Moved GUI2's per-frame drawing trigger to global scope

This is derived from work originally done by @aginor (48bcb277d4). I cherry-picked that commit and made a few alterations.

src/controller_base.cpp

@@ -30,7 +30,8 @@ static lg::log_domain log_display("display");
 #define ERR_DP LOG_STREAM(err, log_display)
 
 controller_base::controller_base(const config& game_config)
-	: game_config_(game_config)
+	: draw_layering(false)
+	, game_config_(game_config)
 	, key_()
 	, scrolling_(false)
 	, scroll_up_(false)

src/editor/controller/editor_controller.cpp

@@ -87,6 +87,8 @@ editor_controller::editor_controller(const config &game_config)
 	get_current_map_context().set_starting_position_labels(gui());
 	cursor::set(cursor::NORMAL);
 
+	join();
+
 	gui().create_buttons();
 	gui().redraw_everything();
 }

src/events.cpp

@@ -403,6 +403,54 @@ static bool remove_on_resize(const SDL_Event& a)
 	return false;
 }
 
+/**
+ * The interval between draw events.
+ *
+ * When the window is shown this value is set, the callback function always
+ * uses this value instead of the parameter send, that way the window can stop
+ * drawing when it wants.
+ */
+static int draw_interval = 0;
+
+SDL_TimerID draw_timer_id;
+
+/**
+ * SDL_AddTimer() callback for the draw event.
+ *
+ * When this callback is called it pushes a new draw event in the event queue.
+ *
+ * @returns                       The new timer interval, 0 to stop.
+ */
+static Uint32 draw_timer(Uint32, void*)
+{
+	//	DBG_GUI_E << "Pushing draw event in queue.\n";
+
+	SDL_Event event;
+	SDL_UserEvent data;
+
+	data.type = DRAW_EVENT;
+	data.code = 0;
+	data.data1 = NULL;
+	data.data2 = NULL;
+
+	event.type = DRAW_EVENT;
+	event.user = data;
+
+	SDL_PushEvent(&event);
+	return draw_interval;
+}
+
+void initialise()
+{
+	draw_interval = 20;
+	draw_timer_id = SDL_AddTimer(draw_interval, draw_timer, NULL);
+}
+
+void finalize()
+{
+	SDL_RemoveTimer(draw_timer_id);
+}
+
 // TODO: I'm uncertain if this is always safe to call at static init; maybe set in main() instead?
 static const boost::thread::id main_thread = boost::this_thread::get_id();
 
@@ -607,6 +655,12 @@ void pump()
 		}
 		}
 
+		const bool is_draw_event = event.type == DRAW_EVENT || event.type == DRAW_ALL_EVENT;
+
+		if(is_draw_event) {
+			CVideo::get_singleton().clear_screen();
+		}
+
 		for(auto global_handler : event_contexts.front().handlers) {
 			global_handler->handle_event(event);
 		}
@@ -616,6 +670,10 @@ void pump()
 				handler->handle_event(event);
 			}
 		}
+
+		if(is_draw_event) {
+			CVideo::get_singleton().render_screen();
+		}
 	}
 
 	// Inform the pump monitors that an events::pump() has occurred

src/events.hpp

@@ -151,6 +151,9 @@ public:
 	virtual void process(pump_info& info) = 0;
 };
 
+void initialise();
+void finalize();
+
 void raise_process_event();
 void raise_resize_event();
 void raise_draw_event();

src/gui/core/event/handler.cpp

@@ -536,13 +536,6 @@ void sdl_event_handler::draw()
 		return;
 	}
 
-	CVideo& video = dynamic_cast<window&>(*dispatchers_.back()).video();
-
-	/**
-	 * Clear the renderer before beginning the draw cycle.
-	 */
-	video.clear_screen();
-
 	/**
 	 * @todo Need to evaluate which windows really to redraw.
 	 *
@@ -552,9 +545,6 @@ void sdl_event_handler::draw()
 	{
 		dispatcher->fire(DRAW, dynamic_cast<widget&>(*dispatcher));
 	}
-
-	// Finally, render the screen.
-	video.render_screen();
 }
 
 void sdl_event_handler::draw_everything()

src/gui/widgets/window.cpp

@@ -113,33 +113,13 @@ namespace
 const unsigned SHOW = debug_layout_graph::SHOW;
 const unsigned LAYOUT = debug_layout_graph::LAYOUT;
 #else
-// values are irrelavant when DEBUG_WINDOW_LAYOUT_GRAPHS is not defined.
+// values are irrelevant when DEBUG_WINDOW_LAYOUT_GRAPHS is not defined.
 const unsigned SHOW = 0;
 const unsigned LAYOUT = 0;
 #endif
 
 /**
- * Pushes a single draw event to the queue. To be used before calling
- * events::pump when drawing windows.
- *
- * @todo: in the future we should simply call draw functions directly
- * from events::pump and do away with the custom drawing events, but
- * that's a 1.15 target. For now, this will have to do.
- */
-static void push_draw_event()
-{
-	//	DBG_GUI_E << "Pushing draw event in queue.\n";
 
-	SDL_Event event;
-	sdl::UserEvent data(DRAW_EVENT);
-
-	event.type = DRAW_EVENT;
-	event.user = data;
-
-	SDL_PushEvent(&event);
-}
-
-/**
  * SDL_AddTimer() callback for delay_event.
  *
  * @param event                   The event to push in the event queue.
@@ -489,8 +469,6 @@ void window::show_non_modal(/*const unsigned auto_close_timeout*/)
 	invalidate_layout();
 	suspend_drawing_ = false;
 
-	push_draw_event();
-
 	events::pump();
 }
 
@@ -538,8 +516,6 @@ int window::show(const unsigned auto_close_timeout)
 		// Start our loop drawing will happen here as well.
 		bool mouse_button_state_initialized = false;
 		for(status_ = SHOWING; status_ != CLOSED;) {
-			push_draw_event();
-
 			// process installed callback if valid, to allow e.g. network
 			// polling
 			events::pump();

src/wesnoth.cpp

@@ -676,12 +676,17 @@ static int do_gameloop(const std::vector<std::string>& args)
 		return 1;
 	}
 
+	events::initialise();
+	events::pump();
+
 	res = image::update_from_preferences();
 	if(res == false) {
 		std::cerr << "could not initialize image preferences\n";
 		return 1;
 	}
 
+	events::pump();
+
 	if(preferences::joystick_support_enabled()) {
 		res = game->init_joystick();
 		if(res == false) {
@@ -693,6 +698,8 @@ static int do_gameloop(const std::vector<std::string>& args)
 	const cursor::manager cursor_manager;
 	cursor::set(cursor::WAIT);
 
+	events::pump();
+
 #if(defined(_X11) && !defined(__APPLE__)) || defined(_WIN32)
 	SDL_EventState(SDL_SYSWMEVENT, SDL_ENABLE);
 #endif