Add seed validation for server world creation and override-seed property

The dedicated server previously picked a completely random seed with no
biome diversity checks (the client validates but the server skipped it).
On top of that, the client's findSeed() was hardcoded to only check a
54-chunk (Classic) area, so Large worlds had no diversity guarantee
beyond the center.

New server worlds now use findSeed() scaled to the full target world
size. Added override-seed in server.properties to fix existing worlds
without deleting them.

Minecraft.Client/Common/Consoles_App.cpp

@@ -206,6 +206,8 @@ CMinecraftApp::CMinecraftApp()
 	m_dwRequiredTexturePackID=0;
 
 	m_bResetNether=false;
+	m_seedOverride = 0;
+	m_hasSeedOverride = false;
 
 #ifdef _XBOX
 	//	m_bTransferSavesToXboxOne=false;

Minecraft.Client/Common/Consoles_App.h

@@ -706,6 +706,8 @@ private:
 	bool			m_bGameNewWorldSizeUseMoat;
 	unsigned int	m_GameNewHellScale;
 #endif
+	int64_t			m_seedOverride;
+	bool			m_hasSeedOverride;
 	unsigned int	FromBigEndian(unsigned int uiValue);
 
 public:
@@ -723,6 +725,10 @@ public:
 	void			SetGameNewHellScale(unsigned int newScale)				{ m_GameNewHellScale = newScale; }
 	unsigned int	GetGameNewHellScale()									{ return m_GameNewHellScale; }
 #endif
+	void			SetSeedOverride(int64_t seed)	{ m_seedOverride = seed; m_hasSeedOverride = true; }
+	bool			HasSeedOverride()				{ return m_hasSeedOverride; }
+	int64_t			GetSeedOverride()				{ return m_seedOverride; }
+
 	void			SetResetNether(bool bResetNether) {m_bResetNether=bResetNether;}
 	bool			GetResetNether() {return m_bResetNether;}
 	bool			CanRecordStatsAndAchievements();

Minecraft.Client/MinecraftServer.cpp

@@ -735,10 +735,11 @@ bool MinecraftServer::initServer(int64_t seed, NetworkGameInitData *initData, DW
 
 	if( findSeed )
 	{
+		int worldSizeChunks = (initData && initData->xzSize > 0) ? (int)initData->xzSize : 54;
 #ifdef __PSVITA__
-		seed = BiomeSource::findSeed(pLevelType, &running);
+		seed = BiomeSource::findSeed(pLevelType, &running, worldSizeChunks);
 #else
-		seed = BiomeSource::findSeed(pLevelType);
+		seed = BiomeSource::findSeed(pLevelType, worldSizeChunks);
 #endif
 	}
 

Minecraft.Server/ServerProperties.cpp

@@ -824,6 +824,20 @@ ServerPropertiesConfig LoadServerPropertiesConfig()
 	config.maxPlayers = ReadNormalizedIntProperty(&merged, "max-players", kDefaultMaxPlayers, 1, kMaxDedicatedPlayers, &shouldWrite);
 	config.seed = 0;
 	config.hasSeed = ReadNormalizedOptionalInt64Property(&merged, "level-seed", &config.seed, &shouldWrite);
+	config.overrideSeed = 0;
+	config.hasOverrideSeed = false;
+	{
+		auto it = merged.find("override-seed");
+		if (it != merged.end() && !TrimAscii(it->second).empty())
+		{
+			__int64 parsed = 0;
+			if (TryParseInt64(TrimAscii(it->second), &parsed))
+			{
+				config.overrideSeed = parsed;
+				config.hasOverrideSeed = true;
+			}
+		}
+	}
 	config.logLevel = ReadNormalizedLogLevelProperty(&merged, "log-level", eServerLogLevel_Info, &shouldWrite);
 	config.autosaveIntervalSeconds = ReadNormalizedIntProperty(&merged, "autosave-interval", kDefaultAutosaveIntervalSeconds, 5, 3600, &shouldWrite);
 

Minecraft.Server/ServerProperties.h

@@ -31,6 +31,9 @@ namespace ServerRuntime
 		bool hasSeed;
 		/** `level-seed` */
 		__int64 seed;
+		/** `override-seed` replaces the seed for biome generation on existing worlds */
+		bool hasOverrideSeed;
+		__int64 overrideSeed;
 		/** `log-level` */
 		EServerLogLevel logLevel;
 		/** `autosave-interval` (seconds) */

Minecraft.Server/Windows64/ServerMain.cpp

@@ -28,6 +28,8 @@
 #include "../../Minecraft.World/TilePos.h"
 #include "../../Minecraft.World/compression.h"
 #include "../../Minecraft.World/OldChunkStorage.h"
+#include "../../Minecraft.World/BiomeSource.h"
+#include "../../Minecraft.World/LevelType.h"
 #include "../../Minecraft.World/net.minecraft.world.level.tile.h"
 #include "../../Minecraft.World/Random.h"
 
@@ -545,6 +547,12 @@ int main(int argc, char **argv)
 	app.SetGameNewHellScale(serverProperties.worldHellScale);
 #endif
 
+	if (serverProperties.hasOverrideSeed)
+	{
+		LogInfof("startup", "Seed override active: %lld", serverProperties.overrideSeed);
+		app.SetSeedOverride(serverProperties.overrideSeed);
+	}
+
 	StorageManager.SetSaveDisabled(serverProperties.disableSaving);
 	// Read world name and fixed save-id from server.properties
 	// Delegate load-vs-create decision to WorldManager
@@ -584,9 +592,17 @@ int main(int argc, char **argv)
 	{
 		param->seed = config.seed;
 	}
+	else if (worldBootstrap.saveData == nullptr)
+	{
+		// Only run seed validation when creating a brand-new world.
+		// Existing worlds already have their seed in level.dat.
+		LogInfof("startup", "Finding seed with biome diversity for %d-chunk world...", config.worldSizeChunks);
+		param->seed = BiomeSource::findSeed(LevelType::lvl_normal, config.worldSizeChunks);
+		LogInfof("startup", "Selected seed: %lld", param->seed);
+	}
 	else
 	{
-		param->seed = (new Random())->nextLong();
+		param->seed = (new Random())->nextLong(); // placeholder; level.dat seed takes priority
 	}
 #ifdef _LARGE_WORLDS
 	param->xzSize = (unsigned int)config.worldSizeChunks;

Minecraft.World/BiomeSource.cpp

@@ -411,9 +411,9 @@ void BiomeSource::update()
 
 // 4J added - find a seed for this biomesource that matches certain criteria
 #ifdef __PSVITA__
-int64_t BiomeSource::findSeed(LevelType *generator, bool* pServerRunning)	// MGH - added pRunning, so we can early out of this on Vita as it can take up to 60 secs
+int64_t BiomeSource::findSeed(LevelType *generator, bool* pServerRunning, int worldSizeChunks)
 #else
-int64_t BiomeSource::findSeed(LevelType *generator)
+int64_t BiomeSource::findSeed(LevelType *generator, int worldSizeChunks)
 #endif
 {
 
@@ -440,8 +440,8 @@ int64_t BiomeSource::findSeed(LevelType *generator)
 			// Raw biome data has one result per 4x4 group of tiles.
 			// Removing a border of 8 from each side since we'll be doing special things at the edge to turn our world into an island, and so don't want to count things
 			// in the edge region in case they later get removed
-			static const int biomeWidth = ( 54 * 4 ) - 16;			// Should be even so we can offset evenly
-			static const int biomeOffset = -( biomeWidth / 2 );
+			const int biomeWidth = ( worldSizeChunks * 4 ) - 16;			// Should be even so we can offset evenly
+			const int biomeOffset = -( biomeWidth / 2 );
 
 			// Storage for our biome indices
 			intArray indices = intArray( biomeWidth * biomeWidth );

Minecraft.World/BiomeSource.h

@@ -36,9 +36,9 @@ private:
 	static void getFracs(intArray indices, float *fracs);	// 4J added
 public:
 #ifdef __PSVITA__
-	static int64_t findSeed(LevelType *generator, bool* pServerRunning);	// MGH - added pRunning, so we can early out of this on Vita as it can take up to 60 secs							// 4J added
+	static int64_t findSeed(LevelType *generator, bool* pServerRunning, int worldSizeChunks = 54);
 #else
-	static int64_t findSeed(LevelType *generator);	// 4J added
+	static int64_t findSeed(LevelType *generator, int worldSizeChunks = 54);
 #endif
 	~BiomeSource();
 

Minecraft.World/LevelData.cpp

@@ -13,6 +13,15 @@ LevelData::LevelData()
 LevelData::LevelData(CompoundTag *tag)
 {
 	seed = tag->getLong(L"RandomSeed");
+
+	// Allow server.properties to override the world seed for biome generation
+	// on existing worlds (e.g. to fix monotonous biomes after world expansion).
+	if (app.HasSeedOverride())
+	{
+		app.DebugPrintf("Overriding world seed: %lld -> %lld\n", seed, app.GetSeedOverride());
+		seed = app.GetSeedOverride();
+	}
+
 	m_pGenerator = LevelType::lvl_normal;
 	if (tag->contains(L"generatorName"))
 	{

README.md

@@ -14,6 +14,12 @@ This project is based on source code of Minecraft Legacy Console Edition v1.6.05
 
 ## Latest:
 
+Dedicated server biome diversity fix:
+- The dedicated server previously used a completely random seed with no biome diversity checks — unlike the client which validates seeds to guarantee varied biomes. This could result in server worlds with large regions dominated by only one or two biome types (e.g. all taiga/snowy)
+- On top of that, the client's seed validation was hardcoded to only check a 54-chunk (Classic) area, so even validated seeds had no diversity guarantee beyond that — making the problem especially noticeable on Large worlds or worlds expanded from Classic to Large
+- New server worlds now validate seeds for biome diversity, and the validation scales to the full target world size
+- Added `override-seed` in server.properties to fix existing worlds without deleting them — set it to any seed number and newly generated chunks will use it instead of the original
+
 Server list and connection improvements:
 - Server edits and deletions now apply immediately without needing to restart the game
 - Connecting to an offline/unreachable server no longer freezes the game indefinitely