clean and add a parameter to the sunset command for tuning the delay

...(in frames) between 2 darkenings

(as suggested by Mordante). You can still use just "sunset" to toogle,
the default is every 5 frames.

src/display.cpp

@@ -59,7 +59,8 @@ namespace {
 
 	const int MinZoom = 4;
 	const int MaxZoom = 200;
-	bool sunset = false;
+	size_t sunset_delay = 0;
+	size_t sunset_timer = 0;
 }
 
 display::display(unit_map& units, CVideo& video, const gamemap& map,
@@ -789,8 +790,12 @@ void display::redraw_everything()
 	draw(true,true);
 }
 
-void display::toggle_sunset() {
-	sunset = !sunset;
+void display::sunset(size_t delay) {
+	if (sunset_delay == 0) {
+		sunset_delay = (delay == 0 ? 5 : delay);
+	} else {
+		sunset_delay = delay;
+	}
 }
 
 void display::flip()
@@ -801,10 +806,9 @@ void display::flip()
 
 	const surface frameBuffer = get_video_surface();
 
-	// this is just the debug function "sunset" to progressively darken the game area
-	// change the frequency for keeping a good framerate (specially if you use use --max-fps)
-	// FIXME: remove the use of random, and use some real timer
-	if (sunset && rand()%100 <= 10) {
+	// this is just the debug function "sunset" to progressively darken the map area
+	if (sunset_delay && ++sunset_timer > sunset_delay) {
+		sunset_timer = 0;
 		SDL_Rect r = map_area(); //use frameBuffer to also test the UI
 		const Uint32 color =  SDL_MapRGBA(video().getSurface()->format,0,0,0,255);
 		// adjust the alpha if you want to balance cpu-cost / smooth sunset

src/display.hpp

@@ -115,6 +115,11 @@ public:
 	//invalidates entire screen, including all tiles and sidebar.
 	void redraw_everything();
 
+	//debug function to toggle the "sunset" mode
+	//the map area become progressively darker except where hexes are refreshed
+	//delay it's the number of frames between each darkening (0 to toggle)
+	void sunset(const size_t delay = 0);
+
 	void flip();
 
 	//draws invalidated items. If update is true, will also copy the
@@ -213,10 +218,6 @@ public:
 	//function to remove a footstep from a specific location
 	void remove_footstep(const gamemap::location& loc);
 
-	//debug function to toggle the "sunset "mode
-	//the map area become progressively darker except where hexes are refreshed
-	void toggle_sunset();
-
 	//function to float a label above a tile
 	void float_label(const gamemap::location& loc, const std::string& text,
 	                 int red, int green, int blue);

src/menu_events.cpp

@@ -1830,7 +1830,8 @@ namespace events{
 		} else if(cmd == "clear") {
 			gui_->clear_chat_messages();
 		} else if(cmd == "sunset") {
-			gui_->toggle_sunset();
+			int delay = lexical_cast_default<int>(data);
+			gui_->sunset(delay);
 		} else if(cmd == "w") {
 			save_game(data,gui::NULL_DIALOG);
 		} else if(cmd == "wq") {