# B - Function Reference

This appendix describes all of the `fl_` functions and `Fl::` methods. For a description of the FLTK widgets, see Appendix A.

## Functions

### int fl_color_chooser(const char *title, double &r, double &g, double &b)
int fl_color_chooser(const char *title, uchar &r, uchar &g, uchar &b)

The double version takes RGB values in the range 0.0 to 1.0. The uchar version takes RGB values in the range 0 to 255. The `title` argument specifies the label (title) for the window.

`fl_color_chooser()` pops up a window to let the user pick an arbitrary RGB color. They can pick the hue and saturation in the "hue box" on the left (hold down CTRL to just change the saturation), and the brighness using the vertical slider. Or they can type the 8-bit numbers into the RGB `Fl_Value_Input` fields, or drag the mouse across them to adjust them. The pull-down menu lets the user set the input fields to show RGB, HSV, or 8-bit RGB (0 to 255).

This returns non-zero if the user picks ok, and updates the RGB values. If the user picks cancel or closes the window this returns zero and leaves RGB unchanged.

If you use the color chooser on an 8-bit screen, it will allocate all the available colors, leaving you no space to exactly represent the color the user picks! You can however use `fl_rectf()` to fill a region with a simulated color using dithering.

### int fl_show_colormap(int oldcol)

`fl_show_colormap()` pops up a panel of the 256 colors you can access with `fl_color()` and lets the user pick one of them. It returns the new color index, or the old one if the user types ESC or clicks outside the window.

### void fl_message(const char *, ...)

Displays a printf-style message in a pop-up box with an "OK" button, waits for the user to hit the button. The message will wrap to fit the window, or may be many lines by putting `\n` characters into it. The enter key is a shortcut for the OK button.

### void fl_alert(const char *, ...)

Same as `fl_message()` except for the "!" symbol.

### int fl_ask(const char *, ...)

Displays a printf-style message in a pop-up box with an "Yes" and "No" button and waits for the user to hit a button. The return value is 1 if the user hits Yes, 0 if they pick No. The enter key is a shortcut for Yes and ESC is a shortcut for No.

### int fl_choice(const char *q, const char *b0, const char *b1, const char *b2, ...)

Shows the message with three buttons below it marked with the strings `b0`, `b1`, and `b2`. Returns 0, 1, or 2 depending on which button is hit. ESC is a shortcut for button 0 and the enter key is a shortcut for button 1. Notice the buttons are positioned "backwards" You can hide buttons by passing `NULL` as their labels.

### const char *fl_input(const char *label, const char *deflt = 0, ...)

Pops up a window displaying a string, lets the user edit it, and return the new value. The cancel button returns `NULL`. The returned pointer is only valid until the next time `fl_input()` is called. Due to back-compatability, the arguments to any printf commands in the label are after the default value.

### const char *fl_password(const char *label, const char *deflt = 0, ...)

Same as `fl_input()` except an `Fl_Secret_Input` field is used.

### void fl_message_font(Fl_Font fontid, uchar size)

Change the font and font size used for the messages in all the popups.

### Fl_Widget *fl_message_icon()

Returns a pointer to the box at the left edge of all the popups. You can alter the font, color, or label (including making it a Pixmap), before calling the functions.

### char *fl_file_chooser(const char * message, const char *pattern, const char *fname)

FLTK provides a "tab completion" file chooser that makes it easy to choose files from large directories. This file chooser has several unique features, the major one being that the Tab key completes filenames like it does in Emacs or tcsh, and the list always shows all possible completions.

`fl_file_chooser()` pops up the file chooser, waits for the user to pick a file or Cancel, and then returns a pointer to that filename or `NULL` if Cancel is chosen.

`message` is a string used to title the window.

`pattern` is used to limit the files listed in a directory to those matching the pattern. This matching is done by `filename_match()`. Use `NULL` to show all files.

`fname` is a default filename to fill in the chooser with. If this is `NULL` then the last filename that was choosen is used (unless that had a different pattern, in which case just the last directory with no name is used). The first time the file chooser is called this defaults to a blank string.

The returned value points at a static buffer that is only good until the next time `fl_file_chooser()` is called.

### void fl_file_chooser_callback(void (*cb)(const char *))

Set a function that is called every time the user clicks a file in the currently popped-up file chooser. This could be used to preview the contents of the file. It has to be reasonably fast, and cannot create FLTK windows.

### int filename_list(const char *d, dirent ***list)

This is a portable and const-correct wrapper for the `fl_scandir` function. `d` is the name of a directory (it does not matter if it has a trailing slash or not). For each file in that directory a "dirent" structure is created. The only portable thing about a dirent is that dirent.d_name is the nul-terminated file name. An array of pointers to these dirents is created and a pointer to the array is returned in `*list`. The number of entries is given as a return value. If there is an error reading the directory a number less than zero is returned, and `errno` has the reason (`errno` does not work under WIN32). The files are sorted in "alphanumeric" order, where an attempt is made to put unpadded numbers in consecutive order.

You can free the returned list of files with the following code:

    for (int i = return_value; i > 0;) free((void*)(list[--i]));
    free((void*)list);

### int filename_isdir(const char *f)

Returns non-zero if the file exists and is a directory.

### const char *filename_name(const char *f)

Returns a pointer to the character after the last slash, or to the start of the filename if there is none.

### const char *filename_ext(const char *f)

Returns a pointer to the last period in `filename_name(f)`, or a pointer to the trailing nul if none.

### char *filename_setext(char *f, const char *ext)

Does `strcpy(filename_ext(f), ext ? ext : "")`. Returns a pointer to `f`.

### int filename_expand(char *out, const char *in)

Splits `in` at each slash character. Replaces any occurrance of `$X` with `getenv("X")` (leaving it as `$X` if the environment variable does not exist). Replaces any occurances of `~X` with user `X`'s home directory (leaving it as `~X` if the user does not exist). Any resulting double slashes cause everything before the second slash to be deleted. Copies the result to `out` (`in` and `out` may be the same buffer). Returns non-zero if any changes were made. In true retro programming style, it is up to you to provide a buffer big enough for the result. 1024 characters should be enough.

### int filename_absolute(char *out, const char *in)

If `in` does not start with a slash, this prepends the current working directory to `in` and then deletes any occurances of `.` and x/.. from the result, which it copies to `out` (`in` and `out` may be the same buffer). Returns non-zero if any changes were made. In true retro programming style, it is up to you to provide a buffer big enough for the result. 1024 characters should be enough.

### int filename_match(const char *f, const char *pattern)

Returns true if `f` matches `pattern`. The following syntax is used by `pattern`:

- `*` matches any sequence of 0 or more characters.
- `?` matches any single character.
- `[set]` matches any character in the set. Set can contain any single characters, or a-z to represent a range. To match ] or - they must be the first characters. To match ^ or ! they must not be the first characters.
- `[^set] or [!set]` matches any character not in the set.
- `{X|Y|Z} or {X,Y,Z}` matches any one of the subexpressions literally.
- `\x` quotes the character x so it has no special meaning.
- `x` all other characters must be matched exactly.

## 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 `Fl::wait()` will call the callback and then return. The callback is passed the `fd` and the arbitrary `void*` argument.

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:

- `FL_SHORTCUT` events that are not recognized by any widget. This lets you provide global shortcut keys.
- System events that FLTK does not recognize. See `fl_xevent`.
- Some other events when the widget FLTK selected returns zero from its `handle()` method. Exactly which ones may change in future versions, however.

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

Adds a callback function that is called every time by `Fl::wait()` and also makes it act as though the timeout is zero (this makes `Fl::wait()` return immediately, so if it is in a loop it is called repeatedly, and thus the idle fucntion is called repeatedly). The idle function can be used to get background processing done.

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, including `Fl::wait()`, `Fl::check()`, and `Fl::ready()`. Fltk will not recursively call the idle callback.

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

Add a one-shot timeout callback. The function will be called by `Fl::wait()` at t seconds after this function is called. The optional `void*` argument is passed to the callback.

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

Inside a timeout callback you can call this to add another timeout. Rather than the time being measured from "now", it is measured from when the system call elapsed that caused this timeout to be called. This will result in far more accurate spacing of the timeout callbacks, it also has slightly less system call overhead. (It will also use all your machine time if your timeout code and fltk's overhead take more than t seconds, as the real timeout will be reduced to zero).

It is undefined what this does if called from outside a timeout callback.

This code will print "TICK" each second on stdout, with a fair degree of accuracy:

    void callback(void*) {
      printf("TICK\n");
      Fl::repeat_timeout(1.0,callback);
    }

    main() {
      Fl::add_timeout(1.0,callback);
      for (;;) Fl::wait();
    }

### 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 first word that does not start with '-'.
- The word '-' (used by many programs to name stdin as a file)
- The first unrecognized switch (return value is 0).
- `argc`

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:

- `-display host:n.n` The X display to use (ignored under WIN32).
- `-geometry WxH+X+Y` The window position and size will be modified according the the standard X geometry string.
- `-name string` Fl_Window::xclass(string) will be done to the window, possibly changing its icon.
- `-title string` Fl_Window::label(string) will be done to the window, changing both its title and the icontitle.
- `-iconic` Fl_Window::iconize() will be done to the window.
- `-bg color` XParseColor is used to lookup the passed color and then Fl::background() is done. Under WIN32 only color names of the form "#xxxxxx" are understood.
- `-bg2 color` XParseColor is used to lookup the passed color and then Fl::background2() is done.
- `-fg color` XParseColor is used to lookup the passed color and then Fl::foreground() is done.

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()

Same as `Fl::wait(0)`. Calling this during a big calculation will keep the screen up to date and the interface responsive:

    while (!calculation_done()) {
     calculate();
     Fl::check();
     if (user_hit_abort_button()) break;
    }

The returns non-zero if any windows are displayed, and 0 if no windows are displayed (this is likely to change in future versions of fltk).

### 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. It returns zero if the last event was not a key press or release.

`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:

- All keys on the main keyboard producing a printable ASCII character use the value of that ASCII character (as though shift, ctrl, and caps lock were not on). The space bar is 32.
- All keys on the numeric keypad producing a printable ASCII character use the value of that ASCII character plus `FL_KP`. The highest possible value is `FL_KP_Last` so you can range-check to see if something is on the keypad.
- All numbered function keys use the number on the function key plus `FL_F`. The highest possible number is `FL_F_Last`, so you can range-check a value.
- Buttons on the mouse are considered keys, and use the button number (where the left button is 1) plus `FL_Button`.
- All other keys on the keypad have a symbol: `FL_Escape, FL_BackSpace, FL_Tab, FL_Enter, FL_Print, FL_Scroll_Lock, FL_Pause, FL_Insert, FL_Home, FL_Page_Up, FL_Delete, FL_End, FL_Page_Down, FL_Left, FL_Up, FL_Right, FL_Down, FL_Shift_L, FL_Shift_R, FL_Control_L, FL_Control_R, FL_Caps_Lock, FL_Alt_L, FL_Alt_R, FL_Meta_L, FL_Meta_R, FL_Menu, FL_Num_Lock, FL_KP_Enter`. Be careful not to confuse these with the very similar, but all-caps, symbols used by `Fl::event_state()` .

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:

- `FL_SHIFT`
- `FL_CAPS_LOCK`
- `FL_CTRL`
- `FL_ALT`
- `FL_NUM_LOCK`
- `FL_META`
- `FL_SCROLL_LOCK`
- `FL_BUTTON1`
- `FL_BUTTON2`
- `FL_BUTTON3`

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 list of shown() windows. If a modal() window is shown this is the top-most modal window, otherwise it is the most recent window to get an event.

### static Fl_Window *Fl::next_window(Fl_Window *)

Returns the next top-level window in the list of shown() windows. You can use this call to iterate through all the windows that are shown().

### static void Fl::first_window(Fl_Window*)

Sets the window that is returned by first_window. The window is removed from wherever it is in the list and inserted at the top. This is not done if Fl::modal() is on or if the window is not shown(). Because the first window is used to set the "parent" of modal windows, this is often useful.

### 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.

On X this reads some common values from the Xdefaults database. KDE users can set these values by running the "krdb" program, and newer versions of KDE set this automatically if you check the "apply style to other X programs" switch in their control panel.

### 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 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()

This is similar to `Fl::check()` except this does not call `Fl::flush()` or any callbacks, which is useful if your program is in a state where such callbacks are illegal. This returns true if `Fl::check()` would do anything (it will continue to return true until you call `Fl::check()` or `Fl::wait()`).

    while (!calculation_done()) {
     calculate();
     if (Fl::ready()) {
       do_expensive_cleanup();
       Fl::check();
       if (user_hit_abort_button()) break;
     }
    }

### static void Fl::redraw()

Redraws all widgets.

### static int Fl::has_idle(void (*cb)(void*), void* = 0)

Returns true if the specified idle callback is currently installed.

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

Removes the specified idle callback, if it is installed.

### static int Fl::has_timeout(void (*cb)(void*), void* = 0)

Returns true if the timeout exists and has not been called yet.

### 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()

As long as any windows are displayed this calls `Fl::wait()` repeatedly. When all the windows are closed it returns zero (supposedly it would return non-zero on any errors, but fltk calls exit directly for these). A normal program will end `main()` with `return Fl::run();`.

### 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 is only allowed before you call show() on any windows. 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:

- `Fl::visual(FL_RGB)`
  Full/true color (if there are several depths FLTK chooses the largest). Do this if you use `fl_draw_image` for much better (non-dithered) output.
- `Fl::visual(FL_RGB8)`
  Full color with at least 24 bits of color. `FL_RGB` will always pick this if available, but if not it will happily return a less-than-24 bit deep visual. This call fails if 24 bits are not available.
- `Fl::visual(FL_DOUBLE|FL_INDEX)`
  Hardware double buffering. Call this if you are going to use `Fl_Double_Window`.
- `Fl::visual(FL_DOUBLE|FL_RGB)`
- `Fl::visual(FL_DOUBLE|FL_RGB8)`
  Hardware double buffering and full color.

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 Fl::wait()

Waits until "something happens" and then returns. Call this repeatedly to "run" your program. You can also check what happened each time after this returns, which is quite useful for managing program state.

What this really does is call all idle callbacks, all elapsed timeouts, call `Fl::flush()` to get the screen to update, and then wait some time (zero if there are idle callbacks, the shortest of all pending timeouts, or infinity), for any events from the user or any `Fl::add_fd()` callbacks. It then handles the events and calls the callbacks and then returns.

The return value is non-zero if there are any visible windows (this may change in future versions of fltk).

### static double Fl::wait(double time)

Same as `Fl::wait()` except it waits a maximum of time seconds. It can return much sooner if something happens.

The return value is positive if an event or fd happens before the time elapsed. It is zero if nothing happens (on Win32 this will only return zero if time is zero). It is negative if an error occurs (this will happen on Unix if a signal happens).

### 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.