Add pen/stylus/tablet API and driver for macOS (#1326)

* define the pen/tablet support API
* add pen event handler stub as a fallback
* add pen device test "penpal".
* Add macOS pen/stylus/tablet driver.
* Add Oxygen documentation.

FL/Fl.H

@@ -28,6 +28,7 @@
 #include <FL/core/function_types.H>   // widget callbacks and services
 #include <FL/core/events.H>           // global event handling
 #include <FL/core/options.H>          // system and application setting
+#include <FL/core/pen_events.H>       // pen and tablet events
 #include <FL/Fl_Widget_Tracker.H>     // historically included here
 
 #ifdef FLTK_HAVE_CAIRO
@@ -109,7 +110,6 @@ FL_EXPORT extern bool idle();
 FL_EXPORT extern const char* scheme_;
 FL_EXPORT extern Fl_Image* scheme_bg_;
 
-//FL_EXPORT extern int e_original_keysym; // late addition
 FL_EXPORT extern int scrollbar_size_;
 FL_EXPORT extern int menu_linespacing_; // STR #2927
 #endif

FL/Fl_Widget_Tracker.H

@@ -76,8 +76,19 @@ class FL_EXPORT Fl_Widget_Tracker {
 public:
 
   Fl_Widget_Tracker(Fl_Widget *wi);
+  // Rule of five. Note that we *can* implement these when we refactor widget
+  // tracking with a C++11 map or unordered_map, for example.
+  Fl_Widget_Tracker(const Fl_Widget_Tracker&) = delete;
+  Fl_Widget_Tracker(Fl_Widget_Tracker&&) = delete;
+  Fl_Widget_Tracker& operator=(const Fl_Widget_Tracker&) = delete;
+  Fl_Widget_Tracker& operator=(Fl_Widget_Tracker&&) = delete;
   ~Fl_Widget_Tracker();
 
+  /**
+   Clear the widget pointer.
+   */
+  void clear() { wp_ = nullptr; }
+
   /**
     Returns a pointer to the watched widget.
     \return nullptr if the widget was deleted.
@@ -88,13 +99,13 @@ public:
     Check if the widget was deleted since the tracker was created.
     \return 1 if the watched widget has been deleted, otherwise 0
   */
-  int deleted() {return wp_ == 0;}
+  int deleted() {return wp_ == nullptr;}
 
   /**
     Check if the widget exists and was not deleted since the tracker was created.
     \return 1 if the watched widget exists, otherwise 0
   */
-  int exists() { return wp_ != 0; }
+  int exists() { return wp_ != nullptr; }
 
 };
 

FL/core/events.H

@@ -71,6 +71,8 @@ FL_EXPORT extern Fl_Widget*         belowmouse_;        ///< Widget under mouse
 FL_EXPORT extern Fl_Widget*         pushed_;            ///< Widget receiving drag events
 FL_EXPORT extern Fl_Widget*         focus_;             ///< Widget with keyboard focus
 
+// Event variables should be private, but would harm back compatibility.
+
 #endif // FL_DOXYGEN
 
 

FL/core/pen_events.H

@@ -0,0 +1,465 @@
+//
+// Pen event header file for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 2025 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/core/pen_events.H
+ \brief Pen event handling variables and functions.
+*/
+
+#ifndef Fl_core_pen_events_H
+#define Fl_core_pen_events_H
+
+#include <FL/fl_config.h>             // build configuration
+#include <FL/Fl_Export.H>             // for FL_EXPORT
+#include <FL/core/function_types.H>   // widget callbacks and services
+
+#include <cstdint>
+
+class Fl_Widget;
+
+namespace Fl {
+
+/** FLTK Pen/Stylus/Tablet input driver API. */
+namespace Pen {
+
+/**
+ \defgroup fl_pen_events Pen and tablet event handling
+ \ingroup fl_events
+ \brief This chapter documents the Fl::Pen namespace API, declared in <FL/core/pen_events.H>
+
+ The FL::Pen namespace contains everything needed to work with a pen type input
+ device, either in connection with an external tablet, or as a stylus for
+ drawing directly onto a screen.
+
+ To receive pen input, call Fl::Pen::subscribe() for one or more widgets. The
+ widget will receive a Fl::Pen::ENTER event when the stylus enters the widget
+ area. By returning 1 to Fl::Pen::ENTER, all further pen events are sent to
+ this widget, and no mouse events are generated until Fl::Pen::LEAVE.
+
+ Returning 0 Fl::Pen::ENTER tells FLTK to suppress further pen events until
+ Fl::Pen::LEAVE, and convert them into mouse events instead.
+
+ Pen events also set Fl::event_x(), Fl::event_y(), Fl::event_x_root(),
+ Fl::event_y_root(), Fl::event_is_click(), and Fl::event_clicks().
+
+ @{
+ */
+
+/**
+ \brief Bitfield of traits.
+ This is used in Fl::Pen::driver_traits() and Fl::Pen::pen_traits().
+ */
+enum class Trait : uint32_t {
+  /// No bits set
+  NONE              = 0x0000,
+  /// Set if FLTK supports tablets and pens on this platform
+  DRIVER_AVAILABLE  = 0x0001,
+  /// Set after the system detected a pen, stylus, or tablet. This bit may not be
+  /// set until a pen is brought into proximity of the tablet.
+  DETECTED          = 0x0002,
+  /// If set, this is a digitizer for a display; if clear, this is a standalone tablet
+  DISPLAY           = 0x0004,
+  /// Driver provides different device IDs for different pens
+  PEN_ID            = 0x0008,
+  /// Pen may have an eraser tip
+  ERASER            = 0x0010,
+  /// Pen returns a pressure value
+  PRESSURE          = 0x0020,
+  /// Pen returns a barrel pressure value (tangential pressure)
+  BARREL_PRESSURE   = 0x0040,
+  /// Pen returns tilt in X direction
+  TILT_X            = 0x0080,
+  /// Pen returns tilt in Y direction
+  TILT_Y            = 0x0100,
+  /// Pen returns a twist value
+  TWIST             = 0x0200,
+  /// Pen returns a proximity value
+  PROXIMITY         = 0x0400,
+};
+
+/**
+ \brief Bitwise OR operator for Trait enum.
+ \param lhs Left-hand side trait flags
+ \param rhs Right-hand side trait flags
+ \return Combined trait flags
+ */
+inline constexpr Trait operator|(Trait lhs, Trait rhs) {
+  return static_cast<Trait>(static_cast<uint32_t>(lhs) | static_cast<uint32_t>(rhs));
+}
+
+/**
+ \brief Bitwise AND operator for Trait enum.
+ \param lhs Left-hand side trait flags
+ \param rhs Right-hand side trait flags
+ \return Intersection of trait flags
+ */
+inline constexpr Trait operator&(Trait lhs, Trait rhs) {
+  return static_cast<Trait>(static_cast<uint32_t>(lhs) & static_cast<uint32_t>(rhs));
+}
+
+/**
+ \brief Bitwise OR assignment operator for Trait enum.
+ \param lhs Left-hand side trait flags (modified in place)
+ \param rhs Right-hand side trait flags
+ \return Reference to modified lhs
+ */
+inline Trait& operator|=(Trait& lhs, Trait rhs) {
+  lhs = lhs | rhs;
+  return lhs;
+}
+
+
+/**
+ \brief Bitfield of pen state flags.
+ \see event_state(), event_trigger()
+ */
+enum class State : uint32_t {
+  /// No button pressed
+  NONE              = 0x0000,
+  /// The tip hovers over the surface but does not touch it
+  TIP_HOVERS        = 0x0001,
+  /// The tip touches the surface
+  TIP_DOWN          = 0x0002,
+  /// The eraser hovers over the surface but does not touch it
+  ERASER_HOVERS     = 0x0004,
+  /// The eraser touches the surface
+  ERASER_DOWN       = 0x0008,
+  /// Barrel button 0, usually the lower button on a pen, is pressed
+  BUTTON0           = 0x0100,
+  /// Barrel button 1, usually the upper button on a pen, is pressed
+  BUTTON1           = 0x0200,
+  /// Barrel button 2 is pressed
+  BUTTON2           = 0x0400,
+  /// Barrel button 3 is pressed
+  BUTTON3           = 0x0800,
+  /// Mask for all buttons, tip, and eraser down
+  ANY_DOWN          = BUTTON0 | BUTTON1 | BUTTON2 | BUTTON3 | TIP_DOWN | ERASER_DOWN,
+};
+
+/**
+ \brief Bitwise OR operator for State enum.
+ \param lhs Left-hand side state flags
+ \param rhs Right-hand side state flags
+ \return Combined state flags
+ */
+inline constexpr State operator|(State lhs, State rhs) {
+  return static_cast<State>(static_cast<uint32_t>(lhs) | static_cast<uint32_t>(rhs));
+}
+
+/**
+ \brief Bitwise AND operator for State enum.
+ \param lhs Left-hand side state flags
+ \param rhs Right-hand side state flags
+ \return Intersection of state flags
+ */
+inline constexpr State operator&(State lhs, State rhs) {
+  return static_cast<State>(static_cast<uint32_t>(lhs) & static_cast<uint32_t>(rhs));
+}
+
+/**
+ \brief Bitwise OR assignment operator for State enum.
+ \param lhs Left-hand side state flags (modified in place)
+ \param rhs Right-hand side state flags
+ \return Reference to modified lhs
+ */
+inline State& operator|=(State& lhs, State rhs) {
+  lhs = lhs | rhs;
+  return lhs;
+}
+
+
+/**
+ \brief List of pen events.
+ These events extend the standard Fl_Event enumeration.
+ \see enum Fl_Event
+ */
+enum Event {
+  /**
+   Pen entered the proximity of the tablet with a new pen.
+   */
+  DETECTED = 0x1000,
+
+  /**
+   Pen entered the proximity of the tablet with a known, but changed pen.
+   User changed to a different pen (event_id() > 0) or the pen or tablet
+   was disconnected (event_id() == -1). Pen IDs, if supported, are assigned by
+   the tablet manufacturer.
+   */
+  CHANGED,
+
+  /**
+   Pen entered the proximity of the tablet with a known pen.
+   */
+  IN_RANGE,
+
+  /**
+   Pen left the proximity of the tablet.
+   */
+  OUT_OF_RANGE,
+
+  /**
+   Pen entered the widget area, either by moving in x/y, or by
+   a proximity change (pen gets closer to the surface).
+   event_trigger() returns 0, TIP_HOVERS, or ERASER_HOVERS.
+   */
+  ENTER,
+
+  /**
+   If no button is pressed, indicates that the pen left the widget area.
+   While any pen button is held down, or the pen touches the surface,
+   Fl::pushed() is set, and the pushed widgets receives DRAG events, even
+   if the pen leaves the widget area. If all buttons are released outside the
+   widget area, a LEAVE event is sent as well as LIFT or BUTTON_RELEASE.
+   */
+  LEAVE,
+
+  /**
+   Pen went from hovering to touching the surface.
+   event_trigger() returns TIP_DOWN or ERASER_DOWN.
+   */
+  TOUCH,
+
+  /**
+   Pen went from touching to hovering over the surface.
+   event_trigger() returns TIP_HOVERS or ERASER_HOVERS.
+  */
+  LIFT,
+
+  /** Pen moved without touching the surface and no button is pressed. */
+  HOVER,
+
+  /** Pen moved while touching the surface, or any button is pressed. */
+  DRAW,
+
+  /**
+   A pen button was pushed.
+   event_trigger() returns BUTTON0, BUTTON1, BUTTON2, or BUTTON3.
+   */
+  BUTTON_PUSH,
+
+  /**
+   A pen button was released.
+   event_trigger() returns BUTTON0, BUTTON1, BUTTON2, or BUTTON3.
+   */
+  BUTTON_RELEASE
+
+};
+
+/**
+ \brief Query the traits supported by the pen/tablet driver.
+
+ This function returns a bitfield of traits that are supported by the FLTK driver
+ for this platform. If a trait is not supported, the corresponding event value
+ will not return a useful value. Note that even if the FLTK driver support a
+ trait, the underlying pen device or driver may not. Fl::Pen will return a
+ known default for those event values.
+
+ The bitfield returned is static.
+
+ \return a bitfield of supported traits
+ \see pen_traits()
+ */
+FL_EXPORT extern Trait driver_traits();
+
+/**
+ \brief Return true if the corresponding bit is set in the driver traits.
+ \param[in] bits check for one or more trait bits
+ \return true if any bit is set
+ */
+inline bool driver_traits(Trait bits) {
+  return ((driver_traits() & bits) != Trait::NONE);
+}
+
+/**
+ \brief Query traits of the current pen or stylus.
+ The value returned by this function may change when pens change or when more
+ information becomes known about the currently used pen.
+ \param[in] pen_id a now pen ID as returned from event_pen_id(),
+    or 0 for the current pen
+ \return a bitfield of supported traits
+ */
+FL_EXPORT extern Trait pen_traits(int pen_id = 0);
+
+/**
+ \brief Return true if the corresponding bit is set in the pen traits.
+ \param[in] bits check for one or more trait bits
+ \param[in] pen_id a now pen ID as returned from event_pen_id(),
+  or 0 for the current pen
+ \return true if any bit is set
+ */
+inline bool pen_traits(Trait bits, int pen_id = 0) {
+  return ((pen_traits() & bits) != Trait::NONE);
+}
+
+/**
+ \brief Receive a Pen::ENTER event when the pen moves inside this widget.
+ Multiple widgets can subscribe to pen events, but every widget must only
+ subscribe once.
+ \param widget Widget to subscribe to pen events
+ */
+FL_EXPORT extern void subscribe(Fl_Widget* widget);
+
+/**
+ \brief Stop receiving Pen::ENTER for this widget.
+ Deleting a widget will automatically unsubscribe it.
+ \param widget Widget to unsubscribe from pen events
+ */
+FL_EXPORT extern void unsubscribe(Fl_Widget* widget);
+
+/**
+ Clear the "pushed" state and forward pen events as mouse events.
+ Call this if another window is popped up during pen event handling, so
+ mouse event handling can resume normal.
+ */
+FL_EXPORT extern void release();
+
+/// \name Query values during event handling
+/// @{
+
+/**
+ \brief Returns the pen x and y position inside the handling widget as doubles.
+ These functions provide high-precision pen coordinates relative to the widget
+ that received the pen event. For integer coordinates, use Fl::event_x() and
+ Fl::event_y() instead.
+ \return Pen position as floating-point coordinate, defaults to 0.0
+ \see Fl::event_x(), Fl::event_y()
+ */
+FL_EXPORT extern double event_x();
+/** \brief Returns pen Y coordinate in widget space, see event_x(). */
+FL_EXPORT extern double event_y();
+
+/**
+ \brief Returns the pen x and y position in global coordinates as doubles.
+ For integer coordinates, use Fl::event_x_root() and Fl::event_y_root().
+ \return Pen position as floating-point coordinate in screen space, defaults to 0.0
+ \see Fl::event_x_root(), Fl::event_y_root()
+ */
+FL_EXPORT extern double event_x_root();
+/** \brief Returns pen Y coordinate in screen space, see event_x_root(). */
+FL_EXPORT extern double event_y_root();
+
+/**
+ \brief Returns the ID of the pen used in the last event.
+ \return Unique pen identifier, or -1 if pen was removed, defaults to 0
+ \see Trait::PEN_ID
+ */
+FL_EXPORT extern int event_pen_id();
+
+/**
+ \brief Returns the pressure between the tip or eraser and the surface.
+ \return pressure value from 0.0 (no pressure) to 1.0 (maximum pressure),
+      defaults to 1.0.
+ \see Trait::PRESSURE
+ */
+FL_EXPORT extern double event_pressure();
+
+/**
+ \brief Returns barrel pressure or tangential pressure.
+ \return Pressure value from -1.0 to 1.0 , defaults to 0.0 .
+ \see Trait::BARREL_PRESSURE
+ */
+FL_EXPORT extern double event_barrel_pressure();
+
+/**
+ \brief Returns the tilt of the pen in the x and y directions between -1 and 1.
+
+ X-axis tilt returns -1.0 when the pen tilts all the way to the left, 0.0 when
+ it is perfectly vertical, and 1.0 all the way to the right. Most pens seem to
+ return a maximum range of -0.7 to 0.7.
+
+ Y-axis tilt returns -1.0 when the pen tilts away from the user, and 1.0 when
+ it tilts toward the user.
+
+ \return Tilt value from -1.0 to 1.0, defaults to 0.0
+ \see Trait::TILT_X, Trait::TILT_Y
+ */
+FL_EXPORT extern double event_tilt_x();
+/** \brief Returns pen Y-axis tilt, see event_tilt_x() */
+FL_EXPORT extern double event_tilt_y();
+
+/**
+ \brief Returns the pens axial rotation in degrees.
+ \return Twist angle in degrees, defaults to 0.0 .
+ \see Trait::TWIST
+ */
+FL_EXPORT extern double event_twist();
+
+/**
+ \brief Returns the proximity of the pen to the surface between 0 and 1.
+ A proximity of 0 is closest to the surface, 1 is farthest away.
+ \return Proximity value from 0.0 (touching) to 1.0 (far away), defaults to 0.0 .
+ \see Trait::PROXIMITY
+ */
+FL_EXPORT extern double event_proximity();
+
+/**
+ \brief Returns the state of the various buttons and tips.
+ \return Current state flags (combination of State values)
+ */
+FL_EXPORT extern State event_state();
+
+/**
+ \brief Return true if the corresponding bit is set in the event state.
+ \param[in] bits check for one or more event state bits
+ \return true if any bit is set
+ */
+inline bool event_state(State bits) {
+  return ((event_state() & bits) != State::NONE);
+}
+
+/**
+ \brief Returns the state change that triggered the event.
+ \return a state with one bit set for the action that triggered this event
+ */
+FL_EXPORT extern State event_trigger();
+
+/** @} */ // group fl_pen_events
+
+
+} // namespace Pen
+
+} // namespace Fl
+
+
+/*
+ Resources:
+
+ Windows:
+ 1. Legacy WinTab API (Win2k), Wintab32.dll, wintab.h
+    https://developer.wacom.com/en-us/developer-dashboard/downloads
+ 2. Windows Ink API (Modern, Win10), Windows.UI.Input.Inking (WinRT API), InkCanvas(), etc.
+    https://learn.microsoft.com/windows/uwp/design/input/windows-ink
+ 3. Pointer Input / WM_POINTER API (Win8), WM_POINTERUPDATE, GetPointerPenInfo
+    https://learn.microsoft.com/windows/win32/inputmsg/wm-pointerupdate
+      return WTInfo(0, 0, NULL) > 0; // Wintab check
+
+ Linux:
+ 1. Low-level: evdev, /dev/input/event*, libevdev,
+    https://www.kernel.org/doc/html/latest/input/event-codes.html
+ 2. Mid-level: XInput2 (for X11), XI_Motion, XI_ButtonPress
+    https://www.x.org/releases/current/doc/inputproto/XI2proto.txt
+    https://www.freedesktop.org/wiki/Software/libevdev/
+ 3. Mid-level: Wayland tablet protocol, tablet-v2 protocol,
+    zwp_tablet_tool_v2_listener, zwp_tablet_v2, zwp_tablet_seat_v2
+    https://wayland.app/protocols/tablet-v2
+
+ SDL3:
+    https://github.com/libsdl-org/SDL/blob/main/include/SDL3/SDL_pen.h
+    https://wiki.libsdl.org/SDL3/CategoryPen
+ */
+
+
+#endif // !Fl_core_pen_events_H

FL/names.h

@@ -24,6 +24,9 @@
 #ifndef FL_NAMES_H
 #define FL_NAMES_H
 
+#include <FL/Fl.H>  // for event constants
+#include <map>
+
 /** \defgroup fl_events Events handling functions
     @{
  */
@@ -43,43 +46,53 @@
   }
   \endcode
  */
-const char * const fl_eventnames[] =
+std::map<int, const char*> fl_eventnames = {
-{
+  { FL_NO_EVENT, "FL_NO_EVENT" },
-  "FL_NO_EVENT",
+  { FL_PUSH, "FL_PUSH" },
-  "FL_PUSH",
+  { FL_RELEASE, "FL_RELEASE" },
-  "FL_RELEASE",
+  { FL_ENTER, "FL_ENTER" },
-  "FL_ENTER",
+  { FL_LEAVE, "FL_LEAVE" },
-  "FL_LEAVE",
+  { FL_DRAG, "FL_DRAG" },
-  "FL_DRAG",
+  { FL_FOCUS, "FL_FOCUS" },
-  "FL_FOCUS",
+  { FL_UNFOCUS, "FL_UNFOCUS" },
-  "FL_UNFOCUS",
+  { FL_KEYDOWN, "FL_KEYDOWN" },
-  "FL_KEYDOWN",
+  { FL_KEYUP, "FL_KEYUP" },
-  "FL_KEYUP",
+  { FL_CLOSE, "FL_CLOSE" },
-  "FL_CLOSE",
+  { FL_MOVE, "FL_MOVE" },
-  "FL_MOVE",
+  { FL_SHORTCUT, "FL_SHORTCUT" },
-  "FL_SHORTCUT",
+  { FL_DEACTIVATE, "FL_DEACTIVATE" },
-  "FL_DEACTIVATE",
+  { FL_ACTIVATE, "FL_ACTIVATE" },
-  "FL_ACTIVATE",
+  { FL_HIDE, "FL_HIDE" },
-  "FL_HIDE",
+  { FL_SHOW, "FL_SHOW" },
-  "FL_SHOW",
+  { FL_PASTE, "FL_PASTE" },
-  "FL_PASTE",
+  { FL_SELECTIONCLEAR, "FL_SELECTIONCLEAR" },
-  "FL_SELECTIONCLEAR",
+  { FL_MOUSEWHEEL, "FL_MOUSEWHEEL" },
-  "FL_MOUSEWHEEL",
+  { FL_DND_ENTER, "FL_DND_ENTER" },
-  "FL_DND_ENTER",
+  { FL_DND_DRAG, "FL_DND_DRAG" },
-  "FL_DND_DRAG",
+  { FL_DND_LEAVE, "FL_DND_LEAVE" },
-  "FL_DND_LEAVE",
+  { FL_DND_RELEASE, "FL_DND_RELEASE" },
-  "FL_DND_RELEASE",
+  { FL_SCREEN_CONFIGURATION_CHANGED, "FL_SCREEN_CONFIGURATION_CHANGED" },
-  "FL_SCREEN_CONFIGURATION_CHANGED",
+  { FL_FULLSCREEN, "FL_FULLSCREEN" },
-  "FL_FULLSCREEN",
+  { FL_ZOOM_GESTURE, "FL_ZOOM_GESTURE" },
-  "FL_ZOOM_GESTURE",
+  { FL_ZOOM_EVENT, "FL_ZOOM_EVENT" },
-  "FL_ZOOM_EVENT",
+  { FL_BEFORE_TOOLTIP, "FL_BEFORE_TOOLTIP" },
-  "FL_BEFORE_TOOLTIP",
+  { FL_BEFORE_MENU, "FL_BEFORE_MENU" },
-  "FL_BEFORE_MENU",
+  { /*FL_EVENT_*/ 30, "FL_EVENT_30" }, // not yet defined, just in case it /will/ be defined ...
-  "FL_EVENT_30", // not yet defined, just in case it /will/ be defined ...
+  { /*FL_EVENT_*/ 31, "FL_EVENT_31" }, // not yet defined, just in case it /will/ be defined ...
-  "FL_EVENT_31", // not yet defined, just in case it /will/ be defined ...
+  { /*FL_EVENT_*/ 32, "FL_EVENT_32" },  // not yet defined, just in case it /will/ be defined ...
-  "FL_EVENT_32"  // not yet defined, just in case it /will/ be defined ...
+  { Fl::Pen::DETECTED, "Fl::Pen::DETECTED" },
+  { Fl::Pen::CHANGED, "Fl::Pen::CHANGED" },
+  { Fl::Pen::ENTER, "Fl::Pen::ENTER" },
+  { Fl::Pen::LEAVE, "Fl::Pen::LEAVE" },
+  { Fl::Pen::TOUCH, "Fl::Pen::TOUCH" },
+  { Fl::Pen::LIFT, "Fl::Pen::LIFT" },
+  { Fl::Pen::HOVER, "Fl::Pen::HOVER" },
+  { Fl::Pen::DRAW, "Fl::Pen::DRAW" },
+  { Fl::Pen::BUTTON_PUSH, "Fl::Pen::BUTTON_PUSH" },
+  { Fl::Pen::BUTTON_RELEASE, "Fl::Pen::BUTTON_RELEASE" }
 };
 
+
 /**
   This is an array of font names you can use to convert font numbers into names.
 

src/CMakeLists.txt

@@ -202,6 +202,12 @@ file(GLOB
   "*.[hH]"
 )
 
+# find all private header files in source directory "src/..."
+file(GLOB
+  PRIVATE_HEADER_FILES
+  "*.[hH]"
+)
+
 # add generated header files in build directory
 list(APPEND HEADER_FILES
   ${CMAKE_CURRENT_BINARY_DIR}/../FL/fl_config.h
@@ -235,6 +241,7 @@ if(FLTK_USE_X11 AND NOT FLTK_USE_WAYLAND)
     drivers/Xlib/Fl_Xlib_Copy_Surface_Driver.cxx
     drivers/Xlib/Fl_Xlib_Image_Surface_Driver.cxx
     drivers/X11/fl_X11_platform_init.cxx
+    drivers/Stubs/Fl_Stubs_Pen_Events.cxx
     Fl_x.cxx
     fl_dnd_x.cxx
     Fl_Native_File_Chooser_FLTK.cxx
@@ -311,6 +318,7 @@ elseif(FLTK_USE_WAYLAND)
     drivers/Wayland/fl_wayland_clipboard_dnd.cxx
     drivers/Wayland/fl_wayland_platform_init.cxx
     drivers/Cairo/Fl_Cairo_Graphics_Driver.cxx
+    drivers/Stubs/Fl_Stubs_Pen_Events.cxx
     Fl_Native_File_Chooser_FLTK.cxx
     Fl_Native_File_Chooser_GTK.cxx
   )
@@ -397,6 +405,7 @@ else()
     drivers/GDI/Fl_GDI_Graphics_Driver_vertex.cxx
     drivers/GDI/Fl_GDI_Copy_Surface_Driver.cxx
     drivers/GDI/Fl_GDI_Image_Surface_Driver.cxx
+    drivers/Stubs/Fl_Stubs_Pen_Events.cxx
     Fl_win32.cxx
     fl_dnd_win32.cxx
     Fl_Native_File_Chooser_WIN32.cxx
@@ -617,6 +626,7 @@ if(APPLE AND NOT FLTK_BACKEND_X11)
   set(MMFILES
     Fl_cocoa.mm
     drivers/Cocoa/Fl_Cocoa_Printer_Driver.mm
+    drivers/Cocoa/Fl_Cocoa_Pen_Events.mm
     Fl_Native_File_Chooser_MAC.mm
     Fl_MacOS_Sys_Menu_Bar.mm
   )

src/Fl_Menu.cxx

@@ -886,7 +886,8 @@ int menuwindow::handle_part1(int e) {
         int item; const Fl_Menu_Item* m = mw.menu->find_shortcut(&item);
         if (m) {
           setitem(m, mymenu, item);
-          if (!m->submenu()) pp.state = DONE_STATE;
+          if (!m->submenu())
+            pp.state = DONE_STATE;
           return 1;
         }
       }

src/Fl_cocoa.mm

@@ -72,6 +72,10 @@ extern int fl_send_system_handlers(void *e);
 // converting cr lf converter function
 static void createAppleMenu(void);
 static void cocoaMouseHandler(NSEvent *theEvent);
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_9
+static bool cocoaTabletHandler(NSEvent *theEvent, bool lock);
+extern bool fl_cocoa_tablet_handler(NSEvent*, Fl_Window*);
+#endif
 static void clipboard_check(void);
 static NSBitmapImageRep* rect_to_NSBitmapImageRep(Fl_Window *win, int x, int y, int w, int h);
 static NSBitmapImageRep* rect_to_NSBitmapImageRep_subwins(Fl_Window *win, int x, int y, int w, int h, bool capture_subwins);
@@ -627,6 +631,10 @@ void Fl_Cocoa_Screen_Driver::breakMacEventLoop()
            endedAtPoint:(NSPoint)screenPoint operation:(NSDragOperation)operation;
 #endif
 - (BOOL)did_view_resolution_change;
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_9
+- (void)tabletProximity:(NSEvent *)theEvent;
+- (void)tabletPoint:(NSEvent *)theEvent;
+#endif
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_14
 - (void)create_aux_bitmap:(CGContextRef)gc retina:(BOOL)r;
 - (void)reset_aux_bitmap;
@@ -1049,21 +1057,52 @@ static void cocoaMagnifyHandler(NSEvent *theEvent)
 #endif
 }
 
+
+static bool cocoaTabletHandler(NSEvent *theEvent, bool lock)
+{
+  if (lock) fl_lock_function();
+  auto theWindow = (Fl_Window*)[(FLWindow*)[theEvent window] getFl_Window];
+  auto ret = fl_cocoa_tablet_handler(theEvent, theWindow);
+  if (lock) fl_unlock_function();
+  return ret;
+}
+
+namespace Fl {
+// Global mouse position at mouse down event
+int e_x_down { 0 };
+int e_y_down { 0 };
+};
+
 /*
  * Cocoa Mouse Button Handler
  */
 static void cocoaMouseHandler(NSEvent *theEvent)
 {
   static int keysym[] = { 0, FL_Button+1, FL_Button+3, FL_Button+2, FL_Button+4, FL_Button+5 };
-  static int px, py;
 
   fl_lock_function();
 
+  // Handle tablet proximity and point subevents
+  if (   ([theEvent type] != NSEventTypeMouseEntered)  // does not have a subtype
+      && ([theEvent type] != NSEventTypeMouseExited) ) // does not have a subtype
+  {
+    if (   ([theEvent subtype] == NSEventSubtypeTabletPoint)
+        || ([theEvent subtype] == NSEventSubtypeTabletProximity) )
+    {
+      if (cocoaTabletHandler(theEvent, false)) {
+        fl_unlock_function();
+        return;
+      }
+      // else fall through into mouse event handling
+    }
+  }
+
   Fl_Window *window = (Fl_Window*)[(FLWindow*)[theEvent window] getFl_Window];
   if (!window || !window->shown() ) {
     fl_unlock_function();
     return;
   }
+
   NSPoint pos = [theEvent locationInWindow];
   float s = Fl::screen_driver()->scale(0);
   pos.x /= s; pos.y /= s;
@@ -1096,7 +1135,8 @@ static void cocoaMouseHandler(NSEvent *theEvent)
     case NSEventTypeOtherMouseDown:
       sendEvent = FL_PUSH;
       Fl::e_is_click = 1;
-      px = (int)pos.x; py = (int)pos.y;
+      Fl::e_x_down = (int)pos.x;
+      Fl::e_y_down = (int)pos.y;
       if ([theEvent clickCount] > 1)
         Fl::e_clicks++;
       else
@@ -1121,7 +1161,8 @@ static void cocoaMouseHandler(NSEvent *theEvent)
     case NSEventTypeOtherMouseDragged: {
       if ( !sendEvent ) {
         sendEvent = FL_MOVE; // Fl::handle will convert into FL_DRAG
-        if (fabs(pos.x-px)>5 || fabs(pos.y-py)>5)
+        if ( (fabs(pos.x - Fl::e_x_down) > 5) ||
+             (fabs(pos.y - Fl::e_y_down) > 5))
           Fl::e_is_click = 0;
       }
       mods_to_e_state( mods );
@@ -1158,6 +1199,7 @@ static void cocoaMouseHandler(NSEvent *theEvent)
   return;
 }
 
+
 @interface FLTextView : NSTextView // this subclass is only needed under OS X < 10.6
 {
   BOOL isActive;
@@ -1847,7 +1889,7 @@ void Fl_Darwin_System_Driver::open_callback(void (*cb)(const char *)) {
     // still needed for the system menu.
     [[NSApp keyWindow] sendEvent:theEvent];
     return;
-    }
+  }
   [NSApp sendEvent:theEvent];
 }
 @end
@@ -2589,6 +2631,14 @@ static FLTextInputContext* fltextinputcontext_instance = nil;
 - (void)mouseExited:(NSEvent *)theEvent {
   cocoaMouseHandler(theEvent);
 }
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_9
+- (void)tabletProximity:(NSEvent *)theEvent {
+  cocoaTabletHandler(theEvent, true);
+}
+- (void)tabletPoint:(NSEvent *)theEvent {
+  cocoaTabletHandler(theEvent, true);
+}
+#endif
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_5
 - (void)updateTrackingAreas {
   if (fl_mac_os_version >= 100500) {

src/Fl_grab.cxx

@@ -27,5 +27,6 @@
 
 void Fl::grab(Fl_Window *win)
 {
+  Fl::Pen::release();
   screen_driver()->grab(win);
 }

src/drivers/Cocoa/Fl_Cocoa_Pen_Events.mm

@@ -0,0 +1,530 @@
+//
+// Definition of macOS Cocoa Pen/Tablet event driver.
+//
+// Copyright 2025 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
+//
+
+
+#include <config.h>
+#include <FL/platform.H>
+#include <FL/core/pen_events.H>
+#include <FL/Fl.H>
+#include <FL/Fl_Window.H>
+#include <FL/Fl_Tooltip.H>
+#include <FL/Fl_Widget_Tracker.H>
+#include "../../Fl_Screen_Driver.H"
+
+#import <Cocoa/Cocoa.h>
+
+#include <map>
+#include <memory>
+
+extern Fl_Window *fl_xmousewin;
+
+/*
+ Widgets and windows must subscribe to pen events. This is to reduce the amount
+ of events sent into the widget hierarchy.
+
+ Usually there is a pretty small number of subscribers, so looping through the
+ subscriber list should not be an issue.
+
+ All subscribers track their widget. If a widget is deleted while subscribed,
+ including during event handling, the driver will remove the subscription.
+ There is no need to explicitly unsubscribe.
+ */
+class Subscriber : public Fl_Widget_Tracker {
+public:
+  Subscriber(Fl_Widget *w) : Fl_Widget_Tracker(w) { }
+};
+
+
+/*
+ Manage a list of subscribers.
+ */
+class SubscriberList : public std::map<Fl_Widget*, std::shared_ptr<Subscriber>> {
+public:
+  SubscriberList() = default;
+  /* Remove subscribers that have a nullptr as a widget */
+  void cleanup() {
+    for (auto it = begin(); it != end(); ) {
+      if (!it->second->widget()) {
+        it = erase(it);
+      } else {
+        ++it;
+      }
+    }
+  }
+  /* Add a new subscriber, or return an existing one. */
+  std::shared_ptr<Subscriber> add(Fl_Widget *w) {
+    cleanup();
+    auto it = find(w);
+    if (it == end()) {
+      auto sub = std::make_shared<Subscriber>(w);
+      insert(std::make_pair(w, sub));
+      return sub;
+    } else {
+      return it->second;
+    }
+  }
+  /* Remove a subscriber form the list. */
+  void remove(Fl_Widget *w) {
+    auto it = find(w);
+    if (it != end()) {
+      it->second->clear();
+      erase(it);
+    }
+  }
+};
+
+static SubscriberList subscriber_list_;
+static std::shared_ptr<Subscriber> pushed_;
+static std::shared_ptr<Subscriber> below_pen_;
+static NSPointingDeviceType device_type_ { NSPointingDeviceTypePen };
+
+// The trait list keeps track of traits for every pen ID that appears while
+// handling events.
+// AppKit does not tell us what traits are available per pen or tablet, so
+// we use the first 5 motion events to discover event values that are not
+// the default value, and enter that knowledge into the traits database.
+typedef std::map<int, Fl::Pen::Trait> TraitList;
+static TraitList trait_list_;
+static int trait_countdown_ { 5 };
+static int current_pen_id_ { -1 };
+static Fl::Pen::Trait current_pen_trait_ { Fl::Pen::Trait::DRIVER_AVAILABLE };
+static Fl::Pen::Trait driver_traits_ {
+  Fl::Pen::Trait::DRIVER_AVAILABLE | Fl::Pen::Trait::PEN_ID |
+  Fl::Pen::Trait::ERASER | Fl::Pen::Trait::PRESSURE |
+  Fl::Pen::Trait::BARREL_PRESSURE | Fl::Pen::Trait::TILT_X |
+  Fl::Pen::Trait::TILT_Y | Fl::Pen::Trait::TWIST
+  // Notably missing: PROXIMITY
+};
+
+struct EventData {
+  double x { 0.0 };
+  double y { 0.0 };
+  double rx { 0.0 };
+  double ry { 0.0 };
+  double tilt_x { 0.0 };
+  double tilt_y { 0.0 };
+  double pressure { 1.0 };
+  double barrel_pressure { 0.0 };
+  double twist { 0.0 };
+  int pen_id { 0 };
+  Fl::Pen::State state { (Fl::Pen::State)0 };
+  Fl::Pen::State trigger { (Fl::Pen::State)0 };
+};
+
+// Temporary storage of event data for the driver;
+static struct EventData ev;
+
+
+namespace Fl {
+
+// Global mouse position at mouse down event
+extern int e_x_down;
+extern int e_y_down;
+
+namespace Pen {
+
+// The event data that is made available to the user during event handling
+struct EventData e;
+
+} // namespace Pen
+
+} // namespace Fl
+
+
+using namespace Fl::Pen;
+
+
+// Return a bit for everything that AppKit could return.
+Trait Fl::Pen::driver_traits() {
+  return driver_traits_;
+}
+
+Trait Fl::Pen::pen_traits(int pen_id) {
+  auto it = trait_list_.find(pen_id);
+  if (pen_id == 0)
+    return current_pen_trait_;
+  if (it == trait_list_.end()) {
+    return Trait::DRIVER_AVAILABLE;
+  } else {
+    return it->second;
+  }
+}
+
+void Fl::Pen::subscribe(Fl_Widget* widget) {
+  if (widget == nullptr) return;
+  subscriber_list_.add(widget);
+}
+
+void Fl::Pen::unsubscribe(Fl_Widget* widget) {
+  if (widget == nullptr) return;
+  subscriber_list_.remove(widget);
+}
+
+void Fl::Pen::release() {
+  pushed_ = nullptr;
+  below_pen_ = nullptr;
+}
+
+double Fl::Pen::event_x() { return e.x; }
+
+double Fl::Pen::event_y() { return e.y; }
+
+double Fl::Pen::event_x_root() { return e.rx; }
+
+double Fl::Pen::event_y_root() { return e.ry; }
+
+int Fl::Pen::event_pen_id() { return e.pen_id; }
+
+double Fl::Pen::event_pressure() { return e.pressure; }
+
+double Fl::Pen::event_barrel_pressure() { return e.barrel_pressure; }
+
+double Fl::Pen::event_tilt_x() { return e.tilt_x; }
+
+double Fl::Pen::event_tilt_y() { return e.tilt_y; }
+
+double Fl::Pen::event_twist() { return e.twist; }
+
+// Not supported in AppKit NSEvent
+double Fl::Pen::event_proximity() { return 0.0; }
+
+State Fl::Pen::event_state() { return e.state; }
+
+State Fl::Pen::event_trigger() { return e.trigger; }
+
+/**
+ Copy the event state.
+ */
+static void copy_state() {
+  Fl::Pen::State tr = (Fl::Pen::State)((uint32_t)Fl::Pen::e.state ^ (uint32_t)ev.state);
+  Fl::Pen::e = ev;
+  Fl::Pen::e.trigger = tr;
+  Fl::e_x = (int)ev.x;
+  Fl::e_y = (int)ev.y;
+  Fl::e_x_root = (int)ev.rx;
+  Fl::e_y_root = (int)ev.ry;
+}
+
+/**
+ Offset coordinates for subwindows and subsubwindows.
+ */
+static void offset_subwindow_event(Fl_Widget *w, double &x, double &y) {
+  Fl_Widget *p = w, *q;
+  while (p) {
+    q = p->parent();
+    if (p->as_window() && q) {
+      x -= p->x();
+      y -= p->y();
+    }
+    p = q;
+  };
+}
+
+/*
+ Check if coordinates are within the widget box.
+ Coordinates are in top_window space. We iterate up the hierarchy to ensure
+ that we handle subwindows correctly.
+ */
+static bool event_inside(Fl_Widget *w, double x, double y) {
+  offset_subwindow_event(w, x, y);
+  if (w->as_window()) {
+    return ((x >= 0) && (y >= 0) && (x < w->w()) && (y < w->h()));
+  } else {
+    return ((x >= w->x()) && (y >= w->y()) && (x < w->x() + w->w()) && (y < w->y() + w->h()));
+  }
+}
+
+/*
+ Find the widget under the pen event.
+ Search the subscriber list for widgets that are inside the same top window,
+ are visible, and are within the give coordinates. Subwindow aware.
+ */
+static Fl_Widget *find_below_pen(Fl_Window *win, double x, double y) {
+  for (auto &sub: subscriber_list_) {
+    Fl_Widget *candidate = sub.second->widget();
+    if (candidate && (candidate->top_window() == win)) {
+      if (candidate->visible() && event_inside(candidate, x, y)) {
+        return candidate;
+      }
+    }
+  }
+  return nullptr;
+}
+
+/*
+ Send the current event and event data to a widget.
+ Note: we will get the wrong coordinates if the widget is not a child of
+ the current event window (LEAVE events between windows).
+ */
+static int pen_send(Fl_Widget *w, int event, State trigger, bool &copied) {
+  // Copy most event data only once
+  if (!copied) {
+    copy_state();
+    copied = true;
+  }
+  // Copy the top_window coordinates again as they may change when w changes
+  e.x = ev.x;
+  e.y = ev.y;
+  offset_subwindow_event(w, e.x, e.y);
+  Fl::e_x = e.x;
+  Fl::e_y = e.y;
+  // Send the event.
+  e.trigger = trigger;
+  return w->handle(event);
+}
+
+/*
+ Send an event to all subscribers.
+ */
+static int pen_send_all(int event, State trigger) {
+  bool copied = false;
+  // use local value because handler may still change ev values
+  for (auto &it: subscriber_list_) {
+    auto w = it.second->widget();
+    if (w)
+      pen_send(w, event, trigger, copied);
+  }
+}
+
+/*
+ Convert the NSEvent button number to Fl::Pen::State,
+ */
+static State button_to_trigger(NSInteger button, bool down)
+{
+  switch (button) {
+    case 0:
+      if ( (ev.state & (State::ERASER_DOWN | State::ERASER_HOVERS)) != State::NONE ) {
+        return down ? State::ERASER_DOWN : State::ERASER_HOVERS;
+      } else {
+        return down ? State::TIP_DOWN : State::TIP_HOVERS;
+      }
+    case 1: return State::BUTTON0;
+    case 2: return State::BUTTON1;
+    case 3: return State::BUTTON2;
+    case 4: return State::BUTTON3;
+    default: return State::NONE;
+  }
+}
+
+/*
+ Handle events coming from Cocoa.
+ TODO: clickCount: store in Fl::event_clicks()
+ capabilityMask is useless, because it is vendor defined
+ If a modal window is open, AppKit will send window specific events only there.
+ */
+bool fl_cocoa_tablet_handler(NSEvent *event, Fl_Window *eventWindow)
+{
+  // Quick access to the main type.
+  auto type = [event type];
+
+  // There seems nothing useful here. Ignore for now.
+  if ((type == NSEventTypeMouseEntered) || (type == NSEventTypeMouseExited)) {
+    return false;
+  }
+
+  // Sort out tablet-only events and mouse plus tablet events.
+  bool is_mouse = ((type != NSEventTypeTabletPoint) && (type != NSEventTypeTabletProximity));
+
+  // Set the subtype if one is available. Only NSEventSubtypeTabletPoint and
+  // NSEventSubtypeTabletProximity matter in this context
+  NSEventSubtype subtype = is_mouse ? [event subtype] : NSEventSubtypeMouseEvent;
+
+  // Is this a change in proximity event?
+  bool is_proximity = ((type == NSEventTypeTabletProximity) || (subtype == NSEventSubtypeTabletProximity));
+
+  // Is this a pen pointer event?
+  bool is_point = ((type == NSEventTypeTabletPoint) || (subtype == NSEventSubtypeTabletPoint));
+
+  // Check if any of the pen down, move, drag, or up events was triggered.
+  bool is_down = ((type == NSEventTypeLeftMouseDown) || (type == NSEventTypeRightMouseDown) || (type == NSEventTypeOtherMouseDown));
+  bool is_up = ((type == NSEventTypeLeftMouseUp) || (type == NSEventTypeRightMouseUp) || (type == NSEventTypeOtherMouseUp));
+  bool is_drag = ((type == NSEventTypeLeftMouseDragged) || (type == NSEventTypeRightMouseDragged) || (type == NSEventTypeOtherMouseDragged));
+  bool is_motion = is_drag || (type == NSEventTypeMouseMoved);
+
+  // Find out if we can get the pen position
+  bool has_position = (eventWindow != nullptr) && (is_up || is_down || is_motion || is_proximity || is_point);
+
+  // Event has extended pen data set:
+  if (has_position) {
+    // Get the position data.
+    auto pt = [event locationInWindow];
+    double s = Fl::screen_driver()->scale(0);
+    ev.x = pt.x/s;
+    ev.y = eventWindow->h() - pt.y/s;
+    ev.rx = ev.x + eventWindow->x();
+    ev.ry = ev.y + eventWindow->y();
+    if (!is_proximity) {
+      // Get the pressure data.
+      ev.pressure = [event pressure];
+      ev.barrel_pressure = [event tangentialPressure];
+      // Get the tilt
+      auto tilt = [event tilt];
+      ev.tilt_x = -tilt.x;
+      ev.tilt_y =  tilt.y;
+      // Other stuff
+      ev.twist = [event rotation]; // TODO: untested
+      // ev.proximity = [event proximity]; // not supported in AppKit
+    }
+    if (device_type_ == NSPointingDeviceTypeEraser) {
+      if ([event buttonMask] & 1)
+        ev.state = State::ERASER_DOWN;
+      else
+        ev.state = State::ERASER_HOVERS;
+    } else {
+      if ([event buttonMask] & 1)
+        ev.state = State::TIP_DOWN;
+      else
+        ev.state = State::TIP_HOVERS;
+    }
+    if ([event buttonMask] & 0x0002) ev.state |= State::BUTTON0;
+    if ([event buttonMask] & 0x0004) ev.state |= State::BUTTON1;
+    if ([event buttonMask] & 0x0008) ev.state |= State::BUTTON2;
+    if ([event buttonMask] & 0x0010) ev.state |= State::BUTTON3;
+    // printf("0x%08x\n", [event buttonMask]);
+  }
+  if (is_proximity) {
+    ev.pen_id = (int)[event vendorID];
+    device_type_ = [event pointingDeviceType];
+  }
+  if (type == NSEventTypeTabletProximity) {
+    if ([event isEnteringProximity]) {
+      // Check if this is the first time we see this pen, or if the pen changed
+      if (current_pen_id_ != ev.pen_id) {
+        current_pen_id_ = ev.pen_id;
+        auto it = trait_list_.find(current_pen_id_);
+        if (it == trait_list_.end()) { // not found, create a new entry
+          trait_list_[current_pen_id_] = Trait::DRIVER_AVAILABLE;
+          trait_countdown_ = 5;
+          pen_send_all(Fl::Pen::DETECTED, State::NONE);
+          // printf("IN RANGE, NEW PEN\n");
+        } else {
+          pen_send_all(Fl::Pen::CHANGED, State::NONE);
+          // printf("IN RANGE, CHANGED PEN\n");
+        }
+        trait_list_[0] = trait_list_[current_pen_id_];  // set current pen traits
+      } else {
+        pen_send_all(Fl::Pen::IN_RANGE, State::NONE);
+        // printf("IN RANGE\n");
+      }
+    } else {
+      pen_send_all(Fl::Pen::OUT_OF_RANGE, State::NONE);
+      // printf("OUT OF RANGE\n");
+    }
+  }
+
+  Fl_Widget *receiver = nullptr;
+  bool pushed = false;
+  bool event_data_copied = false;
+
+  if (has_position) {
+    if (trait_countdown_) {
+      trait_countdown_--;
+      if (ev.tilt_x != 0.0) current_pen_trait_ |= Trait::TILT_X;
+      if (ev.tilt_y != 0.0) current_pen_trait_ |= Trait::TILT_Y;
+      if (ev.pressure != 1.0) current_pen_trait_ |= Trait::PRESSURE;
+      if (ev.barrel_pressure != 0.0) current_pen_trait_ |= Trait::BARREL_PRESSURE;
+      if (ev.pen_id != 0) current_pen_trait_ |= Trait::PEN_ID;
+      if (ev.twist != 0.0) current_pen_trait_ |= Trait::TWIST;
+      //if (ev.proximity != 0) current_pen_trait_ |= Trait::PROXIMITY;
+      trait_list_[current_pen_id_] = current_pen_trait_;
+    }
+    fl_xmousewin = eventWindow;
+    if (pushed_ && pushed_->widget() && (Fl::pushed() == pushed_->widget())) {
+      receiver = pushed_->widget();
+      if (Fl::grab() && (Fl::grab() != receiver->top_window()))
+        return 0;
+      if (Fl::modal() && (Fl::modal() != receiver->top_window()))
+        return 0;
+      pushed = true;
+    } else {
+      if (Fl::grab() && (Fl::grab() != eventWindow))
+        return 0;
+      if (Fl::modal() && (Fl::modal() != eventWindow))
+        return 0;
+      auto bpen = below_pen_ ? below_pen_->widget() : nullptr;
+      auto bmouse = Fl::belowmouse();
+      auto bpen_old = bmouse && (bmouse == bpen) ? bpen : nullptr;
+      auto bpen_now = find_below_pen(eventWindow, ev.x, ev.y);
+
+      if (bpen_now != bpen_old) {
+        if (bpen_old) {
+          pen_send(bpen_old, Fl::Pen::LEAVE, State::NONE, event_data_copied);
+        }
+        below_pen_ = nullptr;
+        if (bpen_now) {
+          State state = (device_type_ == NSPointingDeviceTypeEraser) ? State::ERASER_HOVERS : State::TIP_HOVERS;
+          if (pen_send(bpen_now, Fl::Pen::ENTER, state, event_data_copied)) {
+            below_pen_ = subscriber_list_[bpen_now];
+            Fl::belowmouse(bpen_now);
+          }
+        }
+      }
+
+      receiver = below_pen_ ? below_pen_->widget() : nullptr;
+      if (!receiver)
+        return 0;
+    }
+  } else {
+    // Anything to do here?
+  }
+
+  if (!receiver)
+    return 0;
+
+  int ret = 0;
+  if (is_down) {
+    if (!pushed) {
+      pushed_ = subscriber_list_[receiver];
+      Fl::pushed(receiver);
+    }
+    State trigger = button_to_trigger([event buttonNumber], true);
+    if ([event buttonNumber] == 0) {
+      Fl::e_is_click = 1;
+      Fl::e_x_down = (int)ev.x;
+      Fl::e_y_down = (int)ev.y;
+      if ([event clickCount] > 1)
+        Fl::e_clicks++;
+      else
+        Fl::e_clicks = 0;
+      ret = pen_send(receiver, Fl::Pen::TOUCH, trigger, event_data_copied);
+    } else {
+      ret = pen_send(receiver, Fl::Pen::BUTTON_PUSH, trigger, event_data_copied);
+    }
+  } else if (is_up) {
+    if ( (ev.state & State::ANY_DOWN) == State::NONE ) {
+      Fl::pushed(nullptr);
+      pushed_ = nullptr;
+    }
+    State trigger = button_to_trigger([event buttonNumber], true);
+    if ([event buttonNumber] == 0)
+      ret = pen_send(receiver, Fl::Pen::LIFT, trigger, event_data_copied);
+    else
+      ret = pen_send(receiver, Fl::Pen::BUTTON_RELEASE, trigger, event_data_copied);
+  } else if (is_motion) {
+    if (  Fl::e_is_click &&
+         ( (fabs((int)ev.x - Fl::e_x_down) > 5) ||
+           (fabs((int)ev.y - Fl::e_y_down) > 5) ) )
+      Fl::e_is_click = 0;
+    if (pushed) {
+      ret = pen_send(receiver, Fl::Pen::DRAW, State::NONE, event_data_copied);
+    } else {
+      ret = pen_send(receiver, Fl::Pen::HOVER, State::NONE, event_data_copied);
+    }
+  }
+  // Always return 1 because at this point, we capture pen events and don't
+  // want mouse events anymore!
+  return 1;
+}

src/drivers/Stubs/Fl_Stubs_Pen_Events.cxx

@@ -0,0 +1,73 @@
+//
+// Definition of default Pen/Tablet event driver.
+//
+// Copyright 2025 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
+//
+
+
+#include <config.h>
+#include <FL/platform.H>
+#include <FL/core/pen_events.H>
+#include <FL/Fl.H>
+
+class Fl_Widget;
+
+namespace Fl {
+
+namespace Pen {
+
+// double e_pressure_;
+
+} // namespace Pen
+
+} // namespace Fl
+
+
+using namespace Fl::Pen;
+
+
+Trait Fl::Pen::driver_traits() { return Trait::NONE; }
+
+Trait Fl::Pen::pen_traits(int pen_id) { return Trait::NONE; }
+
+void Fl::Pen::subscribe(Fl_Widget* widget) { }
+
+void Fl::Pen::unsubscribe(Fl_Widget* widget) { }
+
+void Fl::Pen::release() { }
+
+double Fl::Pen::event_x() { return 0.0; }
+
+double Fl::Pen::event_y() { return 0.0; }
+
+double Fl::Pen::event_x_root() { return 0.0; }
+
+double Fl::Pen::event_y_root() { return 0.0; }
+
+int Fl::Pen::event_pen_id() { return 0; }
+
+double Fl::Pen::event_pressure() { return 1.0; }
+
+double Fl::Pen::event_barrel_pressure() { return 0.0; }
+
+double Fl::Pen::event_tilt_x() { return 0.0; }
+
+double Fl::Pen::event_tilt_y() { return 0.0; }
+
+double Fl::Pen::event_twist() { return 0.0; }
+
+double Fl::Pen::event_proximity() { return 0.0; }
+
+State Fl::Pen::event_state() { return Fl::Pen::State::NONE; }
+
+State Fl::Pen::event_trigger() { return Fl::Pen::State::NONE; }

test/CMakeLists.txt

@@ -183,6 +183,7 @@ fl_create_example(navigation navigation.cxx fltk::fltk)
 fl_create_example(output output.cxx fltk::fltk)
 fl_create_example(overlay overlay.cxx fltk::fltk)
 fl_create_example(pack pack.cxx fltk::fltk)
+fl_create_example(penpal penpal.cxx fltk::fltk)
 fl_create_example(pixmap pixmap.cxx fltk::images)
 fl_create_example(pixmap_browser pixmap_browser.cxx fltk::images)
 fl_create_example(preferences preferences.fl fltk::fltk)

test/penpal.cxx

@@ -0,0 +1,314 @@
+//
+// Penpal pen/stylus/tablet test program for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 2025 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
+//
+
+// The Penpal test app is here to test pen/stylus/tablet event distribution
+// in the Fl::Pen driver. Our main window has three canvases for drawing.
+// The first canvas is a child of the main window. The second canvas is
+// inside a group. The third canvas is a subwindow inside the main window.
+// A second application window is itself yet another canvas.
+
+// We can test if the events are delivered to the right receiver, if the
+// mouse and pen offsets are correct. The pen implementation also reacts
+// to pen pressure and angles. If handle() returns 1 when receiving
+// Fl::Pen::ENTER, the event handler should not send any mouse events until
+// Fl::Pen::LEAVE.
+
+#include <FL/Fl.H>
+#include <FL/Fl_Window.H>
+#include <FL/Fl_Box.H>
+#include <FL/Fl_Menu_Item.H>
+#include <FL/platform.H>
+#include <FL/fl_draw.H>
+#include <FL/fl_message.H>
+#include <FL/names.h>
+
+extern Fl_Menu_Item app_menu[];
+extern int popup_app_menu();
+Fl_Widget *cv1 { nullptr };
+Fl_Window *cvwin { nullptr };
+
+//
+// The canvas interface implements incremental drawing and handles draw events.
+// It also implement pressure sensitive drawing with a pen or stylus.
+// And it implements an overlay plane that visualizes pen event data.
+//
+class CanvasInterface {
+  Fl_Widget *widget_ { nullptr };
+  bool in_window_ { false };
+  bool first_draw_ { true };
+  Fl_Offscreen offscreen_ { 0 };
+  Fl_Color color_ { 1 };
+  enum { NONE, HOVER, DRAW, PEN_HOVER, PEN_DRAW } overlay_ { NONE };
+  int ov_x_ { 0 };
+  int ov_y_ { 0 };
+public:
+  CanvasInterface(Fl_Widget *w) : widget_(w) { }
+  CanvasInterface(Fl_Window *w) : widget_(w), in_window_(true) { }
+  ~CanvasInterface() {
+    if (offscreen_) fl_delete_offscreen(offscreen_);
+  }
+  int cv_handle(int event);
+  void cv_draw();
+  void cv_paint();
+  void cv_pen_paint();
+};
+
+
+//
+// Handle mouse and pen events.
+//
+int CanvasInterface::cv_handle(int event)
+{
+  switch (event)
+  {
+    // Event handling for pen events:
+    case Fl::Pen::ENTER: // Return 1 to receive all pen events and suppress mouse events
+      // Pen entered the widget area.
+      color_++;
+      if (color_ > 6) color_ = 1;
+      /* fall through */
+    case Fl::Pen::HOVER:
+      // Pen move over the surface without touching it.
+      overlay_ = PEN_HOVER;
+      ov_x_ = Fl::event_x();
+      ov_y_ = Fl::event_y();
+      widget_->redraw();
+      return 1;
+    case Fl::Pen::TOUCH:
+      // Pen tip or eraser just touched the surface.
+      if (Fl::event_state(FL_CTRL) || Fl::Pen::event_state(Fl::Pen::State::BUTTON0))
+        return popup_app_menu();
+      /* fall through */
+    case Fl::Pen::DRAW:
+      // Pen is dragged over the surface, or hovers with a button pressed.
+      overlay_ = PEN_DRAW;
+      ov_x_ = Fl::event_x();
+      ov_y_ = Fl::event_y();
+      cv_pen_paint();
+      widget_->redraw();
+      return 1;
+    case Fl::Pen::LIFT:
+      // Pen was just lifted from the surface and is now hovering
+      return 1;
+    case Fl::Pen::LEAVE:
+      // The pen left the drawing area.
+      overlay_ = NONE;
+      widget_->redraw();
+      return 1;
+
+    // Event handling for mouse events:
+    case FL_ENTER:
+      color_++;
+      if (color_ > 6) color_ = 1;
+      /* fall through */
+    case FL_MOVE:
+      overlay_ = HOVER;
+      ov_x_ = Fl::event_x();
+      ov_y_ = Fl::event_y();
+      widget_->redraw();
+      return 1;
+    case FL_PUSH:
+      if (Fl::event_state(FL_CTRL) || Fl::event_button() == FL_RIGHT_MOUSE)
+        return popup_app_menu();
+      /* fall through */
+    case FL_DRAG:
+      overlay_ = DRAW;
+      ov_x_ = Fl::event_x();
+      ov_y_ = Fl::event_y();
+      cv_paint();
+      widget_->redraw();
+      return 1;
+    case FL_RELEASE:
+      return 1;
+    case FL_LEAVE:
+      overlay_ = NONE;
+      widget_->redraw();
+      return 1;
+  }
+  return 0;
+}
+
+//
+// Canvas drawing copies the offscreen bitmap and then draws the overlays.
+//
+void CanvasInterface::cv_draw()
+{
+  if (first_draw_) {
+    first_draw_ = false;
+    offscreen_ = fl_create_offscreen(widget_->w(), widget_->h());
+    fl_begin_offscreen(offscreen_);
+    fl_color(FL_WHITE);
+    fl_rectf(0, 0, widget_->w(), widget_->h());
+    fl_end_offscreen();
+  }
+  int dx = in_window_ ? 0 : widget_->x(), dy = in_window_ ? 0 : widget_->y();
+  fl_copy_offscreen(dx, dy, widget_->w(), widget_->h(), offscreen_, 0, 0);
+
+  // Preset values for overlay
+  int r = 10;
+  if (overlay_ == PEN_DRAW)
+    r = static_cast<int>(32.0 * Fl::Pen::event_pressure());
+  fl_color(FL_BLACK);
+  switch (overlay_) {
+    case NONE: break;
+    case PEN_HOVER:
+      fl_color(FL_RED);
+      /* fall through */
+    case HOVER:
+      fl_xyline(ov_x_-10, ov_y_, ov_x_+10);
+      fl_yxline(ov_x_, ov_y_-10, ov_y_+10);
+      break;
+    case PEN_DRAW:
+      fl_color(FL_RED);
+      /* fall through */
+    case DRAW:
+      fl_arc(ov_x_-r, ov_y_-r, 2*r, 2*r, 0, 360);
+      fl_arc(ov_x_-r/2-40*Fl::Pen::event_tilt_x(),
+             ov_y_-r/2-40*Fl::Pen::event_tilt_y(), r, r, 0, 360);
+      break;
+  }
+}
+
+//
+// Paint a circle with mouse events.
+//
+void CanvasInterface::cv_paint() {
+  if (!offscreen_)
+    return;
+  int dx = in_window_ ? 0 : widget_->x(), dy = in_window_ ? 0 : widget_->y();
+  fl_begin_offscreen(offscreen_);
+  fl_draw_circle(Fl::event_x()-dx-12, Fl::event_y()-dy-12, 24, color_);
+  fl_end_offscreen();
+}
+
+//
+// Paint a circle with pen events. If the eraser is touching the surface,
+// draw a white circle.
+//
+void CanvasInterface::cv_pen_paint() {
+  if (!offscreen_)
+    return;
+  int r = static_cast<int>(32.0 * (Fl::Pen::event_pressure()*Fl::Pen::event_pressure()));
+  int dx = in_window_ ? 0 : widget_->x(), dy = in_window_ ? 0 : widget_->y();
+  Fl_Color cc = Fl::Pen::event_state(Fl::Pen::State::ERASER_DOWN) ? FL_WHITE : color_;
+  fl_begin_offscreen(offscreen_);
+  fl_draw_circle(Fl::event_x()-dx-r, Fl::event_y()-dy-r, 2*r, cc);
+  fl_end_offscreen();
+}
+
+
+//
+// A drawing canvas, based on a minimal widget.
+//
+class CanvasWidget : public Fl_Widget, CanvasInterface {
+public:
+  CanvasWidget(int x, int y, int w, int h, const char *l=nullptr)
+  : Fl_Widget(x, y, w, h, l), CanvasInterface(this) { }
+  ~CanvasWidget() override { }
+  int handle(int event) override {
+    auto ret = cv_handle(event);
+    return ret ? ret : Fl_Widget::handle(event);
+  }
+  void draw() override { return cv_draw(); }
+};
+
+//
+// A drawing canvas based on a window. Can be used as a standalone window
+// and also as a subwindow inside another window.
+//
+class CanvasWindow : public Fl_Window, CanvasInterface {
+public:
+  CanvasWindow(int x, int y, int w, int h, const char *l=nullptr)
+  : Fl_Window(x, y, w, h, l), CanvasInterface(this) { }
+  ~CanvasWindow() override { }
+  int handle(int event) override {
+    auto ret = cv_handle(event);
+    return ret ? ret : Fl_Window::handle(event);
+  }
+  void draw() override { return cv_draw(); }
+};
+
+// A popup menu with a few test tasks.
+Fl_Menu_Item app_menu[] = {
+  { "with modal window", 0, [](Fl_Widget*, void*) {
+    fl_message("None of the canvas areas should receive\n"
+            "pen events while this window is open.");
+  } },
+  { "with non-modal window", 0, [](Fl_Widget*, void*) {
+    auto w = new Fl_Window(400, 32, "Toolbox");
+    w->set_non_modal();
+    w->show();
+  } },
+  { "unsubscribe middle canvas", 0, [](Fl_Widget*, void*) {
+    if (cv1) Fl::Pen::unsubscribe(cv1);
+  } },
+  { "resubscribe middle canvas", 0, [](Fl_Widget*, void*) {
+    if (cv1) Fl::Pen::subscribe(cv1);
+  } },
+  { "delete middle canvas", 0, [](Fl_Widget*, void*) {
+    if (cv1) { cv1->top_window()->redraw(); delete cv1; cv1 = nullptr; }
+  } },
+  { nullptr }
+};
+
+//
+// Show the menu and run the callback.
+//
+int popup_app_menu() {
+  auto mi = app_menu->popup(Fl::event_x(), Fl::event_y(), "Tests");
+  if (mi) mi->do_callback((Fl_Widget*)mi);
+  return 1;
+}
+
+//
+// Main app entry point
+//
+int main(int argc, char **argv)
+{
+  // Create our main app window
+  auto window = new Fl_Window(100, 100, 640, 220, "FLTK Pen/Stylus/Tablet test, Ctrl-Tap for menu");
+
+  // One testing canvas is just a regular child widget of the window
+  auto canvas_widget_0 = new CanvasWidget( 10, 10, 200, 200, "CV0");
+
+  // The second canvas is inside a group
+  auto cv1_group = new Fl_Group(215, 5, 210, 210);
+  cv1_group->box(FL_FRAME_BOX);
+  auto canvas_widget_1 = cv1 = new CanvasWidget(220, 10, 200, 200, "CV1");
+  cv1_group->end();
+
+  // The third canvas is a window inside a window, so we can verify
+  // that pen coordinates are calculated correctly.
+  auto canvas_widget_2 = new CanvasWindow(430, 10, 200, 200, "CV2");
+  canvas_widget_2->end();
+
+  window->end();
+
+  // A fourth canvas is a top level window by itself.
+  auto cv_window = cvwin = new CanvasWindow(100, 380, 200, 200, "Canvas Window");
+
+  // All canvases subscribe to pen events.
+  Fl::Pen::subscribe(canvas_widget_0);
+  Fl::Pen::subscribe(canvas_widget_1);
+  Fl::Pen::subscribe(canvas_widget_2);
+  Fl::Pen::subscribe(cv_window);
+
+  window->show(argc, argv);
+  canvas_widget_2->show();
+  cv_window->show();
+
+  return Fl::run();
+}