Issue #359 RFE: access the MacOS windowid .

FL/Fl_Window.H

@@ -556,6 +556,7 @@ public:
   int screen_num();
   void screen_num(int screen_num);
   static bool is_a_rescale();
+  fl_uintptr_t os_id();
 };
 
 #endif

src/Fl_Window.cxx

@@ -876,3 +876,10 @@ const Fl_Image* Fl_Window::shape() {return pWindowDriver->shape();}
 
 /** Returns true when a window is being rescaled */
 bool Fl_Window::is_a_rescale() {return Fl_Window_Driver::is_a_rescale_;}
+
+/** Returns a platform-specific identification of a shown window, or 0 if not shown.
+ \li X11 platform: the window's XID.
+ \li macOS platform: The window number of the window’s window device.
+ \li other platforms: 0.
+ */
+fl_uintptr_t Fl_Window::os_id() { return pWindowDriver->os_id();}

src/Fl_Window_Driver.H

@@ -2,7 +2,7 @@
 // A base class for platform specific window handling code
 // for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 2010-2018 by Bill Spitzak and others.
+// Copyright 2010-2022 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
@@ -190,6 +190,8 @@ public:
   virtual void reposition_menu_window(int x, int y);
   virtual void menu_window_area(int &X, int &Y, int &W, int &H, int nscreen = -1);
   static Fl_Window *menu_parent();
+  
+  virtual fl_uintptr_t os_id() { return 0; }
 };
 
 #endif // FL_WINDOW_DRIVER_H

src/Fl_cocoa.mm

@@ -4665,6 +4665,12 @@ void Fl_Cocoa_Screen_Driver::default_icons(const Fl_RGB_Image *icons[], int coun
   }
 }
 
+
+fl_uintptr_t Fl_Cocoa_Window_Driver::os_id() {
+  return [fl_xid(pWindow) windowNumber];
+}
+
+
 // Deprecated in 1.4 - only for backward compatibility with 1.3
 void Fl::insertion_point_location(int x, int y, int height) {
   Fl_Cocoa_Screen_Driver::insertion_point_location(x, y, height);

src/drivers/Cocoa/Fl_Cocoa_Window_Driver.H

@@ -2,7 +2,7 @@
 // Definition of Apple Cocoa window driver
 // for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 2010-2018 by Bill Spitzak and others.
+// Copyright 2010-2022 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
@@ -162,6 +162,8 @@ public:
   //icons
   virtual void icons(const Fl_RGB_Image *icons[], int count);
   NSImage *icon_image;
+  
+  virtual fl_uintptr_t os_id();
 };
 
 class Fl_Cocoa_Plugin : public Fl_Plugin {

src/drivers/X11/Fl_X11_Window_Driver.H

@@ -2,7 +2,7 @@
 // Definition of X11 window driver
 // for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 2010-2018 by Bill Spitzak and others.
+// Copyright 2010-2022 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
@@ -129,6 +129,7 @@ public:
   void set_icons(); // driver-internal support function
   virtual void capture_titlebar_and_borders(Fl_RGB_Image*& top, Fl_RGB_Image*& left, Fl_RGB_Image*& bottom, Fl_RGB_Image*& right);
   virtual int scroll(int src_x, int src_y, int src_w, int src_h, int dest_x, int dest_y, void (*draw_area)(void*, int,int,int,int), void* data);
+  virtual fl_uintptr_t os_id();
 };
 
 

src/drivers/X11/Fl_X11_Window_Driver.cxx

@@ -1,7 +1,7 @@
 //
 // Definition of X11 window driver.
 //
-// Copyright 1998-2020 by Bill Spitzak and others.
+// Copyright 1998-2022 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
@@ -518,4 +518,10 @@ int Fl_X11_Window_Driver::screen_num() {
   }
   return screen_num_ >= 0 ? screen_num_ : 0;
 }
+
+
+fl_uintptr_t Fl_X11_Window_Driver::os_id() {
+  return fl_xid(pWindow);
+}
+
 #endif // USE_XFT