Add an option to disable FPS limiter

Cherry-pick of commit d7921f31b0.

data/gui/window/preferences/03_display.cfg

@@ -260,6 +260,19 @@
 			[/grid]
 		[/column]
 	[/row]
+	[row]
+		[column]
+			border = "all"
+			border_size = 5
+			horizontal_alignment = "left"
+
+			[toggle_button]
+				id = "fps_limiter"
+				label = _ "FPS limiter"
+				tooltip = _ "Disabling this increases CPU usage to 100 % but may slightly improve performance at high resolutions"
+			[/toggle_button]
+		[/column]
+	[/row]
 #enddef
 
 #define _GUI_PREFERENCES_DISPLAY_GRID_2

src/display.cpp

@@ -1689,7 +1689,7 @@ void display::draw_init()
 void display::draw_wrap(bool update, bool force)
 {
 	static int time_between_draws = preferences::draw_delay();
-	if(time_between_draws == 0) {
+	if(time_between_draws < 0) {
 		time_between_draws = 1000 / screen_.current_refresh_rate();
 	}
 

src/gui/dialogs/preferences_dialog.cpp

@@ -474,6 +474,10 @@ void preferences_dialog::post_build(window& window)
 	register_integer("scaling_slider", true,
 		font_scaling, set_font_scaling);
 
+	/* FPS LIMITER */
+	register_bool("fps_limiter", true,
+		[]() { return draw_delay() != 0; }, [](bool v) { set_draw_delay(v ? -1 : 0); });
+
 	/* SELECT THEME */
 	connect_signal_mouse_left_click(
 			find_widget<button>(&window, "choose_theme", false),

src/preferences/general.cpp

@@ -51,8 +51,6 @@ bool no_preferences_save = false;
 
 bool fps = false;
 
-int draw_delay_ = 0;
-
 config prefs;
 }
 
@@ -974,12 +972,12 @@ void set_show_fps(bool value)
 
 int draw_delay()
 {
-	return draw_delay_;
+	return prefs["draw_delay"].to_int(-1);
 }
 
 void set_draw_delay(int value)
 {
-	draw_delay_ = value;
+	prefs["draw_delay"] = value;
 }
 
 bool use_color_cursors()