osu-lazer/osu.Game.Rulesets.Osu/Mods/OsuModRandom.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 System;
using System.Collections.Generic;
using System.Linq;
using osu.Framework.Utils;
using osu.Game.Beatmaps;
using osu.Game.Rulesets.Mods;
using osu.Game.Rulesets.Objects;
using osu.Game.Rulesets.Osu.Beatmaps;
using osu.Game.Rulesets.Osu.Objects;
using osu.Game.Rulesets.Osu.UI;
using osu.Game.Rulesets.Osu.Utils;

namespace osu.Game.Rulesets.Osu.Mods
{
    /// <summary>
    /// Mod that randomises the positions of the <see cref="HitObject"/>s
    /// </summary>
    public class OsuModRandom : ModRandom, IApplicableToBeatmap
    {
        public override string Description => "It never gets boring!";

        public override Type[] IncompatibleMods => base.IncompatibleMods.Append(typeof(OsuModTarget)).ToArray();

        private static readonly float playfield_diagonal = OsuPlayfield.BASE_SIZE.LengthFast;

        private Random? rng;

        public void ApplyToBeatmap(IBeatmap beatmap)
        {
            if (beatmap is not OsuBeatmap osuBeatmap)
                return;

            Seed.Value ??= RNG.Next();

            rng = new Random((int)Seed.Value);

            var positionInfos = OsuHitObjectGenerationUtils.GeneratePositionInfos(osuBeatmap.HitObjects);

            // Offsets the angles of all hit objects in a "section" by the same amount.
            float sectionOffset = 0;

            // Whether the angles are positive or negative (clockwise or counter-clockwise flow).
            bool flowDirection = false;

            for (int i = 0; i < positionInfos.Count; i++)
            {
                if (shouldStartNewSection(osuBeatmap, positionInfos, i, 0.6f, 0.4f))
                {
                    sectionOffset = OsuHitObjectGenerationUtils.RandomGaussian(rng, 0, 0.0008f);
                    flowDirection = !flowDirection;
                }

                if (i == 0)
                {
                    positionInfos[i].DistanceFromPrevious = (float)(rng.NextDouble() * OsuPlayfield.BASE_SIZE.Y / 2);
                    positionInfos[i].RelativeAngle = (float)(rng.NextDouble() * 2 * Math.PI - Math.PI);
                }
                else
                {
                    // Offsets only the angle of the current hit object if a flow change occurs.
                    float flowChangeOffset = 0;

                    // Offsets only the angle of the current hit object.
                    float oneTimeOffset = OsuHitObjectGenerationUtils.RandomGaussian(rng, 0, 0.002f);

                    if (shouldApplyFlowChange(positionInfos, i, 0.6f))
                    {
                        flowChangeOffset = OsuHitObjectGenerationUtils.RandomGaussian(rng, 0, 0.002f);
                        flowDirection = !flowDirection;
                    }

                    float totalOffset =
                        // sectionOffset and oneTimeOffset should mainly affect patterns with large spacing.
                        (sectionOffset + oneTimeOffset) * positionInfos[i].DistanceFromPrevious +
                        // flowChangeOffset should mainly affect streams.
                        flowChangeOffset * (playfield_diagonal - positionInfos[i].DistanceFromPrevious);

                    positionInfos[i].RelativeAngle = getRelativeTargetAngle(positionInfos[i].DistanceFromPrevious, totalOffset, flowDirection);
                }
            }

            osuBeatmap.HitObjects = OsuHitObjectGenerationUtils.RepositionHitObjects(positionInfos);
        }

        /// <param name="targetDistance">The target distance between the previous and the current <see cref="OsuHitObject"/>.</param>
        /// <param name="offset">The angle (in rad) by which the target angle should be offset.</param>
        /// <param name="flowDirection">Whether the relative angle should be positive or negative.</param>
        private static float getRelativeTargetAngle(float targetDistance, float offset, bool flowDirection)
        {
            float angle = (float)(2.16 / (1 + 200 * Math.Exp(0.036 * (targetDistance - 310))) + 0.5 + offset);
            float relativeAngle = (float)Math.PI - angle;
            return flowDirection ? -relativeAngle : relativeAngle;
        }

        /// <summary>
        /// A new section should be started...<br/>
        /// ...at the beginning of the <see cref="OsuBeatmap"/>.<br/>
        /// ...on every combo start with a probability of <paramref name="newComboProbability"/> (excluding new-combo-spam and 1-2-combos).<br/>
        /// ...on every downbeat.<br/>
        /// ...on every beat with a probability of <paramref name="beatProbability"/>.<br/>
        /// </summary>
        /// <returns>Whether a new section should be started at the current <see cref="OsuHitObject"/>.</returns>
        private bool shouldStartNewSection(
            OsuBeatmap beatmap,
            IReadOnlyList<OsuHitObjectGenerationUtils.ObjectPositionInfo> positionInfos,
            int i,
            float newComboProbability,
            float beatProbability
        ) =>
            i == 0 ||
            (positionInfos[Math.Max(0, i - 2)].HitObject.IndexInCurrentCombo > 1 && positionInfos[i - 1].HitObject.NewCombo && rng?.NextDouble() < newComboProbability) ||
            OsuHitObjectGenerationUtils.IsHitObjectOnBeat(beatmap, positionInfos[i - 1].HitObject, true) ||
            (OsuHitObjectGenerationUtils.IsHitObjectOnBeat(beatmap, positionInfos[i - 1].HitObject) && rng?.NextDouble() < beatProbability);

        /// <summary>
        /// A flow change should occur on every combo start with a probability of <paramref name="probability"/> (excluding new-combo-spam and 1-2-combos).
        /// </summary>
        /// <returns>Whether a flow change should be applied at the current <see cref="OsuHitObject"/>.</returns>
        private bool shouldApplyFlowChange(IReadOnlyList<OsuHitObjectGenerationUtils.ObjectPositionInfo> positionInfos, int i, float probability) =>
            positionInfos[Math.Max(0, i - 2)].HitObject.IndexInCurrentCombo > 1 &&
            positionInfos[i - 1].HitObject.NewCombo &&
            rng?.NextDouble() < probability;
    }
}