From cbf48c4dd9aa4268df835e6ac1207db8094a935d Mon Sep 17 00:00:00 2001
From: Peter Nelson <peter1138@openttd.org>
Date: Mon, 12 Dec 2022 11:17:55 +0000
Subject: [PATCH] Change: Add extra random seed to StartupEngines().

This means that calling reset_engines will rerandomise introduction dates
and reliability.

Probably not necessary.
---
 src/engine.cpp                | 10 ++++++----
 src/engine_func.h             |  2 +-
 src/saveload/oldloader_sl.cpp |  2 +-
 3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/engine.cpp b/src/engine.cpp
index 8bd14849ad..3423c7f40f 100644
--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -648,8 +648,9 @@ void SetYearEngineAgingStops()
  * Start/initialise one engine.
  * @param e The engine to initialise.
  * @param aging_date The date used for age calculations.
+ * @param seed Random seed.
  */
-void StartupOneEngine(Engine *e, Date aging_date)
+void StartupOneEngine(Engine *e, Date aging_date, uint32 seed)
 {
 	const EngineInfo *ei = &e->info;
 
@@ -662,7 +663,7 @@ void StartupOneEngine(Engine *e, Date aging_date)
 	 * Make sure they use the same randomisation of the date. */
 	SavedRandomSeeds saved_seeds;
 	SaveRandomSeeds(&saved_seeds);
-	SetRandomSeed(_settings_game.game_creation.generation_seed ^
+	SetRandomSeed(_settings_game.game_creation.generation_seed ^ seed ^
 	              ei->base_intro ^
 	              e->type ^
 	              e->GetGRFID());
@@ -684,7 +685,7 @@ void StartupOneEngine(Engine *e, Date aging_date)
 		re = Engine::Get(re->info.variant_id);
 	}
 
-	SetRandomSeed(_settings_game.game_creation.generation_seed ^
+	SetRandomSeed(_settings_game.game_creation.generation_seed ^ seed ^
 	              (re->index << 16) ^ (re->info.base_intro << 12) ^ (re->info.decay_speed << 8) ^
 	              (re->info.lifelength << 4) ^ re->info.retire_early ^
 	              e->type ^
@@ -719,9 +720,10 @@ void StartupEngines()
 {
 	/* Aging of vehicles stops, so account for that when starting late */
 	const Date aging_date = std::min(_date, ConvertYMDToDate(_year_engine_aging_stops, 0, 1));
+	uint32 seed = Random();
 
 	for (Engine *e : Engine::Iterate()) {
-		StartupOneEngine(e, aging_date);
+		StartupOneEngine(e, aging_date, seed);
 	}
 	for (Engine *e : Engine::Iterate()) {
 		CalcEngineReliability(e, false);
diff --git a/src/engine_func.h b/src/engine_func.h
index f7d7dad9f8..0d69743bfe 100644
--- a/src/engine_func.h
+++ b/src/engine_func.h
@@ -27,7 +27,7 @@ bool IsEngineRefittable(EngineID engine);
 void GetArticulatedVehicleCargoesAndRefits(EngineID engine, CargoArray *cargoes, CargoTypes *refits, CargoID cargo_type, uint cargo_capacity);
 void SetYearEngineAgingStops();
 void CalcEngineReliability(Engine *e, bool new_month);
-void StartupOneEngine(Engine *e, Date aging_date);
+void StartupOneEngine(Engine *e, Date aging_date, uint32 seed);
 
 uint GetTotalCapacityOfArticulatedParts(EngineID engine);
 
diff --git a/src/saveload/oldloader_sl.cpp b/src/saveload/oldloader_sl.cpp
index 74a2996601..fc09c7e787 100644
--- a/src/saveload/oldloader_sl.cpp
+++ b/src/saveload/oldloader_sl.cpp
@@ -401,7 +401,7 @@ static bool FixTTOEngines()
 		if (oi == 255) {
 			/* Default engine is used */
 			_date += DAYS_TILL_ORIGINAL_BASE_YEAR;
-			StartupOneEngine(e, aging_date);
+			StartupOneEngine(e, aging_date, 0);
 			CalcEngineReliability(e, false);
 			e->intro_date -= DAYS_TILL_ORIGINAL_BASE_YEAR;
 			_date -= DAYS_TILL_ORIGINAL_BASE_YEAR;