From 34e4d90dacebdec3fa4c77374ff31e2e1067bce5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tam=C3=A1s=20B=C3=A1lint=20Misius?= <lbphacker@gmail.com>
Date: Sat, 15 Apr 2023 23:03:54 +0200
Subject: [PATCH] Properly seed rng at load time for saves that don't carry rng
 state

Also save rngState as a user object rather than two separate i64s.
---
 src/client/GameSave.cpp    | 19 ++++++++++++++-----
 src/client/GameSave.h      |  1 +
 src/gui/game/GameModel.cpp |  9 ++++++++-
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/src/client/GameSave.cpp b/src/client/GameSave.cpp
index 02641a47b..75c8b984c 100644
--- a/src/client/GameSave.cpp
+++ b/src/client/GameSave.cpp
@@ -25,13 +25,11 @@ static void CheckBsonFieldFloat(bson_iterator iter, const char *field, float *se
 
 GameSave::GameSave(int width, int height)
 {
-	rngState = RNG().state(); // initialize it with something sane
 	setSize(width, height);
 }
 
 GameSave::GameSave(const std::vector<char> &data, bool newWantAuthors)
 {
-	rngState = RNG().state(); // initialize it with something sane
 	wantAuthors = newWantAuthors;
 	blockWidth = 0;
 	blockHeight = 0;
@@ -543,7 +541,19 @@ void GameSave::readOPS(const std::vector<char> &data)
 		CheckBsonFieldLong(iter, "frameCount", reinterpret_cast<int64_t *>(&frameCount));
 		CheckBsonFieldLong(iter, "rngState0", reinterpret_cast<int64_t *>(&rngState[0]));
 		CheckBsonFieldLong(iter, "rngState1", reinterpret_cast<int64_t *>(&rngState[1]));
-		if (!strcmp(bson_iterator_key(&iter), "signs"))
+		if (!strcmp(bson_iterator_key(&iter), "rngState"))
+		{
+			if (bson_iterator_type(&iter) == BSON_BINDATA && ((unsigned char)bson_iterator_bin_type(&iter)) == BSON_BIN_USER && bson_iterator_bin_len(&iter) == sizeof(rngState))
+			{
+				memcpy(&rngState, bson_iterator_bin_data(&iter), sizeof(rngState));
+				hasRngState = true;
+			}
+			else
+			{
+				fprintf(stderr, "Invalid datatype for rngState: %d[%d] %d[%d] %d[%d]\n", bson_iterator_type(&iter), bson_iterator_type(&iter)==BSON_BINDATA, (unsigned char)bson_iterator_bin_type(&iter), ((unsigned char)bson_iterator_bin_type(&iter))==BSON_BIN_USER, bson_iterator_bin_len(&iter), bson_iterator_bin_len(&iter)>0);
+			}
+		}
+		else if (!strcmp(bson_iterator_key(&iter), "signs"))
 		{
 			if (bson_iterator_type(&iter)==BSON_ARRAY)
 			{
@@ -2550,8 +2560,7 @@ std::pair<bool, std::vector<char>> GameSave::serialiseOPS() const
 		bson_append_bool(&b, "ensureDeterminism", ensureDeterminism);
 		bson_append_binary(&b, "blockAir", (char)BSON_BIN_USER, (const char *)&blockAirData[0], blockAirDataLen);
 		bson_append_long(&b, "frameCount", int64_t(frameCount));
-		bson_append_long(&b, "rngState0", int64_t(rngState[0]));
-		bson_append_long(&b, "rngState1", int64_t(rngState[1]));
+		bson_append_binary(&b, "rngState", (char)BSON_BIN_USER, (const char *)&rngState, sizeof(rngState));
 		RESTRICTVERSION(98, 0);
 	}
 	unsigned int signsCount = 0;
diff --git a/src/client/GameSave.h b/src/client/GameSave.h
index bf94529b9..21335504c 100644
--- a/src/client/GameSave.h
+++ b/src/client/GameSave.h
@@ -97,6 +97,7 @@ public:
 	bool hasAmbientHeat = false;
 	bool hasBlockAirMaps = false; // only written by readOPS, never read
 	bool ensureDeterminism = false; // only taken seriously by serializeOPS; readOPS may set this even if the save does not have everything required for determinism
+	bool hasRngState = false; // only written by readOPS, never read
 	RNG::State rngState;
 	uint64_t frameCount = 0;
 
diff --git a/src/gui/game/GameModel.cpp b/src/gui/game/GameModel.cpp
index 0e8f11ade..595f75fcd 100644
--- a/src/gui/game/GameModel.cpp
+++ b/src/gui/game/GameModel.cpp
@@ -955,7 +955,14 @@ void GameModel::SaveToSimParameters(const GameSave *saveData)
 		sim->grav->stop_grav_async();
 	}
 	sim->frameCount = saveData->frameCount;
-	sim->rng.state(saveData->rngState);
+	if (saveData->hasRngState)
+	{
+		sim->rng.state(saveData->rngState);
+	}
+	else
+	{
+		sim->rng = RNG();
+	}
 	sim->ensureDeterminism = saveData->ensureDeterminism;
 }