Add vehicle preview offer setting and update vehicle introduction logic

src/engine.cpp

@@ -966,6 +966,7 @@ static IntervalTimer<TimerGameCalendar> _calendar_engines_daily({TimerGameCalend
 		c->avail_roadtypes = AddDateIntroducedRoadTypes(c->avail_roadtypes, TimerGameCalendar::date);
 	}
 
+	if (!_settings_game.vehicle.offer_vehicle_preview) return;
 	if (TimerGameCalendar::year >= _year_engine_aging_stops) return;
 
 	for (Engine *e : Engine::Iterate()) {
@@ -1160,7 +1161,7 @@ void CalendarEnginesMonthlyLoop()
 			/* Do not introduce invalid engines */
 			if (!e->IsEnabled()) continue;
 
-			if (!e->flags.Test(EngineFlag::Available) && TimerGameCalendar::date >= (e->intro_date + CalendarTime::DAYS_IN_YEAR)) {
+			if (!e->flags.Test(EngineFlag::Available) && TimerGameCalendar::date >= (e->intro_date + (_settings_game.vehicle.offer_vehicle_preview ? CalendarTime::DAYS_IN_YEAR : 0))) {
 				/* Introduce it to all companies */
 				NewVehicleAvailable(e);
 			} else if (!e->flags.Any({EngineFlag::Available, EngineFlag::ExclusivePreview}) && TimerGameCalendar::date >= e->intro_date) {

src/lang/english.txt

@@ -1508,6 +1508,9 @@ STR_CONFIG_SETTING_WARN_OLD_VEHICLE_HELPTEXT                    :When enabled, a
 STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES                        :Vehicles never expire: {STRING2}
 STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_HELPTEXT               :When enabled, all vehicle models remain available forever after their introduction
 
+STR_CONFIG_SETTING_OFFER_VEHICLE_PREVIEW                        :Show vehicle previews: {STRING2}
+STR_CONFIG_SETTING_OFFER_VEHICLE_PREVIEW_HELPTEXT               :When enabled, the top performing company is sometimes offered a 1 year exclusive preview of a vehicle
+
 STR_CONFIG_SETTING_TIMEKEEPING_UNITS                            :Timekeeping: {STRING2}
 STR_CONFIG_SETTING_TIMEKEEPING_UNITS_HELPTEXT                   :Select the timekeeping units of the game. This cannot be changed later.{}{}Calendar-based is the classic OpenTTD experience, with a year consisting of 12 months, and each month having 28-31 days.{}{}In Wallclock-based time, cargo production and financials are instead based on one-minute increments, which is about as long as a 30 day month takes in Calendar-based mode. These are grouped into 12-minute periods, equivalent to a year in Calendar-based mode.{}{}In either mode there is always a classic calendar, which is used for introduction dates of vehicles, houses, and other infrastructure
 ###length 2

src/settingentry_gui.cpp

@@ -820,6 +820,7 @@ SettingsContainer &GetSettingsTree()
 			limitations->Add(new SettingEntry("construction.max_tunnel_length"));
 			limitations->Add(new SettingEntry("station.never_expire_airports"));
 			limitations->Add(new SettingEntry("vehicle.never_expire_vehicles"));
+			limitations->Add(new SettingEntry("vehicle.offer_vehicle_preview"));
 			limitations->Add(new SettingEntry("vehicle.max_trains"));
 			limitations->Add(new SettingEntry("vehicle.max_roadveh"));
 			limitations->Add(new SettingEntry("vehicle.max_aircraft"));

src/settings_type.h

@@ -511,6 +511,7 @@ struct VehicleSettings {
 	uint8_t  freight_trains;                   ///< value to multiply the weight of cargo by
 	bool   dynamic_engines;                  ///< enable dynamic allocation of engine data
 	bool   never_expire_vehicles;            ///< never expire vehicles
+	bool   offer_vehicle_preview;            ///< offer vehicle preview to companies
 	uint8_t extend_vehicle_life;              ///< extend vehicle life by this many years
 	uint8_t road_side;                        ///< the side of the road vehicles drive on
 	uint8_t  plane_crashes;                    ///< number of plane crashes, 0 = none, 1 = reduced, 2 = normal

src/table/settings/game_settings.ini

@@ -241,6 +241,13 @@ def      = false
 str      = STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES
 strhelp  = STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_HELPTEXT
 
+[SDT_BOOL]
+var      = vehicle.offer_vehicle_preview
+flags    = SettingFlag::NoNetwork
+def      = true
+str      = STR_CONFIG_SETTING_OFFER_VEHICLE_PREVIEW
+strhelp  = STR_CONFIG_SETTING_OFFER_VEHICLE_PREVIEW_HELPTEXT
+
 [SDT_VAR]
 var      = vehicle.max_trains
 type     = SLE_UINT16