From 692a61c94826957073465078b54ec04e7dcb9759 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Wed, 17 Apr 2024 13:01:58 +0200
Subject: [PATCH] Add `Time.Synchronize` to stabilize engine loop

---
 Source/Editor/States/PlayingState.cs |  4 ++++
 Source/Engine/Engine/Engine.cpp      |  4 ++--
 Source/Engine/Engine/Time.cpp        | 10 +++++-----
 Source/Engine/Engine/Time.h          |  8 +++++---
 4 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/Source/Editor/States/PlayingState.cs b/Source/Editor/States/PlayingState.cs
index 1be2a1816..b2654f3d9 100644
--- a/Source/Editor/States/PlayingState.cs
+++ b/Source/Editor/States/PlayingState.cs
@@ -163,6 +163,8 @@ namespace FlaxEditor.States
             Editor.OnPlayBegin();
             IsPlayModeStarting = false;
             Profiler.EndEvent();
+
+            Time.Synchronize();
         }
 
         private void SetupEditorEnvOptions()
@@ -209,6 +211,8 @@ namespace FlaxEditor.States
             Editor.OnPlayEnd();
             IsPlayModeEnding = false;
             Profiler.EndEvent();
+
+            Time.Synchronize();
         }
     }
 }
diff --git a/Source/Engine/Engine/Engine.cpp b/Source/Engine/Engine/Engine.cpp
index 27b35a0b7..abebbdb91 100644
--- a/Source/Engine/Engine/Engine.cpp
+++ b/Source/Engine/Engine/Engine.cpp
@@ -156,7 +156,7 @@ int32 Engine::Main(const Char* cmdLine)
 #endif
     Log::Logger::WriteFloor();
     LOG_FLUSH();
-    Time::OnBeforeRun();
+    Time::Synchronize();
     EngineImpl::IsReady = true;
 
     // Main engine loop
@@ -465,7 +465,7 @@ void Engine::OnUnpause()
     LOG(Info, "App unpaused");
     Unpause();
 
-    Time::OnBeforeRun();
+    Time::Synchronize();
 }
 
 void Engine::OnExit()
diff --git a/Source/Engine/Engine/Time.cpp b/Source/Engine/Engine/Time.cpp
index 6df5275f5..7f4571b32 100644
--- a/Source/Engine/Engine/Time.cpp
+++ b/Source/Engine/Engine/Time.cpp
@@ -54,7 +54,7 @@ void TimeSettings::Apply()
     ::MaxUpdateDeltaTime = MaxUpdateDeltaTime;
 }
 
-void Time::TickData::OnBeforeRun(float targetFps, double currentTime)
+void Time::TickData::Synchronize(float targetFps, double currentTime)
 {
     Time = UnscaledTime = TimeSpan::Zero();
     DeltaTime = UnscaledDeltaTime = targetFps > ZeroTolerance ? TimeSpan::FromSeconds(1.0f / targetFps) : TimeSpan::Zero();
@@ -240,13 +240,13 @@ void Time::SetFixedDeltaTime(bool enable, float value)
     FixedDeltaTimeValue = value;
 }
 
-void Time::OnBeforeRun()
+void Time::Synchronize()
 {
     // Initialize tick data (based on a time settings)
     const double time = Platform::GetTimeSeconds();
-    Update.OnBeforeRun(UpdateFPS, time);
-    Physics.OnBeforeRun(PhysicsFPS, time);
-    Draw.OnBeforeRun(DrawFPS, time);
+    Update.Synchronize(UpdateFPS, time);
+    Physics.Synchronize(PhysicsFPS, time);
+    Draw.Synchronize(DrawFPS, time);
 }
 
 bool Time::OnBeginUpdate()
diff --git a/Source/Engine/Engine/Time.h b/Source/Engine/Engine/Time.h
index 06e0d1cc5..4bb269cb9 100644
--- a/Source/Engine/Engine/Time.h
+++ b/Source/Engine/Engine/Time.h
@@ -225,12 +225,14 @@ public:
     /// <param name="value">The fixed draw/update rate for the time.</param>
     API_FUNCTION() static void SetFixedDeltaTime(bool enable, float value);
 
+    /// <summary>
+    /// Synchronizes update, fixed update and draw. Resets any pending deltas for fresh ticking in sync.
+    /// </summary>
+    API_FUNCTION() static void Synchronize();
+
 private:
-
     // Methods used by the Engine class
 
-    static void OnBeforeRun();
-
     static bool OnBeginUpdate();
     static bool OnBeginPhysics();
     static bool OnBeginDraw();