fltk/FL/Fl.H

//
// Main header file for the Fast Light Tool Kit (FLTK).
//
// Copyright 1998-2023 by Bill Spitzak and others.
//
// This library is free software. Distribution and use rights are outlined in
// the file "COPYING" which should have been included with this file.  If this
// file is missing or damaged, see the license at:
//
//     https://www.fltk.org/COPYING.php
//
// Please see the following page on how to report bugs and issues:
//
//     https://www.fltk.org/bugs.php
//

/** \file FL/Fl.H
  \brief Fl static class.
*/

#ifndef Fl_H
#  define Fl_H

#include <FL/fl_config.h> // build configuration
#include <FL/Fl_Export.H>
#include <FL/platform_types.h> // for FL_SOCKET
#include <FL/fl_casts.H>       // experimental

#ifdef FLTK_HAVE_CAIRO
# include <FL/Fl_Cairo.H>
#endif

#  include "fl_utf8.h"
#  include "Enumerations.H"
#  ifndef Fl_Object
#    define Fl_Object Fl_Widget /**< for back compatibility - use Fl_Widget! */
#  endif

#  ifdef check
#    undef check
#  endif

#  ifdef BSD
#    undef BSD
#  endif

#include <string.h> // FIXME: Fl::is_scheme(): strcmp needs string.h

class Fl_Widget;
class Fl_Window;
class Fl_Image;
struct Fl_Label;
class Fl_Screen_Driver;
class Fl_System_Driver;

// Pointers you can use to change FLTK to another language.
// Note: Similar pointers are defined in FL/fl_ask.H and src/fl_ask.cxx

extern FL_EXPORT const char* fl_local_alt;   ///< string pointer used in shortcuts, you can change it to another language
extern FL_EXPORT const char* fl_local_ctrl;  ///< string pointer used in shortcuts, you can change it to another language
extern FL_EXPORT const char* fl_local_meta;  ///< string pointer used in shortcuts, you can change it to another language
extern FL_EXPORT const char* fl_local_shift; ///< string pointer used in shortcuts, you can change it to another language

/** \defgroup  callback_functions  Callback Function Typedefs

  \brief Typedefs defined in <FL/Fl.H> for callback or handler functions passed as function parameters.

  FLTK uses callback functions as parameters for some function calls, e.g. to
  set up global event handlers (Fl::add_handler()), to add a timeout handler
  (Fl::add_timeout()), and many more.

  The typedefs defined in this group describe the function parameters used to set
  up or clear the callback functions and should also be referenced to define the
  callback function to handle such events in the user's code.

  \see  Fl::add_handler(), Fl::add_timeout(), Fl::repeat_timeout(),
        Fl::remove_timeout() and others

  @{
*/

/** Signature of some label drawing functions passed as parameters */
typedef void (Fl_Label_Draw_F)(const Fl_Label *label, int x, int y, int w, int h, Fl_Align align);

/** Signature of some label measurement functions passed as parameters */
typedef void (Fl_Label_Measure_F)(const Fl_Label *label, int &width, int &height);

/** Signature of some box drawing functions passed as parameters */
typedef void (Fl_Box_Draw_F)(int x, int y, int w, int h, Fl_Color color);

/** Signature of timeout callback functions passed as parameters.
  Please see Fl::add_timeout() for details.
*/
typedef void (*Fl_Timeout_Handler)(void *data);

/** Signature of some wakeup callback functions passed as parameters */
typedef void (*Fl_Awake_Handler)(void *data);

/** Signature of add_idle callback functions passed as parameters */
typedef void (*Fl_Idle_Handler)(void *data);

/** Signature of set_idle callback functions passed as parameters */
typedef void (*Fl_Old_Idle_Handler)();

/** Signature of add_fd functions passed as parameters */
typedef void (*Fl_FD_Handler)(FL_SOCKET fd, void *data);

/** Signature of add_handler functions passed as parameters */
typedef int (*Fl_Event_Handler)(int event);

/** Signature of add_system_handler functions passed as parameters */
typedef int (*Fl_System_Handler)(void *event, void *data);

/** Signature of set_abort functions passed as parameters */
typedef void (*Fl_Abort_Handler)(const char *format,...);

/** Signature of set_atclose functions passed as parameters */
typedef void (*Fl_Atclose_Handler)(Fl_Window *window, void *data);

/** Signature of args functions passed as parameters */
typedef int (*Fl_Args_Handler)(int argc, char **argv, int &i);

/** Signature of event_dispatch functions passed as parameters.
    \see Fl::event_dispatch(Fl_Event_Dispatch) */
typedef int (*Fl_Event_Dispatch)(int event, Fl_Window *w);

/** Signature of add_clipboard_notify functions passed as parameters */
typedef void (*Fl_Clipboard_Notify_Handler)(int source, void *data);

/** @} */ /* group callback_functions */


/**
  The Fl is the FLTK global (static) class containing
  state information and global methods for the current application.
*/
class FL_EXPORT Fl {
  friend class Fl_System_Driver;
  Fl() {} // no constructor!

private:

  static int use_high_res_GL_;
  static int draw_GL_text_with_textures_;
  static int box_shadow_width_;
  static int box_border_radius_max_;
  static int selection_to_clipboard_;

public:

  static Fl_Screen_Driver *screen_driver();
  static Fl_System_Driver *system_driver();
#ifdef __APPLE__ // deprecated in 1.4 - only for compatibility with 1.3
  static void reset_marked_text();
  static void insertion_point_location(int x, int y, int height);
#endif


  /** Get the box shadow width of all "shadow" boxtypes in pixels.
    \since 1.4.0
  */
  static int box_shadow_width() { return box_shadow_width_; }
  /** Set the box shadow width of all "shadow" boxtypes in pixels.
    Must be at least 1, default = 3. There is no upper limit.
    \since 1.4.0
  */
  static void box_shadow_width(int W) { box_shadow_width_ = W < 1 ? 1 : W; }

  /** Get the maximum border radius of all "rounded" boxtypes in pixels.
      \since 1.4.0
  */
  static int box_border_radius_max() { return box_border_radius_max_; }
  /** Set the maximum border radius of all "rounded" boxtypes in pixels.
    Must be at least 5, default = 15.

    \note This does \b not apply to the "round" boxtypes which have really round sides
      (i.e. composed of half circles) as opposed to "rounded" boxtypes that have only
      rounded corners with a straight border between corners.

    The box border radius of "rounded" boxtypes is typically calculated as about 2/5 of
    the box height or width, whichever is smaller. The upper limit can be set by this
    method for all "rounded" boxtypes.
    \since 1.4.0
  */
  static void box_border_radius_max(int R) { box_border_radius_max_ = R < 5 ? 5 : R; }

public: // should be private!

#ifndef FL_DOXYGEN
  static int e_number;
  static int e_x;
  static int e_y;
  static int e_x_root;
  static int e_y_root;
  static int e_dx;
  static int e_dy;
  static int e_state;
  static int e_clicks;
  static int e_is_click;
  static int e_keysym;
  static char* e_text;
  static int e_length;
  static void *e_clipboard_data;
  static const char *e_clipboard_type;
  static Fl_Event_Dispatch e_dispatch;
  static Fl_Callback_Reason callback_reason_;
  static Fl_Widget* belowmouse_;
  static Fl_Widget* pushed_;
  static Fl_Widget* focus_;
  static int damage_;
  static Fl_Widget* selection_owner_;
  static Fl_Window* modal_;
  static Fl_Window* grab_;
  static int compose_state; // used for dead keys (Windows) or marked text (MacOS)
  static void call_screen_init(); // recompute screen number and dimensions
#endif // FL_DOXYGEN


  /**
    If true then flush() will do something.
  */
  static void damage(int d) {damage_ = d;}

public:
  /** Enumerator for global FLTK options.
      These options can be set system wide, per user, or for the running
      application only.
      \see Fl::option(Fl_Option, bool)
      \see Fl::option(Fl_Option)
  */
  typedef enum {
      /// When switched on, moving the text cursor beyond the start or end of
      /// a text in a text widget will change focus to the next text widget.
      /// (This is considered 'old' behavior)
      ///
      /// When switched off (default), the cursor will stop at the end of the text.
      /// Pressing Tab or Ctrl-Tab will advance the keyboard focus.
      ///
      /// See also: Fl_Input_::tab_nav()
      ///
    OPTION_ARROW_FOCUS = 0,
      // When switched on, FLTK will use the file chooser dialog that comes
      // with your operating system whenever possible. When switched off, FLTK
      // will present its own file chooser.
      // \todo implement me
    // OPTION_NATIVE_FILECHOOSER,
      // When Filechooser Preview is enabled, the FLTK or native file chooser
      // will show a preview of a selected file (if possible) before the user
      // decides to choose the file.
      // \todo implement me
    //OPTION_FILECHOOSER_PREVIEW,
      /// If visible focus is switched on (default), FLTK will draw a dotted rectangle
      /// inside the widget that will receive the next keystroke. If switched
      /// off, no such indicator will be drawn and keyboard navigation
      /// is disabled.
    OPTION_VISIBLE_FOCUS,
      /// If text drag-and-drop is enabled (default), the user can select and drag text
      /// from any text widget. If disabled, no dragging is possible, however
      /// dropping text from other applications still works.
    OPTION_DND_TEXT,
      /// If tooltips are enabled (default), hovering the mouse over a widget with a
      /// tooltip text will open a little tooltip window until the mouse leaves
      /// the widget. If disabled, no tooltip is shown.
    OPTION_SHOW_TOOLTIPS,
     /// When switched on (default), Fl_Native_File_Chooser runs GTK file dialogs
     /// if the GTK library is available on the platform (linux/unix only).
     /// When switched off, GTK file dialogs aren't used even if the GTK library is available.
    OPTION_FNFC_USES_GTK,
    /// When switched on (default), Fl_Printer runs the GTK printer dialog
    /// if the GTK library is available on the platform (linux/unix only).
    /// When switched off, the GTK printer dialog isn't used even if the GTK library is available.
    OPTION_PRINTER_USES_GTK,
    /// When switched on (default), the library shows in a transient yellow window the zoom factor
    /// value.
    /// When switched off, no such window gets displayed.
    OPTION_SHOW_SCALING,
    /// Meaningful for the Wayland/X11 platform only. When switched on (default), the library uses a Zenity-based file dialog.
    /// When switched off, the GTK file dialog is used instead.
    OPTION_FNFC_USES_ZENITY,
      // don't change this, leave it always as the last element
      /// For internal use only.
    OPTION_LAST
  } Fl_Option;

private:
  static unsigned char options_[OPTION_LAST];
  static unsigned char options_read_;
  static int program_should_quit_; // non-zero means the program was asked to cleanly terminate

public:
  /*
   Return a global setting for all FLTK applications, possibly overridden
   by a setting specifically for this application.
   */
  static bool option(Fl_Option opt);

  /*
   Override an option while the application is running.
   */
  static void option(Fl_Option opt, bool val);

  /**
    The currently executing idle callback function: DO NOT USE THIS DIRECTLY!

    This is now used as part of a higher level system allowing multiple
    idle callback functions to be called.
    \see add_idle(), remove_idle()
  */
  static void (*idle)();

#ifndef FL_DOXYGEN
private:
  static Fl_Awake_Handler *awake_ring_;
  static void **awake_data_;
  static int awake_ring_size_;
  static int awake_ring_head_;
  static int awake_ring_tail_;
public:
  static const char* scheme_;
  static Fl_Image* scheme_bg_;

  static int e_original_keysym; // late addition
  static int scrollbar_size_;
  static int menu_linespacing_; // STR #2927
#endif


  static int add_awake_handler_(Fl_Awake_Handler, void*);
  static int get_awake_handler_(Fl_Awake_Handler&, void*&);

public:

  // API version number
  static double version();
  static int api_version();

  // ABI version number
  static int abi_version();

  /**
    Returns whether the runtime library ABI version is correct.

    This enables you to check the ABI version of the linked FLTK
    library at runtime.

    Returns 1 (true) if the compiled ABI version (in the header files)
    and the linked library ABI version (used at runtime) are the same,
    0 (false) otherwise.

    Argument \p val can be used to query a particular library ABI version.
    Use for instance 10303 to query if the runtime library is compatible
    with FLTK ABI version 1.3.3. This is rarely useful.

    The default \p val argument is FL_ABI_VERSION, which checks the version
    defined at configure time (i.e. in the header files at program
    compilation time) against the linked library version used at runtime.
    This is particularly useful if you linked with a shared object library,
    but it also concerns static linking.

    \see Fl::abi_version()
  */
  static inline int abi_check(const int val = FL_ABI_VERSION) {
    return val == abi_version();
  }

  // argument parsers:
  static int arg(int argc, char **argv, int& i);
  static int args(int argc, char **argv, int& i, Fl_Args_Handler cb = 0);
  static void args(int argc, char **argv);
  /**
    Usage string displayed if Fl::args() detects an invalid argument.
    This may be changed to point to customized text at run-time.
  */
  static const char* const help;

  // things called by initialization:
  static void display(const char*);
  static int visual(int);
  /**
    This does the same thing as Fl::visual(int) but also requires OpenGL
    drawing to work. This <I>must</I> 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 int gl_visual(int, int *alist=0); // platform dependent
  static void own_colormap();
  static void get_system_colors();
  static void foreground(uchar, uchar, uchar);
  static void background(uchar, uchar, uchar);
  static void background2(uchar, uchar, uchar);

  // schemes:
  static int scheme(const char *name);
  /** See void scheme(const char *name) */
  static const char* scheme() {return scheme_;}

  /** Returns whether the current scheme is the given name.

    This is a fast inline convenience function to support scheme-specific
    code in widgets, e.g. in their draw() methods, if required.

    Use a valid scheme name, not \p NULL (although \p NULL is allowed,
    this is not a useful argument - see below).

    If Fl::scheme() has not been set or has been set to the default
    scheme ("none" or "base"), then this will always return 0 regardless
    of the argument, because Fl::scheme() is \p NULL in this case.

    \note The stored scheme name is always lowercase, and this method will
    do a case-sensitive compare, so you \b must provide a lowercase string to
    return the correct value. This is intentional for performance reasons.

    Example:
    \code
      if (Fl::is_scheme("gtk+")) { your_code_here(); }
    \endcode

    \param[in] name \b lowercase string of requested scheme name.

    \return 1 if the given scheme is active, 0 otherwise.

    \see Fl::scheme(const char *name)
  */
  static int is_scheme(const char *name) {
    return (scheme_ && name && !strcmp(name,scheme_));
  }

  static int reload_scheme(); // defined in 'src/Fl_get_system_colors.cxx'

  static int scrollbar_size();
  static void scrollbar_size(int W);
  static int menu_linespacing();
  static void menu_linespacing(int H);

  // execution:
  static int wait();
  static double wait(double time);
  static int check();
  static int ready();
  static int run();
  /** Returns non-zero when a request for program termination was received and accepted.
   On the MacOS platform, the "Quit xxx" item of the application menu is such a request,
   that is considered accepted when all windows are closed. On other platforms, this function
   returns 0 until \p Fl::program_should_quit(1) is called.
   \version 1.4.0
   */
  static int program_should_quit() {return program_should_quit_;}
  /** Indicate to the FLTK library whether a program termination request was received and accepted.
  A program may set this to 1, for example, while performing a platform-independent command asking the program to cleanly
  terminate, similarly to the "Quit xxx" item of the application menu under MacOS.
   \version 1.4.0
   */
  static void program_should_quit(int should_i) { program_should_quit_ = should_i; }
  static void hide_all_windows();

  static Fl_Widget* readqueue();

  //
  // cross-platform timer support
  //

  static void add_timeout(double t, Fl_Timeout_Handler cb, void *data = 0);
  static void repeat_timeout(double t, Fl_Timeout_Handler cb, void *data = 0);
  static int  has_timeout(Fl_Timeout_Handler cb, void *data = 0);
  static void remove_timeout(Fl_Timeout_Handler cb, void *data = 0);

  static void add_check(Fl_Timeout_Handler, void* = 0);
  static int  has_check(Fl_Timeout_Handler, void* = 0);
  static void remove_check(Fl_Timeout_Handler, void* = 0);

  static Fl_Timestamp now();
  static double seconds_since(Fl_Timestamp& then);
  static double seconds_between(Fl_Timestamp& back, Fl_Timestamp& further_back);
  static long ticks_since(Fl_Timestamp& then);
  static long ticks_between(Fl_Timestamp& back, Fl_Timestamp& further_back);

  // private
  static void run_idle();
  static void run_checks();
  static void add_fd(int fd, int when, Fl_FD_Handler cb, void* = 0); // platform dependent
  static void add_fd(int fd, Fl_FD_Handler cb, void* = 0); // platform dependent
  /** Removes a file descriptor handler. */
  static void remove_fd(int, int when); // platform dependent
  /** Removes a file descriptor handler. */
  static void remove_fd(int); // platform dependent

  static void add_idle(Fl_Idle_Handler cb, void* data = 0);
  static int  has_idle(Fl_Idle_Handler cb, void* data = 0);
  static void remove_idle(Fl_Idle_Handler cb, void* data = 0);
  /** If true then flush() will do something. */
  static int damage() {return damage_;}
  static void redraw();
  static void flush();
  /** \addtogroup group_comdlg
    @{ */
  /**
  FLTK calls Fl::warning() to output a warning message.

  The default version on Windows returns \e without printing a warning
  message, because Windows programs normally don't have stderr (a console
  window) enabled.

  The default version on all other platforms prints the warning message to stderr.

  You can override the behavior by setting the function pointer to your
  own routine.

  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, for example. The default implementation returns after
  displaying the message.
   \note \#include <FL/Fl.H>
  */
  static void (*warning)(const char*, ...);
  /**
  FLTK calls Fl::error() to output a normal error message.

  The default version on Windows displays the error message in a MessageBox window.

  The default version on all other platforms prints the error message to stderr.

  You can override the behavior by setting the function pointer to your
  own routine.

  Fl::error() means there is a recoverable error such as the inability to read
  an image file. The default implementation returns after displaying the message.
   \note \#include <FL/Fl.H>
  */
  static void (*error)(const char*, ...);
  /**
  FLTK calls Fl::fatal() to output a fatal error message.

  The default version on Windows displays the error message in a MessageBox window.

  The default version on all other platforms prints the error message to stderr.

  You can override the behavior by setting the function pointer to your
  own routine.

  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. The default implementation exits with status 1
  after displaying the message.
   \note \#include <FL/Fl.H>
  */
  static void (*fatal)(const char*, ...);
  /** @} */

  /** \defgroup  fl_windows Windows handling functions
      \brief Windows and standard dialogs handling declared in <FL/Fl.H>
    @{ */
  static Fl_Window* first_window();
  static void first_window(Fl_Window*);
  static Fl_Window* next_window(const Fl_Window*);

  /**
    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* modal() {return modal_;}
  /** Returns the window that currently receives all events.

   \return The window that currently receives all events,
   or NULL if event grabbing is currently OFF.
  */
  static Fl_Window* grab() {return grab_;}
  /** Selects the window to 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 <I>does not have
   to be shown()</I> , 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 Windows
   <I>some</I> 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).

   <I>Be careful that your program does not enter an infinite loop
   while grab() is on.  On X this will lock up your screen!</I>
   To avoid this potential lockup, all newer operating systems seem to
   limit mouse pointer grabbing to the time during which a mouse button
   is held down. Some OS's may not support grabbing at all.
   */
  static void grab(Fl_Window*); // platform dependent
  /** @} */

  /** \defgroup fl_events Events handling functions
        Fl class events handling API declared in <FL/Fl.H>
        @{
  */
  // event information:
  /**
    Returns the last event that was processed. This can be used
    to determine if a callback is being done in response to a
    keypress, mouse click, etc.
  */
  static int event()            {return e_number;}
  /**
    Returns the mouse position of the event relative to the Fl_Window
    it was passed to.
  */
  static int event_x()  {return e_x;}
  /**
    Returns the mouse position of the event relative to the Fl_Window
    it was passed to.
  */
  static int event_y()  {return e_y;}
  /**
    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 int event_x_root()     {return e_x_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 int event_y_root()     {return e_y_root;}
  /**
    Returns the current horizontal mouse scrolling associated with the
    FL_MOUSEWHEEL event. Right is positive.
  */
  static int event_dx() {return e_dx;}
  /**
    Returns the current vertical mouse scrolling associated with the
    FL_MOUSEWHEEL event. Down is positive.
  */
  static int event_dy() {return e_dy;}
  /**
    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 get_mouse(int &,int &);
  /**
    Returns non zero if we had a double click event.
    \retval Non-zero if the most recent FL_PUSH or FL_KEYBOARD was a "double click".
    \retval  N-1 for  N clicks.
    A double click is counted if the same button is pressed
    again while event_is_click() is true.

   */
  static int event_clicks()     {return e_clicks;}
  /**
    Manually 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.
    \param[in] i corresponds to no double-click if 0, i+1 mouse clicks otherwise
    \see int event_clicks()
  */
  static void event_clicks(int i) {e_clicks = i;}
  /**
  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.
  */
  static int event_is_click()   {return e_is_click;}
  /**
   Clears the value returned by Fl::event_is_click().
   Useful to prevent the <I>next</I>
   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.
  */
  static void event_is_click(int i) {e_is_click = i;}
  /**
    Gets which particular mouse button caused the current event.

    This returns garbage if the most recent event was not a FL_PUSH or FL_RELEASE event.
    \retval FL_LEFT_MOUSE
    \retval FL_MIDDLE_MOUSE
    \retval FL_RIGHT_MOUSE.
    \see Fl::event_buttons()
  */
  static int event_button()     {return e_keysym-FL_Button;}
  /**
    Returns the keyboard and mouse button states of the last event.

    This is a bitfield of what shift states were on and what mouse buttons
    were held down during the most recent event.

    The legal event state 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
    <I>after</I> the shift key is pressed or released.
  */
  static int event_state()      {return e_state;}

  /** Returns non-zero if any of the passed event state bits are turned on.

    Use \p mask to pass the event states you're interested in.
    The legal event state bits are defined in Fl::event_state().
  */
  static int event_state(int mask) {return e_state&mask;}
  /**
    Gets which key on the keyboard was last pushed.

    The returned integer 'key code' is not necessarily a text
    equivalent for the keystroke. For instance: if someone presses '5' on the
    numeric keypad with numlock on, Fl::event_key() may return the 'key code'
    for this key, and NOT the character '5'. To always get the '5', use Fl::event_text() instead.

    \returns an integer 'key code', or 0 if the last event was not a key press or release.
    \see int event_key(int), event_text(), compose(int&).
  */
  static int event_key()        {return e_keysym;}
  /**
    Returns the keycode of the last key event, regardless of the NumLock state.

    If NumLock is deactivated, FLTK translates events from the
    numeric keypad into the corresponding arrow key events.
    event_key() returns the translated key code, whereas
    event_original_key() returns the keycode before NumLock translation.
  */
  static int event_original_key(){return e_original_keysym;}
  /**
    Returns true if the given \p key was held
    down (or pressed) <I>during</I> 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 <I>now</I>.
    Under X this requires a round-trip to the server and is <I>much</I>
    slower than Fl::event_key(int).

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

    \li 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.
    \li All keys on the numeric keypad producing a printable ASCII
        character use the value of that ASCII character plus FL_KP
        (e.g., FL_KP + '4', FL_KP + '/').
        The highest possible value is FL_KP_Last so you can
        range-check to see if something is  on the keypad.
    \li 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.
    \li Buttons on the mouse are considered keys, and use the button
        number (where the left button is 1) plus FL_Button.
    \li 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_Iso_Key, 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 Windows Fl::get_key(FL_KP_Enter) and Fl::event_key(FL_KP_Enter) do not work.
  */
  static int event_key(int key);
  /**
    Returns true if the given \p key is held down <I>now</I>.
    Under X this requires a round-trip to the server and is <I>much</I>
    slower than Fl::event_key(int). \see event_key(int)
  */
  static int get_key(int key); // platform dependent
  /**
    Returns the text associated with the current event, including FL_PASTE or FL_DND_RELEASE events.
    This can be used in response to FL_KEYUP, FL_KEYDOWN, FL_PASTE, and FL_DND_RELEASE.

    When responding to FL_KEYUP/FL_KEYDOWN, use this function instead of Fl::event_key()
    to get the text equivalent of keystrokes suitable for inserting into strings
    and text widgets.

    The returned string is guaranteed to be NULL terminated.
    However, see Fl::event_length() for the actual length of the string,
    in case the string itself contains NULLs that are part of the text data.

    \returns A NULL terminated text string equivalent of the last keystroke.
   */
  static const char* event_text() {return e_text;}
  /**
    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.
  */
  static int event_length() {return e_length;}

  /** During an FL_PASTE event of non-textual data, returns a pointer to the pasted data.
   The returned data is an Fl_RGB_Image * when the result of Fl::event_clipboard_type() is Fl::clipboard_image.
   */
  static void *event_clipboard() { return e_clipboard_data; }
  /** Returns the type of the pasted data during an FL_PASTE event.
   This type can be Fl::clipboard_plain_text or Fl::clipboard_image.
   */
  static const char *event_clipboard_type() {return e_clipboard_type; }


  static int compose(int &del);
  static void compose_reset();
  static int event_inside(int,int,int,int);
  static int event_inside(const Fl_Widget*);
  static int test_shortcut(Fl_Shortcut);

  static void enable_im();
  static void disable_im();

  // event destinations:
  static int handle(int, Fl_Window*);
  static int handle_(int, Fl_Window*);
  /**  Gets the widget that is below the mouse.
       \see  belowmouse(Fl_Widget*) */
  static Fl_Widget* belowmouse() {return belowmouse_;}
  static void belowmouse(Fl_Widget*);
  /** Gets the widget that is being pushed.
      \see void pushed(Fl_Widget*) */
  static Fl_Widget* pushed()    {return pushed_;}
  static void pushed(Fl_Widget*);
  /** Gets the current Fl::focus() widget. \sa Fl::focus(Fl_Widget*) */
  static Fl_Widget* focus()     {return focus_;}
  static void focus(Fl_Widget*);
  static void add_handler(Fl_Event_Handler h);
  static void remove_handler(Fl_Event_Handler h);
  static void add_system_handler(Fl_System_Handler h, void *data);
  static void remove_system_handler(Fl_System_Handler h);
  static void event_dispatch(Fl_Event_Dispatch d);
  static Fl_Event_Dispatch event_dispatch();
  static Fl_Callback_Reason callback_reason();
  /** @} */

  /** \defgroup  fl_clipboard  Selection & Clipboard functions
        FLTK global copy/cut/paste functions declared in <FL/Fl.H>
   @{ */
  // cut/paste:
  /**
  Copies the data pointed to by \p stuff to the selection buffer
  (\p destination is 0), the clipboard (\p destination is 1), or
  both (\p destination is 2). Copying to both is only relevant on X11,
  on other platforms it maps to the clipboard (1).
  \p len is the number of relevant bytes in \p stuff.
  \p type is always Fl::clipboard_plain_text.
  The selection buffer is used for
  middle-mouse pastes and for drag-and-drop selections. The
  clipboard is used for traditional copy/cut/paste operations.

   \note This function is, at present, intended only to copy UTF-8 encoded textual data.
   To copy graphical data, use the Fl_Copy_Surface class. The \p type argument may allow
   in the future to copy other kinds of data.
  */

  /**
    Copies data to the selection buffer, the clipboard, or both.

    The \p destination can be:
     - 0: selection buffer (see note below)
     - 1: clipboard
     - 2: both

    The selection buffer exists only on the X11 platform and is used for middle-mouse
    pastes and for drag-and-drop selections. The clipboard is used for traditional
    copy/cut/paste operations. On all other platforms the selection buffer
    (\p destination = 0) is mapped to the clipboard, i.e. on platforms other than X11
    all \p destinations are equivalent and the data is always copied to the clipboard.

    \note Please see Fl::section_to_clipboard() to enable duplication of the
      selection buffer to the clipboard on X11, i.e. if \p destination = 0
      (selection buffer) \b and Fl::selection_to_clipboard() is enabled, then
      the data is copied to both the selection buffer and the clipboard.
      This makes the X11 behavior similar to other platforms but keeps the
      selection buffer for X11 specific inter process communication.

    \p type should always be \p Fl::clipboard_plain_text which is the default.
    Other values are ignored and reserved for future extensions.

    \note This function is, at present, intended only to copy UTF-8 encoded
      textual data. To copy graphical data, use the Fl_Copy_Surface class.
      The \p type argument may allow to copy other kinds of data in the future.

    \param[in]  stuff       text data to be copied
    \param[in]  len         the number of relevant bytes in \p stuff
    \param[in]  destination 0 = selection, 1 = clipboard, 2 = both (see description)
    \param[in]  type        usually plain text (see description)

    \internal
      Documented here because it is platform dependent (calls the platform driver):
    \code
      Fl::screen_driver()->copy(stuff, len, clipboard, type);
    \endcode
  */
  static void copy(const char *stuff, int len, int destination = 0,
                   const char *type = Fl::clipboard_plain_text);

  /**
    Copies selections on X11 directly to the clipboard if enabled.

    This method can be called on all platforms. Other platforms than X11 are
    not affected by this feature.

    If this is switched on (\p mode = 1), Fl::copy() copies all data to the
    clipboard regardless of its \p destination argument. If the destination is 0
    (selection buffer) data is copied to both the selection buffer and the clipboard.

    Drag and drop is also affected since drag-and-drop data is copied to the selection
    buffer.

    You can use this to make the experience of data selection and copying more like
    that on other platforms (Windows, macOS, and even Wayland).

    The default operation mode is the standard X11 behavior (disabled).

    \note This feature is experimental and enabling it may have unexpected side effects.
      It is your own responsibility if you enable it.

    \since 1.4.0

    \param[in]  mode  1 = enable selection_to_clipboard, 0 = disable selection_to_clipboard

    \see copy(const char *, int, int, const char *)
  */
  static void selection_to_clipboard(int mode) {
    selection_to_clipboard_ = mode ? 1 : 0;
  }

  /**
    \brief Returns the current selection_to_clipboard mode.

    \see void selection_to_clipboard(int)
  */
  static int selection_to_clipboard() { return selection_to_clipboard_; }

  /**
   Pastes the data from the selection buffer (\p source is 0) or the clipboard
   (\p source is 1) into \p receiver.

   The selection buffer (\p source is 0) is used for middle-mouse pastes and for
   drag-and-drop selections. The clipboard (\p source is 1) is used for
   copy/cut/paste operations.

   If \p source is 1, the optional \p type argument indicates what type of data is requested from the clipboard.
   At present, Fl::clipboard_plain_text (requesting text data) and
   Fl::clipboard_image (requesting image data) are possible.
   Set things up so the handle function of the \p receiver widget will be called with an FL_PASTE event some
   time in the future if the clipboard does contain data of the requested type.

   The handle function of \p receiver can process the FL_PASTE event as follows:
   \li If the \p receiver widget is known to only receive text data, the text string
   from the specified \p source is in Fl::event_text() with UTF-8 encoding, and the
   number of bytes is in Fl::event_length(). If Fl::paste() gets called during the
   drop step of a files-drag-and-drop operation,
   Fl::event_text() contains a list of filenames (see \ref events_dnd).
   \li If the \p receiver widget can potentially receive non-text data, use
   Fl::event_clipboard_type() to determine what sort of data is being sent.
   If Fl::event_clipboard_type() returns Fl::clipboard_plain_text, proceed as above.
   It it returns Fl::clipboard_image, the pointer returned by Fl::event_clipboard()
   can be safely cast to type Fl_RGB_Image * to obtain a pointer to the pasted image.
   If \p receiver accepts the clipboard image, receiver.handle() should return 1 and the
   application should take ownership of this image (that is, delete it after use).
   Conversely, if receiver.handle() returns 0, the application must not use the image.

   The receiver should be prepared to be called \e directly by this, or for
   it to happen \e later, or possibly <i>not at all</i>.  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.

   \par Platform details for image data:
   \li Unix/Linux platform: Clipboard images in PNG or BMP formats are recognized. Requires linking with the fltk_images library.
   \li Windows platform: Both bitmap and vectorial (Enhanced metafile) data from clipboard
   can be pasted as image data.
   \li Mac OS X platform: Both bitmap (TIFF) and vectorial (PDF) data from clipboard
   can be pasted as image data.
   */
  static void paste(Fl_Widget &receiver, int source, const char *type = Fl::clipboard_plain_text);

  /**
  FLTK will call the registered callback whenever there is a change to the
  selection buffer or the clipboard. The source argument indicates which
  of the two has changed. Only changes by other applications are reported.

  Example:
  \code
    void clip_callback(int source, void *data) {
        if ( source == 0 ) printf("CLIP CALLBACK: selection buffer changed\n");
        if ( source == 1 ) printf("CLIP CALLBACK: clipboard changed\n");
    }
    [..]
    int main() {
        [..]
        Fl::add_clipboard_notify(clip_callback);
        [..]
    }
  \endcode
  \note Some systems require polling to monitor the clipboard and may
  therefore have some delay in detecting changes.
  */
  static void add_clipboard_notify(Fl_Clipboard_Notify_Handler h, void *data = 0);
  /**
  Stop calling the specified callback when there are changes to the selection
  buffer or the clipboard.
  */
  static void remove_clipboard_notify(Fl_Clipboard_Notify_Handler h);
  /** Returns non 0 if the clipboard contains data matching \p type.
   \p type can be Fl::clipboard_plain_text or Fl::clipboard_image.
   */
  static int clipboard_contains(const char *type);
  /**  Denotes plain textual data
   */
  static char const * const clipboard_plain_text;
  /**  Denotes image data
   */
  static char const * const clipboard_image;

  /**
    Initiate a Drag And Drop operation. The selection buffer should be
    filled with relevant data before calling this method. FLTK will
    then initiate the system wide drag and drop handling. Dropped data
    will be marked as <i>text</i>.

    Create a selection first using:
    Fl::copy(const char *stuff, int len, 0)
  */
  static int dnd(); // platform dependent

  // These are for back-compatibility only:
  /**  back-compatibility only: Gets the widget owning the current selection
       \see Fl_Widget* selection_owner(Fl_Widget*) */
  static Fl_Widget* selection_owner() {return selection_owner_;}
  static void selection_owner(Fl_Widget*);
  static void selection(Fl_Widget &owner, const char*, int len);
  static void paste(Fl_Widget &receiver);
/** @} */


/** \defgroup  fl_screen  Screen functions
 Fl global screen functions declared in <FL/Fl.H>.

 FLTK supports high-DPI screens using a screen scaling factor.
 The scaling factor is initialized by the library to a value
 based on information obtained from the OS. If this initial value
 is not satisfactory, the FLTK_SCALING_FACTOR environment variable
 can be set to a value FLTK will multiply to the OS-given value.
 The 2 variants of functions Fl::screen_scale() allow to programmatically get and set
 scaling factor values. The scaling factor value can be further changed at runtime
 by typing ctrl-/+/-/0/ (cmd-/+/-/0/ under macOS). FLTK sends the
 \ref FL_ZOOM_EVENT when the factor value is changed, to which a
 callback can be associated with Fl::add_handler().
 By default, FLTK displays the new scaling factor value in a yellow, transient window.
 This can be changed with option Fl::OPTION_SHOW_SCALING.
     @{ */
  static int x(); // via screen driver
  static int y(); // via screen driver
  static int w(); // via screen driver
  static int h(); // via screen driver

  // multi-head support:
  static int screen_count(); // via screen driver
  static void screen_xywh(int &X, int &Y, int &W, int &H); // via screen driver
  static void screen_xywh(int &X, int &Y, int &W, int &H, int mx, int my); // via screen driver
  static void screen_xywh(int &X, int &Y, int &W, int &H, int n); // via screen driver
  static void screen_xywh(int &X, int &Y, int &W, int &H, int mx, int my, int mw, int mh); // via screen driver
  static int screen_num(int x, int y); // via screen driver
  static int screen_num(int x, int y, int w, int h); // via screen driver
  static void screen_dpi(float &h, float &v, int n=0); // via screen driver
  static void screen_work_area(int &X, int &Y, int &W, int &H, int mx, int my); // via screen driver
  static void screen_work_area(int &X, int &Y, int &W, int &H, int n); // via screen driver
  static void screen_work_area(int &X, int &Y, int &W, int &H); // via screen driver
  static float screen_scale(int n); // via screen driver
  static void screen_scale(int n, float factor); // via screen driver
  static int screen_scaling_supported();
  static void keyboard_screen_scaling(int value);

/**   @} */


  /** \defgroup  fl_attributes  Color & Font functions
        fl global color, font functions.
   These functions are declared in <FL/Fl.H> or <FL/fl_draw.H>.
     @{ */

  // color map:
  static void   set_color(Fl_Color, uchar, uchar, uchar);
  static void   set_color(Fl_Color, uchar, uchar, uchar, uchar);
  /**
    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 void   set_color(Fl_Color i, unsigned c); // platform dependent
  static unsigned get_color(Fl_Color i);
  static void   get_color(Fl_Color i, uchar &red, uchar &green, uchar &blue);
  static void   get_color(Fl_Color i, uchar &red, uchar &green, uchar &blue, uchar &alpha);
  /**
    Frees the specified color from the colormap, if applicable.
    If overlay is non-zero then the color is freed from the
    overlay colormap.
  */
  static void   free_color(Fl_Color i, int overlay = 0); // platform dependent

  // fonts:
  static const char* get_font(Fl_Font);
  /**
    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 \p 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.
  */
  static const char* get_font_name(Fl_Font, int* attributes = 0);
  /**
    Return an array of sizes in \p 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 int get_font_sizes(Fl_Font, int*& sizep);
  static void set_font(Fl_Font, const char*);
  static void set_font(Fl_Font, Fl_Font);
  /**
    FLTK will open the display, and add every fonts 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 only argument to this function is somehat obsolete since FLTK and most
    underlying operating systems move to support Unicode. For completeness,
    following is the original documentation and a few updates:

    On X11, 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 the Xft option on Linux, this parameter is ignored.

    With Windows, `NULL` selects fonts with ANSI_CHARSET encoding and non-NULL
    selects all fonts.

    On macOS, this parameter is ignored.

    The return value is how many faces are in the table after this is done.
  */
  static Fl_Font set_fonts(const char* = 0); // platform dependent

  /**   @} */
 /** \defgroup  fl_drawings  Drawing functions
  FLTK global graphics and GUI drawing functions.
  These functions are declared in <FL/fl_draw.H>,
  and in <FL/platform.H> for offscreen buffer-related ones.
     @{ */
  // <Hack to re-order the 'Drawing functions' group>
 /** @} */

  // labeltypes:
  static void set_labeltype(Fl_Labeltype,Fl_Label_Draw_F*,Fl_Label_Measure_F*);
  /** Sets the functions to call to draw and measure a specific labeltype. */
  static void set_labeltype(Fl_Labeltype, Fl_Labeltype from); // is it defined ?

  // boxtypes:
  static Fl_Box_Draw_F *get_boxtype(Fl_Boxtype);
  static void set_boxtype(Fl_Boxtype, Fl_Box_Draw_F*,uchar,uchar,uchar,uchar);
  static void set_boxtype(Fl_Boxtype, Fl_Boxtype from);
  static int box_dx(Fl_Boxtype);
  static int box_dy(Fl_Boxtype);
  static int box_dw(Fl_Boxtype);
  static int box_dh(Fl_Boxtype);

  static int draw_box_active();
  static Fl_Color box_color(Fl_Color);
  static void set_box_color(Fl_Color);

  // back compatibility:
  /** \addtogroup fl_windows
    @{ */
  /** For back compatibility, sets the void Fl::fatal handler callback */
  static void set_abort(Fl_Abort_Handler f) {fatal = f;}
  static void (*atclose)(Fl_Window*,void*);
  static void default_atclose(Fl_Window*,void*);
  /** For back compatibility, sets the Fl::atclose handler callback. You
      can now simply change the callback for the window instead.
      \see Fl_Window::callback(Fl_Callback*) */
  static void set_atclose(Fl_Atclose_Handler f) {atclose = f;}
  /**   @} */

  /** \addtogroup fl_events
    @{ */
  /** Returns non-zero if the Shift key is pressed. */
  static int event_shift() {return e_state&FL_SHIFT;}
  /** Returns non-zero if the Control key is pressed. */
  static int event_ctrl() {return e_state&FL_CTRL;}
  /** Returns non-zero if the FL_COMMAND key is pressed, either FL_CTRL or on OSX FL_META. */
  static int event_command() {return e_state&FL_COMMAND;}
  /** Returns non-zero if the Alt key is pressed. */
  static int event_alt() {return e_state&FL_ALT;}
  /**
    Returns the mouse buttons state bits; if non-zero, then at least one
    button is pressed now.  This function returns the button state at the
    time of the event. During an FL_RELEASE event, the state
    of the released button will be 0. To find out, which button
    caused an FL_RELEASE event, you can use Fl::event_button() instead.
    \return a bit mask value like { [FL_BUTTON1] | [FL_BUTTON2] | [FL_BUTTON3] }
  */
  static int event_buttons() {return e_state&0x7f000000;}
  /**
    Returns non-zero if mouse button 1 is currently held down.
    For more details, see Fl::event_buttons().
  */
  static int event_button1() {return e_state&FL_BUTTON1;}
  /**
    Returns non-zero if button 2 is currently held down.
    For more details, see Fl::event_buttons().
  */
  static int event_button2() {return e_state&FL_BUTTON2;}
  /**
    Returns non-zero if button 3 is currently held down.
    For more details, see Fl::event_buttons().
  */
  static int event_button3() {return e_state&FL_BUTTON3;}
  /**   @} */

  /**
    Sets an idle callback.

    \deprecated This method is obsolete - use the add_idle() method instead.
  */
  static void set_idle(Fl_Old_Idle_Handler cb) {idle = cb;}
  /** See grab(Fl_Window*) */
  static void grab(Fl_Window& win) {grab(&win);}
  /** Releases the current grabbed window, equals grab(0).
  \deprecated Use Fl::grab(0) instead.
  \see grab(Fl_Window*) */
  static void release() {grab(0);}

  // Visible focus methods...
  /**
    Gets or sets the visible keyboard focus on buttons and other
    non-text widgets. The default mode is to enable keyboard focus
    for all widgets.
  */
  static void visible_focus(int v) { option(OPTION_VISIBLE_FOCUS, (v!=0)); }
  /**
    Gets or sets the visible keyboard focus on buttons and other
    non-text widgets. The default mode is to enable keyboard focus
    for all widgets.
  */
  static int  visible_focus() { return option(OPTION_VISIBLE_FOCUS); }

  // Drag-n-drop text operation methods...
  /**
    Sets whether drag and drop text operations are supported.
    This specifically affects whether selected text can
    be dragged from text fields or dragged within a text field as a
    cut/paste shortcut.
  */
  static void dnd_text_ops(int v) { option(OPTION_DND_TEXT, (v!=0)); }
  /**
    Gets whether drag and drop text operations are
    supported. This returns whether selected text can
    be dragged from text fields or dragged within a text field as a
    cut/paste shortcut.
  */
  static int  dnd_text_ops() { return option(OPTION_DND_TEXT); }
  /** \defgroup fl_multithread Multithreading support functions
        fl multithreading support functions declared in <FL/Fl.H>
   @{ */

  // Multithreading support:
  static int lock();
  static void unlock();
  static void awake(void* message = 0);
  /** See void awake(void* message=0). */
  static int awake(Fl_Awake_Handler cb, void* message = 0);
  /**
    The thread_message() method returns the last message
    that was sent from a child by the awake() method.

    See also: \ref advanced_multithreading
  */
  static void* thread_message(); // platform dependent
  /** @} */

  /** \defgroup fl_del_widget Safe widget deletion support functions

    These functions, declared in <FL/Fl.H>, support deletion of widgets inside callbacks.

    Fl::delete_widget() should be called when deleting widgets
    or complete widget trees (Fl_Group, Fl_Window, ...) inside
    callbacks.

    The other functions are intended for internal use. The preferred
    way to use them is by using the helper class Fl_Widget_Tracker.

    The following is to show how it works ...

    There are three groups of related methods:

      -# scheduled widget deletion
        - Fl::delete_widget() schedules widgets for deletion
        - Fl::do_widget_deletion() deletes all scheduled widgets
      -# widget watch list ("smart pointers")
        - Fl::watch_widget_pointer() adds a widget pointer to the watch list
        - Fl::release_widget_pointer() removes a widget pointer from the watch list
        - Fl::clear_widget_pointer() clears a widget pointer \e in the watch list
      -# the class Fl_Widget_Tracker:
        - the constructor calls Fl::watch_widget_pointer()
        - the destructor calls Fl::release_widget_pointer()
        - the access methods can be used to test, if a widget has been deleted
          \see Fl_Widget_Tracker.

   @{ */
  // Widget deletion:
  static void delete_widget(Fl_Widget *w);
  static void do_widget_deletion();
  static void watch_widget_pointer(Fl_Widget *&w);
  static void release_widget_pointer(Fl_Widget *&w);
  static void clear_widget_pointer(Fl_Widget const *w);
  /** @} */

  /**  sets whether GL windows should be drawn at high resolution on Apple
   computers with retina displays
   \version 1.3.4
   */
  static void use_high_res_GL(int val) { use_high_res_GL_ = val; }
  /**  returns whether GL windows should be drawn at high resolution on Apple
   computers with retina displays.
   Default is no.
   \version 1.3.4
   */
  static int use_high_res_GL() { return use_high_res_GL_; }

  /**  sets whether OpenGL uses textures to draw all text.
   By default, FLTK draws OpenGL text using textures, if the necessary
   hardware support is available. Call \p Fl::draw_GL_text_with_textures(0)
   once in your program before the first call to gl_font() to have FLTK
   draw instead OpenGL text using a legacy, platform-dependent procedure.
   It's recommended not to deactivate textures under the MacOS platform
   because the MacOS legacy procedure is extremely rudimentary.
   \param val use 0 to prevent FLTK from drawing GL text with textures
   \see gl_texture_pile_height(int max)
   \version 1.4.0
   */
  static void draw_GL_text_with_textures(int val) { draw_GL_text_with_textures_ = val; }

  /**  returns whether whether OpenGL uses textures to draw all text.
   Default is yes.
   \see draw_GL_text_with_textures(int val)
   \version 1.4.0
   */
  static int draw_GL_text_with_textures() { return draw_GL_text_with_textures_; }

  static int system(const char *command);

#ifdef FLTK_HAVE_CAIRO
  /** \defgroup group_cairo Cairo Support Functions and Classes
      @{
  */
public:
  // Cairo support API

  static cairo_t *cairo_make_current(Fl_Window *w);

  /** When FLTK_HAVE_CAIRO is defined and cairo_autolink_context() is true,
    any current window dc is linked to a current Cairo context.
    This is not the default, because it may not be necessary
    to add Cairo support to all fltk supported windows.
    When you wish to associate a Cairo context in this mode,
    you need to call explicitly in your draw() overridden method,
    Fl::cairo_make_current(Fl_Window*). This will create a Cairo context
    only for this Window.
    Still in custom Cairo application it is possible to handle
    completely this process automatically by setting \p alink to true.
    In this last case, you don't need anymore to call Fl::cairo_make_current().
    You can use Fl::cairo_cc() to get the current Cairo context anytime.

    \note Only available when configure has the --enable-cairo option
  */
  static void cairo_autolink_context(bool alink) {
    cairo_state_.autolink(alink);
  }

  /**
    Gets the current autolink mode for Cairo support.
    \retval false if no Cairo context autolink is made for each window.
    \retval true if any fltk window is attached a Cairo context when it
    is current. \see void cairo_autolink_context(bool alink)
    \note Only available when configure has the --enable-cairo option
 */
  static bool cairo_autolink_context() {
    return cairo_state_.autolink();
  }

  /** Gets the current Cairo context linked with a fltk window. */
  static cairo_t *cairo_cc() {
    return cairo_state_.cc();
  }

  /** Sets the current Cairo context to \p c.
    Set \p own to true if you want fltk to handle this cc deletion.
    \note Only available when configure has the --enable-Cairo option
  */
  static void cairo_cc(cairo_t *c, bool own=false) {
    cairo_state_.cc(c, own);
  }

  /** Flush Cairo drawings on Cairo context \p c.
    This is \b required on Windows if you use the Cairo context provided
    by the "Cairo autolink" option. Call this when all your drawings on
    the Cairo context are finished. This is maybe not necessary on other
    platforms than Windows but it does no harm if you call it always.

    You don't need to use this if you use an Fl_Cairo_Window which does
    this automatically after the draw callback returns.

    Code example for "Cairo autolink" mode:

    In the overridden draw() method of your subclass of Fl_Window or any
    widget:
    \code
      cairo_t *cc = Fl::cairo_cc();   // get the "autolink" Cairo context
      // ... your Cairo drawings are here ...
      Fl::cairo_flush(cc);            // flush Cairo drawings to the device
    \endcode

    If you configure FLTK with \c '--enable-cairo' or CMake option
    \c 'OPTION_CAIRO' (i.e. without \c '--enable-cairoext' or CMake option
    \c 'OPTION_CAIROEXT') or if you don't enable the \c 'autolink' Cairo
    context you may do the equivalent to use Cairo drawings in an
    overridden draw() method of derived classes by using
    \code
      // get the  Cairo context for the \c window
      cairo_t *cc = Fl::cairo_make_current(window);
      // ... your Cairo drawings are here ...
      Fl::cairo_flush(cc); // flush Cairo drawings to the device
    \endcode
    \see Fl::cairo_autolink_context(bool)
    \see Fl::cairo_make_current(Fl_Window*);
  */
  static void cairo_flush(cairo_t *c) {
    // flush Cairo drawings: necessary at least for Windows
    cairo_surface_t *s = cairo_get_target(Fl::cairo_cc());
    cairo_surface_flush(s);
  }

private:
  static cairo_t *cairo_make_current(void *gc);
  static cairo_t *cairo_make_current(void *gc, int W, int H);
  static Fl_Cairo_State cairo_state_;

public:
  /** @} */

#endif // FLTK_HAVE_CAIRO

};

/**
  This class should be used to control safe widget deletion.

  You can use an Fl_Widget_Tracker object to watch another widget, if you
  need to know whether this widget has been deleted during a callback.

  This simplifies the use of the "safe widget deletion" methods
  Fl::watch_widget_pointer() and Fl::release_widget_pointer() and
  makes their use more reliable, because the destructor automatically
  releases the widget pointer from the widget watch list.

  Fl_Widget_Tracker is intended to be used as an automatic (local/stack)
  variable, such that its destructor is called when the object's
  scope is left. This ensures that no stale widget pointers are
  left in the widget watch list (see example below).

  You can also create Fl_Widget_Tracker objects with \c new, but then it
  is your responsibility to delete the object (and thus remove the
  widget pointer from the watch list) when it is no longer needed.

  Example:

  \code
  int MyClass::handle (int event) {

    if (...) {
      Fl_Widget_Tracker wp(this);           // watch myself
      do_callback();                        // call the callback

      if (wp.deleted()) return 1;           // exit, if deleted

      // Now we are sure that the widget has not been deleted,
      // and it is safe to access the widget:

      box(FL_FLAT_BOX);
      color(FL_WHITE);
      redraw();
    }
  }
  \endcode

*/
class FL_EXPORT Fl_Widget_Tracker {

  Fl_Widget* wp_;

public:

  Fl_Widget_Tracker(Fl_Widget *wi);
  ~Fl_Widget_Tracker();

  /**
    Returns a pointer to the watched widget.

    This pointer is \c NULL, if the widget has been deleted.
  */
  Fl_Widget *widget() {return wp_;}

  /**
    Returns 1, if the watched widget has been deleted.

    This is a convenience method. You can also use something like

    <tt>  if (wp.widget() == 0) // ...</tt>

    where \p wp is an Fl_Widget_Tracker object.
  */
  int deleted() {return wp_ == 0;}

  /**
    Returns 1, if the watched widget exists (has not been deleted).

    This is a convenience method. You can also use something like

    <tt>  if (wp.widget() != 0) // ...</tt>

    where \p wp is an Fl_Widget_Tracker object.
  */
  int exists()  {return wp_ != 0;}

};

 /** \defgroup  fl_unicode  Unicode and UTF-8 functions
        fl global Unicode and UTF-8 handling functions declared in <FL/fl_utf8.h>
     @{ */
 /** @} */

#endif // !Fl_H