GUI2/Dispatcher: added a connect_signal convenience wrapper for draw callbacks

Didn't use this in the window widget since that doesn't specify front_child as
the queue position. I need to evaluate whether draw callbacks need to be in that
position anyway. AFAIR I only started adding them there since I noticed the one
in the debug clock dialog used that.

src/gui/core/event/dispatcher.cpp

@@ -181,6 +181,12 @@ void connect_signal_notify_modified(dispatcher& dispatcher, const signal_notific
 	dispatcher.connect_signal<NOTIFY_MODIFIED>(signal);
 }
 
+void connect_signal_on_draw(dispatcher& dispatcher, const signal_function& signal)
+{
+	// TODO: evaluate whether draw events need go in this queue position.
+	dispatcher.connect_signal<DRAW>(signal, dispatcher::front_child);
+}
+
 } // namespace event
 
 } // namespace gui2

src/gui/core/event/dispatcher.hpp

@@ -1013,6 +1013,9 @@ void connect_signal_mouse_left_double_click(dispatcher& dispatcher, const signal
 /** Connects a signal handler for getting a notification upon modification. */
 void connect_signal_notify_modified(dispatcher& dispatcher, const signal_notification_function& signal);
 
+/** Connects a signal handler for a callback when the widget is drawn. */
+void connect_signal_on_draw(dispatcher& dispatcher, const signal_function& signal);
+
 } // namespace event
 
 } // namespace gui2

src/gui/dialogs/debug_clock.cpp

@@ -104,8 +104,7 @@ void debug_clock::pre_show(window& window)
 	clock_ = find_widget<styled_widget>(&window, "clock", false, false);
 
 	signal_ = std::bind(&debug_clock::update_time, this, false);
-	window.connect_signal<event::DRAW>(signal_,
-									   event::dispatcher::front_child);
+	connect_signal_on_draw(window, signal_);
 
 	time_.set_current_time();
 	update_time(true);

src/gui/dialogs/end_credits.cpp

@@ -55,7 +55,7 @@ void end_credits::pre_show(window& window)
 		last_scroll_ = SDL_GetTicks() + 3000;
 	});
 
-	window.connect_signal<event::DRAW>(std::bind(&end_credits::timer_callback, this), event::dispatcher::front_child);
+	connect_signal_on_draw(window, std::bind(&end_credits::timer_callback, this));
 
 	connect_signal_pre_key_press(window, std::bind(&end_credits::key_press_callback, this, _5));
 

src/gui/dialogs/loading_screen.cpp

@@ -131,8 +131,7 @@ void loading_screen::pre_show(window& window)
 	animation_label_ = find_widget<label>(&window, "test_animation", false, true);
 
 	// Add a draw callback to handle the animation, et al.
-	window.connect_signal<event::DRAW>(
-		std::bind(&loading_screen::draw_callback, this), event::dispatcher::front_child);
+	connect_signal_on_draw(window, std::bind(&loading_screen::draw_callback, this));
 
 	set_next_animation_time();
 }

src/gui/dialogs/outro.cpp

@@ -52,8 +52,7 @@ void outro::pre_show(window& window)
 	window.set_enter_disabled(true);
 	window.get_canvas(0).set_variable("outro_text", wfl::variant(text_));
 
-	window.connect_signal<event::DRAW>(
-		std::bind(&outro::draw_callback, this, std::ref(window)), event::dispatcher::front_child);
+	connect_signal_on_draw(window, std::bind(&outro::draw_callback, this, std::ref(window)));
 
 	set_next_draw();
 }

src/gui/dialogs/story_viewer.cpp

@@ -88,8 +88,8 @@ void story_viewer::pre_show(window& window)
 	connect_signal_mouse_left_click(find_widget<button>(&window, "back", false),
 		std::bind(&story_viewer::nav_button_callback, this, std::ref(window), DIR_BACKWARDS));
 
-	window.connect_signal<event::DRAW>(
-		std::bind(&story_viewer::draw_callback, this, std::ref(window)), event::dispatcher::front_child);
+	connect_signal_on_draw(window,
+		std::bind(&story_viewer::draw_callback, this, std::ref(window)));
 
 	display_part(window);
 }