From 50e159ce1e2febfc467ec51322984f427b124921 Mon Sep 17 00:00:00 2001
From: SokyranTheDragon <36712560+SokyranTheDragon@users.noreply.github.com>
Date: Sun, 14 Jul 2024 17:37:30 +0200
Subject: [PATCH] Patch for UndercaveMapComponent (pit gate) (#470)

Info on `UndercaveMapComponent:MapComponentTick` and why it needs patching:
- RNG calls after current map/visible camera area checks
- Majority of the RNG calls are visual/audio effects only
- `TriggerCollapseFX` does have an effect on simulation by spawning collapsed mountain roof
  - The collapsing rocks have minimal impact on the game, as they avoid player pawns

Fixing RNG is easy by just pushing/popping the state.

Fixing the collapsed mountain roof is more complex. Possible solutions:
- Disable rock collapse completely
- Disable current map checks (suboptimal for performance)
- Disable the existing calls to `TriggerCollapseFX` and call it in a deterministic way (used in this PR)

Information about the patch:
- The transpiler will make the call to `Rand.MTBEventOccurs` always fail, making so `TriggerCollapseFX` is never called
  - This could be further improved by removing the RNG call and the current map check altogether to improve performance, but would be more complex
- The prefix and postfix push/pop RNG state, making sure the ticking code doesn't mess with the RNG state
- The postfix re-implements the call to `TriggerCollapseFX` in a deterministic way
  - If the current player is not looking at the current map, it will be called with `0` as both arguments to prevent additional effects from triggering
  - The call to the method is surrounded by RNG push/pop state, as the amount of RNG calls will differ if the player is not looking at the map
    - It's safe as the simulation-affecting RNG calls happen first
    - The call is currently unseeded, but could be easily seeded with `Gen.HashCombineInt(Find.TickManager.TicksGame, __instance.map.uniqueID)` if we care about having a seed here

Remaining issues with `UndercaveMapComponent`/Pit Gate:
- The rock collapse has additional check to not drop rocks on player faction pawns. However, I assume this won't work properly with Multifaction, which could end up crushing pawns of some players.
---
 Source/Client/Patches/Determinism.cs | 60 ++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/Source/Client/Patches/Determinism.cs b/Source/Client/Patches/Determinism.cs
index 1eac7ec5..b6b8a7b2 100644
--- a/Source/Client/Patches/Determinism.cs
+++ b/Source/Client/Patches/Determinism.cs
@@ -524,4 +524,64 @@ static IEnumerable<CodeInstruction> Transpiler(IEnumerable<CodeInstruction> inst
         }
     }
 
+    [HarmonyPatch(typeof(UndercaveMapComponent), nameof(UndercaveMapComponent.MapComponentTick))]
+    static class DeterministicUndercaveRockCollapse
+    {
+        static IEnumerable<CodeInstruction> Transpiler(IEnumerable<CodeInstruction> instr)
+        {
+            var target = MethodOf.Lambda(Rand.MTBEventOccurs);
+
+            foreach (var ci in instr)
+            {
+                yield return ci;
+
+                // Add "& false" to any call to Rand.MTBEventOccurs.
+                // We'll handle those calls in our postfix.
+                if (ci.Calls(target))
+                {
+                    yield return new CodeInstruction(OpCodes.Ldc_I4_0);
+                    yield return new CodeInstruction(OpCodes.And);
+                }
+            }
+        }
+
+        static void Prefix() => Rand.PushState();
+
+        static void Postfix(UndercaveMapComponent __instance)
+        {
+            // Pop the RNG state from the prefix
+            Rand.PopState();
+
+            // Make sure the pit gate is collapsing
+            if (__instance.pitGate is not { IsCollapsing: true })
+                return;
+
+            // Check if the rocks should collapse
+            var mtb = UndercaveMapComponent.HoursToShakeMTBTicksCurve.Evaluate(__instance.pitGate.TicksUntilCollapse / 2500f);
+            if (!Rand.MTBEventOccurs(mtb, 1, 1))
+                return;
+
+            // Since the number of RNG calls will depend on numDustEffecters argument, we need to push/pop the RNG state.
+            // The RNG calls related to simulation will happen first, followed by the one determined by amount of
+            // effecters - it would not be MP safe, but since it happens last it will be fine once we pop the state.
+            Rand.PushState();
+
+            // If not looking at the map, trigger the collapse without shake/effecters (since it's not needed for current player).
+            // The call to play a sound is handled by RW itself, since it targets a specific map already.
+            if (Find.CurrentMap != __instance.map)
+            {
+                // Progress the RNG state, matching the RandomInRange call in other two cases
+                Rand.RangeInclusive(0, 100);
+                __instance.TriggerCollapseFX(0, 0);
+            }
+            // Else, follow vanilla shake/effecter rules
+            else if (__instance.pitGate.CollapseStage == 1)
+                __instance.TriggerCollapseFX(UndercaveMapComponent.StageOneShakeAmount, UndercaveMapComponent.StageOneNumCollapseEffects.RandomInRange);
+            else
+                __instance.TriggerCollapseFX(UndercaveMapComponent.StageTwoShakeAmount, UndercaveMapComponent.StageTwoNumCollapseEffects.RandomInRange);
+
+            Rand.PopState();
+        }
+    }
+
 }