FL:: Methods

static void Fl::add_fd(int fd, void (*cb)(int, void *), void * = 0)
static void Fl::add_fd(int fd, int when, void (*cb)(int, void *), void * = 0)
static void Fl::remove_fd(int)

Add file descriptor fd to listen to. When the fd becomes ready for reading the callback is done. The callback is passed the fd and the arbitrary void * argument. Fl::wait() will return immediately after calling the callback.

The second version takes a when bitfield, with the bits FL_READ, FL_WRITE, and FL_EXCEPT defined, to indicate when the callback should be done.

There can only be one callback of each type for a file descriptor. Fl::remove_fd() gets rid of all the callbacks for a given file descriptor.

Under UNIX any file descriptor can be monitored (files, devices, pipes, sockets, etc.) Due to limitations in Microsoft Windows, WIN32 applications can only monitor sockets.

static void Fl::add_handler(int (*f)(int))

Install a function to parse unrecognized events. If FLTK cannot figure out what to do with an event, it calls each of these functions (most recent first) until one of them returns non-zero. If none of them returns non zero then the event is ignored. Events that cause this to be called are:

static Fl::add_idle(void (*cb)(void *), void *)

Adds a callback function that is called by Fl::wait() when there is nothing to do. This can be used for background processing.

Warning: this can absorb all your machine's time!

You can have multiple idle callbacks. To remove an idle callback use Fl::remove_idle().

Fl::wait() and Fl::check() call idle callbacks, but Fl::ready() does not.

The idle callback can call any FLTK functions. However if you call something that calls Fl::wait() or Fl::check() (such as a message pop-up) you should first remove the idle callback so that it does not recurse.

static void Fl::add_timeout(float t, void (*cb)(void *),void *v=0)

Add a one-shot timeout callback. The timeout will happen as soon as possible after t seconds after the last time wait() was called. The optional void * argument is passed to the callback.

This code will print "TICK" each second on stdout, no matter what else the user or program does:

void callback(void *) {

main() {
static int Fl::arg(int argc, char **argv, int &i)

Consume a single switch from argv, starting at word i. Returns the number of words eaten (1 or 2, or 0 if it is not recognized) and adds the same value to i. You can use this function if you prefer to control the incrementing through the arguments yourself.

static int Fl::args(int argc, char **argv, int &i, int (*callback)(int, char**,int &)=0)
void Fl::args(int argc, char **argv)

FLTK provides an entirely optional command-line switch parser. You don't have to call it if you don't like them! Everything it can do can be done with other calls to FLTK.

To use the switch parser, call Fl::args(...) near the start of your program. This does not open the display, instead switches that need the display open are stashed into static variables. Then you must display your first window by calling window->show(argc,argv), which will do anything stored in the static variables.

callback lets you define your own switches. It is called with the same argc and argv, and with i the index of each word. The callback should return zero if the switch is unrecognized, and not change i. It should return non-zero if the switch is recognized, and add at least 1 to i (it can add more to consume words after the switch). This function is called before any other tests, so you can override any FLTK switch (this is why fltk can use very short switches instead of the long ones all other toolkits force you to use).

On return i is set to the index of the first non-switch. This is either:

The return value is i unless an unrecognized switch is found, in which case it is zero. If your program takes no arguments other than switches you should produce an error if the return value is less than argc.

All switches except -bg2 may be abbreviated one letter and case is ignored:

The second form of Fl::args() is useful if your program does not have command line switches of its own. It parses all the switches, and if any are not recognized it calls Fl::abort(Fl::help).

static void Fl::background(uchar, uchar, uchar)

Changes fl_color(FL_GRAY) to the given color, and changes the gray ramp from 32 to 56 to black to white. These are the colors used as backgrounds by almost all widgets and used to draw the edges of all the boxtypes.

static void Fl::background2(uchar, uchar, uchar)

Changes fl_color(FL_WHITE) and the same colors as Fl::foreground(). This color is used as a background by Fl_Input and other text widgets.

static Fl_Widget *Fl::belowmouse() const
static void Fl::belowmouse(Fl_Widget *)

Get or set the widget that is below the mouse. This is for highlighting buttons. It is not used to send FL_PUSH or FL_MOVE directly, for several obscure reasons, but those events typically go to this widget. This is also the first widget tried for FL_SHORTCUT events.

If you change the belowmouse widget, the previous one and all parents (that don't contain the new widget) are sent FL_LEAVE events. Changing this does not send FL_ENTER to this or any widget, because sending FL_ENTER is supposed to test if the widget wants the mouse (by it returning non-zero from handle()).

static int Fl::box_dh(Fl_Boxtype)

Returns the height offset for the given boxtype.

static int Fl::box_dw(Fl_Boxtype)

Returns the width offset for the given boxtype.

static int Fl::box_dx(Fl_Boxtype)

Returns the X offset for the given boxtype.

static int Fl::box_dy(Fl_Boxtype)

Returns the Y offset for the given boxtype.

static int Fl::check()

This does the same thing as Fl::wait(0), except because it does not have to return the elapsed time value it can be implemented faster on certain systems. Use this to interrupt a big calculation:

while (!calculation_done()) {
  if (user_hit_abort_button()) break;

This returns non-zero if any windows are displayed, and 0 if no windows are displayed.

static int Fl::damage()

If true then flush() will do something.

static void Fl::display(const char *)

Sets the X display to use for all windows. Actually this just sets the environment variable $DISPLAY to the passed string, so this only works before you show() the first window or otherwise open the display, and does nothing useful under WIN32.

static void Fl::enable_symbols()

Enables the symbol drawing code.

static int Fl::event_button()

Returns which mouse button was pressed. This returns garbage if the most recent event was not a FL_PUSH or FL_RELEASE event.

int Fl::event_clicks()
void Fl::event_clicks(int)

The first form returns non-zero if the most recent FL_PUSH or FL_KEYBOARD was a "double click". Returns N-1 for N clicks. A double click is counted if the same button is pressed again while event_is_click() is true.

The second form directly sets the number returned by Fl::event_clicks(). This can be used to set it to zero so that later code does not think an item was double-clicked.

int Fl::event_inside(const Fl_Widget *) const
int Fl::event_inside(int x, int y, int w, int h)

Returns non-zero if the current event_x and event_y put it inside the widget or inside an arbitrary bounding box. You should always call this rather than doing your own comparison so you are consistent about edge effects.

int Fl::event_is_click()
void Fl::event_is_click(0)

The first form returns non-zero if the mouse has not moved far enough and not enough time has passed since the last FL_PUSH or FL_KEYBOARD event for it to be considered a "drag" rather than a "click". You can test this on FL_DRAG, FL_RELEASE, and FL_MOVE events. The second form clears the value returned by Fl::event_is_click(). Useful to prevent the next click from being counted as a double-click or to make a popup menu pick an item with a single click. Don't pass non-zero to this.

int Fl::event_key()
int Fl::event_key(int)
int Fl::get_key(int)

Fl::event_key() returns which key on the keyboard was last pushed.

Fl::event_key(int) returns true if the given key was held down (or pressed) during the last event. This is constant until the next event is read from the server.

Fl::get_key(int) returns true if the given key is held down now. Under X this requires a round-trip to the server and is much slower than Fl::event_key(int).

Keys are identified by the unshifted values. FLTK defines a set of symbols that should work on most modern machines for every key on the keyboard:

On X Fl::get_key(FL_Button+n) does not work.

On WIN32 Fl::get_key(FL_KP_Enter) and Fl::event_key(FL_KP_Enter) do not work.

char *Fl::event_length()

Returns the length of the text in Fl::event_text(). There will always be a nul at this position in the text. However there may be a nul before that if the keystroke translates to a nul character or you paste a nul character.

ulong Fl::event_state()
unsigned int Fl::event_state(ulong)

This is a bitfield of what shift states were on and what mouse buttons were held down during the most recent event. The second version returns non-zero if any of the passed bits are turned on. The legal bits are:

X servers do not agree on shift states, and FL_NUM_LOCK, FL_META, and FL_SCROLL_LOCK may not work. The values were selected to match the XFree86 server on Linux. In addition there is a bug in the way X works so that the shift state is not correctly reported until the first event after the shift key is pressed or released.

char *Fl::event_text()

Returns the ASCII text (in the future this may be UTF-8) produced by the last FL_KEYBOARD or FL_PASTEM or possibly other event. A zero-length string is returned for any keyboard function keys that do not produce text. This pointer points at a static buffer and is only valid until the next event is processed.

Under X this is the result of calling XLookupString().

static int Fl::event_x()
static int Fl::event_y()

Returns the mouse position of the event relative to the Fl_Window it was passed to.

static int Fl::event_x_root()
static int Fl::event_y_root()

Returns the mouse position on the screen of the event. To find the absolute position of an Fl_Window on the screen, use the difference between event_x_root(),event_y_root() and event_x(),event_y().

static Fl_Window *Fl::first_window()

Returns the first top-level window in the widget hierarchy.

static void Fl::flush()

Causes all the windows that need it to be redrawn and graphics forced out through the pipes. This is what wait() does before looking for events.

static Fl_Widget *Fl::focus() const
static void Fl::focus(Fl_Widget *)

Get or set the widget that will receive FL_KEYBOARD events.

If you change Fl::focus(), the previous widget and all parents (that don't contain the new widget) are sent FL_UNFOCUS events. Changing the focus does not send FL_FOCUS to this or any widget, because sending FL_FOCUS is supposed to test if the widget wants the focus (by it returning non-zero from handle()).

static void Fl::foreground(uchar, uchar, uchar)

Changes fl_color(FL_BLACK). Also changes FL_INACTIVE_COLOR and FL_SELECTION __COLOR to be a ramp between this and FL_WHITE.

static void Fl::free_color(Fl_Color, int overlay = 0)

Frees the specified color from the colormap, if applicable. If overlay is non-zero then the color is freed from the overlay colormap.

static unsigned Fl::get_color(Fl_Color)
static void Fl::get_color(Fl_Color, uchar &r, uchar &g, uchar &b)

Returns the color index or RGB value for the given FLTK color index.

static const char *Fl::get_font(int face)

Get the string for this face. This string is different for each face. Under X this value is passed to XListFonts to get all the sizes of this face.

static const char *Fl::get_font_name(int face, int *attributes = 0)

Get a human-readable string describing the family of this face. This is useful if you are presenting a choice to the user. There is no guarantee that each face has a different name. The return value points to a static buffer that is overwritten each call.

The integer pointed to by attributes (if the pointer is not zero) is set to zero, FL_BOLD or FL_ITALIC or FL_BOLD | FL_ITALIC. To locate a "family" of fonts, search forward and back for a set with non-zero attributes, these faces along with the face with a zero attribute before them constitute a family.

int get_font_sizes(int face, int *&sizep)

Return an array of sizes in sizep. The return value is the length of this array. The sizes are sorted from smallest to largest and indicate what sizes can be given to fl_font() that will be matched exactly (fl_font() will pick the closest size for other sizes). A zero in the first location of the array indicates a scalable font, where any size works, although the array may list sizes that work "better" than others. Warning: the returned array points at a static buffer that is overwritten each call. Under X this will open the display.

static void Fl::get_mouse(int &x, int &y)

Return where the mouse is on the screen by doing a round-trip query to the server. You should use Fl::event_x_root() and Fl::event_y_root() if possible, but this is necessary if you are not sure if a mouse event has been processed recently (such as to position your first window). If the display is not open, this will open it.

static void Fl::get_system_colors()

Read the user preference colors from the system and use them to call Fl::foreground(), Fl::background(), and Fl::background2(). This is done by Fl_Window::show(argc,argv) before applying the -fg and -bg switches.

Currently this only does something on WIN32. In future versions for X it may read the window manager (KDE, Gnome, etc.) setup as well.

static int Fl::gl_visual(int)

This does the same thing as Fl::visual(int) but also requires OpenGL drawing to work. This must be done if you want to draw in normal windows with OpenGL with gl_start() and gl_end(). It may be useful to call this so your X windows use the same visual as an Fl_Gl_Window, which on some servers will reduce colormap flashing.

See Fl_Gl_Window for a list of additional values for the argument.

static void Fl::grab(Fl_Window*)
static Fl_Window* Fl::grab()

This is used when pop-up menu systems are active. Send all events to the passed window no matter where the pointer or focus is (including in other programs). The window does not have to be shown() , this lets the handle() method of a "dummy" window override all event handling and allows you to map and unmap a complex set of windows (under both X and WIN32 some window must be mapped because the system interface needs a window id).

If grab() is on it will also affect show() of windows by doing system-specific operations (on X it turns on override-redirect). These are designed to make menus popup reliably and faster on the system.

To turn off grabbing do Fl::grab(0).

Be careful that your program does not enter an infinite loop while grab() is on. On X this will lock up your screen!

static int Fl::h()

Returns the height of the screen in pixels.

static int Fl::handle(int, Fl_Window *)

Sends the event to a window for processing. Returns non-zero if any widget uses the event.

static const char *Fl::help

This is the usage string that is displayed if Fl::args() detects an invalid argument on the command-line.

static Fl_Window *Fl::modal()

Returns the top-most modal() window currently shown. This is the most recently shown() window with modal() true, or NULL if there are no modal() windows shown(). The modal() window has its handle() method called for all events, and no other windows will have handle() called (grab() overrides this).

static Fl_Window *Fl::next_window(Fl_Window *)

Returns the next top-level window in the widget hierarchy.

static void Fl::own_colormap()

Makes FLTK use its own colormap. This may make FLTK display better and will reduce conflicts with other programs that want lots of colors. However the colors may flash as you move the cursor between windows.

This does nothing if the current visual is not colormapped.

static void Fl::paste(Fl_Widget *receiver)

Set things up so the receiver widget will be called with an FL_PASTE event some time in the future. The reciever should be prepared to be called directly by this, or for it to happen later, or possibly not at all. This allows the window system to take as long as necessary to retrieve the paste buffer (or even to screw up completely) without complex and error-prone synchronization code in FLTK.

static Fl_Widget *Fl::pushed() const
static void Fl::pushed(Fl_Widget *)

Get or set the widget that is being pushed. FL_DRAG or FL_RELEASE (and any more FL_PUSH) events will be sent to this widget.

If you change the pushed widget, the previous one and all parents (that don't contain the new widget) are sent FL_RELEASE events. Changing this does not send FL_PUSH to this or any widget, because sending FL_PUSH is supposed to test if the widget wants the mouse (by it returning non-zero from handle()).

static Fl_Widget *Fl::readqueue()

All Fl_Widgets that don't have a callback defined use a default callback that puts a pointer to the widget in this queue, and this method reads the oldest widget out of this queue.

static int Fl::ready()

Returns non-zero if there are pending timeouts or events or file descriptors. This does not call Fl::flush() or any callbacks, which is useful if your program is in a state where such callbacks are illegal:

while (!calculation_done()) {
  if (Fl::ready()) {
    if (user_hit_abort_button()) break;
static void Fl::redraw()

Redraws all widgets.

static void Fl::remove_idle(void (*cb)(void *), void *= 0)

Removes the specified idle callback.

static void Fl::remove_timeout(void (*cb)(void *), void *= 0)

Removes a timeout callback. It is harmless to remove a timeout callback that no longer exists.

static Fl::run()

Runs FLTK until there are no windows displayed, and then returns a zero. Fl::run() is exactly equivalent to:

while (Fl::wait());
return 0;
static void Fl::selection(Fl_Widget *owner, const char *stuff, int len)
static const char* Fl::selection()
static int Fl::selection_length()

The first form changes the current selection. The block of text is copied to an internal buffer by FLTK (be careful if doing this in response to an FL_PASTE as this may be the same buffer returned by event_text()). The selection_owner() widget is set to the passed owner (possibly sending FL_SELECTIONCLEAR to the previous owner). The second form looks at the buffer containing the current selection. The contents of this buffer are undefined if this program does not own the current selection.

static Fl_Widget *Fl::selection_owner() const
static void Fl::selection_owner(Fl_Widget *)

The single-argument selection_owner(x) call can be used to move the selection to another widget or to set the owner to NULL , without changing the actual text of the selection. FL_SELECTIONCLEAR is sent to the previous selection owner, if any.

Copying the buffer every time the selection is changed is obviously wasteful, especially for large selections. An interface will probably be added in a future version to allow the selection to be made by a callback function. The current interface will be emulated on top of this.

static void Fl::set_boxtype(Fl_Boxtype, Fl_Box_Draw_F *, uchar, uchar, uchar, uchar)
static void Fl::set_boxtype(Fl_Boxtype, Fl_Boxtype from)

The first form sets the function to call to draw a specific boxtype.

The second form copies the from boxtype.

static void Fl::set_color(Fl_Color, uchar r, uchar g, uchar b)

Sets an entry in the fl_color index table. You can set it to any 8-bit RGB color. The color is not allocated until fl_color(i) is used.

static int Fl::set_font(int face, const char *)
static int Fl::set_font(int face, int from)

The first form changes a face. The string pointer is simply stored, the string is not copied, so the string must be in static memory.

The second form copies one face to another.

int Fl::set_fonts(const char * = 0)

FLTK will open the display, and add every font on the server to the face table. It will attempt to put "families" of faces together, so that the normal one is first, followed by bold, italic, and bold italic.

The optional argument is a string to describe the set of fonts to add. Passing NULL will select only fonts that have the ISO8859-1 character set (and are thus usable by normal text). Passing "-*" will select all fonts with any encoding as long as they have normal X font names with dashes in them. Passing "*" will list every font that exists (on X this may produce some strange output). Other values may be useful but are system dependent. With WIN32 NULL selects fonts with ISO8859-1 encoding and non-NULL selects all fonts.

The return value is how many faces are in the table after this is done.

static void Fl::set_labeltype(Fl_Labeltype, Fl_Label_Draw_F *, Fl_Label_Measure_F *)
static void Fl:set_labeltype(Fl_Labeltype, Fl_Labeltype from)

The first form sets the functions to call to draw and measure a specific labeltype.

The second form copies the from labeltype.

int Fl::test_shortcut(ulong) const

Test the current event, which must be an FL_KEYBOARD or FL_SHORTCUT, against a shortcut value (described in Fl_Button). Returns non-zero if there is a match. Not to be confused with Fl_Widget::test_shortcut().

static int Fl::visual(int)

Selects a visual so that your graphics are drawn correctly. This does nothing if the default visual satisfies the capabilities, or if no visual satisfies the capabilities, or on systems that don't have such brain-dead notions.

Only the following combinations do anything useful:

This returns true if the system has the capabilities by default or FLTK suceeded in turing them on. Your program will still work even if this returns false (it just won't look as good).

static int Fl::w()

Returns the width of the screen in pixels.

static int wait()
static double wait(double time)

Calls the idle function if any, then calls any pending timeout functions, then calls Fl::flush(). If there are any windows displayed it then waits some time for events (zero if there is an idle(), the shortest timeout if there are any timeouts, or forever) and calls the handle() function on those events, and then returns non-zero.

Your program can check its global state and update things after each call to Fl::wait(), which can be very useful in complex programs.

If there are no windows (this is checked after the idle and timeouts are called) then Fl::wait() returns zero without waiting for any events. Your program can either exit at this point, or call show() on some window so the GUI can continue to operate. The second form of Fl::wait() waits only a certain amount of time for anything to happen. This does the same as wait() except if the given time (in seconds) passes it returns. The return value is how much time remains. If the return value is zero or negative then the entire time period elapsed.

If you do several wait(time) calls in a row, the subsequent ones are measured from when the first one is called, even if you do time-consuming calculations after they return. This allows you to accurately make something happen at regular intervals. This code will accurately call A() once per second (as long as it takes less than a second to execute):

for (;;) {
  for (float time = 1.0; time > 0; ) time = Fl::wait(time);
static void (*Fl::warning)(const char *, ...)
static void (*Fl::error)(const char *, ...)
static void (*Fl::fatal)(const char *, ...)

FLTK will call these to print messages when unexpected conditions occur. By default they fprintf to stderr, and Fl::error and Fl::fatal call exit(1). You can override the behavior by setting the function pointers to your own routines.

Fl::warning means that there was a recoverable problem, the display may be messed up but the user can probably keep working (all X protocol errors call this). Fl::error means there is a recoverable error, but the display is so messed up it is unlikely the user can continue (very little calls this now). Fl::fatal must not return, as FLTK is in an unusable state, however your version may be able to use longjmp or an exception to continue, as long as it does not call FLTK again.