Add fl_message_icon_label() function (STR #2762)

This message icon label (usually one character) will be used in the
next call of one of the common dialogs.

test/ask.cxx: use fl_message_icon_label()

FL/fl_ask.H

@@ -95,6 +95,8 @@ inline void fl_message_position(Fl_Widget &widget) {
 FL_EXPORT void fl_message_title(const char *title);
 FL_EXPORT void fl_message_title_default(const char *title);
 
+FL_EXPORT void fl_message_icon_label(const char *str);
+
 // pointers you can use to change FLTK to another language:
 extern FL_EXPORT const char *fl_no;
 extern FL_EXPORT const char *fl_yes;

src/Fl_Message.cxx

@@ -65,6 +65,8 @@
 const char *Fl_Message::message_title_default_;
 const char *Fl_Message::message_title_;
 
+const char *Fl_Message::message_icon_label_;
+
 Fl_Box *Fl_Message::message_icon_;
 
 char *Fl_Message::input_buffer_;
@@ -123,6 +125,9 @@ void Fl_Message::window_cb_(Fl_Widget *w, void *d) {
   The constructor creates a default message window and sets the icon type
   to the given \p iconlabel which can be any character (or string).
 
+  If fl_message_icon_label() has been called before this label is used
+  instead and reset to NULL after the message window has been created.
+
   Message text box (Fl_Box), icon (Fl_Box), and an input (Fl_Input) widgets
   are created and initialized. Three buttons are created and arranged right to
   left in the message window. The second (middle) button is an Fl_Return_Button.
@@ -157,7 +162,13 @@ Fl_Message::Fl_Message(const char *iconlabel)
   icon_->labelsize(icon_template->labelsize());
   icon_->color(icon_template->color());
   icon_->labelcolor(icon_template->labelcolor());
-  icon_->label(iconlabel);
+
+  if (message_icon_label_) { // fl_message_icon_label() has been called
+    icon_->copy_label(message_icon_label_);
+    message_icon_label_ = 0;
+  } else { // use default (static, per message default string)
+    icon_->label(iconlabel);
+  }
 
   window_->end(); // don't add the buttons automatically
 
@@ -526,6 +537,10 @@ void Fl_Message::message_title_default(const char *title) {
     message_title_default_ = strdup(title);
 }
 
+void Fl_Message::icon_label(const char *str) {
+  message_icon_label_ = str;
+}
+
 /**
   \}
   \endcond

src/Fl_Message.h

@@ -65,6 +65,9 @@ private:
   static const char *message_title_;
   static const char *message_title_default_;
 
+  // icon label for next dialog (STR #2762)
+  static const char *message_icon_label_;
+
   // Note: since Fl_Message objects are destroyed before fl_input()
   // and fl_password() return their input text, we *need* to store
   // the text in an internal (static) buffer. :-(
@@ -89,6 +92,7 @@ public:
   static Fl_Box *message_icon();
   static void message_title(const char *title);
   static void message_title_default(const char *title);
+  static void icon_label(const char *str);
 
   /** Implements fl_message_position(const int, const int y, const int center). */
   static void message_position(const int x, const int y, const int center) {

src/fl_ask.cxx

@@ -560,4 +560,28 @@ void fl_message_title_default(const char *title) {
   Fl_Message::message_title_default(title);
 }
 
+/** Sets the icon label of the dialog window used in many common dialogs.
+
+  This icon label will be used in the next call of one of the
+  common dialogs like fl_message(), fl_alert(), fl_ask(), fl_choice(),
+  fl_input(), fl_password().
+
+  The label \p str is stored internally as a reference, it must be
+  in scope until the dialog function (e.g. fl_choice) is called.
+
+  It applies only to the \b next call of one of the common dialogs and
+  will be reset after that call so the next dialog will use its default
+  label unless set again.
+
+  \note This label string must be short, usually only one character so
+    it fits in the icon box. You can use any valid UTF-8 character, e.g.
+    the Euro sign ("€") which is three bytes in UTF-8 encoding.
+
+  \code #include <FL/fl_ask.H> \endcode
+  \param[in] str    icon label
+*/
+void fl_message_icon_label(const char *str) {
+  Fl_Message::icon_label(str);
+}
+
 /** @} */

test/ask.cxx

@@ -35,10 +35,13 @@
 void rename_button(Fl_Widget *o, void *v) {
   int what = fl_int(v);
   Fl_String input;
-  if (what == 0)
+  if (what == 0) {
+    fl_message_icon_label("§");
     input = fl_input_str(0, "Input (no size limit, use ctrl/j for newline):", o->label());
-  else
+  } else {
+    fl_message_icon_label("€");
     input = fl_password_str(20, "Enter password (max. 20 characters):", o->label());
+  }
   if (input.value()) {
     o->copy_label(input.value());
     o->redraw();