Improve docs and add two new Fl_Menu_Item methods (#875)

This addresses some issues pointed out by GitHub Issue #875.

Documentation lacked details about Fl_Multi_Label assignment and
correct memory handling.

The new methods
 - Fl_Menu_Item::image_label(const Fl_Image *) and
 - Fl_Menu_Item::multi_label(const Fl_Multi_Label *)
provide a cleaner interface to assign images and Fl_Multi_Label's
to menu items.

examples/howto-menu-with-images.cxx: carify some issues, fix leak,
  and use new Fl_Menu_Item::multi_label(const Fl_Multi_Label *).

1 files changed, 93 insertions, 11 deletions

diff --git a/FL/Fl_Menu_Item.H b/FL/Fl_Menu_Item.H
index 4bca0e1ce..94035d097 100644
--- a/FL/Fl_Menu_Item.H
+++ b/FL/Fl_Menu_Item.H
@@ -17,9 +17,10 @@
 #ifndef Fl_Menu_Item_H
 #define Fl_Menu_Item_H
 
-#  include "Fl_Widget.H"
-#  include "Fl_Image.H"
-#  include <FL/platform_types.h> // for FL_COMMAND and FL_CONTROL
+#include <FL/Fl_Widget.H>
+#include <FL/Fl_Image.H>
+#include <FL/Fl_Multi_Label.H>
+#include <FL/platform_types.h> // for FL_COMMAND and FL_CONTROL
 
 // doxygen needs the following line to enable e.g. ::FL_MENU_TOGGLE to link to the enums
 /// @file
@@ -141,19 +142,100 @@ struct FL_EXPORT Fl_Menu_Item {
 
   // methods on menu items:
   /**
-    Returns the title of the item.
+    Returns the title (label) of the menu item.
+
     A NULL here indicates the end of the menu (or of a submenu).
     A '&' in the item will print an underscore under the next letter,
-    and if the menu is popped up that letter will be a "shortcut" to pick
-    that item.  To get a real '&' put two in a row.
+    and if the menu is popped up that letter will be a "shortcut" to
+    pick that item. To get a real '&' put two in a row.
+
+    The returned value depends on the labeltype() that has been used
+    to store the label.
+
+    \returns  A pointer to the label cast to (const char *)
+
+    \retval (a)   A pointer to text (const char *)
+    \retval (b)   A pointer to an image (Fl_Image *)
+    \retval (c)   A pointer to a "multi label" (Fl_Multi_Label *)
+    \retval NULL  End of menu or submenu
+
+    \see Fl_Menu_Item::label(const char *)
+    \see Fl_Menu_Item::label(Fl_Labeltype, const char *)
+    \see Fl_Menu_Item::image_label(const Fl_Image *)
+    \see Fl_Menu_Item::multi_label(const Fl_Multi_Label *)
+    \see Fl_Multi_Label::label(Fl_Menu_Item *)
+  */
+  const char* label() const { return text; }
+
+  /**
+    Sets the title (label) of the menu item.
+
+    \note This does \b not change the labeltype() for backwards compatibility.
+      Take care to assign the correct labeltype() if you assign different
+      label types to the same menu item sequentially.
+
+    The default labeltype() is FL_NORMAL_LABEL.
+
+    \see label(Fl_Labeltype, const char*)
+    \see const char* Fl_Menu_Item::label() const
+  */
+  void label(const char* a) { text = a; }
+
+  /**
+    Sets the title (label) and the label type of the menu item.
+
+    The default Fl_Labeltype when using Fl_Menu_Item::label(const char* a)
+    is FL_NORMAL_LABEL but you can set any other label type, for instance
+    FL_EMBOSSED_LABEL.
+
+    Special labeltypes are:
+
+      - FL_ICON_LABEL:  draws the icon (Fl_Image) associated with the text
+      - FL_IMAGE_LABEL: draws the image (Fl_Image) associated with the text
+      - FL_MULTI_LABEL: draws multiple parts side by side, see Fl_Multi_Label
+
+    \see const char* Fl_Menu_Item::label() const
   */
-  const char* label() const {return text;}
+  void label(Fl_Labeltype a, const char* b) {
+    labeltype_ = a;
+    text = b;
+  }
+
+  /**
+    Sets the title (label()) and labeltype() to an Fl_Multi_Label.
+
+    This sets the labeltype() to \_FL_MULTI_LABEL (note the leading
+    underscore).
 
-  /**    See const char* Fl_Menu_Item::label() const   */
-  void label(const char* a) {text=a;}
+    \see const char* Fl_Menu_Item::label() const
 
-  /**    See const char* Fl_Menu_Item::label() const   */
-  void label(Fl_Labeltype a,const char* b) {labeltype_ = a; text = b;}
+    \since 1.4.0
+
+    \internal Overloading Fl_Menu_Item::image() would lead to ambiguities
+      when used like `item->label(0)`, hence we need our own method name.
+      Otherwise existing programs might not compile w/o error (e.g. fluid).
+  */
+  void multi_label(const Fl_Multi_Label *ml) {
+    label(FL_MULTI_LABEL, (const char *)ml);
+  }
+
+  /**
+    Sets the title (label()) to an icon or image.
+
+    This sets the labeltype() to \_FL_IMAGE_LABEL (note the leading
+    underscore).
+
+    \see const char* Fl_Menu_Item::label() const
+
+    \since 1.4.0
+
+    \internal Overloading Fl_Menu_Item::image() would lead to ambiguities
+      when used like `item->label(0)`, hence we need our own method name.
+      Otherwise existing programs might not compile w/o error (e.g. fluid).
+  */
+  void image_label(const Fl_Image *image) {
+    label(FL_IMAGE_LABEL, (const char *)image);
+  }
 
   /**
     Returns the menu item's labeltype.