From d5db9dd00c5e611ceb5cc386653b03271dfb16e1 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Thu, 8 Jul 2021 10:10:19 +0200
Subject: [PATCH] Optimize physics simulation collisions pair cache

---
 Source/Engine/Core/Collections/Dictionary.h      | 12 ++++++++++++
 .../Engine/Physics/SimulationEventCallback.cpp   | 16 ++++++++++++++--
 Source/Engine/Physics/SimulationEventCallback.h  | 14 +-------------
 3 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/Source/Engine/Core/Collections/Dictionary.h b/Source/Engine/Core/Collections/Dictionary.h
index 1cbeb711f..ab3e986d4 100644
--- a/Source/Engine/Core/Collections/Dictionary.h
+++ b/Source/Engine/Core/Collections/Dictionary.h
@@ -556,6 +556,18 @@ public:
         SetCapacity(0, false);
     }
 
+    /// <summary>
+    /// Swaps the contents of collection with the other object without copy operation. Performs fast internal data exchange.
+    /// </summary>
+    /// <param name="other">The other collection.</param>
+    void Swap(Dictionary& other)
+    {
+        ::Swap(_elementsCount, other._elementsCount);
+        ::Swap(_deletedCount, other._deletedCount);
+        ::Swap(_size, other._size);
+        _allocation.Swap(other._allocation);
+    }
+
 public:
 
     /// <summary>
diff --git a/Source/Engine/Physics/SimulationEventCallback.cpp b/Source/Engine/Physics/SimulationEventCallback.cpp
index 6b2cfe18d..27c8aa785 100644
--- a/Source/Engine/Physics/SimulationEventCallback.cpp
+++ b/Source/Engine/Physics/SimulationEventCallback.cpp
@@ -2,11 +2,9 @@
 
 #include "SimulationEventCallback.h"
 #include "Utilities.h"
-#include "FlaxEngine.Gen.h"
 #include "Colliders/Collider.h"
 #include "Joints/Joint.h"
 #include "Actors/RigidBody.h"
-#include "Engine/Core/Log.h"
 #include <ThirdParty/PhysX/extensions/PxJoint.h>
 #include <ThirdParty/PhysX/PxShape.h>
 
@@ -39,6 +37,20 @@ namespace
     }
 }
 
+void SimulationEventCallback::Clear()
+{
+    PrevCollisions.Swap(Collisions);
+    Collisions.Clear();
+
+    NewCollisions.Clear();
+    RemovedCollisions.Clear();
+
+    NewTriggerPairs.Clear();
+    LostTriggerPairs.Clear();
+
+    BrokenJoints.Clear();
+}
+
 void SimulationEventCallback::CollectResults()
 {
     // Generate new collisions
diff --git a/Source/Engine/Physics/SimulationEventCallback.h b/Source/Engine/Physics/SimulationEventCallback.h
index 00f610717..c2705d255 100644
--- a/Source/Engine/Physics/SimulationEventCallback.h
+++ b/Source/Engine/Physics/SimulationEventCallback.h
@@ -60,19 +60,7 @@ public:
     /// <summary>
     /// Clears the data.
     /// </summary>
-    void Clear()
-    {
-        PrevCollisions = Collisions;
-        Collisions.Clear();
-
-        NewCollisions.Clear();
-        RemovedCollisions.Clear();
-
-        NewTriggerPairs.Clear();
-        LostTriggerPairs.Clear();
-
-        BrokenJoints.Clear();
-    }
+    void Clear();
 
     /// <summary>
     /// Generates the new/old/removed collisions and a valid trigger pairs.