Fix doxygen doc generation and document platform specific files

Pure platform specific files like 'src/*_win32.cxx' are excluded from
doxygen processing and don't need doxygen specific guard macros.

Document this fact prominently at the beginning of each file.

Fix exclude patterns and remove duplicates from Doxyfile.in.

6 files changed, 21 insertions, 11 deletions

diff --git a/src/Fl_get_key_mac.cxx b/src/Fl_get_key_mac.cxx
index c950d439e..ef5ef1ae1 100644
--- a/src/Fl_get_key_mac.cxx
+++ b/src/Fl_get_key_mac.cxx
@@ -1,7 +1,7 @@
 //
 // MacOS keyboard state routines for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2018 by Bill Spitzak and others.
+// 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
@@ -14,6 +14,9 @@
 //     https://www.fltk.org/bugs.php
 //
 
+// Note: this file contains platform specific code and will therefore
+// not be processed by doxygen (see Doxyfile.in).
+
 // Return the current state of a key.  Keys are named by fltk symbols,
 // which are actually X keysyms.  So this has to translate to macOS
 // symbols.
diff --git a/src/Fl_get_key_win32.cxx b/src/Fl_get_key_win32.cxx
index 590df0ff5..cb844722d 100644
--- a/src/Fl_get_key_win32.cxx
+++ b/src/Fl_get_key_win32.cxx
@@ -1,7 +1,7 @@
 //
 // Windows keyboard state routines for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2018 by Bill Spitzak and others.
+// 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
@@ -14,6 +14,9 @@
 //     https://www.fltk.org/bugs.php
 //
 
+// Note: this file contains platform specific code and will therefore
+// not be processed by doxygen (see Doxyfile.in).
+
 // Return the current state of a key.  Keys are named by fltk symbols,
 // which are actually X keysyms.  So this has to translate to Windows
 // VK_x symbols.
diff --git a/src/Fl_win32.cxx b/src/Fl_win32.cxx
index 0837f45b4..8579e0ccd 100644
--- a/src/Fl_win32.cxx
+++ b/src/Fl_win32.cxx
@@ -14,12 +14,13 @@
 //     https://www.fltk.org/bugs.php
 //
 
+// Note: this file contains platform specific code and will therefore
+// not be processed by doxygen (see Doxyfile.in).
+
 // This file contains Windows-specific code for FLTK which is always linked
 // in.  Search other files for "_WIN32" or filenames ending in _win32.cxx
 // for other system-specific code.
 
-#if defined(_WIN32) && !defined(FL_DOXYGEN)
-
 /* We require Windows 2000 features (e.g. VK definitions) */
 # if !defined(WINVER) || (WINVER < 0x0500)
 #  ifdef WINVER
@@ -2741,5 +2742,3 @@ void Fl_WinAPI_Window_Driver::capture_titlebar_and_borders(Fl_RGB_Image *&top, F
   fl_graphics_driver->gc(save_gc);
   Fl_Surface_Device::pop_current();
 }
-
-#endif // defined(_WIN32) and !defined(FL_DOXYGEN)
diff --git a/src/Fl_x.cxx b/src/Fl_x.cxx
index 67f9df744..6922ac819 100644
--- a/src/Fl_x.cxx
+++ b/src/Fl_x.cxx
@@ -14,7 +14,8 @@
 //     https://www.fltk.org/bugs.php
 //
 
-#if !defined(FL_DOXYGEN)
+// Note: this file contains platform specific code and will therefore
+// not be processed by doxygen (see Doxyfile.in).
 
 #  ifndef FLTK_CONSOLIDATE_MOTION
 #  define FLTK_CONSOLIDATE_MOTION 0
@@ -3026,5 +3027,3 @@ void Fl_X11_Window_Driver::show() {
     XMapRaised(fl_display, fl_xid(pWindow));
   }
 }
-
-#endif // !defined(FL_DOXYGEN)
diff --git a/src/fl_dnd_win32.cxx b/src/fl_dnd_win32.cxx
index 9e69c290a..abaa588cc 100644
--- a/src/fl_dnd_win32.cxx
+++ b/src/fl_dnd_win32.cxx
@@ -1,7 +1,7 @@
 //
 // Drag & Drop code for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2022 by Bill Spitzak and others.
+// 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
@@ -14,6 +14,9 @@
 //     https://www.fltk.org/bugs.php
 //
 
+// Note: this file contains platform specific code and will therefore
+// not be processed by doxygen (see Doxyfile.in).
+
 // This file contains Windows-specific code for FLTK which is always linked
 // in.  Search other files for "_WIN32" or filenames ending in _win32.cxx
 // for other system-specific code.
diff --git a/src/fl_dnd_x.cxx b/src/fl_dnd_x.cxx
index 982ed65dd..f48ac599e 100644
--- a/src/fl_dnd_x.cxx
+++ b/src/fl_dnd_x.cxx
@@ -1,7 +1,7 @@
 //
 // Drag & Drop code for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2021 by Bill Spitzak and others.
+// 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
@@ -14,6 +14,9 @@
 //     https://www.fltk.org/bugs.php
 //
 
+// Note: this file contains platform specific code and will therefore
+// not be processed by doxygen (see Doxyfile.in).
+
 #include <FL/Fl.H>
 #include <FL/Fl_Window.H>
 #include <FL/platform.H>