Adding the FL_MENU_CHATTY flag to Fl_Menu_Item.

If set, menu items will also call the callback when highlighting changes.
The reason is given with Fl::callback_reason(). #941

FL/Fl_Menu_Item.H

@@ -34,7 +34,8 @@ enum { // values for flags:
   FL_SUBMENU_POINTER = 0x20,       ///< Indicates user_data() is a pointer to another menu array
   FL_SUBMENU         = 0x40,       ///< Item is a submenu to other items
   FL_MENU_DIVIDER    = 0x80,       ///< Creates divider line below this item. Also ends a group of radio buttons
-  FL_MENU_HORIZONTAL = 0x100       ///< ??? -- reserved, internal (do not use)
+  FL_MENU_HORIZONTAL = 0x100,      ///< reserved, do not use
+  FL_MENU_CHATTY     = 0x200       ///< Menu Item receives additional callbacks
   ///< Note: \b ALL other bits in \p flags are reserved: do not use them for your own purposes!
 };
 
@@ -67,7 +68,8 @@ class Fl_Menu_;
    FL_SUBMENU_POINTER = 0x20,       // Indicates user_data() is a pointer to another menu array
    FL_SUBMENU         = 0x40,       // This item is a submenu to other items
    FL_MENU_DIVIDER    = 0x80,       // Creates divider line below this item. Also ends a group of radio buttons.
-   FL_MENU_HORIZONTAL = 0x100       // ??? -- reserved, internal (do not use)
+   FL_MENU_HORIZONTAL = 0x100       // reserved, do not use
+   FL_MENU_CHATTY     = 0x200       ///< Menu Item receives additional callbacks
   };
   \endcode
 
@@ -120,6 +122,16 @@ class Fl_Menu_;
     variants copies the entire menu to internal storage. Using the
     memory of a static menu array after that would access unused (but not
     released) memory and thus have no effect.
+
+  When a menu item is selected by the user and a callback is set, the callback
+  will be called with FL_REASON_SELECTED. The Fl_Widget pointer is set to the
+  widget that opened the menu, a copy of the menu item's user data. If no menu
+  item callback is set, the callback of the managing widget is called instead.
+
+  If the FL_MENU_CHATTY flag is set, the menu item callback may be called for
+  additional reasons. When a menu item is highlighted, the callback is called
+  with FL_REASON_GOT_FOCUS. If it is no longer highlighted,
+  FL_REASON_LOST_FOCUS is sent.
 */
 struct FL_EXPORT Fl_Menu_Item {
   const char *text;         ///< menu item text, returned by label()
@@ -490,14 +502,18 @@ struct FL_EXPORT Fl_Menu_Item {
     The callback is called with the stored user_data() as its second argument.
     You must first check that callback() is non-zero before calling this.
   */
-  void do_callback(Fl_Widget* o) const {Fl::callback_reason_=FL_REASON_SELECTED; callback_(o, user_data_);}
+  void do_callback(Fl_Widget* o, Fl_Callback_Reason reason=FL_REASON_UNKNOWN) const {
+    Fl::callback_reason_ = reason; callback_(o, user_data_);
+  }
 
   /**
     Calls the Fl_Menu_Item item's callback, and provides the Fl_Widget argument.
     This call overrides the callback's second argument with the given value \p arg.
     You must first check that callback() is non-zero before calling this.
   */
-  void do_callback(Fl_Widget* o,void* arg) const {Fl::callback_reason_=FL_REASON_SELECTED; callback_(o, arg);}
+  void do_callback(Fl_Widget* o, void* arg, Fl_Callback_Reason reason=FL_REASON_UNKNOWN) const {
+    Fl::callback_reason_ = reason; callback_(o, arg);
+  }
 
   /**
     Calls the Fl_Menu_Item item's callback, and provides the Fl_Widget argument.
@@ -506,7 +522,9 @@ struct FL_EXPORT Fl_Menu_Item {
     the callback.
     You must first check that callback() is non-zero before calling this.
   */
-  void do_callback(Fl_Widget* o,long arg) const {Fl::callback_reason_=FL_REASON_SELECTED; callback_(o, (void*)(fl_intptr_t)arg);}
+  void do_callback(Fl_Widget* o, long arg, Fl_Callback_Reason reason=FL_REASON_UNKNOWN) const {
+    Fl::callback_reason_ = FL_REASON_SELECTED; callback_(o, (void*)(fl_intptr_t)arg);
+  }
 
   /** Back compatibility only.
     \deprecated

src/Fl_MacOS_Sys_Menu_Bar.mm

@@ -167,7 +167,7 @@ const char *Fl_Mac_App_Menu::quit = "Quit %@";
 {
   fl_lock_function();
   Fl_Menu_Item *item = (Fl_Menu_Item *)[(NSData*)[self representedObject] bytes];
-  if ( item && item->callback() ) item->do_callback(NULL);
+  if ( item && item->callback() ) item->do_callback(NULL, FL_REASON_SELECTED);
   fl_unlock_function();
 }
 - (void) setKeyEquivalentModifierMask:(int)value

src/Fl_Menu.cxx

@@ -146,6 +146,7 @@ class menuwindow : public window_with_items {
 public:
   menutitle* title;
   int handle(int) FL_OVERRIDE;
+  void hide() override;
   int itemheight;       // zero == menubar
   int numitems;
   int selected;
@@ -480,6 +481,11 @@ menuwindow::~menuwindow() {
   delete title;
 }
 
+void menuwindow::hide() {
+  set_selected(-1);
+  window_with_items::hide();
+}
+
 void menuwindow::position(int X, int Y) {
   if (title) {title->position(X, title->y()+Y-y());}
   Fl_Menu_Window::position(X, Y);
@@ -592,7 +598,20 @@ void menuwindow::draw() {
 }
 
 void menuwindow::set_selected(int n) {
-  if (n != selected) {selected = n; damage(FL_DAMAGE_CHILD);}
+  if (n != selected) {
+    if ((selected!=-1) && (menu)) {
+      const Fl_Menu_Item *mi = menu->next(selected);
+      if ((mi) && (mi->callback_) && (mi->flags & FL_MENU_CHATTY))
+        mi->do_callback(this, FL_REASON_LOST_FOCUS);
+    }
+    selected = n;
+    if ((selected!=-1) && (menu)) {
+      const Fl_Menu_Item *mi = menu->next(selected);
+      if ((mi) && (mi->callback_) && (mi->flags & FL_MENU_CHATTY))
+        mi->do_callback(this, FL_REASON_GOT_FOCUS);
+    }
+    damage(FL_DAMAGE_CHILD);
+  }
 }
 
 ////////////////////////////////////////////////////////////////

src/Fl_Menu_.cxx

@@ -401,8 +401,11 @@ const Fl_Menu_Item* Fl_Menu_::picked(const Fl_Menu_Item* v) {
     value_ = v;
     if (when()&(FL_WHEN_CHANGED|FL_WHEN_RELEASE)) {
       if (changed() || when()&FL_WHEN_NOT_CHANGED) {
-        if (value_ && value_->callback_) value_->do_callback((Fl_Widget*)this);
-        else do_callback();
+        if (value_ && value_->callback_) {
+          value_->do_callback((Fl_Widget*)this, value_->user_data(), FL_REASON_SELECTED);
+        } else {
+          do_callback(FL_REASON_SELECTED);
+        }
       }
     }
   }

test/menubar.cxx

@@ -61,7 +61,19 @@ void test_cb(Fl_Widget* w, void*) {
     G_tty->printf("%s\n", m->label());
 }
 
-void quit_cb(Fl_Widget*, void*) {exit(0);}
+void quit_cb(Fl_Widget*, void*) {
+  switch (Fl::callback_reason()) {
+    case FL_REASON_SELECTED:
+      exit(0);
+    case FL_REASON_GOT_FOCUS:
+      G_tty->printf("Selecting this menu item will quit this application!\n");
+      break;
+    case FL_REASON_LOST_FOCUS:
+      G_tty->printf("Risk of quitting averted.\n");
+      break;
+    default: break;
+  }
+}
 
 Fl_Menu_Item hugemenu[100];
 
@@ -70,7 +82,7 @@ Fl_Menu_Item menutable[] = {
   {"&File",0,0,0,FL_SUBMENU},
     {"&Open",   FL_ALT+'o', 0, 0, FL_MENU_INACTIVE},
     {"&Close",  0,      0},
-    {"&Quit",   FL_ALT+'q', quit_cb, 0, FL_MENU_DIVIDER},
+    {"&Quit",   FL_ALT+'q', quit_cb, 0, FL_MENU_DIVIDER|FL_MENU_CHATTY},
 
 #if (OVERRIDE_SCALING_SHORTCUTS)
     {"CTRL/0",  FL_COMMAND+'0', 0},