Refactor engine loop to have better sync between game update, physics and drawing

Source/Engine/Engine/Engine.cpp

@@ -192,8 +192,11 @@ int32 Engine::Main(const Char* cmdLine)
             OnUnpause();
         }
 
+        // Use the same time for all ticks to improve synchronization
+        const double time = Platform::GetTimeSeconds();
+
         // Update game logic
-        if (Time::OnBeginUpdate())
+        if (Time::OnBeginUpdate(time))
         {
             OnUpdate();
             OnLateUpdate();
@@ -201,7 +204,7 @@ int32 Engine::Main(const Char* cmdLine)
         }
 
         // Start physics simulation
-        if (Time::OnBeginPhysics())
+        if (Time::OnBeginPhysics(time))
         {
             OnFixedUpdate();
             OnLateFixedUpdate();
@@ -209,7 +212,7 @@ int32 Engine::Main(const Char* cmdLine)
         }
 
         // Draw frame
-        if (Time::OnBeginDraw())
+        if (Time::OnBeginDraw(time))
         {
             OnDraw();
             Time::OnEndDraw();

Source/Engine/Engine/Time.cpp

@@ -72,10 +72,9 @@ void Time::TickData::OnReset(float targetFps, double currentTime)
     LastEnd = currentTime;
 }
 
-bool Time::TickData::OnTickBegin(float targetFps, float maxDeltaTime)
+bool Time::TickData::OnTickBegin(double time, float targetFps, float maxDeltaTime)
 {
     // Check if can perform a tick
-    const double time = Platform::GetTimeSeconds();
     double deltaTime;
     if (FixedDeltaTimeEnable)
     {
@@ -126,10 +125,9 @@ void Time::TickData::Advance(double time, double deltaTime)
     TicksCount++;
 }
 
-bool Time::FixedStepTickData::OnTickBegin(float targetFps, float maxDeltaTime)
+bool Time::FixedStepTickData::OnTickBegin(double time, float targetFps, float maxDeltaTime)
 {
     // Check if can perform a tick
-    double time = Platform::GetTimeSeconds();
     double deltaTime, minDeltaTime;
     if (FixedDeltaTimeEnable)
     {
@@ -249,9 +247,9 @@ void Time::Synchronize()
     Draw.Synchronize(DrawFPS, time);
 }
 
-bool Time::OnBeginUpdate()
+bool Time::OnBeginUpdate(double time)
 {
-    if (Update.OnTickBegin(UpdateFPS, MaxUpdateDeltaTime))
+    if (Update.OnTickBegin(time, UpdateFPS, MaxUpdateDeltaTime))
     {
         Current = &Update;
         return true;
@@ -259,9 +257,9 @@ bool Time::OnBeginUpdate()
     return false;
 }
 
-bool Time::OnBeginPhysics()
+bool Time::OnBeginPhysics(double time)
 {
-    if (Physics.OnTickBegin(PhysicsFPS, _physicsMaxDeltaTime))
+    if (Physics.OnTickBegin(time, PhysicsFPS, _physicsMaxDeltaTime))
     {
         Current = &Physics;
         return true;
@@ -269,9 +267,9 @@ bool Time::OnBeginPhysics()
     return false;
 }
 
-bool Time::OnBeginDraw()
+bool Time::OnBeginDraw(double time)
 {
-    if (Draw.OnTickBegin(DrawFPS, 1.0f))
+    if (Draw.OnTickBegin(time, DrawFPS, 1.0f))
     {
         Current = &Draw;
         return true;

Source/Engine/Engine/Time.h

@@ -12,12 +12,12 @@
 /// </summary>
 API_CLASS(Static) class FLAXENGINE_API Time
 {
-DECLARE_SCRIPTING_TYPE_NO_SPAWN(Time);
+    DECLARE_SCRIPTING_TYPE_NO_SPAWN(Time);
     friend class Engine;
     friend class TimeService;
     friend class PhysicsSettings;
-public:
 
+public:
     /// <summary>
     /// Engine subsystem updating data.
     /// Used to invoke game logic updates, physics updates and rendering with possibly different frequencies.
@@ -25,7 +25,6 @@ public:
     class FLAXENGINE_API TickData
     {
     public:
-
         virtual ~TickData() = default;
 
         /// <summary>
@@ -75,14 +74,12 @@ public:
         TimeSpan UnscaledTime;
 
     public:
-
-        virtual void OnBeforeRun(float targetFps, double currentTime);
+        virtual void Synchronize(float targetFps, double currentTime);
         virtual void OnReset(float targetFps, double currentTime);
-        virtual bool OnTickBegin(float targetFps, float maxDeltaTime);
+        virtual bool OnTickBegin(double time, float targetFps, float maxDeltaTime);
         virtual void OnTickEnd();
 
     protected:
-
         void Advance(double time, double deltaTime);
     };
 
@@ -92,25 +89,21 @@ public:
     class FixedStepTickData : public TickData
     {
     public:
-
         /// <summary>
         /// The last few ticks delta times. Used to check if can use fixed steps or whenever is running slowly so should use normal stepping.
         /// </summary>
         SamplesBuffer<double, 4> Samples;
 
     public:
-
         // [TickData]
-        bool OnTickBegin(float targetFps, float maxDeltaTime) override;
+        bool OnTickBegin(double time, float targetFps, float maxDeltaTime) override;
     };
 
 private:
-
     static bool _gamePaused;
     static float _physicsMaxDeltaTime;
 
 public:
-
     /// <summary>
     /// The time at which the game started (UTC local).
     /// </summary>
@@ -140,7 +133,6 @@ public:
     API_FIELD() static float TimeScale;
 
 public:
-
     /// <summary>
     /// The game logic updating data.
     /// </summary>
@@ -162,7 +154,6 @@ public:
     static TickData* Current;
 
 public:
-
     /// <summary>
     /// Gets the current tick data (safety so returns Update tick data if no active).
     /// </summary>
@@ -233,9 +224,9 @@ public:
 private:
     // Methods used by the Engine class
 
-    static bool OnBeginUpdate();
-    static bool OnBeginPhysics();
-    static bool OnBeginDraw();
+    static bool OnBeginUpdate(double time);
+    static bool OnBeginPhysics(double time);
+    static bool OnBeginDraw(double time);
 
     static void OnEndUpdate();
     static void OnEndPhysics();