Add a base container with beat syncing logic

osu.Game/Graphics/Containers/BeatSyncedContainer.cs

@@ -0,0 +1,64 @@
+using osu.Framework.Allocation;
+using osu.Framework.Configuration;
+using osu.Framework.Graphics.Containers;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.Timing;
+
+namespace osu.Game.Graphics.Containers
+{
+    public class BeatSyncedContainer : Container
+    {
+        private Bindable<WorkingBeatmap> beatmap;
+        private int beat;
+        private double timingPointStart;
+        //This is to avoid sending new beats when not at the very start of the beat
+        private const int seek_tolerance = 20;
+        private const double min_beat_length = 1E-100;
+
+        public BeatSyncedContainer()
+        {
+        }
+
+        protected override void Update()
+        {
+            if (beatmap.Value != null)
+            {
+                double currentTime = beatmap.Value.Track.CurrentTime;
+                ControlPoint kiaiControlPoint;
+                ControlPoint controlPoint = beatmap.Value.Beatmap.TimingInfo.TimingPointAt(currentTime, out kiaiControlPoint);
+
+                if (controlPoint != null)
+                {
+                    double oldTimingPointStart = timingPointStart;
+                    double beatLenght = double.MinValue;
+                    int oldBeat = beat;
+                    bool kiai = false;
+
+                    beatLenght = controlPoint.BeatLength;
+                    timingPointStart = controlPoint.Time;
+                    kiai = kiaiControlPoint?.KiaiMode ?? false;
+
+                    beat = beatLenght > min_beat_length ? (int)((currentTime - timingPointStart) / beatLenght) : 0;
+
+                    //should we handle negative beats? (before the start of the controlPoint)
+                    //The beats before the start of the first control point are off by 1, this should do the trick
+                    if (currentTime <= timingPointStart)
+                        beat--;
+
+                    if ((timingPointStart != oldTimingPointStart || beat != oldBeat) && (int)((currentTime - timingPointStart) % (beatLenght)) <= seek_tolerance)
+                        OnNewBeat(beat, controlPoint.BeatLength, controlPoint.TimeSignature, kiai);
+                }
+            }
+        }
+
+        protected virtual void OnNewBeat(int newBeat, double beatLength, TimeSignatures timeSignature, bool kiai)
+        {
+        }
+
+        [BackgroundDependencyLoader]
+        private void load(OsuGameBase game)
+        {
+            beatmap = game.Beatmap;
+        }
+    }
+}

osu.Game/osu.Game.csproj

@@ -74,6 +74,7 @@
     <Compile Include="Audio\SampleInfoList.cs" />
     <Compile Include="Beatmaps\Drawables\BeatmapBackgroundSprite.cs" />
     <Compile Include="Beatmaps\DifficultyCalculator.cs" />
+    <Compile Include="Graphics\Containers\BeatSyncedContainer.cs" />
     <Compile Include="Online\API\Requests\PostMessageRequest.cs" />
     <Compile Include="Online\Chat\ErrorMessage.cs" />
     <Compile Include="Overlays\Chat\ChatTabControl.cs" />