 90, 100, 40, "Status: OK");
  colorbox->color(FL_GREEN);
  colorbox->labelcolor(FL_WHITE);
  
  window->end();
  window->show(argc, argv);
  return Fl::run();
}

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Common Box Types

  • FL_NO_BOX - No box (invisible, default for default constructor)
  • FL_FLAT_BOX - Flat box with color fill
  • FL_UP_BOX - Raised box
  • FL_DOWN_BOX - Sunken box
  • FL_BORDER_BOX - Box with border outline
  • FL_SHADOW_BOX - Box with drop shadow
  • FL_ROUNDED_BOX - Box with rounded corners
  • FL_ENGRAVED_BOX - Engraved border effect

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See Also