Fl (Global Namespace)

The Fl namespace is the FLTK global namespace containing state information and global methods for the current application. It provides the event loop, display management, timing functions, and other system-level functionality.

Event Loop Methods

These methods control the main event loop and application execution.

run()

Runs the main event loop.

int Fl::run();

Returns: 0 if all windows are closed, non-zero otherwise Description: Waits for and processes events until all windows are closed. This is the normal way to start event processing. Example:

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

int main() {
  Fl_Window *window = new Fl_Window(300, 200);
  window->show();
  return Fl::run();
}

wait()

Waits for an event and processes it.

int Fl::wait();
double Fl::wait(double time);

time

double

Maximum time to wait in seconds (optional)

Returns:

For wait(): non-zero if any windows are displayed
For wait(double): the time remaining (negative if time expired)

Description: Waits for events and processes them. Use this for more fine-grained control over event processing compared to run().

check()

Checks for events without waiting.

int Fl::check();

Returns: Same as wait() but returns immediately Description: Processes all pending events and returns immediately. This is useful for updating the display while performing a long operation. Example:

for (int i = 0; i < 1000; i++) {
  // Do some work
  Fl::check();  // Keep GUI responsive
}

ready()

Checks if there are pending events.

int Fl::ready();

Returns: True if there are events to be processed

Timeout and Idle Callbacks

Methods for scheduling deferred and repeated callbacks.

add_timeout()

Adds a one-shot timer callback.

void Fl::add_timeout(double t, Fl_Timeout_Handler cb, void *data = 0);

double

required

Time in seconds before callback is called

Fl_Timeout_Handler

required

Function to call when timeout expires

data

void*

User data passed to callback (optional)

Example:

void timeout_callback(void* data) {
  printf("Timeout fired!\n");
  Fl::redraw();
}

Fl::add_timeout(1.0, timeout_callback);

repeat_timeout()

Reschedules a timeout for repeated callbacks.

void Fl::repeat_timeout(double t, Fl_Timeout_Handler cb, void *data = 0);

double

required

Time in seconds before callback is called again

Fl_Timeout_Handler

required

Function to call when timeout expires

data

void*

User data passed to callback

Description: Call this from inside a timeout callback to reschedule it.

remove_timeout()

Removes a timeout callback.

void Fl::remove_timeout(Fl_Timeout_Handler cb, void *data = 0);

Fl_Timeout_Handler

required

Callback function to remove

data

void*

User data associated with the callback

add_idle()

Adds an idle callback.

void Fl::add_idle(Fl_Idle_Handler cb, void* data = 0);

Fl_Idle_Handler

required

Function to call when idle

data

void*

User data passed to callback

Description: Idle callbacks are called when there are no pending events. They run continuously when the application is idle.

remove_idle()

Removes an idle callback.

void Fl::remove_idle(Fl_Idle_Handler cb, void* data = 0);

Screen and Display Methods

screen_count()

Returns the number of screens.

int Fl::screen_count();

Returns: Number of available screens

screen_xywh()

Gets screen dimensions.

void Fl::screen_xywh(int &X, int &Y, int &W, int &H);
void Fl::screen_xywh(int &X, int &Y, int &W, int &H, int n);
void Fl::screen_xywh(int &X, int &Y, int &W, int &H, int mx, int my);

X, Y, W, H

int&

required

Output parameters for screen position and size

int

Screen number (optional)

mx, my

int

Mouse position to determine which screen (optional)

screen_scale()

Gets or sets screen scaling factor.

float Fl::screen_scale(int n);
void Fl::screen_scale(int n, float factor);

int

required

Screen number

factor

float

Scaling factor to set (for setter)

Description: Screen scaling supports high-DPI displays. The scaling factor is initialized from the OS and can be adjusted programmatically.

redraw()

Schedules all windows for redrawing.

void Fl::redraw();

Description: Marks all windows as needing to be redrawn on the next wait() or flush().

flush()

Forces all pending drawing to be completed.

void Fl::flush();

Description: Causes all windows to be redrawn if they need it, and empties the display queue.

Color Methods

set_color()

Sets an entry in the color map.

void Fl::set_color(Fl_Color i, uchar r, uchar g, uchar b);
void Fl::set_color(Fl_Color i, unsigned c);

Fl_Color

required

Color index to set

r, g, b

uchar

required

RGB color components (0-255)

unsigned

RGB color as 32-bit value

get_color()

Gets a color from the color map.

unsigned Fl::get_color(Fl_Color i);
void Fl::get_color(Fl_Color i, uchar &red, uchar &green, uchar &blue);

Fl_Color

required

Color index to get

red, green, blue

uchar&

Output parameters for RGB components

Scheme Methods

scheme()

Gets or sets the current widget scheme.

const char* Fl::scheme();
int Fl::scheme(const char *name);

name

const char*

Scheme name: “none”, “base”, “gtk+”, “gleam”, “plastic”, or “oxy”

Returns:

Getter: Current scheme name or NULL for default
Setter: 1 if successful, 0 if scheme not found

Example:

Fl::scheme("gtk+");  // Use GTK+ style

is_scheme()

Checks if a specific scheme is active.

int Fl::is_scheme(const char *name);

name

const char*

required

Lowercase scheme name to check

Returns: 1 if the scheme is active, 0 otherwise

Font Methods

set_fonts()

Enumerates available system fonts.

Fl_Font Fl::set_fonts(const char* xfontname = 0);

xfontname

const char*

X11 font pattern (platform-specific)

Returns: Number of fonts in the table

get_font()

Gets the name of a font.

const char* Fl::get_font(Fl_Font font);

font

Fl_Font

required

Font index

Returns: Font name

set_font()

Changes a font in the table.

void Fl::set_font(Fl_Font font, const char* name);
void Fl::set_font(Fl_Font font, Fl_Font from);

font

Fl_Font

required

Font index to change

name

const char*

New font name

from

Fl_Font

Copy font from this index

Window Management

first_window()

Gets the first top-level window.

Fl_Window* Fl::first_window();

Returns: Pointer to first window or NULL

next_window()

Gets the next window in the window list.

Fl_Window* Fl::next_window(const Fl_Window* window);

window

const Fl_Window*

required

Current window

Returns: Pointer to next window or NULL Gets the current modal window.

Fl_Window* Fl::modal();

Returns: The topmost modal window or NULL

grab()

Gets or sets the window grabbing all events.

Fl_Window* Fl::grab();
void Fl::grab(Fl_Window* window);

window

Fl_Window*

Window to grab events, or NULL to release

Description: When grab is active, all events go to the grabbed window regardless of pointer or focus location.

Clipboard Methods

copy()

Copies data to clipboard or selection.

void Fl::copy(const char *stuff, int len, int destination = 0,
              const char *type = Fl::clipboard_plain_text);

stuff

const char*

required

Text data to copy

len

int

required

Length of data in bytes

destination

int

0 = selection buffer, 1 = clipboard, 2 = both

type

const char*

Data type (usually clipboard_plain_text)

paste()

Pastes data from clipboard or selection.

void Fl::paste(Fl_Widget &receiver, int source,
               const char *type = Fl::clipboard_plain_text);

receiver

Fl_Widget&

required

Widget that will receive FL_PASTE event

source

int

required

0 = selection buffer, 1 = clipboard

type

const char*

Requested data type

Version Information

api_version()

Returns the API version number.

int Fl::api_version();

Returns: API version as integer (e.g., 10400 for 1.4.0)

abi_version()

Returns the ABI version number.

int Fl::abi_version();

Returns: ABI version of the linked library

abi_check()

Checks if ABI version is compatible.

int Fl::abi_check(const int val = FL_ABI_VERSION);

val

int

ABI version to check against

Returns: 1 if compatible, 0 otherwise

Fl_Widget - Base widget class
Fl_Window - Window class
Enumerations - Event types and constants

Core Classes

Basic Widgets

Menu Widgets

Container Widgets

Complex Widgets

Drawing & Graphics

Documentation Index

​Event Loop Methods

​run()

​wait()

​check()

​ready()

​Timeout and Idle Callbacks

​add_timeout()

​repeat_timeout()

​remove_timeout()

​add_idle()

​remove_idle()

​Screen and Display Methods

​screen_count()

​screen_xywh()

​screen_scale()

​redraw()

​flush()

​Color Methods

​set_color()

​get_color()

​Scheme Methods

​scheme()

​is_scheme()

​Font Methods

​set_fonts()

​get_font()

​set_font()

​Window Management

​first_window()

​next_window()

​modal()

​grab()

​Clipboard Methods

​copy()

​paste()

​Version Information

​api_version()

​abi_version()

​abi_check()

​Related

Event Loop Methods

run()

wait()

check()

ready()

Timeout and Idle Callbacks

add_timeout()

repeat_timeout()

remove_timeout()

add_idle()

remove_idle()

Screen and Display Methods

screen_count()

screen_xywh()

screen_scale()

redraw()

flush()

Color Methods

set_color()

get_color()

Scheme Methods

scheme()

is_scheme()

Font Methods

set_fonts()

get_font()

set_font()

Window Management

first_window()

next_window()

modal()

grab()

Clipboard Methods

copy()

paste()

Version Information

api_version()

abi_version()

abi_check()

Related