Slider.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.

#nullable disable

using System.Collections.Generic;
using System.Linq;
using System.Threading;
using JetBrains.Annotations;
using Newtonsoft.Json;
using osu.Framework.Bindables;
using osu.Framework.Caching;
using osu.Game.Audio;
using osu.Game.Beatmaps;
using osu.Game.Beatmaps.ControlPoints;
using osu.Game.Rulesets.Judgements;
using osu.Game.Rulesets.Objects;
using osu.Game.Rulesets.Objects.Legacy;
using osu.Game.Rulesets.Objects.Types;
using osu.Game.Rulesets.Osu.Judgements;
using osu.Game.Rulesets.Scoring;
using System.Numerics;

namespace osu.Game.Rulesets.Osu.Objects
{
    public class Slider : OsuHitObject, IHasPathWithRepeats, IHasSliderVelocity, IHasGenerateTicks
    {
        public double EndTime => StartTime + this.SpanCount() * Path.Distance / Velocity;

        [JsonIgnore]
        public double Duration
        {
            get => EndTime - StartTime;
            set => throw new System.NotSupportedException($"Adjust via {nameof(RepeatCount)} instead"); // can be implemented if/when needed.
        }

        public override IList<HitSampleInfo> AuxiliarySamples => cachedAuxiliarySamples ??= CreateSlidingSamples().Concat(TailSamples).ToArray();

        // Cached after ApplyDefaults populates TailSamples — stable for the lifetime of this slider instance.
        private IList<HitSampleInfo>? cachedAuxiliarySamples;

        private readonly Cached<Vector2> endPositionCache = new Cached<Vector2>();

        public override Vector2 EndPosition => endPositionCache.IsValid ? endPositionCache.Value : endPositionCache.Value = Position + this.CurvePositionAt(1);

        public Vector2 StackedPositionAt(double t) => StackedPosition + this.CurvePositionAt(t);

        public SliderPath Path
        {
            get;
            set
            {
                field.ControlPoints.Clear();
                field.ControlPoints.AddRange(value.ControlPoints.Select(c => new PathControlPoint(c.Position, c.Type)));

                field.ExpectedDistance.Value = value.ExpectedDistance.Value;
            }
        } = new SliderPath { OptimiseCatmull = true };

        public double Distance => Path.Distance;

        public override Vector2 Position
        {
            get => base.Position;
            set
            {
                base.Position = value;
                updateNestedPositions();
            }
        }

        public IList<IList<HitSampleInfo>> NodeSamples { get; set; } = new List<IList<HitSampleInfo>>();

        [JsonIgnore]
        public IList<HitSampleInfo> TailSamples { get; private set; }

        public int RepeatCount
        {
            get;
            set
            {
                field = value;
                updateNestedPositions();
            }
        }

        /// <summary>
        /// The length of one span of this <see cref="Slider"/>.
        /// </summary>
        public double SpanDuration => Duration / this.SpanCount();

        /// <summary>
        /// The computed velocity of this <see cref="Slider"/>. This is the amount of path distance travelled in 1 ms.
        /// </summary>
        public double Velocity { get; private set; }

        /// <summary>
        /// Spacing between <see cref="SliderTick"/>s of this <see cref="Slider"/>.
        /// </summary>
        public double TickDistance { get; private set; }

        /// <summary>
        /// An extra multiplier that affects the number of <see cref="SliderTick"/>s generated by this <see cref="Slider"/>.
        /// An increase in this value increases <see cref="TickDistance"/>, which reduces the number of ticks generated.
        /// </summary>
        public double TickDistanceMultiplier = 1;

        /// <summary>
        /// If <see langword="false"/>, <see cref="Slider"/>'s judgement is fully handled by its nested <see cref="HitObject"/>s.
        /// If <see langword="true"/>, this <see cref="Slider"/> will be judged proportionally to the number of nested <see cref="HitObject"/>s hit.
        /// </summary>
        public bool ClassicSliderBehaviour
        {
            get;
            set
            {
                field = value;
                HeadCircle?.ClassicSliderBehaviour = value;
                TailCircle?.ClassicSliderBehaviour = value;
            }
        }

        public BindableNumber<double> SliderVelocityMultiplierBindable { get; } = new BindableDouble(1)
        {
            MinValue = 0.1,
            MaxValue = 10
        };

        public double SliderVelocityMultiplier
        {
            get => SliderVelocityMultiplierBindable.Value;
            set => SliderVelocityMultiplierBindable.Value = value;
        }

        public bool GenerateTicks { get; set; } = true;

        [JsonIgnore]
        public SliderHeadCircle HeadCircle { get; protected set; }

        [JsonIgnore]
        public SliderTailCircle TailCircle { get; protected set; }

        [JsonIgnore]
        [CanBeNull]
        public SliderRepeat LastRepeat { get; protected set; }

        public Slider()
        {
            SamplesBindable.CollectionChanged += (_, _) => UpdateNestedSamples();
            Path.Version.ValueChanged += _ => updateNestedPositions();
        }

        protected override void ApplyDefaultsToSelf(ControlPointInfo controlPointInfo, IBeatmapDifficultyInfo difficulty)
        {
            base.ApplyDefaultsToSelf(controlPointInfo, difficulty);

            TimingControlPoint timingPoint = controlPointInfo.TimingPointAt(StartTime);

            Velocity = BASE_SCORING_DISTANCE * difficulty.SliderMultiplier / LegacyRulesetExtensions.GetPrecisionAdjustedBeatLength(this, timingPoint, OsuRuleset.SHORT_NAME);
            // WARNING: this is intentionally not computed as `BASE_SCORING_DISTANCE * difficulty.SliderMultiplier`
            // for backwards compatibility reasons (intentionally introducing floating point errors to match stable).
            double scoringDistance = Velocity * timingPoint.BeatLength;

            TickDistance = GenerateTicks ? (scoringDistance / difficulty.SliderTickRate * TickDistanceMultiplier) : double.PositiveInfinity;
        }

        protected override void CreateNestedHitObjects(CancellationToken cancellationToken)
        {
            base.CreateNestedHitObjects(cancellationToken);

            // Invalidate the auxiliary-samples cache since TailSamples will be reassigned below.
            cachedAuxiliarySamples = null;

            var sliderEvents = SliderEventGenerator.Generate(StartTime, SpanDuration, Velocity, TickDistance, Path.Distance, this.SpanCount(), cancellationToken);

            foreach (var e in sliderEvents)
            {
                switch (e.Type)
                {
                    case SliderEventType.Tick:
                        AddNested(new SliderTick
                        {
                            SpanIndex = e.SpanIndex,
                            SpanStartTime = e.SpanStartTime,
                            StartTime = e.Time,
                            Position = Position + Path.PositionAt(e.PathProgress),
                            PathProgress = e.PathProgress,
                            StackHeight = StackHeight,
                        });
                        break;

                    case SliderEventType.Head:
                        AddNested(HeadCircle = new SliderHeadCircle
                        {
                            StartTime = e.Time,
                            Position = Position,
                            StackHeight = StackHeight,
                            ClassicSliderBehaviour = ClassicSliderBehaviour,
                        });
                        break;

                    case SliderEventType.Tail:
                        AddNested(TailCircle = new SliderTailCircle(this)
                        {
                            RepeatIndex = e.SpanIndex,
                            StartTime = e.Time,
                            Position = EndPosition,
                            StackHeight = StackHeight,
                            ClassicSliderBehaviour = ClassicSliderBehaviour,
                        });
                        break;

                    case SliderEventType.Repeat:
                        AddNested(LastRepeat = new SliderRepeat(this)
                        {
                            RepeatIndex = e.SpanIndex,
                            StartTime = StartTime + (e.SpanIndex + 1) * SpanDuration,
                            Position = Position + Path.PositionAt(e.PathProgress),
                            StackHeight = StackHeight,
                            PathProgress = e.PathProgress,
                        });
                        break;
                }
            }

            UpdateNestedSamples();
        }

        private void updateNestedPositions()
        {
            endPositionCache.Invalidate();

            foreach (var nested in NestedHitObjects)
            {
                switch (nested)
                {
                    case SliderHeadCircle headCircle:
                        headCircle.Position = Position;
                        break;

                    case SliderTailCircle tailCircle:
                        tailCircle.Position = EndPosition;
                        break;

                    case SliderRepeat repeat:
                        repeat.Position = Position + Path.PositionAt(repeat.PathProgress);
                        break;

                    case SliderTick tick:
                        tick.Position = Position + Path.PositionAt(tick.PathProgress);
                        break;
                }
            }
        }

        protected void UpdateNestedSamples()
        {
            this.PopulateNodeSamples();

            // TODO: remove this when guaranteed sort is present for samples (https://github.com/ppy/osu/issues/1933)
            HitSampleInfo tickSample = (Samples.FirstOrDefault(s => s.Name == HitSampleInfo.HIT_NORMAL) ?? Samples.FirstOrDefault())?.With("slidertick");

            foreach (var nested in NestedHitObjects)
            {
                switch (nested)
                {
                    case SliderTick tick:
                        tick.SamplesBindable.Clear();

                        if (tickSample != null)
                            tick.SamplesBindable.Add(tickSample);
                        break;

                    case SliderRepeat repeat:
                        repeat.Samples = this.GetNodeSamples(repeat.RepeatIndex + 1);
                        break;
                }
            }

            HeadCircle?.Samples = this.GetNodeSamples(0);

            // The samples should be attached to the slider tail, however this can only be done if LastTick is removed otherwise they would play earlier than they're intended to.
            // (see mapping logic in `CreateNestedHitObjects` above)
            //
            // For now, the samples are played by the slider itself at the correct end time.
            TailSamples = this.GetNodeSamples(RepeatCount + 1);
        }

        public override Judgement CreateJudgement() => ClassicSliderBehaviour
            // Final combo is provided by the slider itself - see logic in `DrawableSlider.CheckForResult()`
            ? new OsuJudgement()
            // Final combo is provided by the tail circle - see `SliderTailCircle`
            : new OsuIgnoreJudgement();

        protected override HitWindows CreateHitWindows() => HitWindows.Empty;
    }
}