Implement drift correction (#3)

Makes cinema mod automatically correct drift, making the background stay in sync and letting charters to get a bit more creative

Author: Balint817

DriftCorrector.cs

@@ -0,0 +1,151 @@
+using Il2CppFormulaBase;
+using MelonLoader;
+using UnityEngine;
+
+namespace Cinema
+{
+    internal static class DriftCorrector
+    {
+        // higher == more precise, but may have lower performance
+        private const float CorrectionPrecision = 1f;
+        private const int ForceSetThreshold = 20;
+        private const float DisableCoefficient = 1.1f;
+        private static StageBattleComponent _battleComponent;
+        private static bool _isInit;
+        private static readonly float[] DeltaSamples = new float[50];
+
+        private static int _deltaSampleIndex;
+        private static SpeedState _currentSpeed = SpeedState.Normal;
+
+        /// <summary>
+        ///     In case another mod wants to change the playback speed (such as PracticeMod),
+        ///     <br />
+        ///     we store the original playback speed and use it in our calculations.
+        /// </summary>
+        private static float _originalPlaybackSpeed = 1f;
+
+        private static double _lastUpdateTime;
+
+        internal static void Init()
+        {
+            if (_isInit) return;
+            InitAverageDelta();
+            _isInit = true;
+        }
+
+        internal static void Stop()
+        {
+            var del = LateUpdate;
+            if (MelonEvents.OnLateUpdate.CheckIfSubscribed(del.Method))
+            {
+                MelonEvents.OnLateUpdate.Unsubscribe(LateUpdate);
+            }
+
+            if (Main.Player is not null) Main.Player.playbackSpeed = _originalPlaybackSpeed;
+        }
+
+        internal static void Run()
+        {
+            _originalPlaybackSpeed = Main.Player.playbackSpeed;
+            _lastUpdateTime = 0;
+            _battleComponent = StageBattleComponent.instance;
+            _currentSpeed = SpeedState.Normal;
+            MelonEvents.OnLateUpdate.Subscribe(LateUpdate);
+        }
+
+        private static void CalculateAverageDelta()
+        {
+            DeltaSamples[_deltaSampleIndex++] = Time.deltaTime;
+            if (_deltaSampleIndex == DeltaSamples.Length) _deltaSampleIndex = 0;
+        }
+
+        private static void InitAverageDelta()
+        {
+            CalculateAverageDelta();
+            for (var i = 1; i < DeltaSamples.Length; i++) DeltaSamples[i] = DeltaSamples[0];
+        }
+
+        /// <summary>
+        ///     Calculates playback speed using the given parameters
+        /// </summary>
+        private static float CalculateSpeed(float deltaTime, float drift)
+        {
+            var averageScaled = deltaTime / 10;
+            var relativeDrift = Math.Abs(drift) + 1;
+            var speed = Math.Min((1 + averageScaled) * relativeDrift, 1.05f);
+            if (drift > 0) speed = 2 - speed;
+            ;
+            return speed * _originalPlaybackSpeed;
+        }
+
+        private static void LateUpdate()
+        {
+            if (Main.Player is null || Math.Abs(Main.Player.time - _lastUpdateTime) < 0.000001) return;
+            if (Main.Player.time >= Main.Player.length)
+            {
+                Stop();
+                return;
+            }
+
+            CalculateAverageDelta();
+            _lastUpdateTime = Main.Player.time;
+
+            var averageDelta = DeltaSamples.Average();
+            var drift = (float)(_lastUpdateTime - _battleComponent.timeFromMusicStart);
+            if (Math.Abs(drift) > averageDelta * ForceSetThreshold)
+            {
+                // If the game freezes, (e.g. extreme drift) instantly set the player's time,
+                // instead of slightly speeding up, like when we correct small drifts.
+                // This correction may cause a few Update loops worth of drift,
+                // but is preferable to a multiple second drift.
+                var correct = _battleComponent.timeFromMusicStart + averageDelta * ForceSetThreshold;
+                Main.Player.time = correct;
+                return;
+            }
+
+            var maxDifference = averageDelta / CorrectionPrecision;
+            var disableThreshold = maxDifference / DisableCoefficient;
+            switch (_currentSpeed)
+            {
+                case SpeedState.Slow:
+                    if (drift > disableThreshold) return;
+                    break;
+                case SpeedState.Fast:
+                    if (drift < -disableThreshold) return;
+                    break;
+                case SpeedState.Normal:
+                    break;
+                default:
+                    throw new ArgumentOutOfRangeException();
+            }
+
+            if (drift < -maxDifference)
+            {
+                _currentSpeed = SpeedState.Fast;
+                var speed = CalculateSpeed(averageDelta, drift);
+                Main.Player.playbackSpeed = speed;
+                return;
+            }
+
+            if (drift > maxDifference)
+            {
+                _currentSpeed = SpeedState.Slow;
+                var speed = CalculateSpeed(averageDelta, drift);
+                Main.Player.playbackSpeed = speed;
+                return;
+            }
+
+            if (_currentSpeed is SpeedState.Normal) return;
+
+            Main.Player.playbackSpeed = _originalPlaybackSpeed;
+            _currentSpeed = SpeedState.Normal;
+        }
+
+        private enum SpeedState
+        {
+            Slow,
+            Normal,
+            Fast
+        }
+    }
+}

Main.cs

@@ -13,9 +13,15 @@ public class Main : MelonMod
         internal static VideoPlayer Player;
         internal static bool Christmas;
 
+        public override void OnSceneWasLoaded(int buildIndex, string sceneName)
+        {
+            DriftCorrector.Stop();
+        }
+
         public override void OnInitializeMelon()
         {
             base.OnInitializeMelon();
+            DriftCorrector.Init();
 
             // Clean up old file from v1.1.x and below
             if (File.Exists(Application.persistentDataPath + "/cinema.mp4"))
@@ -56,6 +62,8 @@ internal static void InitCamera(float opacity)
             Player.audioOutputMode = VideoAudioOutputMode.None;
             Player.aspectRatio = VideoAspectRatio.FitOutside;
             Player.url = Application.dataPath + "/cinema.mp4";
+            Player.skipOnDrop = true;
+            Player.Prepare();
         }
 
         internal static void HideSceneElements()
@@ -65,8 +73,6 @@ internal static void HideSceneElements()
                 : $"scene_0{SceneChangeController.curScene}";
             if (Christmas && sceneName == "scene_05") sceneName += "_christmas";
 
-            MelonLogger.Msg("SCENE TO HIDE: " + sceneName);
-
             var sceneObject = GameObject.Find("SceneObjectController").transform.Find(sceneName);
             if (sceneObject == null) return;
 

Patches/GameStartPatch.cs

@@ -12,6 +12,7 @@ private static void Postfix()
 
             Main.GameStarted = true;
             Main.Player.Play();
+            DriftCorrector.Run();
         }
     }
 }

Patches/RestartPatch.cs

@@ -11,6 +11,7 @@ private static void Postfix()
             if (Main.Player == null) return;
 
             Main.GameStarted = false;
+            DriftCorrector.Stop();
         }
     }
 }