Add RestoreMaxPhysicsDT (#95)

When using physics warp, Unity will set the max physics dt to be at least as high as the scaled physics dt.  But KSP will never restore it back to the normal value from the settings.  This can degrade performance as it allows more FixedUpdates to run per frame.

reported by Wilds on the forum: https://forum.kerbalspaceprogram.com/index.php?/topic/184740-solved-losing-300-performance-after-time-warping/

GameData/KSPCommunityFixes/Settings.cfg

@@ -300,6 +300,10 @@ KSP_COMMUNITY_FIXES
   // speed up reading) at the cost of human readability.
   SkipIndentsOnSavesAndCraftFiles = false
 
+  // After using physics warp, Unity's max physics dt will never be returned to the value specified in 
+  // game settings which can degrade performance in some cases
+  RestoreMaxPhysicsDT = true
+
   // The stock ModuleAsteroidDrill and ModuleCometDrill do a lot of unnecessary iterating over all
   // PartModules on the vessel to see if an asteroid or comet is attached.
   // ModuleResourceHarvester already keeps a cache of this information, and all the stock drills

KSPCommunityFixes/BugFixes/RestoreMaxPhysicsDT.cs

@@ -0,0 +1,30 @@
+using HarmonyLib;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using UnityEngine;
+
+namespace KSPCommunityFixes.BugFixes
+{
+    public class RestoreMaxPhysicsDT : BasePatch
+    {
+        protected override void ApplyPatches(List<PatchInfo> patches)
+        {
+            patches.Add(new PatchInfo(
+                PatchMethodType.Prefix,
+                AccessTools.Method(typeof(TimeWarp), "updateRate"),
+                this));
+        }
+
+        static void TimeWarp_updateRate_Prefix()
+        {
+            // when you use physics warp, it increases Time.fixedDeltaTime
+            // Unity will internally increase maximumDeltaTime to be at least as high as fixedDeltaTime
+            // But nothing in the KSP code will ever return maximumDeltaTime to the value from the settings when time warp is over
+            // Setting it just before TimeWarp sets fixedDeltaTime guarantees that all points of code will have the correct value
+            Time.maximumDeltaTime = GameSettings.PHYSICS_FRAME_DT_LIMIT;
+        }
+    }
+}

KSPCommunityFixes/KSPCommunityFixes.csproj

@@ -103,6 +103,7 @@
     <Compile Include="Modding\ModUpgradePipeline.cs" />
     <Compile Include="Performance\AsteroidAndCometDrillCache.cs" />
     <Compile Include="BugFixes\DoubleCurvePreserveTangents.cs" />
+    <Compile Include="BugFixes\RestoreMaxPhysicsDT.cs" />
     <Compile Include="Performance\CommNetThrottling.cs" />
     <Compile Include="Performance\DisableMapUpdateInFlight.cs" />
     <Compile Include="Performance\CommNetSpeedBoost.cs" />