osu/osu.Game/Graphics/Containers/BeatSyncedContainer.cs

// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE

using osu.Framework.Allocation;
using osu.Framework.Audio.Track;
using osu.Framework.Configuration;
using osu.Framework.Graphics.Containers;
using osu.Game.Beatmaps;
using osu.Game.Beatmaps.ControlPoints;

namespace osu.Game.Graphics.Containers
{
    public class BeatSyncedContainer : Container
    {
        protected readonly Bindable<WorkingBeatmap> Beatmap = new Bindable<WorkingBeatmap>();

        private int lastBeat;
        private TimingControlPoint lastTimingPoint;

        /// <summary>
        /// The amount of time before a beat we should fire <see cref="OnNewBeat(int, TimingControlPoint, EffectControlPoint, TrackAmplitudes)"/>.
        /// This allows for adding easing to animations that may be synchronised to the beat.
        /// </summary>
        protected double EarlyActivationMilliseconds;

        protected override void Update()
        {
            if (Beatmap.Value?.Track == null)
                return;

            double currentTrackTime = Beatmap.Value.Track.CurrentTime + EarlyActivationMilliseconds;

            TimingControlPoint timingPoint = Beatmap.Value.Beatmap.ControlPointInfo.TimingPointAt(currentTrackTime);
            EffectControlPoint effectPoint = Beatmap.Value.Beatmap.ControlPointInfo.EffectPointAt(currentTrackTime);

            if (timingPoint.BeatLength == 0)
                return;

            int beatIndex = (int)((currentTrackTime - timingPoint.Time) / timingPoint.BeatLength);

            // The beats before the start of the first control point are off by 1, this should do the trick
            if (currentTrackTime < timingPoint.Time)
                beatIndex--;

            if (timingPoint == lastTimingPoint && beatIndex == lastBeat)
                return;

            double offsetFromBeat = (timingPoint.Time - currentTrackTime) % timingPoint.BeatLength;

            using (BeginDelayedSequence(offsetFromBeat, true))
                OnNewBeat(beatIndex, timingPoint, effectPoint, Beatmap.Value.Track.CurrentAmplitudes);

            lastBeat = beatIndex;
            lastTimingPoint = timingPoint;
        }

        [BackgroundDependencyLoader]
        private void load(OsuGameBase game)
        {
            Beatmap.BindTo(game.Beatmap);
        }

        protected virtual void OnNewBeat(int beatIndex, TimingControlPoint timingPoint, EffectControlPoint effectPoint, TrackAmplitudes amplitudes)
        {
        }
    }
}