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

// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using osu.Framework.Allocation;
using osu.Framework.Audio.Track;
using osu.Framework.Bindables;
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 IBindable<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, ChannelAmplitudes)"/>.
        /// This allows for adding easing to animations that may be synchronised to the beat.
        /// </summary>
        protected double EarlyActivationMilliseconds;

        /// <summary>
        /// The time in milliseconds until the next beat.
        /// </summary>
        public double TimeUntilNextBeat { get; private set; }

        /// <summary>
        /// The time in milliseconds since the last beat
        /// </summary>
        public double TimeSinceLastBeat { get; private set; }

        /// <summary>
        /// How many beats per beatlength to trigger. Defaults to 1.
        /// </summary>
        public int Divisor { get; set; } = 1;

        /// <summary>
        /// An optional minimum beat length. Any beat length below this will be multiplied by two until valid.
        /// </summary>
        public double MinimumBeatLength { get; set; }

        protected bool IsBeatSyncedWithTrack { get; private set; }

        protected override void Update()
        {
            ITrack track = null;
            IBeatmap beatmap = null;

            double currentTrackTime = 0;
            TimingControlPoint timingPoint = null;
            EffectControlPoint effectPoint = null;

            if (Beatmap.Value.TrackLoaded && Beatmap.Value.BeatmapLoaded)
            {
                track = Beatmap.Value.Track;
                beatmap = Beatmap.Value.Beatmap;
            }

            if (track != null && beatmap != null && track.IsRunning && track.Length > 0)
            {
                currentTrackTime = track.CurrentTime + EarlyActivationMilliseconds;

                timingPoint = beatmap.ControlPointInfo.TimingPointAt(currentTrackTime);
                effectPoint = beatmap.ControlPointInfo.EffectPointAt(currentTrackTime);
            }

            IsBeatSyncedWithTrack = timingPoint?.BeatLength > 0;

            if (timingPoint == null || !IsBeatSyncedWithTrack)
            {
                currentTrackTime = Clock.CurrentTime;
                timingPoint = TimingControlPoint.DEFAULT;
                effectPoint = EffectControlPoint.DEFAULT;
            }

            double beatLength = timingPoint.BeatLength / Divisor;

            while (beatLength < MinimumBeatLength)
                beatLength *= 2;

            int beatIndex = (int)((currentTrackTime - timingPoint.Time) / beatLength) - (effectPoint.OmitFirstBarLine ? 1 : 0);

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

            TimeUntilNextBeat = (timingPoint.Time - currentTrackTime) % beatLength;
            if (TimeUntilNextBeat < 0)
                TimeUntilNextBeat += beatLength;

            TimeSinceLastBeat = beatLength - TimeUntilNextBeat;

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

            using (BeginDelayedSequence(-TimeSinceLastBeat, true))
                OnNewBeat(beatIndex, timingPoint, effectPoint, track?.CurrentAmplitudes ?? ChannelAmplitudes.Empty);

            lastBeat = beatIndex;
            lastTimingPoint = timingPoint;
        }

        [BackgroundDependencyLoader]
        private void load(IBindable<WorkingBeatmap> beatmap)
        {
            Beatmap.BindTo(beatmap);
        }

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