Fix VEF issue with thing spawning on map generation (including Vanill…

…a Vehicles Tier 3 wrecks) (#502)

This should fix issues with things being spawned on map generation (ObjectSpawnsDef) by seeding the relevant method.

The issue is that a method passed to `LongEventHandler.ExecuteWhenFinished` during a `MapGenerator:GenerateMap` call (perhaps others as well?) would have a different seed between players. Should this be something we fix in MP? It doesn't affect vanilla only game, as (I believe) every affected `ExecuteWhenFinished` call seeds the RNG. And almost every `ExecuteWhenFinished` call is affecting graphics/audio, so it doesn't affect Multiplayer.

Source/Mods/VanillaExpandedFramework.cs

@@ -51,6 +51,7 @@ public VanillaExpandedFramework(ModContentPack mod)
                 (PatchStaticCaches, "Static caches", false),
                 (PatchGraphicCustomizationDialog, "Graphic Customization Dialog", true),
                 (PatchDraftedAi, "Drafted AI", true),
+                (PatchMapObjectGeneration, "Thing spawning on map generation (ObjectSpawnsDef)", false),
             ];
 
             foreach (var (patchMethod, componentName, latePatch) in patches)
@@ -1701,5 +1702,31 @@ private static void SyncDraftedActionData(SyncWorker sync, ref object draftedAct
         }
 
         #endregion
+
+        #region Thing spawning on map generation (ObjectSpawnsDef)
+
+        private static void PatchMapObjectGeneration()
+        {
+            // When calling "LongEventHandler.ExecuteWhenFinished" inside a
+            // "MapGenerator:GenerateMap" call the seed will differ between
+            // players. Is this something we should look into in MP itself?
+            MpCompat.harmony.Patch(AccessTools.DeclaredMethod("VFECore.MapGenerator_GenerateMap_Patch:DoMapSpawns"),
+                prefix: new HarmonyMethod(PreDoSpawns),
+                finalizer: new HarmonyMethod(PostDoSpawns));
+        }
+
+        private static void PreDoSpawns(Map map)
+        {
+            if (MP.IsInMultiplayer)
+                Rand.PushState(Gen.HashCombineInt(Gen.HashCombineInt(map.uniqueID, map.Tile), Find.TickManager.TicksGame));
+        }
+
+        private static void PostDoSpawns()
+        {
+            if (MP.IsInMultiplayer)
+                Rand.PopState();
+        }
+
+        #endregion
     }
 }